Paul Wender

Abstract

All living systems require biochemical barriers. As a consequence, all drugs, imaging agents, and probes have targets that are either on, in, or inside of these barriers. Fifteen years ago, we initiated research directed at more fully understanding these barriers and at developing tools and strategies for breaching them that could be of use in basic research, imaging, diagnostics, and medicine. At the outset of this research and now to a lesser extent, the "rules" for drug design biased the selection of drug candidates mainly to those with an intermediate and narrow log P. At the same time, it was becoming increasingly apparent that Nature had long ago developed clever strategies to circumvent these "rules." In 1988, for example, independent reports documented the otherwise uncommon passage of a protein (HIV-Tat) across a membrane. A subsequent study implicated a highly basic domain in this protein (Tat49-57) in its cellular entry. This conspicuously contradictory behavior of a polar, highly charged peptide passing through a nonpolar membrane set the stage for learning how Nature had gotten around the current "rules" of transport. As elaborated in our studies and discussed in this Account, the key strategy used in Nature rests in part on the ability of a molecule to change its properties as a function of microenvironment; such molecules need to be polarity chameleons, polar in a polar milieu and relatively nonpolar in a nonpolar environment. Because this research originated in part with the protein Tat and its basic peptide domain, Tat49-57, the field focused heavily on peptides, even limiting its nomenclature to names such as "cell-penetrating peptides," "cell-permeating peptides," "protein transduction domains," and "membrane translocating peptides." Starting in 1997, through a systematic reverse engineering approach, we established that the ability of Tat49-57 to enter cells is not a function of its peptide backbone, but rather a function of the number and spatial array of its guanidinium groups. These function-oriented studies enabled us and others to design more effective peptidic agents and to think beyond the confines of peptidic systems to new and even more effective nonpeptidic agents. Because the function of passage across a cell membrane is not limited to or even best achieved with the peptide backbone, we referred to these agents by their shared function, "cell-penetrating molecular transporters." The scope of this molecular approach to breaching biochemical barriers has expanded remarkably in the past 15 years: enabling or enhancing the delivery of a wide range of cargos into cells and across other biochemical barriers, creating new tools for research, imaging, and diagnostics, and introducing new therapies into clinical trials.

View details for PubMedID 23697862

Abstract

Highly active antiretroviral therapy (HAART) decreases plasma viremia below the limits of detection in the majority of HIV-infected individuals, thus serving to slow disease progression. However, HAART targets only actively replicating virus and is unable to eliminate latently infected, resting CD4(+) T cells. Such infected cells are potentially capable of reinitiating virus replication upon cessation of HAART, thus leading to viral rebound. Agents that would eliminate these reservoirs, when used in combination with HAART, could thus provide a strategy for the eradication of HIV. Prostratin is a preclinical candidate that induces HIV expression from latently infected CD4(+) T cells, potentially leading to their elimination through a virus-induced cytopathic effect or host anti-HIV immunity. Here, we report the synthesis of a series of designed prostratin analogs and report in vitro and ex vivo studies of their activity relevant to induction of HIV expression. Members of this series are up to 100-fold more potent than the preclinical lead (prostratin) in binding to cell-free PKC, and in inducing HIV expression in a latently infected cell line and prostratin-like modulation of cell surface receptor expression in primary cells from HIV-negative donors. Significantly, selected members were also tested for HIV induction in resting CD4(+) T cells isolated from infected individuals receiving HAART and were found to exhibit potent induction activity. These more potent agents and by extension related tunable analogs now accessible through the studies described herein should facilitate research and preclinical advancement of this strategy for HIV/AIDS eradication.

View details for PubMedID 23812750

Abstract

Bryostatin is a unique lead in the development of potentially transformative therapies for cancer, Alzheimer's disease and the eradication of HIV/AIDS. However, the clinical use of bryostatin has been hampered by its limited supply, difficulties in accessing clinically relevant derivatives, and side effects. Here, we address these problems through the step-economical syntheses of seven members of a new family of designed bryostatin analogues using a highly convergent Prins-macrocyclization strategy. We also demonstrate for the first time that such analogues effectively induce latent HIV activation in vitro with potencies similar to or better than bryostatin. Significantly, these analogues are up to 1,000-fold more potent in inducing latent HIV expression than prostratin, the current clinical candidate for latent virus induction. This study provides the first demonstration that designed, synthetically accessible bryostatin analogues could serve as superior candidates for the eradication of HIV/AIDS through induction of latent viral reservoirs in conjunction with current antiretroviral therapy.

View details for DOI 10.1038/NCHEM.1395

View details for Web of Science ID 000308214200007

View details for PubMedID 22914190

Abstract

The polyanionic nature of oligonucleotides and their enzymatic degradation present challenges for the use of siRNA in research and therapy; among the most notable of these is clinically relevant delivery into cells. To address this problem, we designed and synthesized the first members of a new class of guanidinium-rich amphipathic oligocarbonates that noncovalently complex, deliver, and release siRNA in cells, resulting in robust knockdown of target protein synthesis in vitro as determined using a dual-reporter system. The organocatalytic oligomerization used to synthesize these co-oligomers is step-economical and broadly tunable, affording an exceptionally quick strategy to explore chemical space for optimal siRNA delivery in varied applications. The speed and versatility of this approach and the biodegradability of the designed agents make this an attractive strategy for biological tool development, imaging, diagnostics, and therapeutic applications.

View details for DOI 10.1073/pnas.1211361109

View details for Web of Science ID 000307807000017

View details for PubMedID 22847412

Abstract

Multidrug resistance is the major cause of failure of many chemotherapeutic agents. While resistance can arise from several factors, it is often dominated by drug efflux mediated by P-glycoprotein (P-gp), a membrane-bound polysubstrate export pump expressed at high levels in resistant cells. While co-administration of pump inhibitors and a drug could suppress efflux, this two-drug strategy has not yet advanced to therapy. We recently demonstrated that the reversible attachment of a guanidinium-rich molecular transporter, polyarginine, to a drug provides a conjugate that overcomes efflux-based resistance in cells and animals. This study is to determine whether this strategy for overcoming resistance is effective against human disease.Tumor samples from ovarian cancer patients, both malignant ascites cells and dissociated solid tumor cells, were exposed to Taxol-oligoarginine conjugates designed to release free drug only after cell entry. Cell viability was determined via propidium-iodide uptake by flow cytometry. To analyze bystander effect, toxicity of the drug conjugates was also tested on peripheral blood leucocytes.Human ovarian carcinoma specimens resistant to Taxol in vitro demonstrated increased sensitivity to killing by all Taxol-transporter conjugates tested. These studies also show that the drug conjugates were not significantly more toxic to normal human peripheral blood leukocytes than Taxol.These studies with human tumor indicate that oligoarginine conjugates of known drugs can be used to overcome the efflux-based resistance to the drug, providing a strategy that could improve the treatment outcomes of patients with efflux-based drug-resistance.

View details for DOI 10.1016/j.ygyno.2012.03.049

View details for Web of Science ID 000305878400023

View details for PubMedID 22484398

Abstract

Rh COT in the act: a Ni(0)-catalyzed [2+2+2+2] cycloaddition provides a high-yielding, scalable synthesis of the ligand dinaphtho[a,e]cyclooctatetraene (dnCOT). dnCOT complexation with Rh(I) gives [Rh(dnCOT)(MeCN)(2)]SbF(6), an excellent catalyst for [5+2] cycloadditions of vinylcyclopropanes and ?-systems with impressive functional group compatibility.

View details for DOI 10.1002/anie.201108270

View details for Web of Science ID 000301173800038

View details for PubMedID 22298411

Abstract

Inspired originally by peptides that traverse biological barriers, research on molecular transporters has since identified the key structural requirements that govern cellular entry, leading to new, significantly more effective and more readily available agents. These new drug delivery systems enable or enhance cellular and tissue uptake, can be targeted, and provide numerous additional advantages of significance in imaging, diagnostics and therapy.

View details for PubMedID 22712022

Abstract

Bryostatin 1 is a naturally occurring complex macrolide with potent anti-neoplastic activity. However, its extremely low natural occurrence has impeded clinical advancement. We developed a strategy directed at the design of simplified and synthetically more accessible bryostatin analogs. Our lead analog, "picolog", can be step-economically produced. Picolog, compared to bryostatin, exhibited superior growth inhibition of MYC-induced lymphoma in vitro. A key mechanism of picolog's (and bryostatin's) activity is activation of PKC. A novel nano-immunoassay (NIA) revealed that picolog treatment increased phospho-MEK2 in the PKC pathway. Moreover, the inhibition of PKC abrogated picolog's activity. Finally, picolog was highly potent at 100 micrograms/kg and well tolerated at doses ranging from 100 micrograms/kg to 1 milligram/kg in vivo for the treatment of our aggressive model of MYC-induced lymphoma. We provide the first in vivo validation that the bryostatin analog, picolog, is a potential therapeutic agent for the treatment of cancer and other diseases.

View details for Web of Science ID 000303914000009

View details for PubMedID 22308267

Abstract

The daphnane diterpene orthoesters constitute a structurally fascinating family of natural products that exhibit a remarkable range of potent biological activities. Although partial activity information is available for some natural daphnanes, little information exists for non-natural congeners or on how changes in structure affect mode of action, function, potency or selectivity. A gateway strategy designed to provide general synthetic access to natural and non-natural daphnanes is described and utilized in the synthesis of two novel members of this class. In this study, a commercially available tartrate derivative was elaborated through a key late-stage diversification intermediate into B-ring yuanhuapin analogues to initiate exploration of the structure-function relationships of this class. Protein kinase C was identified as a cellular target for these agents, and their activity against human lung and leukaemia cell lines was evaluated. The natural product and a novel non-natural analogue exhibited significant potency, but the epimeric epoxide was essentially inactive.

View details for DOI 10.1038/NCHEM.1074

View details for Web of Science ID 000292999100014

View details for PubMedID 21778981

Abstract

The total synthesis of bryostatin 9 was accomplished using a uniquely step-economical and convergent Prins-driven macrocyclization strategy. At 25 linear and 42 total steps, this is currently the most concise and convergent synthesis of a potent bryostatin.

View details for DOI 10.1021/ja203034k

View details for Web of Science ID 000291915100025

View details for PubMedID 21618969

Abstract

Modern methods for the identification of therapeutic leads include chemical or virtual screening of compound libraries. Nature's library represents a vast and diverse source of leads, often exhibiting exquisite biological activities. However, the advancement of natural product leads into the clinic is often impeded by their scarcity, complexity, and nonoptimal properties or efficacy as well as the challenges associated with their synthesis or modification. Function-oriented synthesis represents a strategy to address these issues through the design of simpler and therefore synthetically more accessible analogs that incorporate the activity-determining features of the natural product leads. This study illustrates the application of this strategy to the design and synthesis of functional analogs of the bryostatin marine natural products. It is specifically directed at exploring the activity-determining role of bryostatin A-ring functionality on PKC affinity and selectivity. The resultant functional analogs, which were prepared by a flexible, modular synthetic strategy, exhibit excellent affinity to PKC and differential isoform selectivity. These and related studies provide the basic information needed for the design of simplified and thus synthetically more accessible functional analogs that target PKC isoforms, major targets of therapeutic interest.

View details for DOI 10.1073/pnas.1015270108

View details for Web of Science ID 000289888500012

View details for PubMedID 21415363

Abstract

The synthesis and biological evaluation of the first members of a new series of designed bryostatin A-ring analogues (bryologs) are described. An advanced intermediate is produced that allows for step economical access to diverse analogs. The first of these analogues, bearing side chains of completely different polarities from alkyl to hydroxyl and carboxyl functionalities, were evaluated. All exhibit potent protein kinase C binding (54.7 to 2.4 nM) with affinities increasing with decreasing side chain polarity. This series of bryostatin analogues demonstrates that A ring surrogates can indeed be used for tuning pharmacophore and ADME characteristics as needed to improve bryolog function.

View details for PubMedID 22247574

Abstract

The first studies on the regioselectivity of Rh(I)-catalyzed (5 + 2) cycloadditions between vinylcyclopropanes (VCPs) and alkynes have been conducted experimentally and analyzed using density functional theory (DFT). The previously unexplored regiochemical consequences for this catalytic, intermolecular cycloaddition were determined by studying the reactions of several substituted VCPs with a range of unsymmetrical alkynes. Experimental trends were identified, and a predictive model was established. VCPs with terminal substitution on the alkene reacted with high regioselectivity (>20:1), as predicted by a theoretical model in which bulkier alkyne substituents prefer to be distal to the forming C-C bond to avoid steric repulsions. VCPs with substitution at the internal position of the alkene reacted with variable regioselectivity (ranging from >20:1 to a reversed 1:2.3), suggesting a refined model in which electron-withdrawing substituents on the alkyne decrease or reverse sterically controlled selectivity by stabilizing the transition state in which the substituent is proximal to the forming C-C bond.

View details for DOI 10.1021/ja103253d

View details for Web of Science ID 000280227700048

View details for PubMedID 20586494

Abstract

A cationic rhodium(I) complex--[(C(10)H(8))Rh(cod)](+) SbF(6)(-)--catalyzes the remarkably efficient intermolecular [5 + 2] cycloaddition of vinylcyclopropanes (VCPs) and various alkynes, providing cycloheptene cycloadducts in excellent yields in minutes at room temperature. The efficacy and selectivity of this catalyst are also shown in a novel diversification strategy, affording a cycloadduct library in one step from nine commercially available components.

View details for DOI 10.1021/ol100337m

View details for Web of Science ID 000275885400058

View details for PubMedID 20196579

Abstract

The bicyclo[5.3.0]decane skeleton is one of the most commonly encountered bicyclic subunits in nature and the core scaffold of a wide range of targets of structural, biological, and therapeutic importance. Prompted by the interest in such structures, we report the first studies of metal-catalyzed [5+2] cycloadditions of vinylcyclopropanes (VCPs) and enynones. The resultant efficiently formed dienone cycloadducts serve as substrates for subsequent Nazarov cyclizations and as intermediates for single-operation [5+2]/Nazarov serial reactions and catalytic cascades. In many cases the one-flask process can be carried out in shorter reaction times and with comparable or superior yields to the two-flask procedure. Significantly, a single catalyst can be used to mediate both transformations. These [5+2]/Nazarov reaction sequences and cascades collectively provide strategically novel and facile access to the bicyclo[5.3.0]decane skeleton from simple and readily available components.

View details for DOI 10.1021/ja910696x

View details for Web of Science ID 000275117900021

View details for PubMedID 20141136

Abstract

Two new glycosylated macrolactones, apoptolidins E (5) and F (6), were isolated from fermentation of the actinomycete Nocardiopsis sp. and their structures assigned. Lacking the C16 and C20 oxygens of apoptolidin A (1), these macrolides are also the first members of this family to display a 4-O-methyl-l-rhamnose at C9 rather than a 6-deoxy-4-O-methyl-l-glucose.

View details for DOI 10.1021/ol902308v

View details for Web of Science ID 000272038200029

View details for PubMedID 19943700

Abstract

A new family of guanidinium-rich molecular transporters featuring a novel oligocarbonate backbone with 1,7-side chain spacing is described. Conjugates can be rapidly assembled irrespective of length in a one-step oligomerization strategy that can proceed with concomitant introduction of probes (or by analogy drugs). The new transporters exhibit excellent cellular entry as determined by flow cytometry and fluorescence microscopy, and the functionality of their drug delivery capabilities was confirmed by the delivery of the bioluminescent small molecule probe luciferin and turnover by its intracellular target enzyme.

View details for DOI 10.1021/ja907363k

View details for Web of Science ID 000271723000030

View details for PubMedID 19860416

Abstract

We report the application of peptide-based catalysts to the site-selective modification of apoptolidin A (1), an agent that displays remarkable selectivity for inducing apoptosis in E1A-transformed cell lines. Key to the approach was the development of an assay suitable for the screening of dozens of catalysts in parallel reactions that could be conducted using only microgram quantities of the starting material. Employing this assay, catalysts (e.g., 11 and ent-11) were identified that afforded unique product distributions, distinct from the product mixtures produced when a simple catalyst (N,N-dimethyl-4-aminopyridine (10)) was employed. Preparative reactions were then carried out with the preferred catalysts so that unique, homogeneous apoptolidin analogues could be isolated and characterized. From these studies, three new apoptolidin analogues were obtained (12-14), each differing from the other in either the location of acyl group substituents or the number of acetate groups appended to the natural product scaffold. Biological evaluation of the new apoptolidin analogues was then conducted using growth inhibition assays based on the H292 human lung carcinoma cell line. The new analogues exhibited activities comparable to apoptolidin A.

View details for DOI 10.1021/np9004932

View details for Web of Science ID 000271950400022

View details for PubMedID 19769383

View details for DOI 10.1038/460197a

View details for Web of Science ID 000267761000029

View details for PubMedID 19587760

Abstract

An efficient cyclocarboamination reaction of nonactivated alkynes with aziridines, catalyzed by Lewis or Bronsted acids, to form 2,3-dihydropyrroles through a formal [3+2] cycloaddition, is described. The reaction provides a wide range of polysubstituted dihydropyrroles in a highly regioselective manner, is scalable, proceeds under mild reaction conditions, and uses low catalyst loadings.

View details for DOI 10.1021/ja901799s

View details for Web of Science ID 000267177900025

View details for PubMedID 19489638

View details for DOI 10.1002/anie.200903859

View details for Web of Science ID 000270436900041

View details for PubMedID 19739178

Abstract

Laulimalide is a potent microtubule stabilizing agent and a promising anticancer therapeutic lead. The identification of stable, efficacious and accessible analogues is critical to clinically exploiting this novel lead. To determine which structural features of laulimalide are required for beneficial function and thus for accessing superior clinical candidates, a series of side chain analogues were prepared through a last step cross metathesis diversification strategy and their biological activities were evaluated. Five analogues, differing in potency from 233 nM to 7.9 muM, effectively inhibit cancer cell proliferation. Like laulimalide, they retain activity against multidrug resistant cells, stabilize microtubules and cause the formation of aberrant mitotic spindles, mitotic accumulation, Bcl-2 phosphorylation and initiation of apoptosis. Structural modifications in the C 23-C 27 dihydropyran side chain can be made without changing the overall mechanism of action, but it is clear that this subunit has more than a bystander role.

View details for DOI 10.1021/mp800043n

View details for Web of Science ID 000259859500014

View details for PubMedID 18662015

Abstract

Many cancer therapeutic agents elicit resistance that renders them ineffective and often produces cross-resistance to other drugs. One of the most common mechanisms of resistance involves P-glycoprotein (Pgp)-mediated drug efflux. To address this problem, new agents have been sought that are less prone to inducing resistance and less likely to serve as substrates for Pgp efflux. An alternative to this approach is to deliver established agents as molecular transporter conjugates into cells through a mechanism that circumvents Pgp-mediated efflux and allows for release of free drug only after cell entry. Here we report that the widely used chemotherapeutic agent Taxol, ineffective against Taxol-resistant human ovarian cancer cell lines, can be incorporated into a releasable octaarginine conjugate that is effective against the same Taxol-resistant cell lines. It is significant that the ability of the Taxol conjugates to overcome Taxol resistance is observed both in cell culture and in animal models of ovarian cancer. The generality and mechanistic basis for this effect were also explored with coelenterazine, a Pgp substrate. Although coelenterazine itself does not enter cells because of Pgp efflux, its octaarginine conjugate does so readily. This approach shows generality for overcoming the multidrug resistance elicited by small-molecule cancer chemotherapeutics and could improve the prognosis for many patients with cancer and fundamentally alter search strategies for novel therapeutic agents that are effective against resistant disease.

View details for DOI 10.1073/pnas.0805374105

View details for Web of Science ID 000258905700008

View details for PubMedID 18713866

Abstract

The first series of systematically varied C7-functionalized bryostatin analogs (12 members in all) have been synthesized through an efficient and convergent route. A new hotspot for PKC affinity, not present in the natural products, has been discovered, allowing for affinity control and potentially for selective regulation of PKC isozymes. Several analogs exhibit single-digit nanomolar affinity to PKC and display superior activity compared to bryostatin against the leukemia cell line K562.

View details for DOI 10.1021/ol801235h

View details for Web of Science ID 000257955100041

View details for PubMedID 18588309

Abstract

To explore the real-time dynamic behavior of molecular transporters of the cell-penetrating-peptide (CPP) type on a biological membrane, single fluorescently labeled oligoarginine conjugates were imaged interacting with the plasma membrane of Chinese hamster ovary (CHO) cells. The diffusional motion on the membrane, characterized by single-molecule diffusion coefficient and residence time (tau R), defined as the time from the initial appearance of a single-molecule spot on the membrane (from the solution) to the time the single molecule disappears from the imaging focal plane, was observed for a fluorophore-labeled octaarginine (a model guanidinium-rich CPP) and compared with the corresponding values observed for a tetraarginine conjugate (negative control), a lipid analogue, and a fluorescently labeled protein conjugate (transferrin-Alexa594) known to enter the cell through endocytosis. Imaging of the oligoarginine conjugates was enabled by the use of a new high-contrast fluorophore in the dicyanomethylenedihydrofuran family, which brightens upon interaction with the membrane at normal oxygen concentrations. Taken as a whole, the motions of the octaarginine conjugate single molecules are highly heterogeneous and cannot be described as Brownian motion with a single diffusion coefficient. The observed behavior is also different from that of lipids, known to penetrate cellular membranes through passive diffusion, conventionally involving lateral diffusion followed by membrane bilayer flip-flop. Furthermore, while the octaarginine conjugate behavior shares some common features with transferrin uptake (endocytotic) processes, the two systems also exhibit dissimilar traits when diffusional motions and residence times of single constructs are compared. Additionally, pretreatment of cells with cytochalasin D, a known actin filament disruptor, produces no significant effect, which further rules out unimodal endocytosis as the mechanism of uptake. Also, the involvement of membrane potential in octaarginine-membrane interaction is supported by significant changes in the motion with high [K(+)] treatment. In sum, this first study of single transporter motion on the membrane of a living cell indicates that the mode by which the octaarginine transporter penetrates the cell membrane appears to either be a multimechanism uptake process or a mechanism different from unimodal passive diffusion or endocytosis.

View details for DOI 10.1021/ja710798b

View details for Web of Science ID 000257796500048

View details for PubMedID 18578528

Abstract

The step-economical synthesis of a new class of bryostatin analogues that contain the complete oxycarbocyclic core ring system of the bryostatin natural products is reported. These agents are convergently assembled via a highly efficient, functional-group-tolerant, and stereoselective Prins-driven macrocyclization. These tetrahydropyranyl B-ring analogues are among our most potent and efficacious analogues to date, exhibiting nanomolar and picomolar activities in protein kinase C affinity assays as well as in cellular antiproliferation assays.

View details for DOI 10.1021/ja8015632

View details for Web of Science ID 000256158200003

View details for PubMedID 18452292

Abstract

Although antiretroviral therapies have been effective in decreasing active viral loads in AIDS patients, the persistence of latent viral reservoirs prevents eradication of the virus. Prostratin and DPP (12-deoxyphorbol-13-phenylacetate) activate the latent virus and thus represent promising adjuvants for antiviral therapy. Their limited supply and the challenges of accessing related structures have, however, impeded therapeutic development and the search for clinically superior analogs. Here we report a practical synthesis of prostratin and DPP starting from phorbol or crotophorbolone, agents readily available from renewable sources, including a biodiesel candidate. This synthesis reliably supplies gram quantities of the therapeutically promising natural products, hitherto available only in low and variable amounts from natural sources, and opens access to a variety of new analogs.

View details for DOI 10.1126/science.1154690

View details for Web of Science ID 000255454300041

View details for PubMedID 18451298

Abstract

The ability of a drug or probe to cross a biological barrier has historically been viewed to be a function of its intrinsic physical properties. This view has largely restricted drug design and selection to agents within a narrow log P range. Molecular transporters offer a strategy to circumvent these restrictions. In the case of guanidinium-rich transporters (GRTs), a typically highly water-soluble conjugate is found to readily pass through the non-polar membrane of a cell and for some across tissue barriers. This activity opens a field of opportunities for the use of GRTs to enable delivery of polar and non-polar drugs or probes as well as to enhance uptake of those of intermediate polarity. The field of transporter enabled or enhanced uptake has grown dramatically in the last decade. Some GRT drug conjugates have been advanced into clinical trials. This review will provide an overview of recent work pertinent to the design and mechanism of uptake of GRTs.

View details for DOI 10.1016/j.addr.2007.10.016

View details for Web of Science ID 000254068000003

View details for PubMedID 18164781

View details for DOI 10.1021/ja076444d

View details for Web of Science ID 000253400900003

View details for PubMedID 18251468

Abstract

This Account provides an overview and examples of function-oriented synthesis (FOS) and its increasingly important role in producing therapeutic leads that can be made in a step-economical fashion. Biologically active natural product leads often suffer from several deficiencies. Many are scarce or difficult to obtain from natural sources. Often, they are highly complex molecules and thus not amenable to a practical synthesis that would impact supply. Most are not optimally suitable for human therapeutic use. The central principle of FOS is that the function of a biologically active lead structure can be recapitulated, tuned, or greatly enhanced with simpler scaffolds designed for ease of synthesis and also synthetic innovation. This approach can provide practical access to new (designed) structures with novel activities while at the same time allowing for synthetic innovation by target design. This FOS approach has been applied to a number of therapeutically important natural product leads. For example, bryostatin is a unique natural product anticancer lead that restores apoptosis in cancer cells, reverses multidrug resistance, and bolsters the immune system. Remarkably, it also improves cognition and memory in animals. We have designed and synthesized simplified analogs of bryostatin that can be made in a practical fashion (pilot scale) and are superior to bryostatin in numerous assays including growth inhibition in a variety of human cancer cell lines and in animal models. Laulimalide is another exciting anticancer lead that stabilizes microtubules, like paclitaxel, but unlike paclitaxel, it is effective against multidrug-resistant cell lines. Laulimalide suffers from availability and stability problems, issues that have been addressed using FOS through the design and synthesis of stable and efficacious laulimalide analogs. Another FOS program has been directed at the design and synthesis of drug delivery systems for enabling or enhancing the uptake of drugs or drug candidates into cells and tissue. We have generated improved transporters that can deliver agents in a superior fashion compared with naturally occurring cell-penetrating peptides and that can be synthesized in a practical and step-economical fashion. The use of FOS has allowed for the translation of exciting, biologically active natural product leads into simplified analogs with superior function. This approach enables the development of synthetically innovative strategies while targeting therapeutically novel structures.

View details for DOI 10.1021/ar700155p

View details for Web of Science ID 000252419500006

View details for PubMedID 18159936

View details for DOI 10.1021/ja0763044

View details for Web of Science ID 000250819200022

View details for PubMedID 17929819

View details for DOI 10.1021/ja072505w

View details for Web of Science ID 000248896400008

View details for PubMedID 17655302

Abstract

Many therapeutic leads fail to advance clinically because of bioavailability, selectivity, and formulation problems. Molecular transporters can be used to address these problems. Molecular transporter conjugates of otherwise poorly soluble or poorly bioavailable drugs or probes exhibit excellent solubility in water and biological fluids and at the same time an enhanced ability to enter tissues and cells and with modification to do so selectively. For many conjugates, however, it is necessary to release the drug/probe cargo from the transporter after uptake to achieve activity. Here, we describe an imaging method that provides quantification of transporter conjugate uptake and cargo release in real-time in animal models. This method uses transgenic (luciferase) reporter mice and whole-body imaging, allowing noninvasive quantification of transporter conjugate uptake and probe (luciferin) release in real time. This process effectively emulates drug-conjugate delivery, drug release, and drug turnover by an intracellular target, providing a facile method to evaluate comparative uptake of new transporters and efficacy and selectivity of linker release as required for fundamental studies and therapeutic applications.

View details for DOI 10.1073/pnas.0703919104

View details for Web of Science ID 000247500000010

View details for PubMedID 17563383

Abstract

[reaction: see text] An efficient synthetic route to the ABC tricyclic core of 1alpha-alkyldaphnanes has been developed. The conformational bias imparted by the C6-C9 oxo-bridge of BC-ring system 12 was used to elaborate the ABC-ring system precursor including the introduction of the beta-C5 hydroxyl group. A completely diastereoselective palladium-catalyzed enyne cyclization was then employed to establish the A-ring with a C1 appendage.

View details for DOI 10.1021/ol0705649

View details for Web of Science ID 000245799200054

View details for PubMedID 17408281

Abstract

The isolation, characterization, and preliminary biological activity of apoptolidin D, a new apoptolidin that exhibits anti-proliferative activity against H292 human lung carcinoma cells at nanomolar concentrations, are reported. Its equilibration with isoapoptolidin D and characterization of the latter are also described. [structure: see text].

View details for DOI 10.1021/ol0630245

View details for Web of Science ID 000244039800037

View details for PubMedID 17286376

Abstract

The Rh(I)-catalyzed [3 + 2] cycloaddition of cyclopropenones and alkynes is found to provide a highly efficient and regiocontrolled route to cyclopentadienones (CPDs), building blocks of widespread use in the synthesis of natural and non-natural products, therapeutic leads, polymers, dendrimers, devices, and antigen presenting scaffolds. The versatility of the method is explored with 23 examples representing a wide range of alkyne variations (arylalkyl-, dialkyl-, heteroarylalkyl-) and diaryl- as well as arylalkylcyclopropenones. The reactions often proceed in high yield using minimal catalyst loadings and in all cases examined proceed with high or complete regioselectivity. The reaction is readily scalable to produce gram quantities of cycloadduct and provides a unique and versatile route to CPDs that would be otherwise difficult to obtain.

View details for DOI 10.1021/ja065868p

View details for Web of Science ID 000242021700040

View details for PubMedID 17105285

Abstract

[Structure: see text] The total synthesis and preliminary biological evaluation of the first bryostatin analogs (bryologs) to incorporate B-ring substitution are reported. Asymmetric syntheses of two new polyketide "spacer" domains are described, one exploiting the pseudosymmetry of the C1-C13 region. These fragments are convergently joined to the "recognition" domain through a remarkably versatile macrotransacetalization process. The resulting new analogs exhibit potent nanomolar or picomolar affinity to protein kinase C (PKC), comparable to or better than that found for bryostatin.

View details for DOI 10.1021/ol0620904

View details for Web of Science ID 000241729500031

View details for PubMedID 17078702

Abstract

[Structure: see text] 12-hydroxydaphnetoxins, members of the structurally fascinating daphnane diterpene family, exhibit a wide range of significant biological activities. A general route to the BC-ring system of 12-hydroxy daphnetoxins is reported based on D-ribose. Depending on the choice of protecting groups and solvent, the oxidopyrylium-alkene [5+2] cycloaddition originating from A provides cycloadduct diastereomer B or C with good to excellent selectivity.

View details for DOI 10.1021/ol062234e

View details for Web of Science ID 000241729500050

View details for PubMedID 17078721

View details for DOI 10.1002/cbic.200600171

View details for Web of Science ID 000241392400004

View details for PubMedID 16972294

Abstract

The design, asymmetric synthesis, and biological evaluation of a new class of bryostatin analogues based on a pseudosymmetric spacer domain are described. An aryl bromide diversification site is incorporated allowing access to systematically varied analogues. The new analogues all exhibit potent, nanomolar affinity to PKC.

View details for DOI 10.1021/ol0618149

View details for Web of Science ID 000240654700050

View details for PubMedID 16986955

Abstract

An efficient synthesis of the macrocyclic core of laulimalide with a pendant vinyl group at C20 is described, allowing for late-stage introduction of various side chains through a selective and efficient cross metathesis diversification step. Representative analogues reported herein are the first to contain modifications to only the side chain dihydropyran of laulimalide and des-epoxy laulimalide. This step-economical strategy enables the rapid synthesis of new analogues using alkenes as an inexpensive, abundantly available diversification feedstock.

View details for DOI 10.1021/ol061619u

View details for Web of Science ID 000239990900055

View details for PubMedID 16928085

Abstract

Some of the most significant therapeutic leads and agents used for the treatment of cancer target microtubule dynamics. Paclitaxel is an exceptional example that is currently used for treating a wide range of tumors. New, non-taxane microtubule stabilizers, including several epothilones, are advancing through clinical trials. Laulimalide is a potent microtubule stabilizer that binds to tubulin at a site that does not overlap the taxane-binding site. It is active against paclitaxel-resistant cancer cells. Notwithstanding its therapeutic potential, laulimalide is relatively unstable, rearranging to a more stable but less active isomer. The goal of this study was to evaluate the ability of laulimalide and two designed laulimalide analogues, C16-C17-des-epoxy laulimalide (LA1) and C20-methoxy laulimalide (LA2), to inhibit cell proliferation in combination with other tubulin-binding and non-tubulin-binding antiproliferative antimitotic agents. The synthetic laulimalide analogues retain the mechanism of action of the natural compound but do not share its instability. We studied the ability of the laulimalides to act synergistically with paclitaxel, 2-methoxyestradiol, and monastrol, an Eg5 kinesin inhibitor. The results show that all three of the laulimalides acted synergistically with paclitaxel and 2-methoxyestradiol to inhibit proliferation with the analogues exhibiting significantly larger synergistic effects. The combination of laulimalide and monastrol was not synergistic and provided only additive effects. The laulimalide analogues LA1 and LA2 had a greater degree of synergy with both paclitaxel and 2-methoxyestradiol than was observed with laulimalide. Our results show that the laulimalides together with other tubulin-binding antimitotic agents provide synergistic antiproliferative actions. The data are consistent with the previously reported ability of laulimalide and paclitaxel to act synergistically to polymerize tubulin in vitro. These important findings suggest that specific combinations of microtubule-targeting agents should be considered for clinical utilities as they have excellent potential to improve clinical response.

View details for DOI 10.1021/mp060016h

View details for Web of Science ID 000203539600011

View details for PubMedID 16889440

Abstract

The design, synthesis, and evaluation of conjugates of arginine-rich transporters and luciferin are described that release luciferin only after entry into cells that are stably transfected with luciferase. Each molecule of free luciferin that is released after entry generates a photon that can be measured allowing for real-time quantification of uptake and release in cells. The process provides a method to assay uptake and release of free luciferin as a function of variations in the releasable linker and in the transporter.

View details for DOI 10.1021/ja0586283

View details for Web of Science ID 000237590500002

View details for PubMedID 16704230

Abstract

As part of our studies of metal-catalyzed [m + n (+...o)] cycloadditions, we have previously reported the rhodium-catalyzed [5 + 2] cycloaddition of vinylcyclopropanes (VCPs) and pi-systems. These studies have led to Rh(I) complexes that catalyze these reactions in minutes at room temperature or in water without organic solvents. We describe a comparative evaluation of several chiral catalysts for the [5 + 2] reaction, evaluation of a preferred catalyst, [((R)-BINAP)Rh]+SbF6-, with substrates differing in substitution and tether types-producing enantiomeric excesses >/=95% for several systems. A predictive model for the selectivity is also presented.

View details for DOI 10.1021/ja058590u

View details for Web of Science ID 000237590400017

View details for PubMedID 16683779

Abstract

Delivery of therapeutics and imaging agents to target tissues requires localization and activation strategies with molecular specificity. Cell-associated proteases can be used for these purposes in a number of pathologic conditions, and their enzymatic activities can be exploited for activation strategies. Here, molecules based on the d-arginine octamer (r8) protein-transduction domain (PTD, also referred to as molecular transporters) have been adapted for selective uptake into cells only after proteolytic cleavage of a PTD-attenuating sequence by the prostate-specific antigen (PSA), an extracellular protease associated with the surface and microenvironment of certain prostate cancer cells. Convergent syntheses of these activatable PTDs (APTDs) are described, and the most effective r8 PTD-attenuating sequence is identified. The conjugates are shown to be stable in serum, cleaved by PSA, and taken up into Jurkat (human T cells) and PC3M prostate cancer cell lines only after cleavage by PSA. These APTD peptide-based molecules may facilitate targeted delivery of therapeutics or imaging agents to PSA-expressing prostate cancers.

View details for DOI 10.1021/bc0503216

View details for Web of Science ID 000237576000029

View details for PubMedID 16704219

Abstract

[structure: see text] The first member of a new class of five-membered B-ring analogs of bryostatin has been synthesized and tested for its ability to bind and translocate protein kinase C (PKC). This synthesis extends the utility of our previously introduced macrotransacetalization strategy to the formation of five-membered dioxolane B-ring analogs. This analog exhibits potent, single-digit nanomolar affinity to PKC and selectively translocates novel PKC isozymes.

View details for DOI 10.1021/ol060457z

View details for Web of Science ID 000237174500037

View details for PubMedID 16623578

Abstract

The first [4+2+2] cycloadditions involving terminal alkynes and diene-enes, including a fully intramolecular example, are reported resulting in the formation of cyclooctadienes using [RhCl(CO)2]2 (5 mol %) treated with AgSbF6 (10 mol %) as a precatalyst. The reaction is general for a variety of terminal alkynes, as well as variously substituted diene-enes (yields up to 88%).

View details for DOI 10.1021/ja060878b

View details for Web of Science ID 000237125100027

View details for PubMedID 16620102

Abstract

[reaction: see text] A step-economical synthesis of 11-desmethyllaulimalide (2) is reported. This simplified analogue is available through an improved second-generation synthetic approach to the laulimalides, in a shorter step count and from much less expensive starting material than the parent compound. This new lead retains the anticancer function of laulimalide.

View details for DOI 10.1021/o1060233g

View details for Web of Science ID 000236397000064

View details for PubMedID 16562928

Abstract

[structure: see text] Apoptolidin (1) exhibits potent and highly selective apoptosis inducing activity against sensitive cancer cell lines and is hypothesized to act by inhibition of mitochondrial F(0)F(1)-ATP synthase. A series of apoptolidin derivatives, including a new intermolecular Diels-Alder adduct, were analyzed for antiproliferative activity in E1A-transformed rat fibroblasts. Potent F(0)F(1)-ATPase inhibition was not a sufficient determinant of antiproliferative activity for several analogues, suggesting the existence of a secondary biological target or more complex mode of action for apoptolidin.

View details for DOI 10.1021/ol052800q

View details for Web of Science ID 000235534800011

View details for PubMedID 16468718

View details for DOI 10.1002/anie.200600806

View details for Web of Science ID 000238501500013

View details for PubMedID 16683295

View details for DOI 10.1002/anie.200600300

View details for Web of Science ID 000236768600029

View details for PubMedID 16526073

Abstract

[reaction: see text] Nine fluorescently labeled structurally varied polyguanidino dendrimers based on diamino acid monomeric units were individually synthesized in an efficient, scalable sequence using a trifluoroacetamide protecting group-perguanidinylation strategy. While the dendrimers varied significantly in their ability to enter a human lymphocyte cell line, the best transporters out-performed an oligoarginine reference standard.

View details for DOI 10.1021/ol051496y

View details for Web of Science ID 000232817700008

View details for PubMedID 16235896

Abstract

[reaction: see text] Apoptolidin (1) is a promising new therapeutic lead that exhibits remarkable selectivity against cancer cells relative to normal cells. We report the isolation, characterization, solution structure, stability, and biological activity of two new members of this family: apoptolidins B (2) and C (3). These new agents are found to have antiproliferative activity on par with or better than apoptolidin itself in an assay with H292 lung cancer cells.

View details for DOI 10.1021/ol051074o

View details for Web of Science ID 000230213100056

View details for PubMedID 15987196

Abstract

The syntheses of three newly designed bryostatin analogues are reported. These simplified analogues, which lack the A-ring present in the natural product but possess differing groups at C9, were obtained using a divergent approach from a common intermediate. All three analogues exhibit potent, single-digit nanomolar affinity to protein kinase C.

View details for DOI 10.1021/ol0504650

View details for Web of Science ID 000228984500028

View details for PubMedID 15876038

Abstract

Initial examples of the intermolecular Rh(I)-catalyzed [5+2] cycloaddition reaction of bifunctional allenes and vinylcyclopropanes are described. The reactions proceed with facility and in yields of up to 99% with a variety of alkyne-, ester-, styrene-, or cyano-substituents on the allene to afford the corresponding cycloadducts. In the presence of CO, the reaction proceeds to an eight-membered ring cycloadduct and its transannularly closed product, providing the first example of a three-component [5+2+1] cycloaddition with allenes.

View details for DOI 10.1021/ja043671w

View details for Web of Science ID 000229055800015

View details for PubMedID 15869263

Abstract

[structure: see text] The C20 region of our bryostatin analogs was identified as a nonpharmacophoric site that could be varied to tune analogs for function and physical properties without significantly affecting their binding affinity for PKC. The use of this site in a late-stage diversification strategy has enabled the facile synthesis of a variety of new C20 analogs, all of which retain nanomolar affinity for PKC, in agreement with our pharmacophore hypothesis.

View details for DOI 10.1021/ol0501931

View details for Web of Science ID 000227621000056

View details for PubMedID 15760168

Abstract

Prompted by the view that intermediates of transition metal-catalyzed reactions could be intercepted by one or more additional components, studies in our laboratory have led to the design and development of new three-component [5+2+1], [4+2+1], and [2+2+1] cycloadditions. These continuing studies have now led to the identification of a fundamentally new four-component [5+1+2+1] cycloaddition reaction of vinylcyclopropanes, alkynes and CO, yielding hydroxyindanone products in generally good yields. Terminal alkynes bearing aryl or alkyl groups are tolerated well. Substitution at any position of the VCP leads predictably to substituted hydroxyindanone products. Using a bis-alkynyl substrate, the reaction can be carried out bi-directionally, forming 10 C-C bonds and four new rings from seven components in a single, operationally simple process.

View details for DOI 10.1021/ja042728b

View details for Web of Science ID 000227479600021

View details for PubMedID 15740103

Abstract

A mechanistic hypothesis is presented for how water-soluble guanidinium-rich transporters attached to small cargoes (MW ca. <3000) can migrate across the non-polar lipid membrane of a cell and enter the cytosol. Positively charged and water-soluble, arginine oligomers can associate with negatively charged, bidentate hydrogen bond acceptor groups of endogenous membrane constituents, leading to the formation of membrane-soluble ion pair complexes. The resultant less polar, ion pair complexes partition into the lipid bilayer and migrate in a direction, and with a rate, influenced by the membrane potential. The complex dissociates on the inner leaf of the membrane and the transporter conjugate enters the cytosol. This mechanism could also be involved in the translocation of guanidinium-rich molecules that are endocytosed due to their size or the conditions of the assay, across the endosomal membrane.

View details for DOI 10.1016/j.addr.2004.10.003

View details for Web of Science ID 000227570500003

View details for PubMedID 15722160

Abstract

Treatment of highly potent and densely functionalized bryostatin analogue 1 with dimethyldioxirane afforded the C-9 hydroxylated hemiketal 2 via oxyfunctionalization of the C9-CH bond, one of 12 CH bonds geminal to an oxygen substituent in 1. When bryostatin analogue 3 was subjected to identical conditions, oxidation of a C-26 secondary hydroxyl group was found to compete with C-9 hydroxylation. Complete selectivity for C-9 hydroxylation was restored upon acylation of the C-26 secondary alcohol.

View details for DOI 10.1021/o1047859w

View details for Web of Science ID 000226072100020

View details for PubMedID 15624982

Abstract

Structurally simplified analogs of bryostatin 1, a marine natural product in clinical trials for the treatment of cancer, have been shown to be up to 50 times more potent than bryostatin 1 at inducing the translocation of PKCdelta-GFP from the cytosol of rat basophilic leukemia (RBL) cells. The end distribution of the protein is similar for all three compounds, despite a significant difference in translocation kinetics. The potency of the compounds for inducing the translocation response appears to be only qualitatively related to their binding affinity for PKC, highlighting the importance of using binding affinity in conjunction with real-time measurements of protein localization for the pharmacological profiling of biologically active agents.

View details for DOI 10.1016/j.chembiol.2004.06.014

View details for Web of Science ID 000224228900009

View details for PubMedID 15380186

Abstract

The results described herein support a mechanistic hypothesis for how guanidine-rich transporters attached to small cargos (MW ca. <3000) can migrate across the lipid membrane of a cell and directly enter the cytosol. Arginine oligomers are found to partition almost completely into the aqueous layer of a water-octanol bilayer. However, when the same partitioning experiment is conducted in the presence of sodium laurate, a representative negatively charged membrane constituent, the arginine oligomer partitions almost completely (>95%) into the octanol layer. In contrast, ornithine oligomers partition almost exclusively into the water layer with and without added sodium laurate. The different partitioning between guanidinium-rich and ammonium-rich oligomers in the presence of sodium laurate is consistent with the ability of the former to form a bidentate hydrogen bonded ion pair. Mono- and dimethylated arginine oligomers, which like ornithine can only efficiently form monodentate hydrogen bonds, were prepared and found to exhibit poor cellular uptake. Ion pair formation converts a once water-soluble agent to a lipid-soluble agent, thereby reducing the energetic penalty for passage of guanidine-rich transporters through the lipid bilayer. Uptake of guanidine-rich transporters is known to be an energy-dependent process, and this requirement for cellular ATP is now rationalized by the inhibition of guanidine-rich transporter uptake in the presence of agents that reduce the membrane potential. Specifically, incubation of cells in buffers with high potassium ion concentrations or pretreatment of cells with gramicidin A reduces the cellular uptake of Fl-aca-arg8-CONH2 by >90%. Furthermore, the reciprocal experiment of hyperpolarizing the cell with valinomycin increased uptake by >1.5 times. In summary, we propose that the water-soluble, positively charged guanidinium headgroups of the transporter form bidentate hydrogen bonds with H-bond acceptor functionality on the cell surface. The resultant ion pair complexes partition into the lipid bilayer and migrate across at a rate related to the membrane potential. The complex dissociates on the inner leaf of the membrane, and the transporter enters the cytosol. This hypothesis does not preclude uptake by other mechanisms, including endocytosis, which is likely to dominate with large cargos.

View details for DOI 10.1021/ja0482536

View details for Web of Science ID 000223110100020

View details for PubMedID 15291531

Abstract

The interactions between various functionalized carbon nanotubes and several types of human cancer cells are explored. We have prepared modified nanotubes and have shown that these can be derivatized in a way that enables attachment of small molecules and of proteins, the latter through a novel noncovalent association. The functionalized carbon nanotubes enter nonadherent human cancer cells as well as adherent cell lines (CHO and 3T3) and by themselves are not toxic. While the fluoresceinated protein streptavidin (MW approximately 60 kD) by itself does not enter cells, it readily enters cells when complexed to a nanotube-biotin transporter and exhibits dose-dependent cytotoxicity. The uptake pathway is consistent with adsorption-mediated endocytosis. The use of carbon nanotubes as molecular transporters could be exploited for various cargos. The biocompatibility and unique physical, electrical, optical, and mechanical properties of nanotubes provide the basis for new classes of materials for drug, protein, and gene delivery applications.

View details for DOI 10.1021/ja0486059

View details for Web of Science ID 000221828200007

View details for PubMedID 15174838

Abstract

Initial examples of a Rh(I)-catalyzed [2+2+1] reaction of diene-enes and CO are described. This method allows for the facile, efficient, and diastereoselective construction of a variety of alkenyl cyclopentanones in good to excellent yields. Control studies show that the diene moiety is required for this process as bis-enes do not give the [2+2+1] products under the same conditions.

View details for Web of Science ID 000221416700010

View details for PubMedID 15137743

Abstract

Bryostatin 1 represents a novel and potent therapeutic lead with a unique activity profile. Its natural and synthetic availability is severely limited. Function oriented synthesis provides a means to address this supply problem through the design of synthetically more accessible simplified structures that at the same time incorporate improved functional activity. Pharmacophore searching and a new computer aided visualization of a possible binding mode are combined with an understanding of function and knowledge of synthesis to design and prepare a new and simplified compound with bryostatin-like function in biological systems. This new compound is a potent ligand for protein kinase C in vitro (K(i) = 8.0 nM). More significantly, the described molecule retains the functional ability to translocate a PKCdelta-GFP fusion protein in RBL cells. The extent of protein translocation and the sub-cellular localization induced by this new compound is similar to that seen in response to bryostatin 1, indicating that the new molecule retains the functional activity of the natural product but is simpler and can be synthesized in a practical fashion.

View details for PubMedID 16472215

View details for DOI 10.1002/anie.200454117

View details for Web of Science ID 000222067400021

View details for PubMedID 15188486

Abstract

[reaction: see text] A new approach to the synthesis of the C ring subunit of known and potential bryostatin analogues is described. The convergent approach, illustrated above, requires fewer steps and offers greater flexibility in rapidly accessing diverse C ring analogues.

View details for DOI 10.1021/ol0355332

View details for Web of Science ID 000186728600005

View details for PubMedID 14627380

Abstract

[reaction: see text] The syntheses of five laulimalide analogues are described, incorporating modifications at the C(16)-C(17)-epoxide, the C(20)-alcohol, as well as the C(1)-C(3)-enoate of the parent natural product. The resultant analogues are active in drug-sensitive HeLa and MDA-MB-435 cell lines. Significantly, like laulimalide, these analogues are poor substrates for the drug transport protein P-glycoprotein (Pgp) and are thus effective against Taxol-resistant cell lines.

View details for DOI 10.1021/ol035339f

View details for Web of Science ID 000185329300036

View details for PubMedID 12967311

Abstract

Oxidative cleavage of the C-20/C-21 bond in apoptolidin (1) provides two fragments of similar complexity, facilitating a divide-and-diversify strategy for the determination of the structural basis for apoptolidin's biological activity, the remarkably selective induction of apoptosis in sensitive cell lines. The ability of compounds derived from this cleavage to inhibit mitochondrial F(0)F(1)-ATPase is reported. [structure: see text]

View details for DOI 10.1021/ol0346335

View details for Web of Science ID 000183692600027

View details for PubMedID 12816433

Abstract

Bromofluoroacetophenone derivatives which produce fluorine substituted phenyl radicals that cleave DNA upon excitation were investigated as a novel photonuclease. Pyrrolecarboxamide-conjugated bromofluoroacetophenones; 4'-bromo-2'-fluoroacetophenone and 2'-bromo-4'-fluoroacetophenone were synthesized and their DNA cleaving activities and sequence selectivities were determined. Bromofluoroacetophenone-pyrrolecarboxamide conjugates were found to be effective DNA cleaving agents upon irradiation in concentration dependent manner based on plasma relaxation assay. The DNA cleaving activities of 2'-bromo-4'-fluoroacetophenone derivatives were larger than those of 4'-bromo-2'-fluoroacetophenone derivatives.

View details for DOI 10.1016/S0960-894X(03)00212-9

View details for Web of Science ID 000182913600034

View details for PubMedID 12729660

Abstract

The use of peptide or peptidomimetic transporters to enable or enhance the uptake of drugs or probe molecules into cells and tissues has received increasing research attention and clinical interest over the past 10 years. This review summarizes a class of transporters that have been studied and focuses on the variation and use of guanidinium based transporters to facilitate the uptake of various types of molecules into cells and tissues. Lead conjugates in this area are currently in clinical trials.

View details for Web of Science ID 000181704200004

View details for PubMedID 12678850

Abstract

[reaction: see text] To investigate the structural basis for the exceptional selectivity and activity of apoptolidin (1), a strategy has been devised that allows for selective functionalization of seven of its eight hydroxyl groups based on progressive silyl protection, derivatization, and deprotection. The syntheses of these derivatives and their ability to inhibit F(0)F(1)-ATPase are reported.

View details for DOI 10.1021/ol027366w

View details for Web of Science ID 000181077200027

View details for PubMedID 12583750

Abstract

[reaction: see text] A concise, asymmetric synthesis of the polyketide spacer domain portion (C1-C13) of a highly potent bryostatin analogue was developed. The route utilizes asymmetric hydrogenation methodology to install the C3, C5, and C11 stereocenters, while a substrate directed syn reduction sets the C9 stereocenter. The spacer domain 1 is obtained in 10 steps with a 25% overall yield and is readily incorporated into the synthesis of 2.

View details for DOI 10.1021/ol0272390

View details for Web of Science ID 000180766400012

View details for PubMedID 12556171

View details for Web of Science ID 000182751700018

View details for PubMedID 12722081

Abstract

The first example of a transition metal-catalyzed hetero-[5 + 2] cycloaddition reaction is described. Use of cyclopropyl imines as five-atom components, an alkyne as a two-carbon component, and a Rh(I) catalyst enables a new route to dihydroazepines. This new hetero-[5 + 2] cycloaddition works well with aldimines, ketimines, and with substituted cyclopropanes and affords the desired dihydroazepines in excellent yields as single regioisomers. Use of serial imine formation/aza-[5 + 2] cycloaddition generates the desired dihydroazepines in one operation from three commercially available starting materials. The reaction has been scaled to give gram quantities of dihydroazepine.

View details for DOI 10.1021/ja0285013

View details for Web of Science ID 000180006600005

View details for PubMedID 12487573

Abstract

Macrocycle 1 is a new highly potent analogue of bryostatin 1, a promising anti-cancer agent currently in human clinical trials. In vitro, 1 displays picomolar affinity for PKC and exhibits over 100-fold greater potency than bryostatin 1 when tested against various human cancer cell lines. Macrocycle 1 can be generated in clinically required amounts by chemical synthesis in only 19 steps (LLS) and represents a new clinical lead for the treatment of cancer.

View details for DOI 10.1021/ja027509+

View details for Web of Science ID 000179269800004

View details for PubMedID 12431074

Abstract

Molecular transporters have the ability to deliver drugs and probe molecules into cells and tissues irrespective of their physical properties. We now report the design, synthesis, and biological evaluation of a new family of molecular transporters, guanidinylated oligocarbamates that enable exceptionally efficient uptake into cells and tissues. The synthesis features a solid-phase stepwise oligomerization to obtain the oligocarbamates and a single step perguanidinylation for the facile introduction of up to nine guanidinium groups. The oligocarbamate 9-mer is found to be among the most efficient transporters known, entering cells faster than even d-Arg9 and HIV-1 Tat49-57. Significantly, this new family of transporters also enables uptake into the formidable skin barrier of a probe molecule that by itself does not penetrate skin.

View details for DOI 10.1021/ja0275109

View details for Web of Science ID 000179122900022

View details for PubMedID 12418880

Abstract

[formula: see text] Apoptolidin (1) is a novel oncolytic lead that induces apoptosis in transformed cell lines with exceptional selectivity. We report the isolation and characterization of a ring-expanded macrolide isomer of apoptolidin: isoapoptolidin (2). The solution conformation of isoapoptolidin is described. The rate of isomerization was measured under biologically relevant conditions and found to approach equilibrium within the time frame of most cell-based assays. Isoapoptolidin's ability to inhibit mitochondrial F0F1-ATPase is over 10-fold less than that of apoptolidin.

View details for DOI 10.1021/o10266222

View details for Web of Science ID 000178877500012

View details for PubMedID 12599467

Abstract

(-)-Laulimalide (1), a structurally novel macrolide isolated in trace amounts from marine sponges, promotes abnormal tubulin polymerization and apoptosis in vitro, with a similar mode of action to that of Taxol(R), but with potentially less susceptibility to multidrug resistance. Herein, a flexible and convergent asymmetric synthesis of (-)-laulimalide is described. This synthesis featured a highly diastereoselective Sakurai reaction of 2 with 3 and a regioselective macrolactonization of an unprotected vicinal diol. Laulimalide was synthesized in 25 steps (longest linear; 36 overall) in 3.5% overall yield, providing a uniquely short and efficient route to 1 and its analogues.

View details for DOI 10.1021/ja0258428

View details for Web of Science ID 000175369100012

View details for PubMedID 11982349

Abstract

Prompted by our studies of transition metal-catalyzed [4+4], [4+2], [5+2], and [6+2] cycloadditions and by the view that these two-component reactions could be intercepted by a third component of one or more atoms, a new three-component transition metal-catalyzed cycloaddition is described. This new [5+2+1] cycloaddition proceeds in good to excellent yield and with high or complete regioselectivity with a variety of carbonyl-substituted alkynes to give bicyclo[3.3.0]octenone adducts, resulting from transannular closure of the intermediate eight-membered-ring cycloadduct. Effects of concentration, temperature, pressure, and catalyst loading on the efficiency of the reaction are discussed. This process provides access to complex building blocks for synthesis based on simple, readily available components.

View details for DOI 10.1021/ja0176301

View details for Web of Science ID 000174520500012

View details for PubMedID 11902870

View details for Web of Science ID 000179752500035

View details for PubMedID 12458535

Abstract

Recently, we reported a novel oligoguanidine transporter system, polyarginine (R(7)), which, when conjugated to spectroscopic probes (e.g., fluorescein) and drugs (e.g., cyclosporin A), results in highly water-soluble conjugates that rapidly enter cells and tissues. We report herein the preparation of the first R(7) peptide conjugates and a study of their cellular and organ uptake and functional activity. The octapeptide (psi)(epsilon)RACK was selected for this study as it is known to exhibit selective epsilon protein kinase C isozyme agonist activity and to reduce ischemia-induced damage in cardiomyocytes. However, (psi)(epsilon)RACK is not cell-permeable.Here we show that an R(7)-(psi)(epsilon)RACK conjugate readily enters cardiomyocytes, significantly outperforming (psi)(epsilon)RACK conjugates of the transporters derived from HIV Tat and from Antennapedia. Moreover, R(7)-(psi)(epsilon)RACK conjugate reduced ischemic damage when delivered into intact hearts either prior to or after the ischemic insult.Our data suggest that R(7) converts a peptide lead into a potential therapeutic agent for the ischemic heart.

View details for Web of Science ID 000173750400001

View details for PubMedID 11755391

Abstract

[reaction: see text]. Short oligomers of arginine function as remarkably efficient molecular transporters of drugs and probe molecules into cells and tissue. Currently, these compounds are prepared on resin through a unidirectional solid-phase synthesis. To extend the utility of these compounds for therapeutic and research applications, a scalable solution-phase synthesis of Arg8 (1) has been developed on the basis of a segment doubling strategy that proceeds in 13 steps and 28% overall yield from 4, including a novel one-step perdeprotection-perguanidinylation reaction.

View details for DOI 10.1021/ol0161108

View details for Web of Science ID 000171708000001

View details for PubMedID 11594801

Abstract

[reaction: see text] A concise asymmetric synthesis of the tricyclic core of cyathane diterpenes is described, based on a novel transition-metal-catalyzed intramolecular [5 + 2] cycloaddition of ynone-vinylcyclopropane 10 (assembled from commercially available (S)-(-)-limonene), which proceeds in 90% yield with >95% selectivity. This strategy provides efficient access (14 steps and 13% overall yield) to potential analogues as well as precursors of nerve growth factor (NGF)-inducing diterpenes.

View details for DOI 10.1021/ol0160699

View details for Web of Science ID 000169487700036

View details for PubMedID 11418060

View details for Web of Science ID 000166258800024

View details for PubMedID 11273617

View details for Web of Science ID 000171698000036

View details for PubMedID 11668567

Abstract

Certain proteins contain subunits that enable their active translocation across the plasma membrane into cells. In the specific case of HIV-1, this subunit is the basic domain Tat(49-57) (RKKRRQRRR). To establish the optimal structural requirements for this translocation process, and thereby to develop improved molecular transporters that could deliver agents into cells, a series of analogues of Tat(49-57) were prepared and their cellular uptake into Jurkat cells was determined by flow cytometry. All truncated and alanine-substituted analogues exhibited diminished cellular uptake, suggesting that the cationic residues of Tat(49-57) play a principal role in its uptake. Charge alone, however, is insufficient for transport as oligomers of several cationic amino acids (histidine, lysine, and ornithine) are less effective than Tat(49-57) in cellular uptake. In contrast, a 9-mer of l-arginine (R9) was 20-fold more efficient than Tat(49-57) at cellular uptake as determined by Michaelis-Menton kinetic analysis. The d-arginine oligomer (r9) exhibited an even greater uptake rate enhancement (>100-fold). Collectively, these studies suggest that the guanidinium groups of Tat(49-57) play a greater role in facilitating cellular uptake than either charge or backbone structure. Based on this analysis, we designed and synthesized a class of polyguanidine peptoid derivatives. Remarkably, the subset of peptoid analogues containing a six-methylene spacer between the guanidine head group and backbone (N-hxg), exhibited significantly enhanced cellular uptake compared to Tat(49-57) and even to r9. Overall, a transporter has been developed that is superior to Tat(49-57), protease resistant, and more readily and economically prepared.

View details for Web of Science ID 000165476300022

View details for PubMedID 11087855

Abstract

Many systemically effective drugs such as cyclosporin A are ineffective topically because of their poor penetration into skin. To surmount this problem, we conjugated a heptamer of arginine to cyclosporin A through a pH-sensitive linker to produce R7-CsA. In contrast to unmodified cyclosporin A, which fails to penetrate skin, topically applied R7-CsA was efficiently transported into cells in mouse and human skin. R7-CsA reached dermal T lymphocytes and inhibited cutaneous inflammation. These data establish a general strategy for enhancing delivery of poorly absorbed drugs across tissue barriers and provide a new topical approach to the treatment of inflammatory skin disorders.

View details for Web of Science ID 000165114800033

View details for PubMedID 11062537

Abstract

A concise asymmetric total synthesis of (+)-aphanamol I is described, based on the transition metal catalyzed [5 + 2] allenyl-vinylcyclopropane cycloaddition. The key cycloaddition precursor is convergently assembled from (R)-(+)-limonene and cyclopropane diester through a novel decarboxylative dehydration reaction. The metal-catalyzed [5 + 2] cycloaddition of this precursor proceeds with complete chemo, endo/exo, and diastereoselectivity in 93% yield, representing an effective general route to bicyclo[5.3.0]decane derivatives.

View details for Web of Science ID 000088346400037

View details for PubMedID 10930274

Abstract

Described herein is an efficient preparative scale synthesis of 1-(2-methyoxyethoxy)-1-vinylcyclopropane and the investigation of the utility of this reagent as a new five-carbon component in metal-catalyzed [5 + 2] cycloadditions. A new cycloaddition procedure is also described that proceeds up to 12-fold faster and with 10-fold less catalyst than previously described, providing cycloheptenones in many cases in minutes and in isolated yields of 75-97%. The procedure is readily conducted on a small or large scale (up to 100 mmol thus far).

View details for PubMedID 10841491

Abstract

[formula: see text] 4'-Bromoacetophenone derivatives which upon excitation can generate monophenyl radicals capable of hydrogen atom abstraction were investigated as photoinducible DNA cleaving agents. Pyrrolecarboxamide-conjugated 4'-bromoacetophenones were synthesized, and their DNA cleaving activities and sequence selectivities were determined.

View details for Web of Science ID 000084980700020

View details for PubMedID 10836065

Abstract

[formula: see text] A unique class of simplified phorbol ester analogues is described for the first time. A highly efficient retro-annelation sequence was developed in order to remove the five-membered ring from the phorbol diterpene core, allowing access to BCD ring analogues of the phorbol esters. The binding of these analogues to protein kinase C (PKC) and the truncated peptide eta PKC-C1B (eta PKC-CRD2) is also reported.

View details for Web of Science ID 000085171900013

View details for PubMedID 10825954

Abstract

Designed bryostatin analogues are assayed for binding affinity to individual cysteine rich domains of several protein kinase C (PKC) isozymes. These analogues exhibit significant selectivity for the PKCdelta-C1B peptide in terms of absolute affinity and the PKCdelta-C1A peptide in terms of relative affinity when compared to phorbol-12,13-dibutyrate.

View details for Web of Science ID 000080896500013

View details for PubMedID 10397502

Abstract

The bryostatins are a unique family of emerging cancer chemotherapeutic candidates isolated from marine bryozoa. Although the biochemical basis for their therapeutic activity is not known, these macrolactones exhibit high affinities for protein kinase C (PKC) isozymes, compete for the phorbol ester binding site on PKC, and stimulate kinase activity in vitro and in vivo. Unlike the phorbol esters, they are not first-stage tumor promoters. The design, computer modeling, NMR solution structure, PKC binding, and functional assays of a unique class of synthetic bryostatin analogs are described. These analogs (7b, 7c, and 8) retain the putative recognition domain of the bryostatins but are simplified through deletions and modifications in the C4-C14 spacer domain. Computer modeling of an analog prototype (7a) indicates that it exists preferentially in two distinct conformational classes, one in close agreement with the crystal structure of bryostatin 1. The solution structure of synthetic analog 7c was determined by NMR spectroscopy and found to be very similar to the previously reported structures of bryostatins 1 and 10. Analogs 7b, 7c, and 8 bound strongly to PKC isozymes with Ki = 297, 3.4, and 8.3 nM, respectively. Control 7d, like the corresponding bryostatin derivative, exhibited weak PKC affinity, as did the derivative, 9, lacking the spacer domain. Like bryostatin, acetal 7c exhibited significant levels of in vitro growth inhibitory activity (1.8-170 ng/ml) against several human cancer cell lines, providing an important step toward the development of simplified, synthetically accessible analogs of the bryostatins.

View details for Web of Science ID 000074131900012

View details for PubMedID 9618462

View details for PubMedID 11848741

View details for PubMedID 11667717

Abstract

The family of homologous enzymes known as protein kinase C (PKC) has been the object of intense interest because of its crucial role in cellular signal transduction. Although considerable information about the activation of PKC has been gained through structure-activity, molecular modeling, and synthetic studies of both natural and designed activators, information about the structure of PKC itself has been limited by its large size and requirement for phospholipid cofactors. Additionally, difficulties in the purification of truncated mutants of PKC have thus far prevented their analysis by nuclear magnetic resonance (NMR) or x-ray crystallographic methods. We describe the identification, synthesis, ligand-binding analysis, cofactor requirements, and preliminary NMR evaluation of two subdomains (peptides B and C) of the regulatory domain of PKC-gamma. Peptides B and C bind [3H]phorbol 12,13-dibutyrate with good affinity (Kd = 6.4 microM and 414 nM, respectively) in the presence of phosphatidylserine. In comparison, the binding affinity of [3H]phorbol 12,13-dibutyrate for PKC was found to be 2.6 nM. Like PKC itself, these peptides also recognize other PKC activators, including dioctanoylglycerol and teleocidin B-4, and exhibit an ability to differentiate phorbol ester from its C-4 epimer. NMR studies of PKC subdomains are also described, indicating that both peptides B and C are well behaved in solution and do not exhibit any concentration-dependent changes. Finally, these studies reveal that peptide B becomes conformationally ordered only in the presence of phospholipid, suggesting that the regulatory domain of PKC itself might be organized for activation only when associated with the lipid bilayer, where its activator (diacylglycerol) is encountered.

View details for Web of Science ID A1995QB23800049

View details for PubMedID 7816824

Abstract

Dynemicin A is a recently identified antitumor antibiotic. Upon activation, dynemicin is reported to cause double-stranded cleavage of DNA, putatively through the intermediacy of a diradical. Computer modeling of this activation and cleavage process is described herein as part of an effort to establish a structural hypothesis for this mechanistic sequence and for the design of simple analogues. Intercalation complexes of duplex dodecamers [d(CGCGAATTCGCG)]2 and [d(GC)6]2 with both enantiomers of dynemicin and of all related mechanistic intermediates are evaluated. Examination of these structures shows that cycloaromatization of dynemicin to a diradical intermediate results in the rotation of the diradical-forming subunit with respect to the intercalation plane that is of an opposite sense for the two dynemicin enantiomers. In addition, the activation of the (2S) enantiomer of dynemicin occurs by a less restricted approach trajectory than the corresponding (2R) enantiomer. In all complexes, the 5'-3' strand is at least 1 A closer than the 3'-5' strand to the diyl intermediate. As a result, complexes are produced in which the diyl moiety is aligned along [(2S)] or across [(2R)] the minor groove, leading to different predictions for the selectivity of radical-initiated, oxidative lesion of DNA. Molecular dynamics simulations are found to support these predictions, including the 3-base-pair offset cleavage reported for dynemicin.

View details for Web of Science ID A1991GH80500114

View details for PubMedID 1924343

Abstract

The bryostatins are macrocyclic lactones that represent an additional structural class of potent activators of protein kinase C. These marine animal biosynthetic products are of unusual interest because they induce only a subset of the biological responses induced by the phorbol esters. We have now determined the binding affinities of naturally occurring and semisynthetic bryostatins for protein kinase C by competition analysis with [26-3H]bryostatin 4 as the radioactive ligand. Esterification of the hydroxyl group at C26 caused dramatic loss of activity as did inversion of the asymmetric center at this position. In contrast, neither of the ester groups at C7 and C20 had a major influence on activity. Computer modeling of the phorbol esters, related diterpenes, and indole alkaloids suggested that the C20, C9, and C4 oxygens of phorbol represented critical elements of the phorbol ester pharmacophore. The C26 oxygen of the bryostatins, together with the C1 and C19 oxygens, gave an excellent spatial correlation with this model, with a root-mean-square deviation of 0.16 A (compared to 0.10-0.35 A among phorbol-related diterpenes). The extension of the phorbol ester pharmacophore model to the bryostatins and its agreement with the structure-activity relations for the bryostatin class of compounds provide additional support for the validity of the model.

View details for Web of Science ID A1988Q358500033

View details for PubMedID 3174627