Justin Annes, Postdoctoral Faculty Sponsor
Given the sudden and unexplained rise in the cost of (+)- and (-)-sparteine, an alternative method for the resolution of vaulted biaryls has been developed. This method involves the reaction of a racemic vaulted biaryl ligand with one equivalent of BH3ĚSMe2 and one equivalent of either quinine or quinidine. A precipitate then forms from the resulting mixture of diastereomeric borates as a result of differential solubilities. Hydrolysis of the precipitate then liberates the (S)-ligand in the case of quinine and the (R)-ligand in the case of quinidine, both with >99% ee. This method has been applied to 16 different vaulted biaryl ligands, including 10 whose preparation is described here for the first time. In addition, proof of principle has been demonstrated for the dynamic thermodynamic resolution of the vaulted biaryl ligands with this method in combination with a nonchiral copper(II) complex that can racemize the ligand.
View details for DOI 10.1021/acs.joc.0c00494
View details for PubMedID 32687706
A multicomponent trans-aziridination of aldehydes, amines, and diazo compounds with BOROX catalysts is developed. The optimal protocol is slightly different for aryl aldehydes than for aliphatic aldehydes. The key to the success with aryl aldehydes was allowing the catalyst, aldehyde, and amine to react for 20 min before addition of the diazo compound. A variety of 11 different electron-poor and electron-rich aryl aldehydes were screened to give trans-aziridines in 73-90% yield with 82-99% ee and trans/cis selectivities of 19:1 to >99:1. The optimal protocol for the trans-aziridination of aliphatic aldehydes did not require prereaction of the catalyst, aldehyde, and amine, and instead, the diazo compound could be added directly. The scope of the reaction is limited to unbranched aliphatic aldehydes and was tolerant of a number of functional groups including ethers, esters, epoxides, carbamates, and phthalimides. A total of 10 aliphatic aldehydes were examined and found to give trans-aziridines in 60-88% yield with 60-98% ee and trans/cis selectivities of 6:1 to >99:1. Alkenyl aldehydes did not react, but an alkynyl aldehyde gave a 71% yield and 95% ee of an aziridine that was found to be the cis- and not the trans-diastereomer. The aryl and aliphatic aldehydes both gave the trans-aziridines with the same absolute configuration with the same catalyst; however, in those cases where cis-aziridines were formed, the configuration was opposite for those formed from aryl versus aliphatic aldehydes.
View details for DOI 10.1021/acs.joc.7b02184
View details for Web of Science ID 000418392600017
View details for PubMedID 29084386
Biomolecule labeling using chemical probes with specific biological activities has played important roles for the elucidation of complicated biological processes. Selective bioconjugation strategies are highly-demanded in the construction of various small-molecule probes to explore complex biological systems. Bioorthogonal reactions that undergo fast and selective ligation under bio-compatible conditions have found diverse applications in the development of new bioconjugation strategies. The development of new bioorthogonal reactions in the past decade has been summarized with comments on their potentials as bioconjugation method in the construction of various biological probes for investigating their target biomolecules. For the applications of bioorthogonal reactions in the site-selective biomolecule conjugation, examples have been presented on the bioconjugation of protein, glycan, nucleic acids and lipids.
View details for DOI 10.3390/molecules20023190
View details for Web of Science ID 000350748200082
View details for PubMedID 25690284
View details for PubMedCentralID PMC6290559
Stimuli-responsive hydrogels are "smart" materials with diverse applications. We now report short peptide conjugates with merocyanine (MC) that are able to form stimuli-responsive hydrogels. Systematic investigation reveals that merocyanine is a highly effective promoter for the self-assembly of its oligopeptide conjugates. Hydrogels formed by MC-peptide conjugates showed responses towards light and heat, and their sol-gel phase transition could be manipulated by the reverse photochromism of the corresponding spiropyran moiety. Impressively, a MCI-RGD conjugate formed a supramolecular hydrogel with responses to multiple stimuli, including visible light irradiation, pH change and the presence of Ca(2+) ions. An erasable photo-lithograph on the MCI-RGD hydrogel was demonstrated using visible light to write and heat-and-cool treatment to erase for multiple rounds without significant loss of sensitivity.
View details for DOI 10.1039/c5ob01912e
View details for Web of Science ID 000365412400012
View details for PubMedID 26456175
A supramolecular hydrogel formed by dipeptide Gly-Ala linked with biphenyl-substituted tetrazole serves not only as a 3D matrix for live cells, but also as a carrier to deliver microRNA into the encapsulated cells.
View details for DOI 10.1039/c4cc00156g
View details for Web of Science ID 000332927500020
View details for PubMedID 24577244