Deprotection Strategies for Thioimidates During Fmoc Solid-Phase Peptide Synthesis: A Safe Route to Thioamides

Thioamides are important biophysical probes of peptide folding, but are prone to alpha-C epimerization during Fmoc solid-phase peptide synthesis. The stereochemical integrity of thioamide-containing peptides can be dramatically improved by protecting the thioamide as a thioimidate during synthesis. A drawback of this approach, however, is that once synthesis of the peptide is complete, regeneration of the thioamide requires the toxic, corrosive, and flammable gas H2S. This work examines several approaches to supplant H2S as a deprotection reagent in favor of a safer and more convenient alternative. Ultimately, a new application of the 4-azidobenzyl protecting group to thioamides was found to provide the most suitable means of both protection of alpha-C stereochemistry and conversion back to thioamide.

Deprotection Strategies for Thioimidates During Fmoc Solid-Phase Peptide Synthesis: A Safe Route to Thioamides

Thioamides are important biophysical probes of peptide folding, but are prone to alpha-C epimerization during Fmoc solid-phase peptide synthesis. The stereochemical integrity of thioamide-containing peptides can be dramatically improved by protecting the thioamide as a thioimidate during synthesis. A drawback of this approach, however, is that once synthesis of the peptide is complete, regeneration of the thioamide requires the toxic, corrosive, and flammable gas H2S. This work examines several approaches to supplant H2S as a deprotection reagent in favor of a safer and more convenient alternative. Ultimately, a new application of the 4-azidobenzyl protecting group to thioamides was found to provide the most suitable means of both protection of alpha-C stereochemistry and conversion back to thioamide.

Recombinant thiopeptides containing noncanonical amino acids

Thiopeptides are a subclass of ribosomally synthesized and posttranslationally modified peptides (RiPPs) with complex molecular architectures and an array of biological activities, including potent antimicrobial activity. Here we report the generation of thiopeptides containing noncanonical amino acids (ncAAs) by introducing orthogonal amber suppressor aminoacyl-tRNA synthetase/tRNA pairs into a thiocillin producer strain ofBacillus cereus. We demonstrate that thiopeptide variants containing ncAAs with bioorthogonal chemical reactivity can be further postbiosynthetically modified with biophysical probes, including fluorophores and photo-cross-linkers. This work allows the site-specific incorporation of ncAAs into thiopeptides to increase their structural diversity and probe their biological activity; similar approaches can likely be applied to other classes of RiPPs.

Biological chemistry of the carbon–sulfur bond

Carbon–sulfur biological chemistry encompasses a fascinating area of biochemistry and medicinal chemistry and includes the roles that methionine and S-adenosyl-l-methionine play in cells as well as the chemistry of intracellular thiols such as glutathione. This article, based on the 2014 Bernard Belleau Award lecture, provides an overview of some of the key investigations that were undertaken in this area from a bioorganic perspective. The research has ameliorated our fundamental knowledge of several of the enzymes utilizing these sulfur-containing molecules, has led to the development of several novel 19F biophysical probes, and has explored some of the medicinal chemistry associated with these processes.