Thioamide Labeling of Proteins through a Combination of Semisynthetic Methods

Biosynthesis and Chemical Applications of Thioamides

“…Destabilizing effects in α-helices however, were comparatively mild, and some of the destabilizing effects in α-helices can be 'rescued' with the incorporation of a second thioamide. 140 However, the observed effects cannot fully be rationalized using crystal structures of the native proteins. Determining high-resolution structures of the thioamide proteins themselves will benefit the field substantially.…”

“…Although there have been various approaches to this problem, 135,141 the use of a 2% (v/ v) solution of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) seems to give the best combination of high deprotection efficiency and minimal epimerization. This is particularly important for the synthesis of peptides containing multiple adjacent thioamides, 137,142 motifs found in the thioviridamide family of compounds. While alternate methods such as recently developed ynamide-based couplings may lead to further improvements, 143 with these considerations, the thioacylbenzotriazoles can be used to access many thioamidecontaining peptides.…”

“…Destabilizing effects in α-helices, however, were comparatively mild, and some of the destabilizing effects in αhelices can be "rescued" with the incorporation of a second thioamide. 142 While Raines and others have shown that thioamides can exert stabilizing effects in model peptide systems by increasing the strength of n → π* interactions between i and i + 1 carbonyls, these have not obviously contributed to the stabilizing effects observed to date in protein systems. 137,171,172 However, many of the observed effects cannot fully be rationalized using crystal structures of the native proteins.…”

“…8 Biophysical chemists have used thioamides for perturbing protein folding or introducing spectroscopic probes. 9 The discovery of thioamides in several natural products and in a single protein provides new perspective and prompts investigations of the role of the thioamide as well as a search for additional natural thioamide-containing molecules.…”

Site-Specific Incorporation of Multiple Thioamide Substitutions into a Peptide Backbone via Solid Phase Peptide Synthesis

“…Alkyl dithioesters, thiobenzimidazolones, and thioacylnitrobenzotriazoles have been employed as active thioacylating reagents for thioamide-substituted peptide synthesis. Thioacylnitrobenzotriazoles prepared via a three-step transformations from natural α-amino acids (Figure , eq 1) make up the only class of thioacylating reagents that could be used to introduce a thioamide bond via solid phase peptide synthesis (SPPS). , However, this method is limited to 15 of the 20 common proteinogenic α-amino acids . In addition, the preparation of thioacylnitrobenzotriazole involves the use of toxic and malodour thionating reagents.…”