Endothiopeptides synthesis

JR has found application in endothiopeptide synthesis. One carbonyl group of a cyclohexapeptide is selectively thionated with JR (eq 7). The cyclic thiopeptide exhibits enhanced effectiveness as an inhibitor of triosephosphate isomerase (TIM). This results from the pronounced alteration of the backbone conformation which is due to different hydrogen bridges. Belleau s reagent, BR, can be used similarly to JR to prepare thiooligopep-tides selectively or thiono esters of the carbohydrate series (eq 8). ... 

A few a-acylamino dithioesters were successfully synthesized by the Pinner reaction in the early 1970s. 6 9 However, many amino acid and peptide dithioesters have now been prepared by this procedure and used for the synthesis of endothiopeptides 10 and spectroscopic studies of dithioesters. 1 ... 

Amino acid dithioesters have been used as building blocks for the synthesis of en-dothiopeptides, the dithioesters will condense with a-amino groups of N-unprotected amino acids to form thioamides. Preparation of optically active amino acid dithioesters and subsequent formation of thioamide bonds without racemization are two problems that need to be addressed when using this approach to prepare endothiopeptides. The Pinner reaction (Section 15.1.11.1) 1 and Lawesson s procedure (Section 15.1.11.2)M have been successfully used to prepare optically active amino acid dithioesters a modification of Lawesson s procedure via thioamides is also successful.[81... 

In a similar manner, D-camphor-lO-sulfonic acid (10-CSA) has heen used in the synthesis of 2-thiazolines. In the example shown in Scheme 82, endothiopeptide 208 was converted into thiazol-5(4//)-one 209 . 

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