Site-selective incorporation of thioamide-linkages into a growing peptide

The use of endothiodipeptide anilides, which were obtained in high yields b y a variation of the 'azirine/oxazolone method', for the synthesis of longe r endothiopeptides is described. With this novel methodology, epimerically pure endothiopeptides with the thiocarbonyl group next to the bulky Aib wer e prepared in satisfactory yields. The structures of two endothiotripeptide s and one endothiotetrapeptide were established by single-crystal X-ray cry stallography. (C) 1999 Published by Elsevier Science Ltd. All rights reserv ed.