Dehydrooligopeptides. II. The Synthesis of Dehydrodehydrodipeptides by Direct Coupling and Base-catalyzed β-Elimination

Abstract
The direct coupling between N-protected α-dehydroamino acid (1) and N-free α-dehydroamino acid ester (2) by the acid-chloride method was carried out to give several dehydrodehydrodipeptides (7). Furthermore, the two kinds of dehydrodipeptides with a hydroxyl group, obtained by the coupling of 1 with a serine or threonine ester, and that of N-protected serine or threonine with 2, followed by mesylation and subsequent base-catalyzed β-elimination gave a number of 7 substances in good yields. The configurational structures of 7 obtained by both direct condensation and elimination were found to have (Z,Z)-geometry.