Benzotriazole-Mediated Syntheses of Depsipeptides and Oligoesters

Reactions of O-Pg(alpha-hydroxyacyl)benzotriazoles with (a) unprotected alpha-hydroxycarboxylic acids, (b) amino acids, and (c) amines afforded, respectively, chirally pure (a) oligoesters, (b) depsidipeptides, and (c) amide conjugates (yields 52-94%). N-Pg(alpha-Aminoacyl)benzotriazoles reacted with alpha-hydroxycarboxylic acids to yield depsidipeptides (47-87%). N-Pg(depsidipeptidoyl)benzotriazoles, obtained from depsidipeptides, gave depsitripeptides (yields 55-78%) on reaction with amino acids and alpha-hydroxycarboxylic acids. O-Acylation of alpha-hydroxycarboxylic acids with N-Pg(alpha-aminoacyl)benzotriazoles followed by deprotection produced unprotected depsides useful for the preparation of depsitripeptides.