Stereochemical Elucidation of New Sagittamides C - F from a Didemnid Ascidian

Abstract

Four new minor congeners, sagittamides C–F, were isolated from an unidentified Didemnid tunicate that previously afforded sagittamides A and B. The structures were determined by interpretation of spectroscopic data, degradation to amino acids, and comparisons with sagittamide A. An unexpected change in relative configuration of the hexacetoxy C5–C10 stereoelement is present in sagittamides D and F. A tentative assignment of configuration was possible through a systematic deduction based on analysis of 13C NMR data and symmetry considerations.