New Cyclic Peptides from the AscidianLissoclinumpatella

Abstract

Four new cyclic peptides, patellamide G (2) and ulithiacyclamides E−G (3−5), along with the known patellamides A−C (6−8) and ulithiacyclamide B (9), were isolated from the ascidian Lissoclinum patella collected in Pohnpei, Federated States of Micronesia. The planar structures of these peptides were determined from 1D and 2D ¹H and ¹³C NMR spectra. The absolute stereochemistries of the amino acid units, except for cysteine, were assigned by chiral GC analysis of N(O)-trifluoroacetyl isopropyl ester derivatives of amino acids obtained by acid hydrolysis of the intact and ozonized peptides. The structures of ulithiacyclamides E−G (3−5) were confirmed by chemical conversion. Patellamides B (7) and C (8) exhibited in vitro modulation of multidrug resistance in CEM/VBL₁₀₀ cells.