New cyclic peptides from the ascidian Lissoclinum patella

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), w ere isolated from the ascidian Lissoclinum patella collected in Pohnpei, Fe derated States of Micronesia. The planar structures of these peptides were determined from 1D and 2D H-1 and C-13 NMR spectra. The absolute stereochem istries of the amino acid units, except for cysteine, were assigned by chir al 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 conve rsion. Patellamides B (7) and C (8) exhibited in vitro modulation of multid rug resistance in CEM/VBL100 cells.