RESUMO
Two new steroidal glycosides, 3beta-O-(3'-O-acetyl-beta-D-arabinopyranosyl)-25xi-choles tan e-3beta, 5alpha,6beta,26-tetrol-26-acetate (riisein A, 2) and 3beta-O-(4'-O-acetyl-beta-D-arabinopyranosyl)-25xi-choles tan e-3beta, 5alpha,6beta,26-tetrol-26-acetate (riisein B, 3), were isolated from extracts of the Brazilian telestacean octocoral Carijoa (Telesto) riisei collected near Rio de Janeiro. The new glycosides co-occur with the polyhydroxy sterol, 25xi-cholestane-3beta,5alpha,6beta, 26-tetrol-26-acetate (1), an inseparable diastereomeric mixture previously reported from Telesto riisei collected in Micronesia. The structures of the new glycosides were assigned by spectroscopic methods and by comparison with spectral data for sterol 1. Riiseins A and B showed in vitro cytotoxicity toward HCT-116 human colon adenocarcinoma with IC(50) values of 2.0 microg/mL.
Assuntos
Antineoplásicos/isolamento & purificação , Cnidários/química , Glicosídeos/isolamento & purificação , Esteróis/isolamento & purificação , Animais , Antineoplásicos/química , Glicosídeos/química , Espectroscopia de Ressonância Magnética , Esteróis/químicaRESUMO
The structures of two new, naturally occurring cytotoxic depsipeptides, tamandarins A and B (1 and 2), are presented. The tamandarins were isolated from an unidentified Brazilian marine ascidian of the family Didemnidae. The structures of the new cytotoxins were assigned by interpretation of FABMS data and by extensive 2D NMR analyses. The absolute configurations of the tamandarins were assigned by acid and alkaline hydrolysis to yield their corresponding amino acids, which were then analyzed as their Marfey derivatives. The cytotoxicity of tamandarin A (1) was evaluated against various human cancer cell lines and shown to be slightly more potent than didemnin B. A qualitative discussion of the conformation of tamandarin A (1) in solution, obtained from NMR J-value data, variable temperature experiments, and NOESY/ROESY data, is included.