Stylissamides E and F, Cyclic Heptapeptides from the Caribbean Sponge <i>Stylissa caribica</i>

Abstract

In addition to the four known stylissamides, A (1), B (2), C, and D, two new cyclic heptapeptides, stylissamides E (3) and F (4), were isolated from the Caribbean sponge Stylissa caribica. The structures of 3 and 4 were elucidated from a combination of mass spectrometric and NMR spectroscopic data as cyclo-(cis-Pro(1)-Tyr(2)-trans-Pro(3)-Ala(4)-Ile(5)-Gln(6)-Ile(7)) for stylissamide E (3) and cyclo-(trans-Pro(1)-cis-Pro(2)-Phe(3)-Asp(4)-trans-Pro(5)-Arg(6)-Phe(7)) for stylissamide F (4).