A New Diketopiperazine from the Marine Sponge Callyspongia Species

Chemical investigation of the sponge Callyspongia sp. from the South China Sea afforded one new diketopiperazine, cyclo-(R-Pro-6-hydroxyl-S-Ile) (1), along with six known diketopiperazines: staphyloamide A (2), cyclo(S-Pro-S-Phe) (3), cyclo-(R-Pro-R-Phe) (4), cyclo-(S-Pro-R-Leu) (5), cyclo-(S-Pro-R-Ala) (6), cyclo(R-Tyr-R-Phe) (7), and three known tryptophan-derived alkaloids: C 2 -α-D-mannosylpyranosyl-tryptophan (8), (1R, 3S)-1-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylic acid (9), and (1R,3R)-1-methyl2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylic acid (10). The structures were determined on the basis of NMR and MS analysis, and the absolute configuration was determined by comparison of the optical rotation with the known compounds. This is the first report of compounds 1, 2 , 8–10 from the sponge Callyspongia. Cyclo-(S-Pro-R-Leu) (5), and cyclo-(S-Pro-R-Ala) (6) exhibited antifouling activity against cyprid larvae of the barnacle with the LC50 values of 3.5 μg/cm 2 and 6.0 μg/cm 2 , respectively.