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 d iketopiperazines : 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), (1 R , 3 S )-1-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylic acid (9), and (1R,3R)-1-methyl-2,3,4,9-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 LC 50 values of 3.5 μg/cm 2 and 6.0 μg/cm 2, respectively .