Alkaloids and polyketides from the South China Sea sponge Agelas aff. nemoechinata

A chemical investigation of the South China Sea sponge Agelas aff. nemoechinata yielded three pairs of new enantiotopic pyrrole alkaloids nemoechines A-C (1-3), one new diterpene-adenine alkaloid nemoechine D (8), and one new polyketide nemoechioxide A (10), together with nine known analogues (4-7, 9, 11-14). Compounds 1-3 were initially obtained as racemates and were further separated by chiral HPLC chromatography to afford the three pairs of enantiomers. Their structures including absolute configurations of compounds 1-3 were elucidated on the basis of comprehensive spectroscopic analysis and quantum chemical calculation. Nemoechine A (1), possessing an unusual cyclopentane-fused imidazole ring system, represents the first monomeric precursor of nagelamide J. Compounds 8 and 9 showed cytotoxicity against HL-60 cell lines with IC50 values of 9.9 and 0.9 mu M, respectively, and compound 9 was also cytotoxic against HeLa cell lines with IC50 value of 8.9 mu M.