Abstract
Extracts of the Egyptian marine actinomycete, Nocardia sp. ALAA 2000, were found to be highly bioactive. It was isolated from the marine red alga Laurenica spectabilis collected off the Ras-Gharib coast of the Red Sea, Egypt. According to detailed identification studies, the strain was classified as a member of the genus Nocardia. The cultivation and chemical analysis of this species yielded four structurally related compounds namely, chrysophanol 8-methyl ether (1), asphodelin; 4,7'-bichrysophanol (2) and justicidin B (3), in addition to a novel bioactive compound ayamycin; 1,1-dichloro-4-ethyl-5-(4-nitro-phenyl)-hexan-2-one (4) which is unique in contain both chlorination and a rarely observed nitro group. The compounds were isolated by a series of chromatographic steps and their structures of 1 similar to 3 secured by detailed spectroscopic analysis of the MS and NMR data whereas that of 4 was elucidated by single crystal X-ray diffraction studies. These compounds displayed different potent antimicrobial activity against both Gram-positive and Gram-negative bacteria as well as fungi with MIC ranging from 0. 1 to 10 mu g/ml.