New potent DPPH radical scavengers from a marine-derived actinomycete strain USF-TC31

Six compounds were isolated as radical scavengers from the culture broth of a marine-derived actinomycete strain USF-TC31. The structures of two novel compounds were determined to be those of N-carbamoyl-2,3-dihydroxybenzamide (5) and 2-acetamido-3-(2,3-dihydroxybenzoylthio)propanoic acid (6), and four known compounds were identified to be anthranilic acid (1), 2,3-dihydroxybenzoic acid (2), 2,3-dihydroxybenzamide (3) and benadrostin (4) on the basis of spectroscopic data. Compound 6 was characterized as a racemate by its specific rotation. Each of the obtained compounds was evaluated for DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity, and compounds 2, 3, 5 and 6 each exhibited potent activity in comparison with the butylhydroxytoluene (BHT) positive control.