The biological transformation of the biologically active chlorogentisyl alcohol (1), isolated from the marine-derived fungus Aspergillus sp., was studied. Preparative-scale fermentation of chlorogentisyl alcohol with marine-derived fungus Chrysosporium synchronum resulted in the isolation of a new glycosidic metabolite, 1-O-(α-D-mannopyranosyl)chlorogentisyl alcohol (2). The stereostructure of the new metabolite obtained was assigned on the basis of detailed spectroscopic data analyses, chemical reaction, and chemical synthesis. Compounds 1 and 2 exhibited significant radical-scavenging activity against 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) with IC₅₀ values of 1.0 and 4.7 μM, respectively. The compounds 1 and 2 were more active than the positive control, L-ascorbic acid (IC₅₀, 20.0 μM).