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A marine fungal isolate, identified as Acremonium sp., was mass cultivated and found to produce two novel hydroquinone derivatives, 7-isopropenylbicyclo[4.2.0]octa-1,3,5-triene-2,5-diol (1) and 7-isopropenylbicyclo[4.2.0]octa-1,3,5-triene-2,5-diol-5-beta-D-glucopyranoside (2). Compound 1 and its glucoside 2 possess a most unusual ring system. The new natural products (3R,4S)-3,4-dihydroxy-7-methyl-3,4-dihydro-1(2H)naphthalenone (3) and (3S,4S)-3,4-dihydroxy-7-methyl-3,4-dihydro-1(2H)-naphthalenone (4) were obtained as a 1:0.8 mixture. 2-(1-Methylethylidene)pentanedioic acid (5) was isolated for the first time as a natural product and its structure proven by X-ray analysis. In addition to these compounds an inseparable mixture of three new isomeric compounds, pentanedioic acid 2-(1-methylethylidene)-5-methyl ester (6), pentanedioic acid 2-(1-methylethylidene)-1-methyl ester (7), and pentanedioic acid 2-(1-methylethenyl)-5-methyl ester (8), was also obtained. Isolated together with the new compounds were three known hydroquinone derivatives, 9, 10, and 11. The structures of all compounds were determined by interpretation of their spectroscopic data (1D and 2D NMR, MS, UV, and IR). Each isolate was tested for its antioxidant properties, and compounds 1 and 9-11 were found to have significant activity.

Six new tetraprenyltoluquinol derivatives (1-6), two new triprenyltoluquinol derivatives (7 and 8), and two new tetraprenyltoluquinone derivatives (9 and 10) were isolated from the brown alga Cystoseira crinita Duby together with four known tetraprenyltoluquinol derivatives (11-14). All structures were elucidated by employing spectroscopic techniques (NMR, MS, UV, and IR). Each compound was evaluated for its antioxidative properties in the TBARS and DPPH assay, and compounds 1, 2, 6, and 10-14 were additionally assessed in the TEAC and PCL assay. Hydroquinones were found to have powerful antioxidant activity.