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Six new polyketides named paraverrucsins A−F (1− 6) with oxabicyclic and dioxatricyclic skeletons, together with eight known metabolites (7−14), were discovered and isolated from the fermentation medium of Paraphaeosphaeria verruculosa. Paraverrucsin A−C possessed a novel decarboxylated skeleton compared with that of trichocladinols. Their structures were elucidated by extensive spectral analysis and DP4+ calculations. Paraverrucsins B/C and D/E were isolated as a mixture for the mutarotation occurred at C-2. Paraverrucsins B/C, D/E, F/ trichocladinol B, 8, and 9 displayed antifeedant activities against silkworm larvae, with antifeedant index percentages ranging from 62.5 to 93.0%, at a concentration of 50 μg/cm 2 . Among them, Paraverrucsins B/C and 9 had EC 50 values at 13.9 and 18.2 μg/cm 2 . Most compounds showed antifungal activities against phytopathogenic fungi with minimum inhibitory concentration (MIC) values of 16−64 μg/mL. Coculture of P. verruculosa and host plant Dendrobium officinale leads to the enhancement of antifeedant and antiphytopathogenic activities. Compounds 1, 2/3, 4/5, 6/14 were tested for cytotoxicity against five human carcinoma cell lines, HL-60, A549, MCF-7, SW480, and SMMC-7721, while they exhibited selected cytotoxicity against SW480 with inhibition ratios of 32−38% at a concentration of 40 μM.

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