Metabolites from Combretum dolichopetalum and its associated endophytic fungus Nigrospora oryzae — Evidence for a metabolic partnership

A new altersolanol derivative, 4-dehydroxyaltersolanol A (9), along with two known sesquiterpenoids, (S)-7′-hydroxyabscisic acid (7) and (S)-abscisic acid (8) were obtained from the endophytic fungus, Nigrospora oryzae, isolated from leaves of Combretum dolichopetalum. The host plant yielded six known compounds including ellagic acid (1), 3, 3′, 4-tri-O-methylellagic acid (2), arjunolic acid (3), 4′-dihydrophaseic acid (4), echinulin (5) and arestrictin B (6). Close structural similarities with regard to compounds 4, 7 and 8 were observed between the metabolites from the host plant and those of the endophytic fungus. Furthermore compounds 5 and 6 are related to alkaloids isolated from N. oryzae previously thus stressing the notion that some of the isolated plant metabolites may actually be of fungal origin. The structures of the isolated compounds were established by spectroscopic methods including 1D, 2D NMR, MS, and by comparison with the literature. 4-Dehydroxyaltersolanol A (9) and 3, 3′, 4-tri-O-methylellagic acid (2) showed cytotoxicity against L5178Y mouse lymphoma cells with IC50 values of 9.4 and 29.0 μM, respectively.

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