Four new isocoumarins from Cajanus cajan

Four novel new isocoumarins, cajanolactone B, C, D1 and D2 (1-4), were isolated from ethanolic extracts of the leaves of Cajanus cajan. The structural elucidation has been completed mainly depending on extensive spectroscopic analysis including UV, IR, NMR (1D and 2D), HRESIMS and chiral analysis. Notably, all these new isocoumarins were found to exist in racemic forms, among which compounds 3 and 4 share the same planar structure. This finding suggests that at least the biosynthesis of isocoumarin in C. cajan is chiral tolerant. A plausible biogenetic pathway of compounds 1-4 is proposed.