Globunoids A−D, Undescribed Bichalconoid and Biflavanoids with -Glucosidase and -Amylase Inhibitory Activities from Stems

A bichalconoid, globunoid A (1) and three biflavanones, globunoids B–D (2−4), previously undescribed, were isolated from the stems of Knema globularia, along with fourteen known analogues 5−18. The chemical structures of 1−4 were elucidated by the comprehensive spectroscopic analysis including UV, IR, HRESIMS, and NMR; the absolute configurations were determined based on their NOESY data, DP4+ statistical analysis, and ECD calculation. Up to now, compounds 2 and 3 represent the first 3,3″-linked biflavanone structures. Among the isolated compounds, 2, 3, and 2,3-dihydrocalodenin B (6) potently inhibited α-glucosidase and α-amylase activities, with IC50 values in the range 1.1–7.5 μM. Furthermore, the most active compound 6 was found to be a non-competitive inhibitor against these two enzymes.