Novel 24-nor-, 24-nor-2,3-seco-, and 3,24-dinor-2,4-seco-ursane triterpenes from Diospyros decandra: evidences for ring A biosynthetic transformations

Novel 24-nor-, 24-nor-2,3-seco, and 3,24-dinor-2,4-seco-ursane type triterpenes have been isolated along with one known compound from the stem bark of Diospyros decandra. The structures of these highly oxidized metabolites were established on the basis of extensive NMR and MS studies. They possibly represent intermediates in the biosynthetic transformation of ring A in an ursane triterpene. Some isolates showed mild anti-mycobacterial activity against Mycobacterium tuberculosis with MIC values ranging from 25 to 200 μg/mL.