Bisleuconins A–D: a pair of epimeric ent-kauranoid dimers and two new asymmetric analogues isolated from Isodon leucophyllus

A phytochemical investigation of Isodon leucophyllus led to the isolation of four novel ent-kauranoid dimers: bisleuconins A–D (1–4), and one known compound, rabdoloxin A (5). It was interesting that the structures of bisleuconins A (1) and B (2) were elucidated as a pair of epimeric ent-kauranoid dimers with unique linkage pattern C-16→C-17′ to connect two monomers. Bisleuconins C (3) and D (4) were two new asymmetric ent-kauranoid dimers. A possible biogenetic pathway of 1 and 2 was also proposed.