Isoxerophilusins A and B, Two Novel Polycyclic Asymmetric Diterpene Dimers from Isodon xerophilus : Structural Elucidation, Modification, and Inhibitory Activities against α-Glucosidase.

Isoxerophilusins A ( 1 ) and B ( 2 ), two unprecedented diterpene heterodimers biogenetically from ent -atisanes and abietanes, were isolated from the rhizomes of Isodon xerophilus . Their structures were determined by extensive spectroscopic analysis and single-crystal X-ray diffraction. Selective esterification of 1 generated 11 new derivatives. All derivatives showed excellent α -glucosidase inhibitory activity in comparison to acarbose. Compounds 12 and 13 demonstrated significant inhibition against α -glucosidase with IC ₅₀ values of 4.92 and 3.83 μ M, respectively.