Bioassay-guided isolation of the antidiabetic principle from Sorbus decora (Rosaceae) used traditionally by the Eeyou Istchee Cree First Nations.

Bioassay-guided fractionation of a crude extract (80% EtOH in H2O) of stem bark of Sorbus decora led the isolation of three new pentacycle triterpenes (compounds 1-3). The structures of 1-3 were established on the basis of spectroscopic methods (IR, HREIMS, ID and 2D NMR) as 23,28-dihydroxyursan-12-ene-3 beta-caffeate, 23,28-dihydroxylupan-20(29)-ene-3 beta-caffeate, and 3 beta,23,28-trihydroxy-12-ursene, respectively. Compound 2 significantly enhanced glucose uptake in C2C12 cells, but compounds 1 and 3 did not. In addition, triterpenoids 4-8, catechin, and epicatechin were also isolated. This is the first comprehensive report of the phytochemical constituents of S. decora since the initial study by Narashmachari and von Rudloff (1962) and includes evaluation of their antidiabetic activity.