Inhibition of protein tyrosine phosphatase 1B by lupeol and lupenone isolated from Sorbus commixta

Protein tyrosine phosphatase 1B (PTP1B) appears to be an attractive target for the development of new drugs for type 2 diabetes and obesity. In our preliminary test, a MeOH extract of the stem barks of Sorbus commixta Hedl. (Rosaceae) showed strong PTP1B inhibitory activity. Bioassay-guided fractionation of the MeOH extract resulted in the isolation of two lupane-type triterpenes, lupenone (1) and lupeol (2). Compounds I and 2 inhibited PTP1B with IC50 values of 13.7 +/- 2.1 and 5.6 +/- 0.9 mu M, respectively. Kinetic studies revealed that both the compounds 1 and 2 are non-competitive inhibitors of PTP1B that decrease V-max values with no effect on K-m values.