Protein tyrosine phosphatase 1B inhibitory activity of triterpenes isolated from Astilbe koreana

Bioassay-guided fractionation of a MeOH extract of the rhizomes of Astilbe koreana (Saxifragaceae), using an in vitro protein tyrosine phosphatase 1B (PTP1B) inhibitory assay, resulted in the isolation of a new triterpene, 3α,24-dihydroxyolean-12-en-27-oic acid (4), along with four triterpenes, 3-oxoolean-12-en-27-oic acid (1), 3β-hydroxyolean-12-en-27-oic acid (β-peltoboykinolic acid; 2), 3β-hydroxyurs-12-en-27-oic acid (3), and 3β,6β-dihydroxyolean-12-en-27-oic acid (astilbic acid; 5). Compounds 1–5 inhibited PTP1B with IC50 values of 6.8 ± 0.5, 5.2 ± 0.5, 4.9 ± 0.4, 11.7 ± 0.9, and 12.8 ± 1.1 μM, respectively. Our results indicate that 3-hydroxyl group and a carboxyl group in this type of triterpenes may be required for the activity, while addition of one more hydroxyl group at C-6 or C-24 may be responsible for a loss of activity. Thus, compounds 2 and 3 which possess only one hydroxyl group at C-3 and a carboxyl group at C-27 could be potential PTP1B inhibitors.