Triterpenoids from the Leaves of Diospyros kaki (Persimmon) and Their Inhibitory Effects on Protein Tyrosine Phosphatase 1B

Phytochemical study on a methanol-soluble extract of the leaves of persimmon (Diospyros kaki) resulted in the isolation of two new ursane-type triterpenoids, 3α,19α-dihydroxyurs-12,20(30)-dien-24,28-dioic acid (1) and 3α,19α-dihydroxyurs-12-en-24,28-dioic acid (2), together with 12 known ursane- and oleanane-type triterpenoids (3−14). Triterpenoids with a 3β-hydroxy group were found to inhibit protein tyrosine phosphatase 1B (PTP1B) activity, with IC50 values ranging from 3.1 ± 0.2 to 18.8 ± 1.3 μM, whereas those with a 3α-hydroxy moiety were not active.