Triterpenoids and a sterol from the stem‐bark of Styrax japonica and their protein tyrosine phosphatase 1B inhibitory activities

Five pentacyclic triterpenoids (1-5) and a sterol (6) were isolated from the stem-bark of Styrax japonica. The six compounds, 1-6, were determined to be 3beta-acetoxy-28-hydroxyolean-12-ene (1), 3beta-acetoxyolean-12-en-28-acid (2), 3beta-acetoxyolean-12-en-28-aldehyde (3), 3beta-acetoxy-17beta-hydroxy-28-norolean-12-ene (4), taraxerol (5) and stigmasterol (6), respectively, by spectroscopic means, including the 2D-NMR technique. Compound 4 is a newly discovered natural compound. The protein tyrosine phosphatase 1B (PTP1B) inhibitory activities of the isolated compounds (1-6) were determined in vitro. Among the isolated compounds, 3beta-acetoxyolean-12-en-28-acid (2) and 3beta-acetoxyolean-12-en-28-aldehyde (3) had the most potent inhibitory PTP1B activity, with IC50 values of 7.8 and 9.3 microm, respectively.