Three new isopimaric acid diterpenoids from the bark of Cryptomeria japonica and their xanthine oxidase inhibitory activity

Abstract Three new isopimaric acid diterpenoids, 6-oxoisopimaric acid (1), 6α-hydroxyisopimaric acid (2), and isopimara-7,9(11),15-trien-18-oic acid (4), together with two known isopimaric acid diterpenoids, isopimaric acid (3), and 8(14),15-isopimaradien-18-oic acid (5), were isolated from the bark of Cryptomeria japonica D. Don. Their structures were determined by analysis of spectroscopic data and comparison with the spectral data of known analogues. At the concentration of 50 μM, compounds 1–5 inhibited xanthine oxidase activity by 17.3, 16.5, 2.6, 30.5, and 24.5 %, respectively.