Cytotoxic diterpenoids from the bark of Pseudolarix kaempferi and their structure-activity relationships.

Four new diterpenoids, 11S-deacetylpseudolaric acid A (2), deacetylpseudolaric acid A O-beta-d-glucopyranoside (3), deacetylpseudolaric acid A 2,3-dihydroxypropyl ester (4), and deacetylpseudolaric acid B 2,3-dihydroxypropyl ester (5), and nine known diterpenoids were isolated from the bark of Pseudolarix kaempferi. Their structures were determined on the basis of chemical and spectroscopic analyses. In addition, their in vitro cytotoxic activities against three human cancer cell lines and their structure-activity relationships were evaluated.