Chaiyo ChaichantipyuthAmorn PetsomPagorn TaweechotipatrNongnuj MuangsinNarongsak ChaichitSongchan PuthongSophon RoengsumranMasatoshi KawahataToshiko WatanabeTsutomu IshikawaChulalongkorn UniversityMahidol UniversityThammasat UniversityChiba University2018-06-212018-06-212005-04-01Heterocycles. Vol.65, No.4 (2005), 809-822038554142-s2.0-33744474346https://repository.li.mahidol.ac.th/handle/20.500.14594/16447Eight new labdane-type diterpenoids (1-3) and (5-9) and hardwickiic acid(4), a clerodane, were isolated from the stem bark of Croton oblongifolius. Their structures were established to be 3-oxygenated ent-manoyl oxide derivatives with a 8,13-epoxytricyclic ring system and hydroxylabdandienes on the basis of spectroscopic and X-Ray crystallographic analysis. The absolute stereochemistry of the core labdane skeleton was deduced to be (5S,8S,9S,10R,13S) from the X-Ray crystallographic analysis of the p-bromobenzoate of ent-3α-hydroxymanoyl oxide (3) and mutual chemical correlation. Cytotoxicity of these compounds was tested against a panel of human tumor cell lines. © 2005 The Japan Institute of Heterocyclic Chemistry.Mahidol UniversityChemistryPharmacology, Toxicology and PharmaceuticsArticleSCOPUS10.3987/COM-05-10327