title: Structures, biogenetic relationships, and cytotoxicity of pimarane-derived diterpenes from Petalostigma pubescens.
abstract: Extraction of Petalostigma pubescens heartwood followed by chromatographic purifications and crystallizations afforded five tricyclic diterpenes: 5,9-syn-rosanes petalostigmones A and B (1 and 2), the erythroxylane petalostigmone C (3), the norditerpene lactone pubescenone (4), and the known ent-cleistanthane diterpene (-)-sonderianol (5). The structures and relative stereochemistry were elucidated by means of spectroscopic methods, chemical correlations, and, in the cases of 1 and 4, by X-ray crystallographic analyses. The new isolates 1-4 are assumed to belong to the same absolute configurational family (9alphaCH3) of ent-pimarane-derived diterpenes as the known co-occurring (-)-5 (10alphaCH3). Biogenetic schemes originating from a common ent-copalyl diphosphate intermediate are presented to rationalize the structures of these natural products. A novel ring contraction-ring expansion mechanism is suggested to account for the 7-membered B ring of pubescenone. Compounds 1-5 were evaluated for their cytotoxicity; sonderianol (5) showed the highest activity against mouse leukemia cell lines L1210, P388 and mouse liver cancer cells HEPA1c1c7.
authors.affiliation: Department of Chemistry, University of Illinois, Urbana, IL 61801, USA.
authors.forename: Mary H
authors.initials: MH
authors.lastname: Grace
authors.forename: Yinghua
authors.initials: Y
authors.lastname: Jin
authors.forename: George R
authors.initials: GR
authors.lastname: Wilson
authors.forename: Robert M
authors.initials: RM
authors.lastname: Coates
mesh_terms: D045784:Abietanes / Q000737:chemistry*; D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology; D045744:Cell Line, Tumor; D018360:Crystallography, X-Ray; D004224:Diterpenes / Q000737:chemistry* / Q000494:pharmacology*; D004354:Drug Screening Assays, Antitumor; D007939:Leukemia L1210 / Q000473:pathology; D009682:Magnetic Resonance Spectroscopy; D029581:Malpighiaceae / Q000737:chemistry* / Q000235:genetics; D051379:Mice; D008958:Models, Molecular; D015394:Molecular Structure; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet
chemical_list: D045784:Abietanes; D000970:Antineoplastic Agents; D004224:Diterpenes; C433018:pimarane