title: Chuktabularins E-T, 16-Norphragmalin Limonoids from Chukrasia tabularis var. velutina.
abstract: Chuktabularins E-T (1-16), 16 new 16-norphragmalin limonoids, together with four known compounds, chuktabularins A-D, were isolated from the stem bark of Chukrasia tabularis var. velutina. These compounds possess a biosynthetically extended propionyl or acetyl group at C-15 and a characteristic ketal moiety between the limonoid skeleton and the acyl substituent at C-15. The structures of these compounds were established on the basis of detailed spectroscopic analysis, and that of 1 was confirmed by a single-crystal X-ray diffraction experiment, representing the first verification of the skeleton of 16-norphragmalin limonoids. Chuktabularins K-O (7-11) were found to be the first 19-acetoxylated 16-norphragmalin limonoids. Variable-temperature (1)H NMR experiments suggested that 7 exists as an equilibrium mixture of conformational isomers in solution. The absolute configuration of 5 was determined by the CD exciton chirality method on its 11,12-di-p-chlorobenzoate (5a), and those of 1-4 and 6-16 were proposed by correlating with 5 spectroscopically and biogenetically.
authors.affiliation: Department of Natural Medicinal Chemistry, China Pharmaceutical University, 24 Tong Jia Xiang, Nanjing 210009, People's Republic of China.
authors.forename: Jun
authors.initials: J
authors.lastname: Luo
authors.forename: Jun-Song
authors.initials: JS
authors.lastname: Wang
authors.forename: Xiao-Bing
authors.initials: XB
authors.lastname: Wang
authors.forename: Jian-Guang
authors.initials: JG
authors.lastname: Luo
authors.forename: Ling-Yi
authors.initials: LY
authors.lastname: Kong
mesh_terms: D018360:Crystallography, X-Ray; D004365:Drugs, Chinese Herbal / Q000737:chemistry* / Q000302:isolation & purification*; D036701:Limonins / Q000737:chemistry* / Q000302:isolation & purification*; D029582:Meliaceae / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D024301:Plant Bark / Q000737:chemistry; D018547:Plant Stems / Q000737:chemistry
chemical_list: D004365:Drugs, Chinese Herbal; D036701:Limonins