title: The isomeric compounds nimbolide and isonimbolide.
abstract: Nimbolide [systematic name: (4alpha,5alpha,6alpha,7alpha,15beta,17alpha)-7,15:21,23-diepoxy-6-hydroxy-4,8-dimethyl-1-oxo-18,24-dinor-11,12-secochola-2,13,20,22-tetraene-4,11-dicarboxylic acid gamma-lactone methyl ester], C27H30O7, was isolated from the leaves of Azadirachta indica, and its isomer, isonimbolide [systematic name: (4alpha,5alpha,6alpha,7alpha,15alpha)-7,15:21,23-diepoxy-6-hydroxy-4,8-dimethyl-1-oxo-18,24-dinor-11,12-secochola-2,16,20,22-tetraene-4,11-dicarboxylic acid gamma-lactone methyl ester], was prepared from a novel rearrangement reaction of nimbolide, using boron trifluoride etherate and tetrabutylammonium bromide. The reaction conditions are probably responsible for the ether cleavage, double-bond rearrangement and reformation of the ether linkage. As a result, there are conformational changes in two cyclopentane rings and the side-chain -CH2COOMe group. In isonimbolide, an R(4)(4)(24) hydrogen-bond motif is observed.
authors.affiliation: Department of Crystallography and Biophysics, University of Madras, Guindy Campus, Chennai, India.
authors.forename: K
authors.initials: K
authors.lastname: Anand Solomon
authors.forename: R
authors.initials: R
authors.lastname: Malathi
authors.forename: S S
authors.initials: SS
authors.lastname: Rajan
authors.forename: G
authors.initials: G
authors.lastname: Anitha
authors.forename: J
authors.initials: J
authors.lastname: Josepha Lourdu Raj
authors.forename: S
authors.initials: S
authors.lastname: Narasimhan
authors.forename: G
authors.initials: G
authors.lastname: Suresh
authors.forename: Geetha
authors.initials: G
authors.lastname: Gopalakrishnan
mesh_terms: D031601:Azadirachta / Q000737:chemistry; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D007536:Isomerism; D036701:Limonins / Q000737:chemistry*; D015394:Molecular Structure; D018515:Plant Leaves / Q000737:chemistry
chemical_list: D036701:Limonins; C042198:nimbolide