The first biarylic bis-morphinanedienone alkaloids, saludimerines A (3a) and B (3b), isolated from a tree of Croton flavens (Euphorbiaceae) are described. These naturally occurring dimers of the known alkaloid salutaridine are joined together via a rotationally hindered biaryl axis, giving rise to atropo-diastereomers that are configurationally stable at room temperature but slowly interconvert in methanolic solution within several days. Their structures were established by spectroscopic methods and by partial synthesis, which was achieved by a highly atropo-diastereoselective biomimetic oxidative coupling of the monomeric precursor, salutaridine. Their axial configurations were elucidated by circular dichroism (CD) investigations, which succeeded despite the fact that the two atropo-diastereomers exhibit near-identical CD spectra. This remarkable phenomenon was rationalized by quantum chemical CD calculations. The configurational assignment of saludimerines A (3a) as P-axial and B (3b) as M was corroborated by atropisomer-specific NOE interactions between protons of the one molecular half with nuclei in the other.
Phytochemical investigation of several plants of Croton flavens L. from Barbados has led to the isolation of the tetrahydroprotoberberine alkaloids scoulerine and coreximine, as well as the morphinanedienones salutaridine and its racemic form salutarine, sebiferine, norsinoacutine and flavinantine. In a screening for 3H-GABA displacing activity coreximine showed the highest affinity to the GABA(A) receptor.
Phytochemical investigations of the leaves of Croton flavens L. var. balsamiferus (Jacq.) Muell. Arg. has led to the isolation of the novel 2,5-dihydroxy-3,6-dimethoxyphenanthrene crotoflavol. The structure was elucidated on the basis of spectroscopic evidence. This is the first report on the isolation of a phenanthrene from a Croton species.
Axes. -Saludimerine A (Ia) and saludimerine B (Ib), are isolated from the tree of Croton flavens (Euphorbiaceae). -(BRACHER, F.; EISENREICH, W. J.; MUEHLBACHER, J.; DREYER, M.; BRINGMANN*, G.; J.
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