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Enantioselective syntheses and absolute configuration of the ladybird defence alkaloids (+)-calvine and (+)-2-epicalvine

par Laurent, Pascal ;Braekman, Jean Claude ;Daloze, Désiré
Référence European Journal of Organic Chemistry, 11, page (2057-2062)
Publication Publié, 2000

Article révisé par les pairs

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Résumé :

Enantiomerically pure (+)-calvine (1a) and (+)-2-epicalvine (1b), two piperidine alkaloids isolated from ladybird beetles of the genus Calvia (Coccinellidae), were synthesized by two different strategies starting from (−)-2,3,6,7,8,8a-hexahydro-3-phenyl-5H-[1,3]oxazolo[3,2-a]pyridine-5-carbonitrile (2). The key steps of these syntheses are the stereocontrolled formation of an asymmetric centre α to the nitrogen atom of 2 and the subsequent introduction of the methoxycarbonylmethyl substituent at the α′-position. Comparison of the optical rotations of the synthetic benzoates (12a) and (12b) with those of the corresponding benzoates derived from the natural compounds has revealed the absolute configuration of (+)-calvine to be (2S,6S) and that of (+)-2-epicalvine to be (2R,6S).