Isolation of Four 2,3,5,6,11,11b-Hexahydro-3-oxo-1H-indolizino[8,7-b]indole-5-carboxylic Acids from Clerodendron Trichotomum Thunb and Properties of Their Derivatives

Four 2,3,5,6,11,11b-hexahydro-3-oxo-1H-indolizino[8,7-b]indole-5-carboxylic acids, plausible precursors of trichotomine, were isolated as the methyl esters from Clerodendron trichotomum Thunb, and the structures elucidated on the basis of their spectral and chemical evidences. The existence of two pairs of the C-11b epimers in the above plant were supported by the methoxide-catalyzed equilibrations of the compounds having the substituent on C-11b. Blue pigments were formed from the isolated compounds.