The C20 Alkaloids

During the nineteen-fifties and early sixties, there was intense interest and activity in the study of calabash curare alkaloids. These researches led to structural solutions for all the major alkaloids and an impressive body of knowledge was gained concerning the chemistry of these fascinating and complex alkaloids. All this work was covered in Volume VIII. With the major problems solved, there has inevitably been less activity in the field the following sections outline new work published over the past three or four years. 

The small quantities available of C-mavacurine and C-fluorocurine had precluded any further structural investigations beyond those leading 

The tertiary alkaloid pleiocarpamine, C20H22N2O2 (mp 159°), was first isolated 2) from the roots of Pleiocarpa mutica Benth. and subsequently (3) from the bark of Hunteria eburnea Pichon (both Apocynaceae). It possesses (2) an A-substituted indole chromophore and its IR-spectrum indicated the presence of a carbonyl group (1727 cm i in Nujol or KBr) OH and NH absorptions were absent. Analysis revealed the presence of one methoxyl and one C-methyl group and the absence of A-methyl groups. 

Reduction of pleiocarpamine with lithium aluminum hydride gave the crystalline base pleiocarpaminol, C19H22N2O (mp 187°-189° Mn +114°, 0 = 0.266 in methanol), also with an A-substituted indole chromophore but showing hydroxyl absorption (3584 cm i) and no carbonyl absorption in the IR-spectrum. Pleiocarpamine was thus assumed to have a methoxycarbonyl group and pleiocarpaminol therefore contains a primary hydroxyl group (I). 

C-mavacurine therefore has a primary hydroxyl group and the earlier formula can be revised to the biogenetically acceptable I. (Evidence for the illustrated stereochemistry is given later.) It then followed from 

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