An examination of the n.m.r. spectra of ceanothic acid and derivatives has led to its formulation as 2a-carboxy-3~-hydroxy-~(1)-norlup-20(29)-en-28-oic acids (1; R = H ) in which the carboxy and hydroxy groups attached to ring A have the inverse of the trans configuration originally assigned to them by de Mayo and Starratt.1 Ceanothic acid (1 ; R = H) was originally isolated by Julian, Pikl, and Dawson2 from Ceanothus awericanus and has since been isolated from a number of Australian Rhamnaceae species.3>4 De Nayo and Starratt5 related ceanothic acid to betulic acid by converting it into the known betulic acid derivative, the norketone (Z), thus establishing the structure of ceanothic acid except for the stereochemistry of the carboxy and hydroxy groups attached to ring A. MechoulamG assigned the P-configuration t o both these ring A substituents but de Mayo and Starrattl later showed from hydrogen bonding studies that the hydroxyl and carboxyl in question had a trans relationship. De Mayo and Starratt preferred the P-configuration for the carboxy group since the keto ester (3a)// readily epimerized; they considered from an * Part X, Aust.
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