Isolierung, Konstitution und Synthese der ( R )‐(−)‐Eucominsäure

From the bulbs of Eucomis punctata L'Hérit . ( Liliaceae ) and of a hitherto undefined species of Eucomis a new optically active phenolic carboxylic acid, eucomic acid, was isolated. Structure 1 was assigned on the basis of chemical and spectral evidence. The absolute configuration of eucomic acid was determined by its correlation with piscidic acid ((2 R , 3 S )‐2‐(4′‐hydroxybenzyl)‐tartaric acid) ( 8 ). Consequently, eucomic acid is ( R )‐(−)‐2‐(4′‐hydroxybenzyl)‐malic acid ( 1 ). For the stereospecific synthesis, methyl cis‐p ‐methoxybenzylidene‐succinic acid ( 22 ) was transformed into the γ‐lactone 24 which, by catalytic hydrogenolysis, yielded (±)‐2‐(4′‐hydroxybenzyl)‐malic acid 1‐methyl ester ( 27 ). Resolution with (−)‐quinine led to the enantiomeric acids 29 and 30 . The methyl ester of the levorotatory enantiomer 30 was identical with the dimethyl ester 3 of 4′‐O‐methyl‐eucomic acid.