22ß-[(S)-2-Methylbutanoyloxy]-3-oxoolean-12-en-28-oic acid, a new constituent of Lantanu camara L. is closely related to lantadene A and lantadene B. Although hydrolysis gives 2-methylbutanoic acid as a partial racemate, it has been shown by n.m.r. spectroscopy that the natural ester is theoptically pure (S)-isomer. Catalytic hydrogenation of lantadene A gives a mixture of diastereoisomeric esters in which the (S)-2-methylbutanoate predominates, and a 1 : 1 mixture of the (R)- and(S)-esters was obtained by esterification with (RS)-2-methylbutanoyl chloride of 22ß-hydroxy-3-oxoolean-12-en-28-oic acid protected as the diphenylmethyl ester.