A method for the resolution of a mixture of the cis or trans enantiomers of a compound of the formula ##STR00001## wherein R.sup.1 is --O--C(O)alkyl, --O--C(O)aryl or --O--C(O)cycloalkyl by contacting the mixture with a carboxylic ester hydrolase enzyme which catalyzes the stereoselective hydrolysis of the mixture and the use of such enantiomers to produce antitumor compounds which are especially suitable for oral administration.