An antitumor compound of formula (5) ##STR1## in which R is Ac or H, and R.sub.1, R.sub.2 is an alkyl group such as Me, Et, Pr, i-Pr, n-Bu or t-Bu, R.sub.3 is H; R.sub.1 and R.sub.2 and R.sub.3 are H; R.sub.1 is an alkyl group such as Me, Et, Pr, i-Pr, n-Bu or t-Bu, R.sub.2, R.sub.3 is H; R.sub.1 and R.sub.3 are H, R.sub.2 is an alkyl group such as Me, Et, Pr, i-Pr, n-Bu or t-Bu; R.sub.1 is H, R.sub.2 and R.sub.3 are an alkyl group such as Me, Et, Pr, i-Pr, n-Bu or t-Bu; R.sub.1 and R.sub.2 and R.sub.3 are an alkyl group Me, Et, Pr, i-Pr, n-Bu or t-Bu. Me is an abbreviation for methyl, Et is ethyl, Pr is propyl, i-Pr is isopropyl, n-Bu is n-butyl, and t-Bu is tert-butyl. Also provided by the invention is a one step method of preparing a compound of formula (5) whereby a taxane having a tiglate group attached to the side chain is contacted with an oxidizing reagent resulting in the formation of an epoxide having antitumor activity.