Compounds of the general formula (I) or a pharmaceutically acceptable salt, derivative, prodrug or stereoisomer thereof are provided: wherein the substituent groups defined by R are each independently selected from the group consisting of H, SiR'.sub.3, SOR', SO.sub.2X, C(.dbd.O)R', C(.dbd.O)OR', C(.dbd.O)NR', substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, aryl, heteroaryl or aralkyl; the group R' is selected from substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, aminoalkyl, aryl, aralkyl and heterocyclic groups; and the group R'' is selected from the group consisting of H, OH, OR', OCOR', SH, SR', SOR', SO.sub.2R', NO.sub.2, NH.sub.2, NHR', N(R').sub.2, NHCOR', N(COR').sub.2, NHSO.sub.2R', CN, halogen, C(.dbd.O)H, C(.dbd.O)R', CO.sub.2H, CO.sub.2R', CH.sub.2OR, substituted or unsubstituted alkyl, substituted or unsubstituted haloalkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkylidene, substituted or unsubstituted alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted aralkyl and substituted or unsubstituted heteroaromatic; with the proviso that the compound is not compound 1, 3 or 4 of U.S. Pat. No. 5,514,708. The compounds have antitumour activity. A synthetic route is also provided. ##STR00001##