Maytansinoids

A maytansinoid compound of the formula:

• ##STR26## wherein when R.sub.3 designates hydrogen or alkanoyl containing not more than 5 carbon atoms except ##STR27## R.sub.1 is hydroxyl and R.sub.2 is hydrogen;
• when R.sub.3 designates hydrogen or alkanoyl containing not more than 5 carbon atoms, R.sub.1 is hydrogen and R.sub.2 is hydroxyl;
• when R.sub.3 designates hydrogen or alkanoyl of 2 to 5 carbon atoms other than ##STR28## R.sub.2 is hydrogen and R.sub.1 is formyloxy, alkanoyloxy of 2 to 7 carbon atoms, alkenylcarbonyloxy of 3 to 5 carbon atoms or ArCOO, Ar being selected from the group consisting of phenyl, benzyl, cinnamyl, phenethyl and styryl, and wherein the said alkanoyloxy, alkenylcarbonyloxy or ArCOO may optionally be substituted by at most three substituents X and the radical Ar may be optionally substituted with 1 to 3 C.sub.1-4 -alkyl groups;
• when R.sub.3 designates ##STR29## R.sub.2 is hydrogen, and R.sub.1 is formyloxy, acetoxy, alkanoyloxy of 3 to 7 carbon atoms, alkenylcarbonyloxy of 3 to 5 carbon atoms, or ArCOO, Ar being selected from the group consisting of phenyl, benzyl, cinnamyl, phenethyl and styryl, and wherein said alkanoyloxy, alkenylcarbonyloxy or ArCOO may optionally be substituted by at most three substituents X and the radical Ar may be optionally substituted with 1 to 3 C.sub.1-4 -alkyl groups;
• and when R.sub.3 designates hydrogen or alkanoyl containing not more than 5 carbon atoms, R.sub.1 is hydrogen and R.sub.2 is alkanoyloxy of 2 to 5 carbon atoms;
• wherein X is selected from the group consisting of C.sub.1-4 -alkoxy, C.sub.2-4 alkanoyl, C.sub.2-4 alkanoyloxy, C.sub.2-4 alkoxycarbonyl, halogen, nitro, cyano, trifluoromethyl, di-C.sub.1-4 -alkylamino, C.sub.1-4 alkylthio, methylsulfinyl, methylsulfonyl, oxo, thioxo, C.sub.1-4 alkanoylamino and carboxyl.