Chemical Modification of Ansamitocins. I. Synthesis and Properties of 4, 5-Deoxymaytansinoids

4, 5-Deoxymaytansinoids, e.g., 4, 5-deoxyansamitocin P-3 (VI) and 4, 5-deoxymaytansine (VII), were synthesized a) by conversion of maytansinol into 4, 5-deoxymaytansinol (V), followed by acylation using active esters of appropriate carboxylic acids, and b) by direct deoxygenation of the parent maytansinoids. Chromatographic and spectral analyses proved that conformational isomerism exists among these 4, 5-deoxymaytansinoids. Compounds VI and VII showed biological activities characteristic of maytansine ; thus, the epoxide function in maytansinoids is not essential for their biological properties.