4,24-Dioxa-9,22-diazatetracyclo[19.3.1.110,14.03,5]hexacosane, maytansine deriv. 57103-69-2 Ansamitocin P-1 MAYTANACINE Maytansine, O3-acetyl-O3-de[2-(acetylmethylamino)-1-oxopropyl]- NSC239387