II maytansine (1) maytanbutine (2) maytanprine (z) solution afforded a common crystalline ethyl derivative also in low yield. Accordingly, when fraction G was treated with 3- bromopropanol and p-toluenesulfonic acid in dichloromethane at room temperature, the crystalline 3-bromopropyl derivative, 11, C37H51BrClN3010, was obtained in 10% yield. Treatment of 11 with 2 N hydrochloric acid in aqueous methanol afforded a crystalline ...