Because its three methyl groups attached to heteroatoms could be added simultaneously, dipeptide 14 was synthesized as a unit as shown in Scheme 2. To provide convergence in the synthesis, the Gly-N-Me-Leu-Gly tripeptide 19 was synthesized as shown in Scheme 3. Scheme 4 shows the assembly of the units used to synthesize dolastatin 11 (1). The hydroxyacid Hmp (22) was prepared from l-Ile by treatment with nitrous acid under conditions used on l-Leu ...