Results Synthesis. Two tripeptide specifiers, D-Val-Leu-Lys and D-Val-Leu-D-Lys, were synthesized in suitably protected forms as outlined in Scheme I. Boc-D-valine was condensed with leucine methyl ester by using N, N-dicyclohexylcarbodiimide (DCC) and 1- hydroxybenzotriazole (HOBT) 5 to give the dipeptide methyl ester 1 (91%), which gave the corresponding dipeptide acid, Boc-D-Val-Leu (3) after saponification (72%). An alternative ...