2.2. Chemistry. The synthetic route to the final compounds 5-7 is outlined in Scheme 1. The peptidic fragment 1 was initially synthesized from Boc-protected L-leucine and L-phenylalanine ethyl ester using a HATU-mediated coupling in the presence of diisopropylethylamine (DIPEA). Intermediate 1 was deprotected with 4M HCl in dioxane to obtain the free amine 2, which was reacted with selected carboxylic acids through a HATU-supported amide coupling to give the corresponding acyl dipeptides 3a-i. Compounds 3a, 3b, and 3i were saponified with NaOH in MeOH to receive the carboxylic acids 4a, b, and i, which were subjected to HATUassisted coupling reactions, leading to the pyridinyl esters 5b and 5i, as well as to the peptide nitriles 6 and 7.