Compounds 5.1a-d are novel compounds which were fully characterized by 1H and 13C NMR spectroscopy and elemental analysis. (S, S) SN CH3 H NH H 0 OH 1 l N (RS, S) z 0 N CH3 H NH OH (S,S) (R, S) 1 Fig.5-2 1H NMR spectra of compound 5.2f (left) and racemized 5.2f (right) in CDC13 (CH3 signal in L-Ala) 5.2.2 Preparation of N-Z-Dipeptides. Coupling reactions of 5.1a-d were carried out with diverse unprotected amino acids in partially aqueous solution (CH3CN/H20) in the presence of Et3N for 10 to 40 min. After washing with 6 N HC1, the resulting peptides 5.2a-i were obtained in 85-98% yields (Table 5-2). The crude products were estimated to be >95% pure and the absence of epimerization was established by 1H NMR experiments. Thus, Z-L-Phe-Bt (5.1c) was reacted with racemic DL-Ala-OH. While enantiopure Z-L-Phe-L-Ala-OH (5.2f) showed the methyl group on the alanine fragment at 1.32 ppm as a doublet, the methyl groups in