N-BOC-S-trityl-cysteine-4-amino-3- methoxybenzoyl methionine methyl ester (0.18 g, 0.24 mmol) was deprotected with LiOH at room temperature as described above to give the free acid. The free acid was then further deprotected in CH2Cl2 (1.2 ml) with Et3SiH (0.04 ml, 0.24 mmol) and TFA (1.2 ml). The product was worked up as described for HCl-cysteine-4-aminobenzoyl methionine in Example 1, and HPLC revealed that the product was impure. The crude material was then purified on the HPLC using 0.1% TFA in water and acetonitrile as eluting solvents to result in two pure samples that were expected to be diastereomers. The major component (determined according to the major compound in the HPLC trace) was characterized as follows. mp sub 109° C., decomp 191°-193° C.; [α]25D =-30.0° (c=1, H2O), [α]25D =+19.0° (c=1, H2O); 1H NMR (CD3OD) 2.10 (3 H, s), 2.12-2.18 (1 H, m), 2.20-2.32 (1 H, m), 2.53-2.71 (2 H, m), 3.00 (1 H, dd, J=14.6, 7.5), 3.15 (1 H, dd, J=14.58, 4.8), 4.77 (1 H, dd, J=7.5, 4.8), 7.50 (1 H, d, J=8.4 Hz), 7.56 (1 H, s), 8.23 (1 H, d, J=8.4 Hz); 13C NMR (CD3OD) 15.20, 26.65, 31.60, 31.76, 53.27, 56.58, 56.76, 111.04, 121.08, 122.14, 130.85, 131.85, 150.88, 167.21, 169.61, 175.36; m/ z (FAB) for free amine, 402 (M+1).
