N-BOC-S-trityl-cysteine-4-amino-1-naphthoyl methionine methyl ester (83.3 mg, 0.11 mmol) was taken up in THF (0.7 ml) and to this mixture was added 0.5 M LiOH (0.43 ml) at 0° C. The mixture was stirred at 0° C. for 35 minutes. The solvent was removed in vacuo using a cold water bath. The residue was worked up as described for TFA.cysteine-4-amino-3-methylbenzoyl methionine in Example 2, and 74.1 mg of the free acid was obtained. This was then dissolved into CH2Cl2 (1 ml) and Et3SiH (0.015 ml) was added followed by TFA (1 ml). The reaction mixture was stirred at room temperature for 1 h and worked up as further described for TFA.cysteine-4-amino-3-methylbenzoyl methionine in Example 2. After lyophilization, 42.4 mg of crude material was obtained which was then purified on the HPLC using 0.1% TFA in water and acetonitrile. mp 121-125° C.; [α]25D =+2.4° (c=0.8, H2O); 1H NMR (CD3OD) 2.03-2.13 (4H, m), 2.22-2.36 (1H, m), 2.59-2.74 (2H, m), 3.16-3.33 (2H, m), 4.42 (1H, m), 4.84-4.89 (1H, m), 7.57-7.61 (2H, m), 7.64 (1H, d, J=7.7 Hz), 7.70 (1H, d, J=7.7 Hz), 8.08-8.11 (1H, m), 8.29-8.32 (1H, m), 8.98 (1H, d, J=7.7 Hz); 13C NMR (CD3OD) 15.19, 26.45, 31.50, 31.63, 53.20, 56.72, 122.52, 123.43, 126.43, 126.12, 127.02, 127.96, 128.32, 129.49, 132.27, 134.15, 135.12, 168.11, 172.41, 175.17; anal. calc. for C21H23F3N3O6S2, C: 47.19, H: 4.34, N: 7.86; found, C: 46.53, H: 4.56, N: 7.59; Note: difference for C is 0.65.
