Reaction Steps
To a mixture of 4-amino-2-phenylbenzoyl-(S)-methionine methyl ester hydrochloride (1.27 g, 3.22 mmol) in 20 mL of methanol was added N-Boc-S-trityl-(L)-cysteinal (1.0 eq, according to 1H NMR determination of aldehyde percentage) and sodium cyanoborohydride (400 mg, 2.0 eq). The mixture was stirred for 12 hr. After the evaporation of solvents, the residue was extracted with ethyl acetate and concentrated sodium bicarbonate. After removing solvents, the residue was purified through flash column chromatography (1:1=hexane:ethyl acetate, silica) to give the product 1.67 g (yield 67%). 1H NMR (CDCl3) δ 7.65 (d, 8.6 Hz, 1H), 7.34-7.42 (m, 11H), 7.18-7.29 (m, 9H), 6.52 (dd, 2.3 and 8.1 Hz, 1H), 6.34 (d, 2.3 Hz, 1H), 5.65 (d, 7.7 Hz, 1H), 4.64 (ddd, 1H), 4.55 (d, 8.1 Hz, 1H), 4.19 (br t, 1H), 3.78 (br m, 1H), 3.64 (s, 3H), 3.09 (t, 6.1 Hz, 2H), 2.44 (m, 2H), 2.04-2.10 (m, 2H), 2.00 (s, 3H), 1.81-1.90 (m, 1H), 1.60-1.70 (m, 1H), 1.41 (s, 9H); 13C NMR (CDCl3) δ 172.0, 168.3, 155.7, 149.4, 144.3, 141.6, 141.1, 131.3, 129.5, 128.7, 128.5, 127.9, 127.7, 126.8, 122.6, 113.6, 111.3, 79.8, 67.1, 52.2, 51.7, 49.5, 47.2, 34.3, 31.6, 29.4, 28.2, 15.2.
