Carotegrast methyl

Step 1: Synthesis of N^α-(2,6-dichlorobenzoyl) -4-{2-ethoxycarbonylamino-5-dimethyl- amino-benzoylamino}-L-phenylalanine methyl ester To 1.96 g of 2-amino-5-dimethylaminobenzoic acid, there were added 12 mL of acetonitrile and 5.29 mL of pyridine to form a suspension and then the resulting suspension was cooled to 4°C. To this suspension there was dropwise added 4.17 mL of ethyl chloroformate over 5 minutes and then the mixture was stirred at 25°C for one hour. After confirming the disappearance of the starting material by HPLC, 0.7 mL of ethanol was added to the mixture to thus decompose the excess ethyl chloroformate and the mixture was further stirred for additional one hour. To this reaction solution there were added 4.0 g of 4-amino-N^α-(2,6-dichlorobenzoyl)-L-phenylalanine methyl ester and 12 mL of N,Ndimethylformamide, and the resulting mixture was stirred overnight. Subsequently, 48 mL of methanol was drop-wise added, the resulting mixture was stirred at 10°C overnight and then the solid separated from the mixture was isolated through filtration under reduced pressure. The solid was then washed with 8 mL of methanol and dried at 70°C for 5 hours under reduced pressure. Title compound 5.50 g was obtained as pale yellow solid. ¹H-NMR (400MHz, DMSO-d₆): δ 10.29 (s, 1H), 9.42 (bs, 1H), 9.24 (d, 1H, J=7.9Hz), 7.73 (bs, 1H), 7.62 (d, 2H, J=8.4Hz), 7.48-7.44 (m, 2H), 7.41 (dd, 1H, J=9.5, 6.2Hz), 7.27 (d, 2H,J=8.4Hz), 7.01 (d, 1H, J=2.7Hz), 6.93 (dd, 1H, J=9.1, 2.9Hz), 4.71 (ddd, 1H, J=9.2, 8.1, 5.7Hz), 4.05 (q, 2H, J=7.0Hz), 3.66 (s, 3H), 3.10 (dd, 1H, J=14.0, 5.6Hz), 2.96 (dd, 1H, J=14.0, 9.2Hz), 2.93 (s, 6H), 1.18 (t, 3H, J=7.2Hz); MS (ESI+): m/z 601.2 (MH⁺) and 623.2 (M+Na), (ESI^–): m/z 599.1 (M-H^–).