CO[CH:3](OC)[CH2:4][NH:5][C:6]1[C@H:12]([NH:13][C:14](=[O:23])[O:15][CH2:16][C:17]2[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=2)[CH2:11][CH2:10][C:9]2[CH:24]=[CH:25][CH:26]=[CH:27][C:8]=2[N:7]=1>C(O)=O>[CH:3]1[N:7]2[C:8]3[CH:27]=[CH:26][CH:25]=[CH:24][C:9]=3[CH2:10][CH2:11][C@@H:12]([NH:13][C:14](=[O:23])[O:15][CH2:16][C:17]3[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=3)[C:6]2=[N:5][CH:4]=1Dissolve benzyl N-[(3R)-2-(2,2-dimethoxyethylamino)-4,5-dihydro-3H-1-benzazepin-3-yl]carbamate (9.78 g, 24.61 mmol) in formic acid (60 mL, 96%) and heat at 100° C. for 1.5 hours. Allow the mixture to cool and remove the black sediment by filtering it through a glass wool plug. Concentrate the filtrate under reduced pressure, pour it into water, and basify it with 1M NaOH. Add ethyl acetate to the resulting precipitate and separate the organic layer. Extract the aqueous layer with ethyl acetate. Combine, wash (brine), dry over sodium sulfate, and concentrate the organic layers under reduced pressure to give the title compound (6.95 g, 85%): MS (m/z): 334 (M+1), 97.8% ee, Retention time for Isomer 1 (R Isomer), 4.58 min; Isomer 2 (S Isomer), 3.20 min. (Chiralpak AD-H column; 100% EtOH with 0.2% dimethylethylamine; flow rate 1.0 mL/min; 225 nM).
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