[CH3:1][O:2][C:3](=[O:23])[CH2:4][C:5]1([CH2:21][CH3:22])[C:10]2[NH:11][C:12]3[C:17]([C:9]=2[CH:8]([NH2:20])[CH2:7][O:6]1)=[CH:16][CH:15]=[CH:14][C:13]=3[CH2:18][CH3:19].Cl.[O-:25][C:26]#[N:27].[K+]>C(O)C.O>[CH3:1][O:2][C:3](=[O:23])[CH2:4][C:5]1([CH2:21][CH3:22])[C:10]2[NH:11][C:12]3[C:17]([C:9]=2[CH:8]([NH:20][C:26]([NH2:27])=[O:25])[CH2:7][O:6]1)=[CH:16][CH:15]=[CH:14][C:13]=3[CH2:18][CH3:19]To a solution of 4-amino-1,8-diethyl-1,3,4,9-tetrahydro[3,4-b]indole-1-acetic acid methyl ester 12 (prepared in Example 1) (1.10 g, 3.48 mmol) in ethanol (20 mL), stirred at room temperature under nitrogen, was added aqueous 1N HCl (6.96 mL) followed by potassium cyanate (0.565 g, 6.96 mmol) dissolved in a little water. After 2 hours the ethanol was removed in vacuo and the residue was extracted with ethyl acetate. Drying (MgSO4) and flash chromatography (1% MeOH in EtOAc eluent) afforded the product (0.714 g, 75%) as a mixture of diastereomers which were separated by reverse phase chromatography (C18 silica gel; 30% acetonitrile in water). The less polar Isomer A (190 mg) had m.p. 179.5°-180.5° C. (methylene chloride-petroleum ether).
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