[BH4-].[Na+].[NH2:3][C:4]1[N:5]=[C:6]([NH2:17])[C:7]2[C:13]([CH3:14])=[C:12]([CH:15]=[O:16])[CH:11]=[N:10][C:8]=2[N:9]=1.C([O-])(=O)C>CO>[NH2:3][C:4]1[N:5]=[C:6]([NH2:17])[C:7]2[C:13]([CH3:14])=[C:12]([CH2:15][OH:16])[CH:11]=[N:10][C:8]=2[N:9]=1NaBH4 (500 mg, 13.2 mmol) was added in portions during a 10 minute interval to a stirred suspension of crude 13 (2.73 g), in MeOH (500 mL) at 20°-23° C. Stirring was continued for two hours, then NaBH4 (500 mg) was again added as before. After the mixture had been stirred overnight, HPLC (acetate buffer of pH 3.6-MeOH, 9:1) showed the conversion of 13 to the more polar 14 was complete. After removal of the MeOH by evaporation, the residue was stirred with H2O (90 mL) and treated with 1N HCl to lower the pH to 8.0 (from 11.3 initially). This mixture was stirred while being heated at about 70° C. (bath temperature) for 20 minutes. The solid filtered from the cooled mixture amounted to 2.63 g and was used without further purification in the conversion to crude 15 described below. Spectral data: mass, m/e 206 (M+1)+ ; 1H NMR (Me2SO-d6) δ2.68 (s, CH3), 4.52 (s, CH2), 8.48 (s, C7 --H).
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