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0 °C

To a solution of 5-benzyloxy-6-hydroxy-2-(1-naphthalen-1-yl-cyclopentylmethyl)-pyrimidine-4-carboxylic acid (2-hydroxyethyl)-methyl-amide (351) (85 mg, 0.17 mmol) in dichloromethane (20 mL) was added triphenyl phosphine (174 mg, 0.67 mmol) and the reaction mixture was cooled to 0° C., followed by the addition of diisopropyl azodicarboxylate (0.2 mL, 0.1 mmol). The reaction mixture was stirred for 15 min at the same temperature (silica TLC, 5% methanol in ethyl acetate; Rf=0.3). The dichloromethane was removed in vacuum and the crude mass was purified by silica gel (normal, 100-200 mesh) column chromatography using a gradient eluent mixture of 50% ethyl acetate in hexane to 100% ethyl acetate to get 9-benzyloxy-2-methyl-6-(1-naphthalen-1-yl-cyclopentylmethyl)-3,4-dihydro-2H-pyrazino[1,2-c]pyrimidine-1,8-dione (352) (85 mg, semi pure) as a white sticky solid.

1. customThe dichloromethane was removed in vacuum
2. customthe crude mass was purified by silica gel (normal, 100-200 mesh) column chromatography
3. additiona gradient eluent mixture of 50% ethyl acetate in hexane to 100% ethyl acetate