Dimethyl Sulfate → 1H-Purine-2,6-dione, 3,7-dihydro-8-(2-(1,1'-biphenyl)-4-ylethenyl)-1,3-diethyl-7-methyl-, (E)-

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Reaction Steps

Compound 170 (1.50 g, 3.89 mmol) obtained in Reference Example 167 was suspended in a mixed solvent of 13 ml of water, 3.9 ml of a 2N aqueous solution of sodium hydroxide, and 7 ml of methanol. To the suspension was dropwise added 0.55 ml (5.83 mmol) of dimethyl sulfate, and the resultant mixture was stirred at 60° C. for 4 hours. Water (10 ml) was added thereto, and the deposited crystals were collected by filtration and dried. The obtained crude crystals were purified by silica gel column chromatography, followed by recrystallization from ethyl acetate to give 480 mg (yield 28%) of Compound 171 as yellow columns.

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