To a solution of the compound obtained in Example 30 (5) (0.0592 g) in tetrahydrofuran (2 ml), 2.0 M lithium diisopropylamide solution (0.0852 ml) was added dropwise at −78° C. and the mixture was stirred for 30 minutes. 4-Fluorobenzyl bromide (0.02 ml) was then added to the mixture, followed by stirring at the same temperature for, 30 minutes. The reaction solution was poured into a saturated aqueous ammonium chloride solution and extracted with ethyl acetate. The organic layer was washed with a saturated aqueous NaCl solution, dried over anhydride magnesium sulfate, filtered and concentrated under reduced pressure. The resulting residue was separated using silica gel preparative thin-layer chromatography (hexane:ethyl acetate=1:1) to obtain 0.005 g of the desired product.
