L-Phenylalanine → N,N-Dibenzyl-L-phenylalanine

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Reaction Steps

L-Phenylalanine (16.5 g) and potassium carbonate (27.6 g) were added to a mixed solvent of methanol (100 ml) and water (100 ml). Then, benzyl bromide (68.4 g) was added to the obtained mixture, and they were stirred under heating and reflux for 3 hours. The reaction mixture was cooled to room temperature, and poured on ice/water. After the extraction with diethyl ether (300 ml), the obtained solution in diethyl ether was dried over anhydrous sodium sulfate. Sodium sulfate was filtered out. 4 N solution (25 ml) of dioxane in hydrochloric acid was added to the obtained solution in diethyl ether. After stirring under cooling on ice followed by the crystallization, the crystals were separated and washed with diethyl ether. The obtained crystals were added to a mixture of water (100 ml) and toluene (100 ml) to obtain a slurry. After the neutralization with a saturated aqueous sodium hydrogencarbonate solution followed by the division into layers, the product was extracted again with toluene. The obtained toluene layers were combined together and dried over anhydrous magnesium sulfate. Magnesium sulfate was filtered out and the solvent was evaporated under reduced pressure to obtain the intended benzyl ester of N,N-dibenzyl-L-phenylalanine (37.06 g) in a yield of 85%.

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