4-Toluenesulfonyl chloride → di-tert-butyl 4-{3-{[(4-methylphenyl)sulfonyl)oxy]propyl}-N-trityl-L-glutamate

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Reaction Conditions

Reaction Steps

At 0° C. triethylamine (0.31 mL, 2.2 mmol) and 4-methylbenzenesulfonyl chloride (0.141 g, 0.74 mmol) were added to a solution of di-tert-butyl 4-(3-hydroxypropyl)-N-trityl-L-glutamate (0.239 g, 0.427 mmol) in dichloromethane (10 mL). The resulting mixture was stirred at 0° C. for 2 h and for 16 h at room temperature. The solution was concentrated and the crude product was purified by flash chromatography (silica, ethyl acetate/hexane) to afford di-tert-butyl 4-{3-{[(4-methylphenyl)sulfonyl)oxy]propyl}-N-trityl-L-glutamate (0.255 mg, 67%) as a mixture of (4S,4S)/(2S,4R) diastereoisomers. The isomers were separated by chiral HPLC (Chiralpak AD-H 5 μm 250×20 mm, hexane/2-propanol 9:1, 25 mL/min):

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