L-(+)-Cysteine → 2(R)-(9H-fluoren-9-ylmethoxycarbonylamino)-3-tritylsulfanyl-propionic acid tert-butyl ester

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In one incarnation of the present invention, as illustrated below, the cysteine derivative is 2(R)-(benzhydrylidene-amino)-3-tritylsulfanyl-propionic acid tert-butyl ester. 2(R)-(Benzhydrylidene-amino)-3-tritylsulfanyl-propionic acid tert-butyl ester can be formed by the following process: (1) 2(R)-(9H-Fluoren-9-ylmethoxycarbonylamino)-3-tritylsulfanyl-propionic acid (i.e., (R)-cysteine with Fmoc a protected amino group and with a trityl protected —SH group), is reacted with t-butyl alcohol and dicyclohexyl carbodiimide (DCC) in 4-(dimethylamino)pyridine (DMAP) and tetrahydrofuran (THF) at room temperature to form 2(R)-(9H-fluoren-9-ylmethoxycarbonylamino)-3-tritylsulfanyl-propionic acid tert-butyl ester; (2) the Fmoc group is removed from the 2(R)-(9H-fluoren-9-ylmethoxycarbonylamino)-3-tritylsulfanyl-propionic acid tert-butyl ester using either diethylamine in dichloromethane or piperidine in dichloromethane to form 2(R)-amino-3-tritylsulfanyl-propionic acid tert-butyl ester; and (3) the 2(R)-amino-3-tritylsulfanyl-propionic acid tert-butyl ester is reacted with benzhydrylideneamine in dichloromethane at room temperature to form 2(R)-(benzhydrylidene-amino)-3-tritylsulfanyl-propionic acid tert-butyl ester.

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