Fig. 2. (A) The new amino acid derivatives Fmoc-AA*-OH and the commercially available Fmoc-R5-OH and Fmoc-S5-OH used in this work. (B) The synthetic routes for the key intermediates 5a–g. (C) The synthetic route for Fmoc-AA*-OH 1a–g. Fmoc = fluorenylmethyloxycarbonyl; tBu = tert-butyl; Boc = tert-butyloxycarbonyl; Cbz = benzoxycarbonyl; RT = room temperature; DCM = dichloromethane; LiHMDS = lithium bis(trimethylsilyl)amide; HMPA = hexamethyl phosphoryl triamide; Ph = Benzene; MeCN = acetonitrile.
