合成路线1

D-Alaninol (I) was protected as the tert-butyl carbamate (II) and then converted to mesylate (III). Displacement of the mesylate group of (III) with NaCN furnished nitrile (IV), which was hydrogenated over Raney Nickel to give diamine (V). Condensation of (V) with benzaldehyde (VI) in the presence of molecular sieves produced imine (VII) and subsequent reduction by means of NaBH4 gave rise to the benzyl amine (VIII). This amine was alkylated with 4-chlorobutyronitrile (IX) to afford nitrile (X), which was further converted to the triamino compound (XI) by hydrogenation over Raney Nickel. Reaction of (XI) with methyl 2-[(phenoxycarbonyl)oxy]acetate (XII) provided carbamate (XIII). The ester group of (XIII) was then hydrolyzed with NaOH to give carboxylic acid (XIV).