Coupling of N-Boc-phenylalanine (I) with amine (II) by means of HBTU and DIEA provides amide (III), whose Boc group is removed by treatment with HCl in dioxane to afford amine hydrochloride (IV). Finally, the target compound is obtained by reductive amination between amine (IV) and aldehyde (V) in MeOH in the presence of NaCNBH3.