Acylation of 2-amino-5-nitrobenzophenone (I) with phenylacetic acid chloride (II) in refluxing toluene yields derivative (III), whose nitro group is reduced by means of SnCl2 in refluxing EtOAc to afford amine (IV). Coupling of (IV) with protected cysteine (V) by means of isobutyl chloroformate and N-methylmorpholine (NMM) in DMF provides protected derivative (VI), which is finally treated with TFA and Et3SiH in CH2Cl2 to furnish the target compound.