The condensation of N-(tert-butoxycarbonyl)-4-nitro-L-phenylalanine (I) with 4-ethylpiperiine (II) by means of diisopropylethylamine (DIEA) in dichloromethane gives the corresponding protected piperidide (III), which is treated with TFA to eliminate the carbamate group yielding (IV). The sulfonation of (IV) with 4-chloropyridine-3-sulfonyl chloride (V) by means of DIEA in dichloromethane affords the sulfonamide (VI), which is condensed with 2-(2(S)-amino-3-phenylpropoxy)ethanol (VII) by means of DIEA in ethanol giving the intermediate (VIII). Finally, the reduction of the nitro group of (VIII) with H2 over Pd/C in methanol affords the target compound.

The intermediate 2-(2(S)-amino-3-phenylpropoxy)ethanol (VII) has been obtained as follows: The condensation of 2(S)-(dibenzylamino)-3-phenyl-1-propanol (IX) with tert-butyl 2-bromoacetate (X) by means of tetrabutylammonium hydrogen sulfate and NaOH in dichloromethane/water gives 2-[2(S)-(dibenzylamino)-3-phenylpropoxy]acetic acid tert-butyl ester (XI), which is reduced with LiAlH4 in THF yielding 2-[2(S)-(dibenzylamino)-3-phenylpropoxy]ethanol (XII). Finally, this compound is debenzylated by hydrogenation with H2 over Pd/C in methanol/acetic acid affording the target intermediate (VII).