Treatment of naltrexone hydrochloride (I) with 2-nitrophenylhydrazine (II) under Fischer conditions in HCl:HOAc provides nitroindole derivative (III), which is reduced by means of hydrazine and Ni Raney in EtOH to afford amine (IV). Separately, 3,4-dimethylbenzoic acid (V) is brominated with NBS and benzoyl peroxide in refluxing CCl4 to furnish tetrabromo derivative (VI), which is then hydrolyzed with Na2CO3 in H2O to yield 3,4-diformylbenzoic acid (VII). Bis acetalization of (VII) with ethylene glycol (VIII) in benzene in the presence of p-TsOH affords carboxylic acid (IX), which is then coupled with intermediate (IV) by means of DCC and HOBt in DMF to give the corresponding amido ester derivative (X). Selective saponification of (X) with K2CO3 in MeOH affords amide (XI), which is finally converted into the target compound by hydrolysis with HCl in acetone.