10.1039/b920864j
The research presents an environmentally friendly method for synthesizing naltrindole (NTI), naltriben (NTB), and their analogs using Fischer indole synthesis under mildly acidic, purely aqueous conditions. The study explores the preparation of these compounds, which are valuable tools for opioid receptor pharmacology studies, using hydrochloride salts of naltrexone and various phenylhydrazines in boiling water, achieving good to excellent yields and high purities without the need for organic solvents or harsh acids. The chemicals that played a crucial role in this research include naltrexone hydrochloride (NTX·HCl), phenylhydrazine hydrochloride, and other substituted phenylhydrazines such as 1-methyl-1-phenylhydrazine, o-chlorophenylhydrazine, o-fluorophenylhydrazine, and o-nitrophenylhydrazine. The study also utilized dilute hydrochloric acid (HCl) to facilitate the synthesis, and in some cases, sulfuric acid (H?SO?) for comparison. The products were obtained through simple filtration or centrifugation, highlighting the simplicity and efficiency of the aqueous Fischer synthesis method.