Design and synthesis of 3-[N-(cyclopropylmethyl) amino]-7-(methoxy or hydroxy)-2, 2-dimethyl-1-tetralone analogs as potential opioid receptor antagonists
A series of 3-aminotetralins were synthesized as potential opioid antagonists. Each proposed target compound was based on a 3-(mono- or dialkylamino )-7 -(hydroxy or methoxy)-2, 2-dimethyl-1-tetralone parent structure. Three synthetic schemes were developed utilizing the common intermediate, ethyl3-benzylamino-2, 2-dimethyl-4-(4- methoxyphenyl)butyrate 3. In Scheme I, compound 3 was modified through a series of six steps to obtain 3-(N-methyl-N-cyclopropanecarboxamido )-7 -methoxy-2, 2-dimethyl- 1-hydroxy-1-phenyltetralin (9). To carry out further synthetic steps on the intermediate 9 required the reduction of the amide function, which proved to be problematic in terms of product isolation. Scheme II was a four-step procedure, which utilized the intermediate ethyl 3- amino-2, 2 dimethyl-4-(4-methoxyphenyl)butyrate (4), also utilized in Scheme I. Ester hydrolysis of the amino ester 4 produced the amino acid 12. Internal cyclization of 12 yielded the key intermediate, 3-amino-7 -methoxy-2, 2-dimethyl-1-tetralone (13). TheNalkylation step was carried out on 13 and this yielded the target compounds, 3-[N- ( cyclopropylmethyl)amino ]- and 3-[N, N-( dicyclopropylmethyl)amino ]-7 -methoxy-2, 2- dimethyl-1-tetralone (14, 15). Subsequently, compounds 14 and 15 were 0-demethylated to obtain the respective target compounds, 3-[N-(cyclopropylmethyl)amino]- and 3-[N, N-(dicyclopropylmethyl)amino ]-7-hydroxy-2, 2-dimethyl-1-tetralone (16, 17). Scheme III was an alternate synthetic route to obtain the target compounds 3-[Nmethyl- N-( cyclopropylmethyl)amino ]-2, 2-dimethyl-7-(hydroxy or methoxy)-1-hydroxy- 1-phenyltetralin (10, 11) without the amide reduction step required in Scheme I. The intermediate 3 was N-methylated to form the 3-N-methyl-N-benzylamino ester 18 by the Eschweiler-Clarke procedure. Compound 18 was converted through a series of four steps to obtain 3-[ N-methyl-N-( cyclopropylmethyl)amino ]-7 -methoxy-2, 2-dimethyl-1- tetralone (22), a target compound which was 0-demethylated to obtain compound 23, the 7-0H analog. The mono- and dialkylated 3-aminotetralins were synthesized and confirmed for purity and correct molecular formula by utilizing 1H NMR, 13C NMR, mass spectrometry, and elemental analysis. The target compounds 14, 15, 16, 17,22 and 23 were converted to their salts and are being analyzed for opioid-related activity in receptor binding assays.
Pharmaceutical chemistry Methods;Drugs Design, Chemistry, Medicinal and Pharmaceutical Chemistry, Medicinal-Pharmaceutical Chemistry, Pharmacy and Pharmaceutical Sciences
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