N-modified analogues of cocaine: synthesis and inhibition of binding to the cocaine receptor.

Cocaine methiodide (2), N-norcocaine (1b), N-benzyl-N-norcocaine (1c), and N-nor-N-acetylcocaine (1d) were synthesized and evaluated for their ability to inhibit binding of [3H]-3 beta-(4-fluorophenyl)tropane-2 beta-carboxylic acid methyl ester (WIN 35,428) to the cocaine receptor. The study showed that removal of the N-methyl group to give 1b, or replacement with the larger N-benzyl group to give 1c, has a relatively small effect on binding potency. In contrast, replacement of the N-methyl group by the acetyl moiety to give 1d, or the addition of a methyl group to give 2, reduces affinity for the receptor by a large factor. In order to gain preliminary information concerning the importance of the nitrogen location on the tropane ring system, the receptor binding affinity of 8-methyl-8-azabicyclo[3.2.1]octan-3 beta-ol benzoate (5, beta-tropacocaine) was compared to that of the isomeric 6-methyl-6-azabicyclo[3.2.1]octan-3 beta-ol benzoate (4d). The fact that both compounds have similar binding affinities for the cocaine receptor suggests that 3 beta-(benzoyloxy)-6-methyl-6-azabicyclo[3.2.1] octane-2-carboxylic acid methyl ester, which is isomeric with cocaine, may possess binding potency similar to cocaine.