Substituted 1-phenyl-2-cyclopropylmethylamines with high affinity and selectivity for sigma sites

A series of 1-phenyl-2-cyclopropylmethylamines structurally related to (+)- and (-)-MPCB were synthesized and their binding affinities for sigma1, sigma2, opioid and dopamine (D2) receptors were evaluated. Substitution of the cis-N-normetazocine with different aminic moieties provided compounds with high affinity and selectivity for sigma binding sites with respect to opioid and dopamine (D2) receptors. The observed increase in sigma2 affinity as compared to the parent (+)-MPCB, supports the idea that the particular stereochemistry of (+)-cis-N-normetazocine affects sigma1 selectivity but does not affect sigma1 affinity. The (+/-)-cis isomers of methyl 2-[(1-adamantylamino)methyl]-1-phenylcyclopropane-1-carboxyl ate (18) displayed a higher affinity and selectivity for the sigma1 and sigma2 receptor subtypes compared to the (+/-)-trans 19. Interestingly, the enantiomer (-)-cis 18 displayed a preference for sigma1 receptor subtype whereas the (+)-cis 18 did for sigma2. These results prompt us to synthesize compounds with modification of nitrogen and carboxyl groups. The compounds obtained showed high affinities and selectivity for sigma sites. Moreover, modifications of carboxyl groups provided compounds with the highest affinities in the series. In particular, compound 25 with reverse-type ester showed a Ki of 0.6 and 4.05 nM for sigma1 and sigma2 binding sites, respectively.