Synthesis and Evaluation of Conformationally Restricted N--N-methyl-2-(1-pyrrolidinyl)ethylamines at ? Receptors. 2. Piperazines, Bicyclic Amines, Bridged Bicyclic Amines, and Miscellaneous Compounds

Article abstract of DOI:10.1021/jm00068a007

As a continuation of our earlier study (J.Med.Chem. 1992, 35, 4334-4343) we conformationally restricted the ?-receptor ligand 2-(1-pyrrolidinyl)-N-<2-(3,4-dichlorophenyl)ethyl>-N-methylethylamine (1) by incorporating it into a series of homologous piperazines 3-9 and homopiperazines 10 and 11, diazabicyclononanes and decanes, bridgehead bicyclooctanes and nonanes as well as other miscellaneous compounds. ?-Receptor binding affinites were obtained using <3H>(+)-pentazocine in guinea pig brain membrane ?₁ sites.The studies suggest that the nitrogen lone pair orient ation found in the piperazines affords the strongest binding interaction.Other nitrogen lone pair orientations or compounds representing unlikely staggered conformations of 1 -1,4-diazabicyclo<3.2.2>nonane (16)> show very weak ? interaction.Comperison of the binding data of different N-substituted homologues of 1 with those of the 1-<2-(3,4-dichlorophenyl)ethyl>-4-alkylpiperazines suggests that the two nitrogen atoms of 1 are working in opposition to one another in terms of their sensitivity to steric bulk.The high binding affinity of the 1,4-diazabicyclo<4.3.0>nonanes 12 suggests that these may approximate the methyl and pyrrolidine ring conformations found in 1 when it is bound to the ? receptor.Compound 12 exhibited a 4-fold enantioselectivity favoring (+)-12.The synthesis of 6,7-dichloro-2-<<2-(1-pyrrolidinyl)ethyl>amino>tetralin (19) and its desmethyl derivative 20 permitted constraint of the 3,4-dichlorophenyl and N-methyl moieties of 1 into a gauche orientation.The binding data suggests that this conformation in 1 favors strong binding interaction at ?-receptors. ?-Receptor K₁'s ra nged from 0.55 nM for 1-<2-(3,4-dichlorophenyl)ethyl>-4-n-butylpiperazine (7) to 654 nM for 16.Overall comparison of the results indicate that 1 is subject to considerable conformational freedom and suggests that the ?-receptor is not subject to rigid stereochemical restraints with 1.These results add to our earlier study where we restrained 1 using simple monocyclic heterocycles.