A study of the effect of transposition of the internal nitrogen atom for the adjacent benzylic carbon atom in delta -selective agonists such as BW373U86 (1) and SNC-80 (2) has been undertaken. It was shown that high-affinity, fully efficacious, and delta opioid receptor-selective compounds can be obtained from this transposition. In addition to the N,N-diethylamido group needed as the delta address, the structural features identified to promote delta receptor affinity in the set of compounds studied included a cis relative stereochemistry between the 3- and 4-substituents in the piperidine ring, a trans-crotyl or allyl substituent on the basic nitrogen, the lack of a 2-methyl group in the piperidine ring, and either no substitution or hydroxyl substitution in the aryl ring not substituted with the N,N-diethylamido group. Structural features found to be important for mu affinity include hydroxyl substitution in the aryl ring, the presence of a 2-methyl group in a cis relative relationship to the 4-amino group as well as N-substituents such as cyclopropylmethyl. It was also determined that mu receptor affinity could be increased while maintaining delta receptor affinity, especially when hydroxyl-substituted compounds are considered. Additionally, it was discovered that the somewhat lower mu/delta selectivities observed for the piperidine compounds relative to the piperazine-based ligands appear to arise as a consequence of the carbon-nitrogen transposition which imparts an overall lower delta and higher mu affinity to the piperidine-based ligands. This higher affinity for the mu receptor, apparently intrinsic to the piperidine-based compounds, suggests that ligands of this class will more easily be converted to mu/delta combination agonists compared to the piperazine ligands such as 1. This is particularly important since analogues of 1, which show both mu- and delta -type activity, are now recognized as important for their strong analgesia and cross-canceling of many of the side effects found in agonists operating exclusively from either the delta or mu opioid receptor.
Factors influencing agonist potency and selectivity for the opioid delta receptor are revealed in structure-activity relationship studies of the 4-[(N-substituted-4-piperidinyl) arylamino]-N,N-diethylbenzamides
Thomas, J., Herault, X., Rothman, RB., Atkinson, R., Burgess, J., Mascarella, S., Dersch, CM., Xu, H., Flippen-Anderson, JL., George, CF., & Carroll, F. (2001). Factors influencing agonist potency and selectivity for the opioid delta receptor are revealed in structure-activity relationship studies of the 4-[(N-substituted-4-piperidinyl) arylamino]-N,N-diethylbenzamides. Journal of Medicinal Chemistry, 44(6), 972-987.