3-(αR)-α-((2S,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-hydroxybenzyl)- N-alkyl-N-arylbenzamides:  Potent, Non-Peptidic Agonists of Both the μ and δ Opioid Receptors

Opioid analgesics with both μ and δ opioid receptor activation represent a new approach to the treatment of severe pain with an improved safety profile. Compounds with this profile may exhibit strong analgesic properties due to μ agonism, with a reduced side effect profile resulting from δ agonism. Replacing the p-diethylamide of the known potent δ opioid receptor selective agonist BW373U86 with a m-diethylamide resulted in a compound with agonist activity at both the μ and δ opioid receptors. Modifying the amide to an N-methyl-N-phenylamide increased agonist potency at both receptors. A series of 3-(αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-hydroxybenzyl)-N-alkyl-N-arylbenzamides have been made to explore the structure−activity relationship (SAR) around the N-methyl-N-phenylamide. Several potent agonists of both the μ and δ opioid receptors have been identified, including (+)-3-((αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-hydroxybenzyl)-N-(4-fluorophenyl)-N-methylbenzamide (23), which has EC50 values of 0.67 and 1.1 nM at the μ (guinea pig ileum assay) and δ (mouse vas deferens assay) opioid receptors, respectively.