Bioisosteric modification of salvinorin a, a potent and selective kappa-opioid receptor agonist

Salvinorin A ((2S,4aR,6aR,7R,9S,10aS, 10bR)-2H-naphtho[2,1-c]pyran-7-carboxylic acid, 9-(acetyloxy)-2-(3-furanyl)dodecahydro-6a,10b-dimethyl-4,10-dioxo methyl ester, 1, CAS 83729-01-5) has been shown to bind with high affinity and selectivity to the kappa-opioid receptor (KOR) as an agonist. Bioisosteres of 1 were developed and biologically evaluated in binding and functional assays. The C-2 thioacetate isoster produced comparable activity to 1, but nitrogen substitution had a diminishing effect. Intermediates, which lack a beta-carbonyl at C-2, displayed moderate affinity. The derivatives were tested against all opioid subtypes and were selective towards KOR.