A route to potent, selective and biased salvinorin chemical space

The salvinorins serve as templates for next generation analgesics, antipruritics and dissociative hallucinogens via selective and potent agonism of the kappa-opioid receptor (KOR). In contrast to most opioids, the salvinorins lack basic amines and bind with high affinity and selectivity via complex polyoxygenated scaffolds that have frustrated deep-seated modification by synthesis. Here we describe a short asymmetric synthesis that relies on a sterically-confined organocatalyst to dissociate acidity from reactivity and effect Robinson annulation of an unactivated nucleophile / unstable electrophile pair. Combined with a cobalt-catalyzed polarized diene-alkyne cycloaddition, the route allows divergent access to a focused library of salvinorins. We appraise the synthesis by its generation of multiple analogs that exceed the potency, selectivity, stability and functional bias of salvinorin A itself.