Synthesis of novel twin drug consisting of 8-oxaendoethanotetrahydromorphides with a 1,4-dioxane spacer and its pharmacological activities: mu, kappa, and putative epsilon opioid receptor antagonists.

A twin drug consisting of 8-oxaendoethanotetrahydromorphides with a 1,4-dioxane spacer, NS29, was synthesized from a naltrexone derivative. The structure of compound 8, the precursor of NS29, was determined by X-ray crystallography. Monomeric NS28 showed mu opioid receptor antagonist activity, whereas dimeric NS29, consisting of two NS28 units, showed antagonist activities for mu, kappa, and the putative epsilon opioid receptor agonists. Twin drug NS29 and its derivatives are expected to be unique pharmacological tools for investigation of opioid receptor types.