Chronic clinical pain remains poorly treated. The use of mu opioid analgesics such as morphine can treat the pain, but the severe undesired effects of morphine and other mu agonists limit their use. Indeed, the rapid development of tolerance causes ever increasing doses to be administered, increasing the severity of the undesired effects. Studies have shown the coadministration of a delta opioid antagonist, together with morphine causes a slower build-up of tolerance than administration of morphine alone. Further, the use of a peptide with a dual profile of mu agonism/delta antagonism has been reported to give rise to little tolerance. Thus, the aim of this continuing research project is to develop potent non-peptide mu agonists, which also possess a profile of delta antagonism. The orvinols (e.g. etorphine) are a class of potent mu opioid agonists, that also interact with kappa and delta receptors, generally displaying delta agonism. Our hypothesis is that the delta efficacy of the orvinols can be reduced by the introduction of an aromatic group in a position that corresponds to the position of the indole in the indolomorphinans (e.g. naltrindole) or the benzylidene in the opioid benzylidenes (e.g. benzylidenenaltrexone (BNTX)), two important classes of low efficacy delta opioid ligands. By reducing delta efficacy and retaining high mu efficacy, analogs of the orvinols with the desired profile will result. The approach to be used consists of the development of a pharmacophore model of delta efficacy using a novel molecular modeling approach, and the design of target molecules with a suitably positioned aromatic ring. Included are 5,14-bridged and 6,14-bridged-morphinan based orvinols selected by the model. Novel chemical methodology will be developed and applied to the synthesis of 6,14-bridged-4,5-epoxymorphinan targets, analogs very closely related to the orvinols. The ultimate goal of this proposal is to develop potent mu opioid analgesics, to which tolerance develops slowly, or not at all, in order to reduce the undesired effects seen in the chronic treatment of clinical pain.
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