The 2-methoxy methyl analogue of salvinorin A attenuates cocaine-induced drug seeking and sucrose reinforcements in rats.

κ Opioid receptor activation by traditional arylacetamide agonists and the novel neoclerodane diterpene κ opioid receptor agonist Salvinorin A (Sal A) results in attenuation of cocaine-seeking behavior in pre-clinical models of addiction. However, adverse effects such as sedation, depression and aversion limit their clinical utility. The Sal A analogue, 2-methoxy-methyl salvinorin B (MOM Sal B) is a longer acting Sal A analogue with high affinity for κ opioid receptors. In this study, we tested MOM Sal B for its ability to modulate cocaine-seeking behavior in rats. MOM Sal B (0.3mg/kg) successfully attenuated cocaine-seeking but also attenuated sucrose reinforcement. No change in activity was observed in either cocaine-induced hyperactivity or spontaneous open field activity tests but increased immobility and decreased swimming times in the forced swim test were observed. This study indicates that κ opioid receptor activation by more potent Sal A analogues modulates cocaine-seeking behavior non-selectively without causing sedation, suggesting an improved side effects profile. However, pro-depressive effects are seen, which may limit the therapeutic potential of this compound. Future studies with Sal A analogues having affinities at other opioid receptors are warranted as they have the potential to identify compounds having effective anti-addiction properties.

Semisynthetic neoclerodanes as kappa opioid receptor probes.

Modification of the furan ring of salvinorin A (1), the main active component of Salvia divinorum, has resulted in novel neoclerodane diterpenes with opioid receptor affinity and activity. Conversion of the furan ring to an aldehyde at the C-12 position (5) has allowed for the synthesis of analogues with new carbon-carbon bonds at that position. Previous methods for forming these bonds, such as Grignard and Stille conditions, have met with limited success. We report a palladium catalyzed Liebeskind-Srogl cross-coupling reaction of a thioester and a boronic acid that occurs at neutral pH and ambient temperature to produce ketone analogs at C-12. To the best of our knowledge, this is the first reported usage of the Liebeskind-Srogl reaction to diversify a natural product scaffold. We also describe a one-step protocol for the conversion of 1 to 12-epi-1 (3) through microwave irradiation. Previously, this synthetically challenging process has required multiple steps. Additionally, we report in this study that alkene 9 and aromatic analogues 12, 19, 23, 25, and 26 were discovered to retain affinity and selectivity at kappa opioid receptors (KOP). Finally, we report that the furan-2-yl analog of 1 (31) has similar affinity to 1. Collectively, these findings suggest that different aromatic groups appended directly to the decalin core may be well tolerated by KOP receptors, and may generate further ligands with affinity and activity at KOP receptors.

Synthesis of neoclerodane diterpenes and their pharmacological effects.

Salvinorin A is a neoclerodane diterpene that has been shown to be an agonist at kappa opioid receptors. Its unique structure makes it an attractive target for synthetic organic chemists due to its seven chiral centers and diterpene scaffold. This molecule is also interesting to pharmacologists because it is a non-serotonergic hallucinogen, and the first opioid ligand discovered that lacks a basic nitrogen. There have been several total synthesis approaches to salvinorin A, and these will be detailed within this chapter. Additionally, research efforts have concentrated on structure modification of the salvinorin A scaffold through semi-synthetic methods. Most modifications have focused on the manipulation of the acetate at C-2 and the furan ring. However, chemistry has also been developed to generate analogs at the C-1 ketone, the C-4 methyl ester, and the C-17 lactone. The synthetic methodologies developed for the salvinorin A scaffold will be described, as well as specific analogs with interesting biological activities.

Potential Drug Abuse Therapeutics Derived from the Hallucinogenic Natural Product Salvinorin A.

Previous structure-activity relationship studies of salvinorin A have shown that modification of the acetate functionality off the C-2 position to a methoxy methyl or methoxy ethyl ether moiety leads to increased potency at KOP receptors. However, the reason for this increase remains unclear. Here we report our efforts towards the synthesis and evaluation of C-2 constrained analogs of salvinorin A. These analogs were evaluated at opioid receptors in radioligand binding experiments as well as in the GTP-γ-S functional assay. One compound, 5, was found to have affinity and potency at κ opioid (KOP) receptors comparable to salvinorin A. In further studies, 5 was found to attenuate cocaine-induced drug seeking behavior in rats comparably to salvinorin A. This finding represents the first example of a salvinorin A analog that has demonstrated anti-addictive capabilities.

New therapeutic potential for psychoactive natural products.

Much of our knowledge in neuroscience was discovered through the study of mind-altering natural products. However, although much has been learned about human physiology and basic biological processes, the underlying causes of CNS disorders and other disease states are still elusive. Based on its main past successes, the continued study of mind-altering compounds promises to yield novel agents that may be developed into medications and to identify new targets for the treatment of diseases. This Highlight describes the history of investigations into several classes of mind-altering natural products and relates recent and potential therapeutic uses for these agents.