Informed by previous semisynthetic work on salvinorin A, a modular total synthesis has been developed capable of producing novel compounds targeting the κ-opioid receptor. The strategy has permitted the deliberate simplification and introduction of functionality about the target molecule to provide access to molecular features on salvinorin A otherwise unattainable by semisynthesis. Using this approach, a potent pseudo-neoclerodane κ-opioid receptor ligand (2) has been realized.

Previous structure–activity studies on the neoclerodane diterpenoid salvinorin A have demonstrated the importance of the acetoxy functionality on the A-ring in its activity as a κ-opioid receptor agonist. Few studies have focused on understanding the role of conformation in these interactions. Herein we describe the synthesis and evaluation of both flexible and conformationally restricted compounds derived from salvinorin A. One such compound, spirobutyrolactone 14, was synthesized in a single step from salvinorin B and had similar potency and selectivity to salvinorin A (EC50 = 0.6 ± 0.2 nM at κ; >10000 nM at μ and δ). Microsomal stability studies demonstrated that 14 was more metabolically resistant than salvinorin A. Evaluation of analgesic and anti-inflammatory properties revealed similar in vivo effects between 14 and salvinorin A. To our knowledge, this study represents the first example of bioisosteric replacement of an acetate group by a spirobutyrolactone to produce a metabolically resistant derivative.

Columbin (1) is a furanolactone diterpene isolated from the roots of Jateorhiza and Tinospora species. These species generally grow in Asia and Africa and have been used in folk medicine for their apparent analgesic and antipyretic activities. Columbin (1) is of particular interest due to its structural similarity to the known kappa-opioid receptor (KOR) agonist salvinorin A. Given that the KOR is of interest in the study of many serious diseases, such as anxiety, depression, and drug addiction, obtaining natural or semisynthetic molecules with KOR activity recently has gained much interest. For this reason, in the present study, derivatives of 1 were designed and synthesized using known structure–activity relationships of salvinorin A at KORs. The structures of the columbin analogues prepared were elucidated by NMR spectroscopy and mass spectroscopy, and their KOR activity was investigated in vitro by inhibition of forskolin-induced cAMP accumulation. Slight improvements in KOR activity were observed in columbin derivatives over their parent compound. However, despite the structural similarities to salvinorin A, neither columbin (1) nor its derivatives were potent KOR ligands. This work represents not only the first evaluation of columbin (1) at the KOR but also one of the first works to explore synthetic strategies that are tolerated on the columbin core.

Opioids are widely used to treat millions suffering from pain, but their analgesic utility is limited due to associated side effects. Herein we report the development and evaluation of a chemical probe exhibiting analgesia and reduced opioid-induced side effects. This compound, kurkinorin (5), is a potent and selective μ-opioid receptor (MOR) agonist (EC50 = 1.2 nM, >8000 μ/κ selectivity). 5 is a biased activator of MOR-induced G-protein signaling over β-arrestin-2 recruitment. Metadynamics simulations of 5’s binding to a MOR crystal structure suggest energetically preferred binding modes that differ from crystallographic ligands. In vivo studies with 5 demonstrate centrally mediated antinociception, significantly reduced rewarding effects, tolerance, and sedation. We propose that this novel MOR agonist may represent a valuable tool in distinguishing the pathways involved in MOR-induced analgesia from its side effects.

The neoclerodane diterpene salvinorin A, found in the leaves of Salvia divinorum, is a potent κ-opioid receptor agonist, making it an attractive scaffold for development into a treatment for substance abuse. Although several successful semisynthetic studies have been performed to elucidate structure–activity relationships, the lack of analogues with substitutions to the furan ring of salvinorin A has prevented a thorough understanding of its role in binding to the κ-opioid receptor. Herein we report the synthesis of several salvinorin A derivatives with modified furan rings. Evaluation of these compounds in a functional assay indicated that sterically less demanding substitutions are preferred, suggesting the furan ring is bound in a congested portion of the binding pocket. The most potent of the analogues successfully reduced drug-seeking behavior in an animal model of drug-relapse without producing the sedation observed with other κ-opioid agonists.

The success rate for central nervous system (CNS) drug candidates in the clinic is relatively low compared to the industry average across other therapeutic areas. Penetration through the blood–brain barrier (BBB) to reach the therapeutic target is a major obstacle in development. The rapid CNS penetration of salvinorin A has suggested that the neoclerodane nucleus offers an excellent scaffold for developing antiproliferative compounds that enter the CNS. The Liebeskind–Srogl reaction was used as the main carbon–carbon bond-forming step toward the synthesis of quinone-containing salvinorin A analogues. Quinone-containing salvinorin A analogues were shown to have antiproliferative activity against the MCF7 breast cancer cell line, but show no significant activity at the κ-opioid receptors. In an in vitro model of BBB penetration, quinone-containing salvinorin A analogues were shown to passively diffuse across the cell monolayer. The analogues, however, are substrates of P-glycoprotein, and thus further modification of the molecules is needed to reduce the affinity for the efflux transporter.

Transformations that selectively modify the furan ring present in a variety of naturals products would be useful in the synthesis of biological probes but remain largely underexplored. The neoclerodane diterpene salvinorin A, isolated from Salvia divinorum, is an example of a furan-containing natural product. Following selective bromination of salvinorin A, Suzuki–Miyaura and Sonogashira couplings were accomplished in moderate to good yields without hydrolyzing the labile C-2 acetate or altering the stereochemistry of the epimerizable centers.

Attenuation of increased endocannabinoid signaling with a CB1R neutral antagonist might offer a new therapeutic direction for treatment of alcohol abuse. We have recently reported that a monohydroxylated metabolite of the synthetic aminoalkylindole cannabinoid JHW-073 (3) exhibits neutral antagonist activity at CB1Rs and thus may serve as a promising lead for the development of novel alcohol abuse therapies. In the current study, we show that systematic modification of an aminoalkylindole scaffold identified two new compounds with dual CB1R antagonist/CB2R agonist activity. Similar to the CB1R antagonist/inverse agonist rimonabant, analogues 27 and 30 decrease oral alcohol self-administration without affecting total fluid intake and block the development of alcohol-conditioned place preference. Collectively, these initial findings suggest that design and systematic modification of aminoalkylindoles such as 3 may lead to development of novel cannabinoid ligands with dual CB1R antagonist/CB2R agonist activity with potential for use as treatments of alcohol abuse.

The neoclerodane diterpene salvinorin A is the major active component of the hallucinogenic mint plant Salvia divinorum Epling and Játiva (Lamiaceae). Since the finding that salvinorin A exerts its potent psychotropic actions through the activation of opioid receptors, the site of action of morphine and related analogues, there has been much interest in elucidating the underlying mechanisms behind its effects. These effects are particularly remarkable because (1) salvinorin A is the first reported non-nitrogenous opioid receptor agonist and (2) its effects are not mediated through the previously investigated targets of psychotomimetics. This Perspective outlines our research program, illustrating a new direction to the development of tools to further elucidate the biological mechanisms of drug tolerance and dependence. The information gained from these efforts is expected to facilitate the design of novel agents to treat pain, drug abuse, and other central nervous system disorders.

As part of our continuing efforts toward more fully understanding the structure−activity relationships of the neoclerodane diterpene salvinorin A, we report the synthesis and biological characterization of unique cycloadducts through [4+2] Diels−Alder cycloaddition. Microwave-assisted methods were developed and successfully employed, aiding in functionalizing the chemically sensitive salvinorin A scaffold. This demonstrates the first reported results for both cycloaddition of the furan ring and functionalization via microwave-assisted methodology of the salvinorin A skeleton. The cycloadducts yielded herein introduce electron-withdrawing substituents and bulky aromatic groups into the C-12 position. Kappa opioid (KOP) receptor space was explored through aromatization of the bent oxanorbornadiene system possessed by the cycloadducts to a planar phenyl ring system. Although dimethyl- and diethylcarboxylate analogues 5 and 6 retain some affinity and selectivity for KOP receptors and are full agonists, their aromatized counterparts 13 and 14 have reduced affinity for KOP receptors. The methods developed herein signify a novel approach toward rapidly probing the structure−activity relationships of furan-containing natural products.

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.

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.

Pain is a complex sensory experience, involving cognitive factors, environment (setting, society, and culture), experience, and gender and is modulated significantly by the central nervous system (CNS). The mechanisms by which opioid analgesics work are understood, but this class of drugs is not ideal as either an analgesic or anti-hyperalgesic. Accordingly, considerable effort continues to be directed at improved understanding of nociceptor function and development of selective analgesics that do not have the unwanted effects associated with opioid analgesics.The purpose of this paper is to provide a review of the role of KOP receptors in the modulation of pain and highlight several chemotypes currently being explored as peripherally restricted KOP ligands.A growing body of literature has shown that KOP receptors are implicated in a variety of behavioral pain models. Several different classes of peripherally restricted peptidic and nonpeptidic KOP agonists have been identified and show utility in treating painful conditions.The pharmacological profile of KOP agonists in visceral pain models suggest that peripherally restricted KOP agonists are potentially useful for a variety of peripheral pain states. Further, clinical investigation of peripherally restricted KOP agonists will help to clarify the painful conditions where KOP agonists will be most effective.

Much of what we know about the neurosciences is the direct result of studying psychoactive natural products. Unfortunately, there are many gaps in our understanding of the basic biological processes that contribute to the etiology of many CNS disorders. The investigation of psychoactive natural products offers an excellent approach to identify novel agents to treat CNS disorders and to find new chemical tools to better elucidate their biological mechanisms. This review will detail recent progress in a program directed toward investigating psychoactive natural products with the goal of treating drug abuse by targeting κ opioid receptors.

Further synthetic modification of the furan ring of salvinorin A (1), the major active component of Salvia divinorum, has resulted in novel neoclerodane diterpenes with opioid receptor affinity and activity. A computational study has predicted 1 to be a reproductive toxicant in mammals and is suggestive that use of 1 may be associated with adverse effects. We report in this study that piperidine 21 and thiomorpholine 23 have been identified as selective partial agonists at kappa opioid receptors. This indicates that additional structural modifications of 1 may provide ligands with good selectivity for opioid receptors but with reduced potential for toxicity.

Diterpenes are a structural class of molecules that are derived from four isoprene subunits and are widespread throughout nature. A number of neoclerodane diterpenes have been found to have biological activity but a limited number of chemical investigations have been conducted. Recently, the neoclerodane diterpene, salvinorin A (12) has been investigated due to its unique pharmacological profile. This review will discuss the chemical methods used to chemically modify and synthesize 12.

Salvinorin A is a psychoactive natural product that has been found to be a potent and selective κ opioid receptor agonist in vitro and in vivo. The activity of salvinorin A is unusual compared to other opioids such as morphine in that it mediates potent κ opioid receptor signaling yet leads to less receptor downregulation than observed with other κ agonists. Our initial chemical modifications of salvinorin A have yielded one analogue, herkinorin (1c), with high affinity at the μOR. We recently reported that 1c does not promote the recruitment of β-arrestin-2 to the μOR or receptor internalization. Here we describe three new derivatives of 1c (3c, 3f, and 3i) with similar properties and one, benzamide 7b, that promotes recruitment of β-arrestin-2 to the μOR and receptor internalization. When the important role μ opioid receptor regulation plays in determining physiological responsiveness to opioid narcotics is considered, μ opioids derived from salvinorin A may offer a unique template for the development of functionally selective μ opioid receptor–ligands with the ability to produce analgesia while limiting adverse side effects.

Modification of the C-1 ketone of salvinorin A (2a) produces analogues with opioid antagonist properties. Of particular significance is the finding that 1-deoxo-1,10-dehydrosalvinorin A (11a) is a moderately potent antagonist at all three opioid receptor subtypes, and that herkinorin (2b), a μ agonist, is converted to a weak antagonist by removal of the C-1 ketone (3b and 11b). These observations suggest that the ketone of 2b is a key structural feature responsible for μ agonist activity.

Further synthetic modification of the furan ring of salvinorin A (1), the major active component of Salvia divinorum, has resulted in novel neoclerodane diterpenes with opioid receptor affinity and activity. A computational study has predicted 1 to be a reproductive toxicant in mammals and is suggestive that use of 1 may be associated with adverse effects. We report in this study that piperidine 21 and thiomorpholine 23 have been identified as selective partial agonists at kappa opioid receptors. This indicates that additional structural modifications of 1 may provide ligands with good selectivity for opioid receptors but with reduced potential for toxicity.