Indol-3-ylcycloalkyl Ketones: Effects of N1 Substituted Indole Side Chain Variations on CB2 Cannabinoid Receptor Activity

Recent Advances in Selective CB2 Agonists for the Treatment of Pain

The cannabinoid CB2 receptor is one of a family of GPCRs that mediate the effects of endocannabinoids. Several agonists of this receptor are currently in clinical trials for the treatment of pain and inflammation, indications that have been validated by pre-clinical studies on agonists and in receptor knockout mice. Key to the clinical advancement of CB2 agonists is achieving selectivity over the related CB1 receptor, whose activation results in undesirable CNS effects, limiting therapeutic utility. A variety of CB2 receptor agonist chemotypes are reviewed including mono-, bi- and tricyclic cores and bi- and triaryl cores. Pharmacology, with a focus on selectivity requirements and a variety of pre-clinical animal models to assess activity and selectivity, is presented.

Design, synthesis, and pharmacological characterization of indol-3-ylacetamides, indol-3-yloxoacetamides, and indol-3-ylcarboxamides: potent and selective CB2 cannabinoid receptor inverse agonists

In our search for new cannabinoid receptor modulators, we describe herein the design and synthesis of three sets of indole-based ligands characterized by an acetamide, oxalylamide, or carboxamide chain, respectively. Most of the compounds showed affinity for CB2 receptors in the nanomolar range, with K(i) values spanning 3 orders of magnitude (377-0.37 nM), and moderate to good selectivity over CB1 receptors. Their in vitro functional activity as inverse agonists was confirmed in vivo in the formalin test of acute peripheral and inflammatory pain in mice, in which compounds 10a and 11e proved to be able to reverse the effect of the CB2 selective agonist COR167.

Identification and structural characterization of the synthetic cannabinoid 3-(1-adamantoyl)-1-pentylindole as an additive in 'herbal incense'

Since the end of 2010, more than 20 synthetic cannabimimetics have been identified in 'Spice' products, demonstrating the enormous dynamic in this field. In an effort to cope with the problem, many countries have already undertaken legal measures by putting some of these compounds under control. Nevertheless, once a number of compounds were scheduled, they were soon replaced by other synthetic cannabinoids. In this article, we report the identification of a new--and due to its substitution pattern rather uncommon--cannabimimetic found in several 'herbal incense' products. The GC-EI mass spectrum first led to misidentification as the alpha-methyl-derivative of JWH-250. However, since both substances show different retention indices, thin-layer chromatography was used to isolate the unknown compound. After application of nuclear magnetic resonance spectroscopy, high-resolution MS and GC-MS/MS techniques, the compound was identified as 3-(1-adamantoyl)-1-pentylindole, a derivative of JWH-018 carrying an adamantoyl moiety instead of a naphthoyl group. This finding supports that the listing of synthetic cannabinoids as prohibited substances triggers the appearance of compounds with uncommon substituents. Moreover, it emphasizes the necessity of being aware of the risk of misidentification when using techniques sometimes providing only limited structural information like GC-MS.

Synthesis and preliminary evaluation of [18F]-labeled 2-oxoquinoline derivatives for PET imaging of cannabinoid CB2 receptor

INTRODUCTION

The cannabinoid receptor type 2 (CB(2)) is an important target for development of drugs and imaging agents for diseases, such as neuroinflammation, neurodegeneration and cancer. Recently, we reported synthesis and results of in vitro receptor binding of a focused library of fluorinated 2-oxoquinoline derivatives as CB(2) receptor ligands. Some of the compounds demonstrated to be good CB(2)-specific ligands with Ki values in the nanomolar to subnanomolar concentrations; therefore, we pursued the development of their (18)F-labeled analogues that should be useful for positron emission tomography (PET) imaging of CB(2) receptor expression. Here, we report the radiosynthesis of two (18)F-labeled 2-oxoquinoline derivatives and the preliminary in vitro and ex vivo evaluation of one compound as a CB(2)-specific radioligand.

METHODS

4-[(18)F]fluorobenzyl amine [(18)F]-3 was prepared by radiofluorination of 4-cyano-N,N,N-trimethylanilinium triflate salt followed by reduction with LiAlH(4) and then coupled with acid chlorides 11 and 12 to afford [(18)F]-13 and [(18)F]-14. In vitro CB(2) receptor binding assay was performed using U87 cells transduced with CB(2) and CB(1) receptor. Ex vivo autoradiography was performed with [(18)F]-14 on spleen and on CB(2)- and CB(1)-expressing and wild-type U87 subcutaneous tumors grown in mice.

RESULTS

The radiochemical yields of [(18)F]-13 and [(18)F]-14 were 10%-15.0% with an average of 12% (n=10); radiochemical purity was >99% with specific activity 1200 mCi/μmol. The dissociation constant Kd for [(18)F]-14 was 3.4 nM. Ex vivo autoradiography showed accumulation of [(18)F]-14 in the CB(2)-expressing tumor.

CONCLUSION

Two new [(18)F]-labeled CB(2) ligands have been synthesized. Compound [(18)F]-14 appears to be a potential PET imaging agent for the assessment of CB(2) receptor expression; however, poor solubility restrain its use in vivo.

Current and emerging "at-site" pain medications: a review

The myriad pain pathophysiology has intrigued and challenged humanity for centuries. In this regard, the traditional pain therapies such as opioids and nonsteroidal anti-inflammatory drugs have been highly successful in treating acute and chronic pain. However, their drawback includes adverse events such as psychotropic effects, addiction potential, and gastrointestinal toxicities, to mention a few. These factors combined with the likelihood of an increase in chronic pain conditions due to an aging population calls for the development of novel mechanism-based or "site-specific" agents to target novel pain pathways. In this regard, rapid progress has been made in understanding the molecular mechanisms of novel pain targets such as cannabinoid receptors, fatty acid hydrolase, voltage-gated and ligand-gated ion channels such as P2 receptors, transient receptor potential channels and glial cell modulators. Accordingly, preclinical studies indicate that the site-specific/selective agents exhibit sufficient efficacy and reduced side effects such as lack of psychotropic effects indicating their clinical potential. This review provides a brief summary of some "at-site" pain targets and their role in the pain pathophysiology, and describes the efforts in developing some small molecules as novel pain therapeutics.

Detection and identification of the new potential synthetic cannabinoids 1-pentyl-3-(2-iodobenzoyl)indole and 1-pentyl-3-(1-adamantoyl)indole in seized bulk powders in Hungary

3-Naphthoyl- and 3-phenylacetylindoles represent a group of substances of cannabimimetic activity with affinities - strongly influenced by their functional groups - to cannabinoid receptors CB1 and CB2. Some of them have been described as ingredients of herbal blends also known as "smart products" by several research groups. Recently further cannabimimetic substances possessing new chemical structures like benzoylindoles and adamantoylindoles have emerged. In Hungary, two powder samples were seized by the authorities and identified as 1-pentyl-3-(2-iodobenzoyl)indole (AM-679) and 1-pentyl-3-(1-adamantoyl)indole. Structure elucidation was carried out by LC-UV-MS/MS, LC-TOF-MS, GC-MS and NMR. The benzoylindole AM-679 is a known agonist of cannabinoid receptors while the adamantoylindole derivative also carries chemical features typical for cannabimimetics. It is thus assumed that both substances might be detected in "smart products" in the future.

Three-dimensional quantitative structure-selectivity relationships analysis guided rational design of a highly selective ligand for the cannabinoid receptor 2

This paper describes a three-dimensional quantitative structure-selectivity relationships (3D-QSSR) study for selectivity of a series of ligands for cannabinoid CB1 and CB2 receptors. 3D-QSSR exploration was expected to provide design information for drugs with high selectivity toward the CB2 receptor. The proposed 3D computational model was performed by Phase and generated taking into account a number of structurally diverse compounds characterized by a wide range of selectivity index values. The model proved to be predictive, with r2 of 0.95 and Q2 of 0.63. In order to get prospective experimental validation, the selectivity of an external data set of 39 compounds reported in the literature was predicted. The correlation coefficient (r2=0.56) obtained on this unrelated test set provided evidence that the correlation shown by the model was not a chance result. Subsequently, we essayed the ability of our approach to help the design of new CB2-selective ligands. Accordingly, based on our interest in studying the cannabinergic properties of quinolones, the N-(adamantan-1-yl)-4-oxo-8-methyl-1-pentyl-1,4-dihydroquinoline-3-carboxamide (65) was considered as a potential synthetic target. The log(SI) value predicted by using our model was indicative of high CB2 selectivity for such a compound, thus spurring us to synthesize it and to evaluate its CB1 and CB2 receptor affinity. Compound 65 was found to be an extremely selective CB2 ligand as it displayed high CB2 affinity (Ki=4.9 nM), while being devoid of CB1 affinity (Ki>10,000 nM). The identification of a new selective CB2 receptor ligand lends support for the practicability of quantitative ligand-based selectivity models for cannabinoid receptors. These drug discovery tools might represent a valuable complementary approach to docking studies performed on homology models of the receptors.