The CB2 cannabinoid receptor-selective agonist O-3223 reduces pain and inflammation without apparent cannabinoid behavioral effects.

Although Δ(9)-tetrahydrocannabinol (THC) and other mixed CB(1)/CB(2) receptor agonists are well established to elicit antinociceptive effects, their psychomimetic actions and potential for abuse have dampened enthusiasm for their therapeutic development. Conversely, CB(2) receptor-selective agonists have been shown to reduce pain and inflammation, without eliciting apparent cannabinoid behavioral effects. In the present study, we developed a novel ethyl sulfonamide THC analog, O-3223, and compared its pharmacological effects to those of the potent, mixed CB(1)/CB(2) receptor agonist, CP55,940, in a battery of preclinical pain models. Competitive cannabinoid receptor binding experiments revealed that O-3223 was approximately 80-fold more selective for CB(2) than CB(1) receptors. Additionally, O-3223 behaved as a full CB(2) receptor agonist in [(35)S]GTPγS binding. O-3223 reduced nociceptive behavior in both phases of the formalin test, reduced thermal hyperalgesia in the chronic constriction injury of the sciatic nerve (CCI) model, and reduced edema and thermal hyperalgesia elicited by intraplantar injection of LPS. These effects were blocked by pretreatment with the CB(2) receptor-selective antagonist SR144528, but not by the CB(1) receptor antagonist, rimonabant. Unlike CP55,940, O-3223 did not elicit acute antinociceptive effects in the hot-plate test, hypothermia, or motor disturbances, as assessed in the rotarod test. These data indicate that the CB(2) receptor-selective agonist, O-3223, reduces inflammatory and neuropathic nociception, without affecting basal nociception or eliciting overt behavioral effects. Moreover, this compound can serve as a template to develop new CB(2) receptor agonists with increased receptor selectivity and increased potency in treating inflammatory and neuropathic pain.

Addition of the phenoxathiin cation radical to alkenes and nonconjugated dienes. Formation of (E)- and (Z)-(10-phenoxathiiniumyl)alkenes and (E)- and (Z)-(10-phenoxathiiniumyl)dienes on basic alumina.

Addition of phenoxathiin cation radical (PO*+) to acyclic alkenes in acetonitrile (MeCN) solution occurred stereospecifically to form bis(10-phenoxathiiniumyl)alkane adducts. Stereospecific trans addition is ascribed to the intermediacy of an episulfonium cation radical. The alkenes used were cis- and trans-2-butene, cis- and trans-2-pentene, cis- and trans-4-methyl-2-pentene, cis- and trans-4-octene, trans-3-hexene, trans-3-octene, trans-5-decene, cis-2-hexene, and cis-2-heptene. The erythro bisadducts (compounds 6) were obtained with trans-alkenes, while threo bisadducts (compounds 7) were obtained with cis-alkenes. The assigned structures of 6 and 7 were consistent with their NMR spectra and, in one case, 6c (the adduct of trans-4-methyl-2-pentene) was confirmed with X-ray crystallography. Additions of PO*+ to 1,4-hexa-, 1,5-hexa-, 1,6-hepta-, and 1,7-octadiene gave bis(10-phenoxathiiniumyl)alkenes (compounds 8), the assigned structures of which were consistent with their NMR spectra. Each of these adducts lost a proton and phenoxathiin (PO) when treated with basic alumina in MeCN solution. Compounds 6 (from trans-alkenes) gave mixtures of (Z)- (9) and (E)-(10-phenoxathiiniumyl)alkenes (10) in which the (Z)-isomers (9) were dominant. On the other hand, compounds 7 (from cis-alkenes) gave mixtures of 9 and 10 in which, with one exception (the adduct 7c of cis-4-methyl-2-pentene), compounds 10 were dominant. The path to elimination is discussed. The alkenes 9 and 10 were characterized with NMR spectroscopy and, in one case (9a), with X-ray crystallography. Reactions of 8b-d with basic alumina gave mixtures of (E)- (13) and (Z)-(10-phenoxathiiniumyl)dienes (14), in which compounds 13 were dominant. The configuration of the product from 8a (the adduct of 1,4-hexadiene) could not be settled. Noteworthy features in the coupling patterns and chemical shifts in the NMR spectra of some of the adducts and their products are discussed and related to adduct conformations.

Reaction of thianthrene and phenoxathiin cation radicals with 2,3-dimethyl-2-butene. Chemical and electrochemical studies.

Thianthrene cation radical tetrafluoroborate (Th*+ BF4-) has been found to add to 2,3-dimethyl-2-butene (DMB) at 0 degrees C and -15 degrees C. The adduct, 2,3-dimethyl-2,3-(5,10-thianthreniumdiyl)butane ditetrafluoroborate (12), was isolated at -15 degrees C, and its 1H NMR spectrum was recorded at that temperature. The adduct was stable in CD3CN solution at -15 degrees C but decomposed slowly at 0 degrees C and quickly at 23 degrees C, forming the salt of 2,4,4,5,5-pentamethyl-2-oxazoline (8) with loss of thianthrene (Th). These results explain why earlier attempts to prepare 12 and detect its formation at room temperature with NMR spectroscopy were not successful. Reaction of Th*+ with DMB was followed with cyclic voltammetry and was found to exhibit redox catalysis in which Th was regenerated. With the faster scanning techniques of cyclic voltammetry, the formation of 12 was detectable, with a reduction potential of about -1.0 V at 25 degrees C and 3 degrees C. The observed reduction potential was in harmony with reduction potentials of a number of other, stable monoadducts. Thus, the redox catalysis involved the rapid formation of 12 and its rapid decomposition into 8 and Th, the newly formed Th being responsible for the observed enhanced oxidation currents. In contrast, 8 appears to be formed directly by oxidation of DMB by PO*+PF6-.

Decomposition of alkene adducts of thianthrene cation radical in nitrile solvents. Formation of alkyl-2-oxazolines and a new class of four-component products: 5-[(1-alkoxyalkylidene)ammonio]alkylthianthrenium diperchlorates.

The monoadducts (4a-d) of thianthrene cation radical perchlorate (1a) and isobutene, 2-methylbutene, 2-methyl-2-butene, and 2-methylpentene decompose spontaneously in acetonitrile (MeCN) solution, with the formation of thianthrene (Th). Decomposition of 4a (1,2-(5,10-thianthreniumdiyl)-2-methylpropane diperchlorate) and 4a', the corresponding dihexafluorophosphate, was studied in depth and extensively with (1)H and (13)C NMR spectroscopy. Decomposition of 4a was found to involve the solvent itself as well as water in the solvent, remaining from incomplete drying, and gave, apart from Th, successively, the perchlorate salts of 2,4,4-trimethyl-2-oxazoline (6) and 2-amino-2-methylpropyl acetate (7). These salts, 6-HClO(4) and 7-HClO(4), respectively, were prepared and used in understanding the reactions of 4a as well as the relationships among 6, 7, and 2-(acetylamino)-2-methyl propanol (8) in acidified MeCN solution. Decompositions of 4a-d in MeCN and other nitriles (RCN) containing an added alcohol (R'OH) led to new products, 5-[(1-alkoxyalkylidene)ammonio]alkylthianthrenium diperchlorates (5a-u). These compounds were identified with (1)H and (13)C NMR spectroscopy and, in part, with X-ray crystallography and elemental analysis. The mechanisms of formation of 5-7 are discussed.

Adducts of phenoxathiin and thianthrene cation radicals with alkenes and cycloalkenes.

Phenoxathiin cation radical perchlorate (PO.+ClO4(-)) added stereospecifically to cyclopentene, cyclohexene, cycloheptene, and 1,5-cyclooctadiene to give 1,2-bis(5-phenoxathiiniumyl)cycloalkane diperchlorates (4-7) in good yield. The diaxial configuration of the PO+ groups was confirmed with X-ray crystallography. Unlike additions of thianthrene cation radical perchlorate (Th.+ClO4(-)) to these cycloalkenes, no evidence for formation of monoadducts was found in the reactions of PO.+ClO4(-). This difference is discussed. Addition of Th.+ClO4(-) to five trans alkenes (2-butene, 2-pentene, 4-methyl-2-pentene, 3-octene, 5-decene) and four cis alkenes (2-pentene, 2-hexene, 2-heptene, 5-decene) gave in each case a mixture of mono- and bisadducts in which the configuration of the alkene was retained. Thus, cis alkenes gave erythro monoadducts and threo bisadducts, whereas trans alkenes gave threo monoadducts and erythro bisadducts. In these additions to alkenes, cis alkenes gave predominantly bisadducts, while trans alkenes (except for trans-2-butene) gave predominantly monoadducts. This difference is explained. 1,2-Bis(5-phenoxathiiniumyl)cycloalkanes (4-7) and 1,2-bis(5-thianthreniumyl)cycloalkanes underwent fast elimination reactions on activated alumina forming, respectively, 1-(5-phenoxathiiniumyl)cycloalkenes (8-11) and 1-(5-thianthreniumyl)cycloalkenes (12-16). Among adducts of Th.+ClO4(-) and alkenes, monoadducts underwent fast ring opening on alumina to give (5-thianthreniumyl)alkenes, while bisadducts underwent fast eliminations of H+ and thianthrene (Th) to give (5-thianthreniumyl)alkenes also. Ring opening of monoadducts was a stereospecific reaction in which the configuration of the original alkene was retained. Thus, erythro monoadducts (from cis alkenes) gave (E)-(5-thianthreniumyl)alkenes and threo monoadducts (from trans alkenes) gave (Z)-(5-thianthreniumyl)alkenes. Among bisadducts, elimination of a proton and Th occurred and was more complex, giving both (E)- and (Z)-(5-thianthreniumyl)alkenes. These results are explained. Configurations of adducts and (5-thianthreniumyl)alkenes were deduced with the aid of X-ray crystallography and (1)H and (13)C NMR spectroscopy. In the NMR spectra of (E)- and (Z)-(5-thianthreniumyl)alkenes, the alkenyl proton of Z isomers always appeared at a lower field (0.8-1.0 ppm) than that of E isomers.