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To examine the effect of changing the amide bond of anandamide (5, AN) to a less hydrolyzable moiety, analogues 1a-1l, 2a-2c, 3a-3c, and 4a-4h were synthesized from commercially available arachidonyl alcohol or arachidonic acid and tested for their pharmacological activity. Arachidonyl ethers 1a-1k were obtained through the coupling of the arachidonyl mesylate (6) (generated from the mesylation of arachidonyl alcohol) with the appropriate alcohol in potassium hydroxide. Arachidonyl ether 1l was obtained through the phase-transfer coupling of arachidonyl alcohol with 2-(2-iodoethoxy)tetrahydropyran (which was generated from its bromide) followed by cleavage of the tetrahydropyran group with Dowex resin. Arachidonyl carbamates 2a-2c were obtained through the coupling of arachidonyl alcohol with the appropriate isocyanates. Norarachidonyl carbamates 3a-3c and ureas 4a-4h were obtained through the coupling of the norarachidonyl isocyanate (generated from arachidonic acid using diphenyl phosphorazidate and triethylamine upon heating) with the appropriate alcohols and amines, respectively. AN analogues 1-3 have shown poor binding affinities to the CB1 receptor and fail to produce significant pharmacological effect at doses up to 30 mg/kg. Several ether analogues 1 were also evaluated in the CB2 binding assay and were found to be of low affinity. However, norarachidonyl urea analogues 4 have shown generally good binding affinities to the CB1 receptor (Ki = 55-746 nM) and pharmacological activity with AN-like profiles. The most potent analogue of this series is the 2-fluoroethyl analogue 4f which binds 2 times better than AN and was more active in several mouse behavioral assays. It was also observed that urea analogues 4a and 4g, which have weak binding affinities to the CB1 receptor (Ki = 436 and 347 nM, respectively), produced surprisingly potent pharmacological activity. These urea analogues have also shown hydrolytic stability toward the amidase enzymes, responsible for the primary degradation pathway of anandamide, in binding affinity assays in the absence of the enzyme inhibitor PMSF.

1 The activities of a number of side-chain analogues of delta-8-tetrahydrocannabinol (D 8 -THC) in rat cerebellar membrane preparations were tested. 4 The e cacies of these compounds varied greatly, ranging from the very low e cacy exhibited to acetylenic compounds such as 1'-heptyn-D 8 -THC and 4'-octyn-D 8 -THC to higher e cacy compounds such as 5'-(4-cyanophenoxy)-1',1'-dimethyl-D 8 -THC and 5'-[N-(4-aminosulphonylphenyl)]-1',1' dimethyl-carboxamido D 8 -THC. All agonist activities were antagonized by the CB 1 -selective antagonist SR141716A. 5 It was found that a ligand's CB 1 a nity and e cacy are di erentially altered by modi®cations in the side-chain. Decreasing the¯exibility of the side-chain reduced e cacy but largely did not alter a nity. Additionally, the positioning of electrostatic moieties, such as cyano groups, within the sidechain also has contrasting e ects on these two properties. 6 In summary, this report details the characterization of a number of novel D 8 -THC analogues in rat cerebellar membranes. It provides the ®rst detailed pharmacological analysis of how the inclusion of electrostatic moieties in the side-chain and also how alteration of the side-chain's¯exibility may di erentially a ect a CB 1 cannabinoid receptor ligand's a nity and e cacy.