Unique analogues of anandamide: Arachidonyl ethers and carbamates and norarachidonyl carbamates and ureas

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 s ynthesized from commercially available arachidonyl alcohol or arachidonic a cid and tested for their pharmacological activity. Arachidonyl ethers 1a-1k were obtained through the coupling of the arachidonyl mesylate (6) (genera ted from the mesylation of arachidonyl alcohol) with the appropriate alcoho l in potassium hydroxide. Arachidonyl ether 1l was obtained through the pha se-transfer coupling of arachidonyl alcohol with 2-(2-iodoethoxy)tetrahydro pyran (which was generated from its bromide) followed by cleavage of the te trahydropyran group with Dowex resin. Arachidonyl carbamates 2a-2c were obt ained through the coupling of arachidonyl alcohol with the appropriate isoc yanates. Norarachidonyl carbamates 3a-3c and ureas 4a-4h were obtained thro ugh the coupling of the norarachidonyl isocyanate (generated from arachidon ic acid using diphenyl phosphorazidate and triethylamine upon heating) with the appropriate alcohols and amines, respectively. AN analogues 1-3 have s hown poor binding affinities to the CB1 receptor and fail to produce signif icant pharmacological effect at doses up to 30 mg/kg. Several ether analogu es 1 were also evaluated in the CB2 binding assay and were found to be of l ow affinity. However, norarachidonyl urea analogues 4 have shown generally good binding affinities to the CB1 receptor (K-i = 55-746 nM) and pharmacol ogical activity with AN-like profiles. The most potent analogue of this ser ies 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 t hat urea analogues 4a and 4g, which have weak binding affinities to the CBI receptor (K-i = 436 and 347 nM, respectively), produced surprisingly poten t pharmacological activity. These urea analogues have also shown hydrolytic stability toward the amidase enzymes, responsible for the primary degradat ion pathway of anandamide, in binding affinity assays in the absence of the enzyme inhibitor PMSF.