Synthesis of 3-heterocyclic phenyl N-alkyl carbamates and their activity as FAAH inhibitors

摘要

Fatty acid amide hydrolase (FAAH) is an intracellular serine hydrolase that catalyzes the hydrolysis of the endocannabinoid N-arachidonoylethanolamide (AEA) to arachidonic acid and ethanolamine. FAAH also hydrolyze another important endocannabinoid, 2-arachidonoylglycerol (2-AG), although the main enzyme responsible for hydrolysis of 2-AG is MGL. Inhibition of FAAH or MGL enzymatic activity potentially leads to beneficial effects in many physiological disorders such as pain, inflammation and anxiety, due to increased endocannabinoid induced activation of cannabinoid receptors CB1 and CB2. In the present study a total of 101 compounds were designed, synthesized, characterized and tested against FAAH and MGL enzyme activity. Altogether 47 compounds were found to inhibit FAAH with half-maximal inhibition concentrations (IC50) between 0.74 and 100 nM. All potent compounds belong to the structural family of carbamates. Other carbonyl-containing compounds were prepared for comparison and they were found not to inhibit either FAAH or MGL. The synthesized carbamate derivatives were found to be selective for FAAH as the inhibition of MGL enzyme by these compounds was negligible. From the library of phenyl N-alkyl carbamates the most potent FAAH inhibitors were meta-substituted N-cyclohexylcarbamates. 4,5-Dihydrooxazol-2-yl (221), oxazol-2-yl (242), 2-methyltetrazol-5-yl (273a), imidazol-4-yl (252) and 1,2,3-thiadiazol-4-yl (314) were found to be the best heterocycle substituents of phenolic N-alkyl carbamate. Methyl ester (276) was the best acyclic substituent. These compounds inhibited FAAH with IC50 values between 0.74-3.9 nM. Various synthesis methods were used to achieve the desired compounds. Microwave assisted novel or little known reactions applied in synthesis including condensation of acids and 2-aminophenol/2-amino-3-hydroxypyridine to prepare corresponding fused 2-oxazoles, oxazole formation via condensation of bromoketones and amides, and cleavage of benzyl and methyl ethers using ionic liquids. In conclusion, the results of this work provide useful structure-activity relationship (SAR) information of carbamate compounds as FAAH inhibitors which can be utilized in further developments in this area.