The urea derivatives a e were obtained from

The urea derivatives 7a–e were obtained from 1-(3-phenoxybenzyl)-piperazine (6) by reaction of isocyanate, or triphosgene and subsequent reaction of produced carbamoyl chloride with the amine RH as shown in Scheme 2. The imidazole urea 7g was prepared by reaction of 6 with 1,1′-carbonyldiimidazole. O-hexafluoroisopropyl (HFIP) carbamate 7f (JW642) was synthesized by the reaction of hexafluoroisopropanyl chloride, generated by treatment of hexafluoroisopropanol with triphosgene, with 6. The 4-phenoxybenzyl carbamate 9a (JJKK-011) was made by carbamoylation of 1-(4-phenoxybenzyl)-piperazine (8) with 4-nitrophenyl chloroformate and urea analogs 9b–c were prepared by microwave assisted synthesis from 8 coupling with 1,1′-carbonyldiimidazole (CDI) and 1,1′-carbonylbis-benzotriazole, respectively, as shown in Scheme 3. 4-(Bis(3,4-dioxymethylenephenyl)methyl and -methylene derivatives 11a–b were obtained by carbamoylation of piperidine derivatives 10a–b with 4-nitrophenyl chloroformate as shown in Scheme 4. The 4-bisarylcarbinol derivatives 12b–c (TP-TK-042, JJKK-053) were prepared from 4-(bis(3,4-dioxymethylene phenyl)hydroxymethyl)piperidine (15, TP-TK-038) coupling with 1,1′-carbonyl-di-(1,2,4-triazole) (CDT) and 2,2,2-trichloroethyl chloroformate, respectively, as shown in Scheme 5. The intermediate 15 was synthesized starting from ethyl isonipecotate 13. In a first step 13 was protected with CbzCl to yield 1-benzyl 4-ethyl piperidine-1,4-dicarboxylate (14). In the following step, lithitiaton of 1-bromo-3,4-(methylenedioxy)benzene at −78°C with t-BuLi and subsequent reaction with 14 gave Cbz-protected piperidine 12a. Finally, elimination of the Cbz group by hydrogenation afforded the piperidinealcohol 15.
Results and discussion
Conclusion In this Epalrestat paper , we have demonstrated that the triazole, benzotriazole, and triazolopyridine ureas show activity against MAGL (JJKK-048 and 12c) whereas the other leaving groups were significantly less active or inactive. As we concluded in our previous paper, triazole heterocycles are good leaving groups because their relatively low conjugate acid pKa values (8–10), that are optimal for the nucleophilic attack by the MAGL active site catalytic serine. On the other hand, the compounds having the p-nitrophenoxy leaving group were effective only in the micromolar-high nanomolar range against MAGL in our assay conditions. The low activity may be due to low pKa of the p-nitrophenol (7.15), which makes these compounds excessively reactive so that p-nitrophenoxy group is released before reaching the active site of MAGL. In contrast, imidazole (pKa 14.4), benzyloxy (pKa∼16), 2,2,2-trichloroethoxy (pKa 12) and arylamines (pKa>18) are poor leaving groups, and therefore, compounds with these groups were poor MAGL inhibitors. Interesting observation is that O-hexafluoroisopropoxy (HFIP) (7f) seems to be selective leaving group for MAGL inhibition. The good MAGL inhibition of 7f can be explained by the optimal pKa of HFIP (9.3) that is close to that of triazole heterocycles, while the low FAAH inhibition potency of 7f can be explained by the bulkiness of the HFIP moiety, which makes it difficult to access the FAAH active cite. In the case of FAAH inhibition, the imidazole moiety seems to be a good leaving group for phenoxyphenyl analogs (7g and 9c), which were approximately 190-fold selective for the inhibition of FAAH. The imidazole urea based FAAH inhibitors have been previously described by Astellas Pharma, which asserts the desirable FAAH inhibition of imidazole ureas. The general conclusion is that diverse leaving groups are tolerated for FAAH inhibitors, while MAGL inhibitors should comprise leaving-groups with a conjugate acid pKa of 8–10.
Experimental
Acknowledgements This work was supported by the Academy of Finland (Grants 139620 to J.T.L. and 139140 J.T.N.) Biocenter Finland/DDCB (T.L.). The authors are grateful to Mrs. Tiina Koivunen for technical assistance. CSC–Scientific Computing, Ltd is greatly acknowledged for software licenses and computational resources.