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  • br Acknowledgments The research in


    Acknowledgments The research in this study was supported by grants from CMHS, UAE University and Qatar University. The authors gratefully acknowledge Dr. R Lukas (Barrow Neurological Institute, Phoenix, AZ, USA) for SH-EP1 WEHI-539 hydrochloride stably expressing the human α7 nACh and human α4β2 nACh receptor and cordially thank to Dr. Suhail Doi for his valuable help in statistical analysis of the data.
    Introduction Prostanoid receptors, which are members of the G-protein coupled receptor superfamily, were classified into PGE, PGF, PGD, PGI, and TXA, named EP, FP, DP, IP, and TP receptors, respectively. The EP receptor was further classified into four subtypes EP1-4 that each responds to the natural agonist PGE2 in a different manner. The molecular characterization of these receptors has resulted in renewed interest because selectivity of compounds on human prostanoid receptors can now be determined. In our previous paper, we reported the discovery of 1 (Fig. 1) as a highly selective EP1 receptor antagonist that contains a highly lipophilic benzenesulfonyl moiety. It should be noted that highly lipophilic compounds have been known to cause a problem regarding their in vivo efficacy, PK profiles, and safety. In fact, 1 exhibited remarkably decreased antagonist activity for its strong receptor affinity. Thus, the high lipophilicity (clogP 6.91) of compound 1 should be lowered for it to be a drug candidate. We here report on highly potent EP1 receptor antagonists 2–4 as chemical leads for a drug candidate.
    Chemistry All the compounds listed in Table 1, Table 2 were synthesized as outlined in Scheme 1. Oxidative hydroxylation of a commercially available 1-nitro-4-(trifluoromethyl)benzene 16 resulted in a nitrophenol 17, and O-alkylation with methyl 4-bromomethylbenzoate provided 18. Hydrogenation of the nitrobenzene derivative 18 resulted in the corresponding aniline 19, which was used as a key intermediate. N-Sulfonylation of 19 with various kinds of sulfonyl chlorides resulted in sulfonamides 20a–o, N-alkylation of which resulted in 21a–o, respectively. Alkaline hydrolysis of 21a–o resulted in the corresponding carboxylic acids 1–15, respectively. Structurally new heteroarylsulfonyl chlorides 23, 26, and 28 were prepared as outlined in Scheme 2. Successive treatment of 2-bromothiazole (22) with n-butyllithium and then sulfur dioxide, followed by the treatment with N-chlorosuccinimide, resulted in thiazole-2-sulfonyl chloride (23) (Scheme 2a). N-Methylation of 4-iodopyrazole (24) produced 25, which was converted to 26 according to essentially the same procedures as described above (Scheme 2b). Oxidation of the mercapto group of 2-mercapto-5-methyl-1,3,4-thiadiazole (27) with chlorine resulted in the desired sulfonyl chloride 28 (Scheme 2c).
    Results and discussion The test compounds listed in Table 1, Table 2 were biologically evaluated for inhibition of the specific binding of a radiolabeled ligand [3H]PGE2 to membrane fractions prepared from cells stably expressing each mouse prostanoid receptor. The EP1 antagonist properties of these compounds were determined by a Ca2+ assay using mouse EP1 receptors expressed on CHO cells in the presence of 0.1% bovine serum albumin (BSA). Focus was placed on the chemical modification of the benzenesulfonyl moiety of 1 with special focus on lowering its relatively high lipophilicity (clogP 6.91) for reasons described above. Replacement of the benzenesulfonyl moiety of 1 with more hydrophilic pyridine-2-sulfonyl and pyridine-3-sulfonyl moieties resulted in 5 (clogP 5.66) and 2 (clogP 5.56), respectively. As shown in Table 1, the pyridine-3-sulfonyl analog 2 showed a slightly more potent EP1 receptor affinity and a 33-fold more potent antagonist activity relative to the activity of 1, while the pyridine-2-sulfonyl analog 5 showed a 3.8-fold less potent EP1 receptor affinity and a 2.7-fold more potent antagonist activity compared to the activity of 1. These results strongly suggest that the lipophilic phenylsulfonyl moiety of 1 could be successfully replaced with more hydrophilic bioisosteres of a phenylsulfonyl moiety such as furansulfonyl, thiophenesulfonyl, and others. As illustrated in Table 2, all listed analogs 3–4 and 6–15 demonstrated lower clogP values than the chemical lead 1. Replacement of the phenylsulfonyl moiety of 1 with a furan-2-sulfonyl moiety resulted in 6 with a retention of the potent EP1 receptor affinity and antagonist activity. The corresponding N-methylpyrrole-2-sulfonyl analog 3 showed a 2.4-fold less potent EP1 receptor affinity relative to 1, while it showed a 59-fold more potent antagonist activity. Based on the successful result obtained with the transformation from 5 to 2, compounds 7–10 were synthesized and evaluated. Unexpectedly, all of them showed a less potent EP1 receptor affinity relative to 1. Compounds 7–8 and 10 exhibited a more potent antagonist activity relative to 1, while 9 showed more than 10-fold increase in antagonist activity. Compounds 8 and 10 showed less potent EP1 receptor affinity than their corresponding 2-sulfonyl isomers 6 and 3, respectively. The thiophene-3-sulfonyl analog 7 demonstrated a slightly less potent EP1 receptor affinity and antagonist activity relative to those of the corresponding furan-3-sulfonyl analog 8. Especially the pyrrole-3-sulfonyl analog 9 was considerably less potent relative to 1 in both the EP1 receptor affinity and antagonist activity. N-Methylation of 9 resulted in 10 with a marked recovery of the antagonist activity.