Furan analogs and N methylpyrrole analogs had completely

Furan analogs and N-methylpyrrole analogs had completely different SARs. For example, replacement of the furan-2-sulfonyl moiety of 6 with the furan-3-sulfonyl moiety resulted in 8 with a decreased EP1 FDA-approved Drug Library affinity and an increased antagonist activity, while the corresponding chemical modification of N-methylpyrrole analog 3 provided 10 with a decreased potency in both the EP1 receptor affinity and antagonist activity. Furthermore, the pyrrole-3-sulfonyl analog 9 showed a remarkable reduction in its antagonist activity and a slight reduction in its EP1 receptor affinity relative to that of the corresponding N-methylpyrrole analog 10. Introduction of more than two heteroatoms into the five-membered aromatic ring resulted in 4 and 11–15 with lower clogP values compared to 3 and 6–10. The imidazole-2-sulfonyl analog 11 showed a remarkable reduction in EP1 receptor affinity and antagonist activity relative to 1, while the thiazole-2-sulfonyl analog 4 showed a retained EP1 receptor affinity and a 21-fold more potent antagonist activity relative to 1. Another imidazole analog, 13, showed substantially lower activities than 1 although it showed a 2.7-fold more potent EP1 receptor affinity and a more potent antagonist activity than 11. The N-Methylpyrazole-4-sulfonyl analog 12 also showed a remarkable reduction of EP1 receptor affinity and a slight reduction of antagonist activity relative to 1. The 3,5-dimethyl isooxazole-4-sulfonyl analog 14 showed a 7.4-fold less potent EP1 receptor affinity and a 3.3-fold more potent antagonist activity relative to 1. The 5-methyl-1,3,4-thiadiazole-2-sulfonyl analog 15 possessed the lowest clogP value among the tested compounds and showed a 5.4-fold less potent EP1 receptor affinity and a nearly equipotent antagonist activity relative to 1. As such, the antagonist activity does not always correlate with clogP values. Nitrogen-containing heteroaromatic analogs 2–5 and 9–13 were predicted to posses a lower lipophilicity than furan analogs 6, 8 and thiophene analog 7 based on their clogP values. Some of the nitrogen-containing heteroaromatic analogs 2–4 showed a marked increase in their antagonist activities relative to 1, while furan and thiophene analogs 6–7 and 8 showed a retained or increased antagonist activity. Another nitrogen-containing heteroaromatic analog 9 resulted in the reduction of antagonist activity relative to 1. The in vivo EP1 receptor antagonist activity was evaluated using sulprostone, which is known as an EP1 receptor agonist, and the selected compounds 2–4, which were identified as potent in vitro receptor antagonists. Compounds 2–4 were tested for their ability to inhibit sulprostone-induced bladder contraction in rats. As shown in Figure 2, all the tested compounds demonstrated an in vivo efficacy in a time dependent manner. Compounds 2 and 4 showed 46.6±5.7% inhibition and 65.3±4.3% inhibition, respectively, against sulprostone-induced bladder pressure 60min after an intra-duodenal (id) dose of 3mg/kg, while 3 showed the lowest potency while it exhibited the most potent in vitro antagonist activity among the tested compounds. This was probably due to its presumed poor PK profiles such as low oral absorption and metabolic instability. In summary, nitrogen-containing hetoro-aromatic sulfonyl moieties, such as pyridine-3-sulfonyl, N-methylpyrrole-2-sulfonyl and thiazole-2-sulfonyl, were identified as more hydrophilic substitutes for the phenylsulfonyl moiety. Compounds 1 and 6 exhibited similar potencies regarding receptor affinity and antagonist activity regardless of their clogP value. Furan-2-sulfonyl analog 6 and unsubstituted pyrrole-3-sulfonyl analog 9 showed remarkably weak antagonist activity despite a strong receptor affinity. As illustrated in 1, 6, and 9, the unsubstituted imidazole analog 11, which exhibited relatively weak receptor affinity, also was estimated to show remarkably weak antagonist activity (IC50>10μM) despite its EP1 receptor affinity.