Given the potency enhancing effect
Given the potency enhancing effect of the 4--butyl group, this substitution was incorporated into the Eastern portion of the molecule for further SAR investigations (). Removal of the phenol group (SR19822) or moving it from the -position to the -position (SR19552) or led to significant loss of activity. The -substituted phenol (SR19538) and the bis-hydroxy analog SR19553 were both 10 times less potent than SR209906. Methylation of the phenol (SR19537) was also not tolerated, indicating a AZD6738 receptor donor at the -position was likely required for activity. A carboxyl group (SR19638) was not a suitable replacement for the phenol group. It is perhaps too bulky, or of the wrong pKa. A secondary -methylamide (SR19541), is also perhaps too bulky and results in loss of activity. The primary amide SR19639 is slightly better, and the acetamide (SR19539) a bit more active, although both are partial agonists. Nonetheless, it was quite difficult to find a suitable replacement for the phenolic group on the benzoyl ring. The last portion of the molecule to investigate was the -acyl hydrazone (). It was unclear whether the -acyl hydrazone moiety was simply a linker required to hold in place the -butyl phenyl and phenol rings, or whether it was indeed required for activity. Numerous attempts were made to replace the hydrazone with other bioisosteres of the same or similar length, but most led to substantial losses in potency. The only viable substitution was the simple phenethylamine found in SR19797. While there is a 10-fold loss in activity, we have successfully replaced the metabolically labile -acyl hydrazone residue with something potentially much more tolerable. Efforts then focused on optimizing SR19797 to build back the potency lost from replacing the hydrazone linkage (, ). Similar to the SAR observed in the hydrazone series (), movement of the -substituted phenol residue was not well tolerated. In fact, movement to the -position as in SR19886 seemed to lead to a switch in pharmacology conferring ERRγ inverse agonism. The phenol residue could not be replaced by a phenyl ring (SR20010), 4-pyridyl ring (SR19889) or aniline (SR19887) without significant loss in potency. Neither aminopyridine analog (SR19888) or hydroxy-pyridine analogs (SR20123, 20253) were tolerated nor was a hydroxy-thiophene analog (SR20255). Benzyl alcohol analog SR19895 were also inactive, however its isostere SR19894 was essentially equipotent to SR19797. Attempts to replace the 4-phenol ring with various indoles were not successful (SR19890, 19891, 19892). The saturated versions of the 4-phenolic group, 4-hydroxy cyclohexane, were not viable replacements (SR20256, 20257). Finally, substituted phenols were equipotent to SR19797, when the substitutent was meta to the phenol group as in SR20011 and 20012, but 10 times less potent when substituted ortho to the phenol (SR20122, 20338). These results highlight the importance of the phenol ring hydroxy group to its activity and its resistance to replacement. Inspection of the X-ray crystal structure of GSK-4716 with ERRγ indicates an additional hydrophobic pocket orthogonal to the binding of the molecule adjacent to the hydrazone amide group. In an attempt to reach this binding pocket and take advantage of hydrophobic interactions in this region, addition analogs were prepared incorporating substitution meta to the phenol group (). Virtually all attempts at substitution including dimethylamine, acetamide, methoxy, hydroxyl, cyanide, florine, trifloromethyl, nitro, different phenyl rings, and pyridines ledd to loss of activity. The 2-aminosubstituted compound was slightly more potent as a partial agonist. Its possible SR19797 which lacks the rigid hydrazone group found in GSK4716, adopts a slightly different conformation within the receptor and R-substitution ortho to the amide group cannot reach this hydrophobic pocket. Finding it difficult to modify the phenolic ring, we turned our attention back to the Eastern portion of the molecule ( and ). Attempts to simplify the molecule by incorporating simpler amides were not tolerated (SR21580-21585). Bromine and phenyl substitutions were not viable replacements for the -butyl group and led to loss of activity (SR19878, 19884). The more rigid amide (SR19885) was not active although it also lacked -substitution. Shortening the linker between the amide and phenyl ring by one carbon atom (SR19879) led to loss of activity, whereas a one carbon extension led to ∼6x drop in potency (SR20739). Unexpectedly, the one carbon extension in a compound lacking the -butyl group was only 2-fold less potent than the lead, so there may be room for additional modifications here (SR19887). Attempts to shorten the linker between the amide nitrogen atom and the phenyl ring, at the same time increasing the length of the substituent at the -position of the phenyl ring wasn’t tolerated (SR20118, 20119). However, rigidifying the linker in the amide side chain by incorporating it into a ring led to a compound with similar potency to SR19737 (SR20043).