t-Butyl pyridine and phenyl C-region analogues of 2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides as potent TRPV1 antagonists.

A series of 2-substituted 6-t-butylpyridine and 4-t-butylphenyl C-region analogues of 2-(3-fluoro-4-methylsulfonamidophenyl)propanamides were investigated for hTRPV1 antagonism. The analysis of structure activity relationships indicated that the pyridine derivatives generally exhibited a little better antagonism than did the corresponding phenyl surrogates for most of the series. Among the compounds, compound 7 showed excellent antagonism toward capsaicin activation with Ki=0.1nM and compound 60S demonstrated a strong antiallodynic effect with 83% MPE at 10mg/kg in the neuropathic pain model. The docking study of 7S in our hTRPV1 homology model indicated that the interactions between the A/B-regions of 7S with Tyr511 and the interactions between the t-butyl and ethyl groups in the C-region of 7S with the two hydrophobic binding pockets of hTRPV1 contributed to the high potency.

Structure activity relationships of benzyl C-region analogs of 2-(3-fluoro-4-methylsulfonamidophenyl)propanamides as potent TRPV1 antagonists.

A series of 2-substituted 4-(trifluoromethyl)benzyl C-region analogs of 2-(3-fluoro-4-methylsulfonamidophenyl)propanamides were investigated for hTRPV1 antagonism. The analysis indicated that the phenyl C-region derivatives exhibited better antagonism than those of the corresponding pyridine surrogates for most of the series examined. Among the phenyl C-region derivatives, the two best compounds 43 and 44S antagonized capsaicin selectively relative to their antagonism of other activators and showed excellent potencies with K(i(CAP))=0.3 nM. These two compounds blocked capsaicin-induced hypothermia, consistent with TRPV1 as their site of action, and they demonstrated promising analgesic activities in a neuropathic pain model without hyperthermia. The docking study of 44S in our hTRPV1 homology model indicated that its binding mode was similar with that of its pyridine surrogate in the A- and B-regions but displayed a flipped configuration in the C-region.

2-Aryl substituted pyridine C-region analogues of 2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides as highly potent TRPV1 antagonists.

A series of 2-aryl pyridine C-region derivatives of 2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides were investigated as hTRPV1 antagonists. Multiple compounds showed highly potent TRPV1 antagonism toward capsaicin comparable to previous lead 7. Among them, compound 9 demonstrated anti-allodynia in a mouse neuropathic pain model and blocked capsaicin-induced hypothermia in a dose-dependent manner. Docking analysis of 9 with our hTRPV1 homology model provided insight into its specific binding mode.

2-Alkyl/alkenyl substituted pyridine C-region analogues of 2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides as highly potent TRPV1 antagonists.

A series of 2-alkyl/alkenyl pyridine C-region derivatives of 2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides were investigated as hTRPV1 antagonists. Multiple compounds showed excellent and stereospecific TRPV1 antagonism with better potency than previous lead 2. Among them, compound 15f demonstrated a strong analgesic profile in a rat neuropathic pain model and blocked capsaicin-induced hypothermia in a dose-dependent manner. Docking analysis of (S)-15f with our hTRPV1 homology model provided insight into its specific binding mode.

TRPV1 antagonist with high analgesic efficacy: 2-Thio pyridine C-region analogues of 2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides.

A series of 2-thio pyridine C-region analogues of 2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides were investigated as hTRPV1 antagonists. Among them, compound 24S showed stereospecific and excellent TRPV1 antagonism of capsaicin-induced activation. Further, it demonstrated strong anti-allodynic in a rat neuropathic pain model. Consistent with its action in vitro being through TRPV1, compound 24S blocked capsaicin-induced hypothermia in mice. Docking analysis of 24S with our hTRPV1 homology model was performed to identify its binding mode.

N-4-t-Butylbenzyl 2-(4-methylsulfonylaminophenyl) propanamide TRPV1 antagonists: Structure-activity relationships in the A-region.

Structure-activity relationships for the A-region in a series of N-4-t-butylbenzyl 2-(4-methylsulfonylaminophenyl) propanamides as TRPV1 antagonists have been investigated. Among them, the 3-fluoro analogue 54 showed high binding affinity and potent antagonism for both rTRPV1 and hTRPV1 in CHO cells. Its stereospecific activity was demonstrated with marked selectivity for the (S)-configuration (54S versus 54R). A docking study of 54S with our hTRPV1 homology model highlighted crucial hydrogen bonds between the ligand and the receptor contributing to its potency.

2-(4-Methylsulfonylaminophenyl) propanamide TRPV1 antagonists: Structure-activity relationships in the B and C-regions.

On the basis of the previous lead N-4-t-butylbenzyl 2-(3-fluoro-4-methylsulfonylaminophenyl) propanamide (3) as a potent TRPV1 antagonist, structure-activity relationships for the B (propanamide part) and C-region (4-t-butylbenzyl part) have been investigated for rTRPV1 in CHO cells. The B-region was modified with dimethyl, cyclopropyl and reverse amides and then the C-region was replaced with 4-substituted phenyl, aryl alkyl and diaryl alkyl derivatives. Among them, compound 50 showed high binding affinity with K(i)=21.5nM, which was twofold more potent than 3 and compound 54 exhibited potent antagonism with K(i(ant))=8.0nM comparable to 3.

Structural insights into transient receptor potential vanilloid type 1 (TRPV1) from homology modeling, flexible docking, and mutational studies.

The transient receptor potential vanilloid subtype 1 (TRPV1) is a non-selective cation channel composed of four monomers with six transmembrane helices (TM1-TM6). TRPV1 is found in the central and peripheral nervous system, and it is an important therapeutic target for pain relief. We describe here the construction of a tetrameric homology model of rat TRPV1 (rTRPV1). We experimentally evaluated by mutational analysis the contribution of residues of rTRPV1 contributing to ligand binding by the prototypical TRPV1 agonists, capsaicin and resiniferatoxin (RTX). We then performed docking analysis using our homology model. The docking results with capsaicin and RTX showed that our homology model was reliable, affording good agreement with our mutation data. Additionally, the binding mode of a simplified RTX (sRTX) ligand as predicted by the modeling agreed well with those of capsaicin and RTX, accounting for the high binding affinity of the sRTX ligand for TRPV1. Through the homology modeling, docking and mutational studies, we obtained important insights into the ligand-receptor interactions at the molecular level which should prove of value in the design of novel TRPV1 ligands.

Non-vanillyl resiniferatoxin analogues as potent and metabolically stable transient receptor potential vanilloid 1 agonists.

A series of non-vanillyl resiniferatoxin analogues, having 4-methylsulfonylaminophenyl and fluorophenyl moieties as vanillyl surrogates, have been investigated as ligands for rat TRPV1 heterologously expressed in Chinese hamster ovary cells. Although lacking the metabolically problematic 4-hydroxy substituent on the A-region phenyl ring, the compounds retained substantial agonist potency. Indeed, the 3-methoxy-4-methylsulfonylaminophenyl analog (1) was modestly (2.5-fold) more potent than RTX, with an EC(50)=0.106 nM. Further, it resembled RTX in its kinetics and pattern of stimulation of the levels of intracellular calcium in individual cells, as revealed by imaging. Compound 1 displayed modestly enhanced in vitro stability in rat liver microsomes and in plasma, suggesting that it might be a pharmacokinetically more favorable surrogate of resiniferatoxin. Molecular modeling analyses with selected analogues provide evidence that the conformational differences could affect their binding affinities, especially for the ester versus amide at the B-region.

Stereospecific high-affinity TRPV1 antagonists: chiral N-(2-benzyl-3-pivaloyloxypropyl) 2-[4-(methylsulfonylamino)phenyl]propionamide analogues.

Previously, we reported the thiourea antagonists 2a and 2b as potent and high affinity TRPV1 antagonists. For further optimization of the lead compounds, a series of their amide and alpha-substituted amide surrogates were investigated and novel chiral N-(2-benzyl-3-pivaloyloxypropyl) 2-[4-(methylsulfonylamino)phenyl]propionamide analogues were characterized as potent and stereospecific rTRPV1 antagonists. In particular, compounds 72 and 73 displayed high binding affinities, with K i values of 4.12 and 1.83 nM and potent antagonism with K i values of 0.58 and 5.2 nM, respectively, in rTRPV1/CHO cells. These values are comparable or more potent than those of 5-iodoRTX under the same assay conditions. A distinctive binding model that includes two hydrophobic pockets is proposed for this series of compounds based on docking studies of 57 and 72 with a homology model of the TM3/4 region of TRPV1.

Differential modulation of agonist and antagonist structure activity relations for rat TRPV1 by cyclosporin A and other protein phosphatase inhibitors.

The transient receptor potential V1 channel (vanilloid receptor, TRPV1) represents a promising therapeutic target for inflammatory pain and other conditions involving C-fiber sensory afferent neurons. Sensitivity of TRPV1 is known to be subject to modulation by numerous signaling pathways, in particular by phosphorylation, and we wished to determine whether TRPV1 structure activity relations could be differentially affected. We demonstrate here that the structure activity relations of TRPV1, as determined by (45)Ca(2) uptake, were substantially altered by treatment of the cells with cyclosporin A, an inhibitor of protein phosphatase 2B. Whereas the potency of resiniferatoxin for stimulation of (45)Ca(2) was not altered by cyclosporin A treatment, the potencies of some other agonists were increased up to 8-fold. Among the antagonists examined, potencies were reduced to a lesser extent, ranging from 1- to 2.5-fold. Finally, the efficacy of partial agonists was increased. In contrast to cyclosporin A, okadaic acid, an inhibitor of protein phosphatases 1 and 2A, had little effect on agonist potencies, and calyculin A, an inhibitor of protein phosphatases 1 and 2A but with somewhat different selectivity from that of okadaic acid, caused changes in structure activity relations distinct from those induced by cyclosporin A. Because phosphatase activity differentially modulates the structure activity relations of TRPV1 agonists and antagonists, our findings predict that it may be possible to design agonists and antagonists selective for TRPV1 in a specific regulatory environment. A further implication is that it may be desirable to tailor screening approaches for drug discovery to reflect the desired regulatory state of the targeted TRPV1.

Pyridine C-region analogs of 2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides as potent TRPV1 antagonists.

A series of pyridine derivatives in the C-region of N-((6-trifluoromethyl-pyridin-3-yl)methyl) 2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides were investigated as hTRPV1 antagonists. The SAR analysis indicated that 6-difluorochloromethyl pyridine derivatives were the best surrogates of the C-region for previous leads. Among them, compound 31 showed excellent antagonism to capsaicin as well as to multiple hTRPV1 activators. It demonstrated strong analgesic activity in the formalin test in mice with full efficacy and it blocked capsaicin-induced hypothermia in vivo.

2-(3-Fluoro-4-methylsulfonylaminophenyl)propanamides as potent TRPV1 antagonists: structure activity relationships of the 2-oxy pyridine C-region.

The structure activity relationships of 2-oxy pyridine derivatives in the C-region of N-(6-trifluoromethyl-pyridin-3-ylmethyl) 2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides as hTRPV1 antagonists were investigated. The analysis indicated that the lipophilicity of the 2-oxy substituents was critical for potent antagonism and 4 or 5 carbons appeared to be optimal for activity. Multiple compounds proved to have comparable activity to 1, which had been reported as the most potent antagonist for capsaicin activity among the previous series of compounds. Further analysis of compounds 22 (2-isobutyloxy) and 53 (2-benzyloxy) in the formalin test in mice demonstrated strong analgesic activity with full efficacy. Docking analysis of 53S using our hTRPV1 homology model indicated that the A- and B-region 2-(3-fluoro-4-methylsulfonylaminophenyl)propanamide made important hydrophobic and hydrogen bonding interactions with Tyr511 and that the C-region 6-trifluoromethyl and 2-benzyloxy groups of pyridine occupied the two hydrophobic binding pockets, respectively.

2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides as potent transient receptor potential vanilloid 1 (TRPV1) antagonists: structure-activity relationships of 2-amino derivatives in the N-(6-trifluoromethylpyridin-3-ylmethyl) C-region.

A series of N-(2-amino-6-trifluoromethylpyridin-3-ylmethyl)-2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides were designed combining previously identified pharmacophoric elements and evaluated as hTRPV1 antagonists. The SAR analysis indicated that specific hydrophobic interactions of the 2-amino substituents in the C-region of the ligand were critical for high hTRPV1 binding potency. In particular, compound 49S was an excellent TRPV1 antagonist (K(i(CAP)) = 0.2 nM; IC(50(pH)) = 6.3 nM) and was thus approximately 100- and 20-fold more potent, respectively, than the parent compounds 2 and 3 for capsaicin antagonism. Furthermore, it demonstrated strong analgesic activity in the rat neuropathic model superior to 2 with almost no side effects. Compound 49S antagonized capsaicin induced hypothermia in mice but showed TRPV1-related hyperthermia. The basis for the high potency of 49S compared to 2 is suggested by docking analysis with our hTRPV1 homology model in which the 4-methylpiperidinyl group in the C-region of 49S made additional hydrophobic interactions with the hydrophobic region.

Conformationally constrained analogues of N'-(4-tert-butylbenzyl)-N-(4-methylsulfonylaminobenzyl)thiourea as TRPV1 antagonists.

A series of bicyclic analogues having indan and tetrahydronaphthalene templates in the A-region were designed as conformationally constrained analogues of our previously reported potent TRPV1 antagonists (1, 3). The activities for rat TRPV1 of the conformationally restricted analogues were moderately or markedly diminished, particularly in the case of the tetrahydronaphthalene analogues. The analysis indicated that steric constraints at the benzylic position in the bicyclic analogues may be an important factor for their unfavorable interaction with the receptor.

Halogenation of 4-hydroxy-3-methoxybenzyl thiourea TRPV1 agonists showed enhanced antagonism to capsaicin.

Selected potent TRPV1 agonists (1-6) have been modified by 5- or 6-halogenation on the aromatic A-region to analyze their effects on potency and efficacy (agonism versus antagonism). The halogenation caused enhanced functional antagonism at TRPV1 compared to the corresponding prototype agonists. The analysis of SAR indicated that the antagonism was enhanced as the size of the halogen increased (I>Br>Cl) and when the 6-position was halogenated. Compounds 23c and 31b were found to be potent full antagonists with K(i) (as functional antagonist)=23.1 and 30.3 nM in rTRPV1/CHO system, respectively.

Alpha-substituted N-(4-tert-butylbenzyl)-N'-[4-(methylsulfonylamino)benzyl]thiourea analogues as potent and stereospecific TRPV1 antagonists.

A series of alpha-substituted N-(4-tert-butylbenzyl)-N'-[4-(methylsulfonylamino)benzyl]thiourea analogues have been investigated as TRPV1 receptor antagonists. alpha-Methyl substituted analogues showed potent and stereospecific antagonism to the action of capsaicin on rat TRPV1 heterologously expressed in Chinese hamster ovary cells. In particular, compounds 14 and 18, which possess the R-configuration, exhibited excellent potencies (respectively, K(i)=41 and 39.2 nM and K(i(ant))=4.5 and 37 nM).