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

Pyrazole C-region analogues of 2-(3-fluoro-4-methylsulfonylaminophenyl)propanamides as potent TRPV1 antagonists

A series of 1-substituted 3-(t-butyl/trifluoromethyl)pyrazole C-region analogues of 2-(3-fluoro-4-methylsulfonamidophenyl)propanamides were investigated for hTRPV1 antagonism. The structure activity relationship indicated that the 3-chlorophenyl group at the 1-position of pyrazole was the optimized hydrophobic group for antagonistic potency and the activity was stereospecific to the S-configuration, providing exceptionally potent antagonists 13S and 16S with K_i(CAP)=0.1nM. Particularly significant, 13S exhibited antagonism selective for capsaicin and NADA and not for low pH or elevated temperature. Both compounds also proved to be very potent antagonists for rTRPV1, blocking in vivo the hypothermic action of capsaicin, consistent with their in vitro mechanism. The docking study of compounds 13S and 16S in our hTRPV1 homology model indicated that the binding modes differed somewhat, with that of 13S more closely resembling that of GRT12360.

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.

Medicinal Chemistry, Pharmacology, and Clinical Implications of TRPV1 Receptor Antagonists

Transient receptor potential vanilloid 1 (TRPV1) is an ion channel expressed on sensory neurons triggering an influx of cations. TRPV1 receptors function as homotetramers responsive to heat, proinflammatory substances, lipoxygenase products, resiniferatoxin, endocannabinoids, protons, and peptide toxins. Its phosphorylation increases sensitivity to both chemical and thermal stimuli, while desensitization involves a calcium-dependent mechanism resulting in receptor dephosphorylation. TRPV1 functions as a sensor of noxious stimuli and may represent a target to avoid pain and injury. TRPV1 activation has been associated to chronic inflammatory pain and peripheral neuropathy. Its expression is also detected in nonneuronal areas such as bladder, lungs, and cochlea where TRPV1 activation is responsible for pathology development of cystitis, asthma, and hearing loss. This review offers a comprehensive overview about TRPV1 receptor in the pathophysiology of chronic pain, epilepsy, cough, bladder disorders, diabetes, obesity, and hearing loss, highlighting how drug development targeting this channel could have a clinical therapeutic potential. Furthermore, it summarizes the advances of medicinal chemistry research leading to the identification of highly selective TRPV1 antagonists and their analysis of structure-activity relationships (SARs) focusing on new strategies to target this channel.

Discovery of N-(3-fluoro-4-methylsulfonamidomethylphenyl)urea as a potent TRPV1 antagonistic template

A series of homologous analogues of prototype antagonist 1 and its urea surrogate were investigated as hTRPV1 ligands. Through one-carbon elongation in the respective pharmacophoric regions, N-(3-fluoro-4-methylsulfonamidomethylphenyl)urea was identified as a novel and potent TRPV1 antagonistic template. Its representative compound 27 showed a potency comparable to that of lead compound 1. Docking analysis of compound 27 in our hTRPV1 homology model indicated that its binding mode was similar with that of 1S.

2-Sulfonamidopyridine C-region analogs of 2-(3-fluoro-4-methylsulfonamidophenyl)propanamides as potent TRPV1 antagonists

A series of 2-sulfonamidopyridine C-region derivatives of 2-(3-fluoro-4-methylsulfonamidophenyl)propanamide were investigated as hTRPV1 ligands. Systematic modification on the 2-sulfonamido group provided highly potent TRPV1 antagonists. The N-benzyl phenylsulfonamide derivatives 12 and 23 in particular showed higher affinities than that of lead compound 1. Compound 12 exhibited strong analgesic activity in the formalin pain model. Docking analysis of its chiral S-form 12S in our hTRPV1 homology model indicated that its high affinity might arise from additional hydrophobic interactions not present in lead compound 1S.

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.

α-Substituted 2-(3-fluoro-4-methylsulfonamidophenyl)acetamides as potent TRPV1 antagonists

A series of α-substituted acetamide derivatives of previously reported 2-(3-fluoro-4-methylsulfonamidophenyl)propanamide leads (1, 2) were investigated for antagonism of hTRPV1 activation by capsaicin. Compound 34, which possesses an α-m-tolyl substituent, showed highly potent and selective antagonism of capsaicin with Ki(CAP)=0.1 nM. It thus reflected a 3-fold improvement in potency over parent 1. Docking analysis using our homology model indicated that the high potency of 34 might be attributed to a specific hydrophobic interaction of the m-tolyl group with the receptor.

Crystal structure of 2,2-dimethyl-N-(pyridin-3-yl)propanamide

In the title compound, C10H14N2O, the pyridine ring is inclined to the mean plane of the amide moiety [N-C(=O)C] by 17.60 (8)°. There is an intra-molecular C-H⋯O hydrogen bond present involving the carbonyl O atom. In the crystal, mol-ecules are linked via N-H⋯N hydrogen bonds, forming chains propagating along [100]. The tert-butyl group is disordered over two sets of sites with a refined occupancy ratio of 0.758 (12):0.242 (12).

Structural insight into tetrameric hTRPV1 from homology modeling, molecular docking, molecular dynamics simulation, virtual screening, and bioassay validations

The transient receptor potential vanilloid type 1 (TRPV1) is a heat-activated cation channel protein, which contributes to inflammation, acute and persistent pain. Antagonists of human TRPV1 (hTRPV1) represent a novel therapeutic approach for the treatment of pain. Developing various antagonists of hTRPV1, however, has been hindered by the unavailability of a 3D structure of hTRPV1. Recently, the 3D structures of rat TRPV1 (rTRPV1) in the presence and absence of ligand have been reported as determined by cryo-EM. rTRPV1 shares 85.7% sequence identity with hTRPV1. In the present work, we constructed and reported the 3D homology tetramer model of hTRPV1 based on the cryo-EM structures of rTRPV1. Molecular dynamics (MD) simulations, energy minimizations, and prescreen were applied to select and validate the best model of hTRPV1. The predicted binding pocket of hTRPV1 consists of two adjacent monomers subunits, which were congruent with the experimental rTRPV1 data and the cyro-EM structures of rTRPV1. The detailed interactions between hTRPV1 and its antagonists or agonists were characterized by molecular docking, which helped us to identify the important residues. Conformational changes of hTRPV1 upon antagonist/agonist binding were also explored by MD simulation. The different movements of compounds led to the different conformational changes of monomers in hTRPV1, indicating that TRPV1 works in a concerted way, resembling some other channel proteins such as aquaporins. We observed that the selective filter was open when hTRPV1 bound with an agonist during MD simulation. For the lower gate of hTRPV1, we observed large similarities between hTRPV1 bound with antagonist and with agonist. A five-point pharmacophore model based on several antagonists was established, and the structural model was used to screen in silico for new antagonists for hTRPV1. By using the 3D TRPV1 structural model above, the pilot in silico screening has begun to yield promising hits with activity as hTRPV1 antagonists, several of which showed substantial potency.

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.

Crystal structure of 1-benzyl-4-(2,4-di-chloro-phenyl)-2-imino-1,2,5,6,7,8,9,10-octa-hydro-cyclo-octa-[b]pyridine-3-carbo-nitrile

In the title compound, the cyclo­octene ring adopts a twist chair–chair conformation. No directional inter­actions could be identified in the crystal and the packing is governed by van der Waals inter­actions.

In the title compound, C₂₅H₂₃Cl₂N₃, the cyclo­octene ring adopts a twist chair–chair conformation. The dihedral angles between the central pyridine ring (r.m.s. deviation = 0.013 Å) and the pendant chloro­benzene and benzyl rings are 78.07 (11) and 87.47 (12)°, respectively. No directional inter­actions could be identified in the crystal and the packing is governed by van der Waals inter­actions.

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.

2,2-Dimethyl-N-(4-methyl-pyridin-2-yl)propanamide

In the title compound, C11H16N2O, the dihedral angle between the mean plane of the 4-methypyridine group and the plane of the amide link is 16.7 (1)°, and there is a short intra-molecular C-H⋯O contact. Hydrogen bonding (N-H⋯O) between amide groups forms chains parallel to the b axis. Pairs of methyl-pyridine groups from mol-ecules in adjacent chains are parallel but there is minimal π-π inter-action.

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.