Ying-Duo Gao

Functional Mapping of the Transient Receptor Potential Vanilloid 1 Intracellular Binding Site

Capsaicin (vanilloid) sensitivity has long served as the functional signature of a subset of nociceptive sensory neurons. Mutagenesis studies have revealed seemingly distinct regions involved in mediating ligand binding and channel activation at the capsaicin binding site. Residue 547 (transmembrane region 4) mediates significant species differences in resiniferatoxin (RTX) sensitivity, and the Ser512 residue is critical in discriminating between pH and capsaicin gating. In the present study, the pharmacological profiles of a variety of ligands were studied to investigate cross-talk between these two regions. Exchange of residue 547 between species mediated a difference in capsaicin and RTX-dependent gating. Likewise, the potency of iodoresiniferatoxin (I-RTX) and a novel transient receptor potential vanilloid 1 antagonist were also altered. Experiments using the S512Y mutant channel have confirmed the importance of residue 512 for functional interaction of capsaicin and our novel antagonist. In this study, we were surprised to find that the mutation S512Y converted the activity of the antagonist I-RTX into an intrinsic agonist, albeit with a lower potency than its parent compound, RTX. Recent studies have proposed a novel model for the receptor, based on the X-ray crystal structure of the voltage-dependent potassium channel, in which both the 512 and 547 amino acid residues are in close proximity. Our data support the model whereby intracellular ligand interaction occurs within an S3-S4 “sensor” domain, enabling binding of ligands to be transduced to functional gating of the channel. The binding pocket also seems to be exquisitely sensitive to residue-specific interaction with ligands, because subtle changes in either ligand or channel structure can have profound effects on channel activity.

Novel tetrahydropyran analogs as dipeptidyl peptidase IV inhibitors: Profile of clinical candidate (2R,3S,5R)-2-(2,5-difluorophenyl)-5-[2-(methylsulfonyl)-2,6-dihydropyrrolo[3,4-c]pyrazol-5(4H)-yl]tetrahydro-2H-pyran-3-amine (23)

A series of novel tri-2,3,5-substituted tetrahydropyran analogs were synthesized and evaluated as inhibitors of dipeptidyl peptidase IV (DPP-4) for the treatment of type 2 diabetes. Optimization of the series provided inhibitors with good DPP-4 potency and selectivity over other peptidases (QPP, DPP8, and FAP). Compound 23, which is very potent, selective, efficacious in the diabetes PD model, and has an excellent pharmacokinetic profile, is selected as a clinical candidate.

Discovery of Benzodiazepine Sulfonamide-Based Bombesin Receptor Subtype 3 Agonists and Their Unusual Chirality

We report herein the discovery of benzodiazepine sulfonamide-based bombesin receptor subtype 3 (BRS-3) agonists and their unusual chirality. Starting from a high-throughput screening lead, we prepared a series of BRS-3 agonists with improved potency and pharmacokinetic properties, of which compound 8a caused mechanism-based, dose-dependent food intake reduction and body weight loss after oral dosing in diet-induced obese mice. This effort also led to the discovery of a novel family of chiral molecules originated from the conformationally constrained seven-membered diazepine ring.

The design and synthesis of potent, selective benzodiazepine sulfonamide bombesin receptor subtype 3 (BRS-3) agonists with an increased barrier of atropisomerization.

Bombesin receptor subtype 3 (BRS-3) is an orphan G-protein coupled receptor expressed primarily in the hypothalamus which plays a role in the onset of both diabetes and obesity. We report herein our progress made towards identifying a potent, selective bombesin receptor subtype-3 (BRS-3) agonist related to the previously described MK-7725(1) Chobanian et al. (2012) that would prevent atropisomerization through the increase of steric bulk at the C-2 position. This would thereby make clinical development of this class of compounds more cost effective by inhibiting racemization which can occur over long periods of time at room/elevated temperature.

Modeling directed design and biological evaluation of quinazolinones as non-peptidic growth hormone secretagogues

Quinazolinone derivatives were synthesized and evaluated as non-peptidic growth hormone secretagogues. Modeling guided design of quinazolinone compound 21 led to a potency enhancement of greater than 200-fold compared to human growth hormone secretagogue affinity of a screening lead 4.

Discovery of 8-Amino-imidazo[1,5-a]pyrazines as Reversible BTK Inhibitors for the Treatment of Rheumatoid Arthritis.

Brutons tyrosine kinase (BTK) is a Tec family kinase with a well-defined role in the B cell receptor (BCR) pathway. It has become an attractive kinase target for selective B cell inhibition and for the treatment of B cell related diseases. We report a series of compounds based on 8-amino-imidazo[1,5-a]pyrazine that are potent reversible BTK inhibitors with excellent kinase selectivity. Selectivity is achieved through specific interactions of the ligand with the kinase hinge and driven by aminopyridine hydrogen bondings with Ser538 and Asp539, and by hydrophobic interaction of trifluoropyridine in the back pocket. These interactions are evident in the X-ray crystal structure of the lead compounds 1 and 3 in the complex with the BTK enzyme. Our lead compounds show desirable PK profiles and efficacy in the preclinical rat collagen induced arthritis model.

Discovery of isoxazole voltage gated sodium channel blockers for treatment of chronic pain

A series of novel isoxazole voltage gated sodium channel blockers have been synthesized and evaluated. Substitutions on the benzylic position of benzamide were investigated to determine their effect on Na(v)1.7 inhibitory potency. The spirocyclobutyl substitution had the most significant enhancement on Na(v)1.7 inhibitory activity.

Discovery of new binding elements in DPP-4 inhibition and their applications in novel DPP-4 inhibitor design.

Probing with tool molecules, and by modeling and X-ray crystallography the binding modes of two structurally distinct series of DPP-4 inhibitors led to the discovery of a rare aromatic fluorine H-bond and the spatial requirement for better biaryl binding in the DPP-4 enzyme active site. These newly found binding elements were successfully incorporated into novel DPP-4 inhibitors.

Discovery of Novel Tricyclic Heterocycles as Potent and Selective DPP-4 Inhibitors for the Treatment of Type 2 Diabetes

In our efforts to develop second generation DPP-4 inhibitors, we endeavored to identify distinct structures with long-acting (once weekly) potential. Taking advantage of X-ray cocrystal structures of sitagliptin and other DPP-4 inhibitors, such as alogliptin and linagliptin bound to DPP-4, and aided by molecular modeling, we designed several series of heterocyclic compounds as initial targets. During their synthesis, an unexpected chemical transformation provided a novel tricyclic scaffold that was beyond our original design. Capitalizing on this serendipitous discovery, we have elaborated this scaffold into a very potent and selective DPP-4 inhibitor lead series, as highlighted by compound 17c.

Discovery of a novel class of isoxazoline voltage gated sodium channel blockers.

Analogs of the previously reported voltage gated sodium channel blocker CDA54 were prepared in which one of the amide functions was replaced with aromatic and non-aromatic heterocycles. Replacement of the amide with an aromatic heterocycle resulted in significant loss of sodium channel blocking activity, while non-aromatic heterocycle replacements were well tolerated.