Nonpeptidic Ligands for Peptide-Activated G Protein-Coupled Receptors

Structure, function and pathophysiology of protease activated receptors

Discovered in the 1990s, protease activated receptors(1) (PARs) are membrane-spanning cell surface proteins that belong to the G protein coupled receptor (GPCR) family. A defining feature of these receptors is their irreversible activation by proteases; mainly serine. Proteolytic agonists remove the PAR extracellular amino terminal pro-domain to expose a new amino terminus, or tethered ligand, that binds intramolecularly to induce intracellular signal transduction via a number of molecular pathways that regulate a variety of cellular responses. By these mechanisms PARs function as cell surface sensors of extracellular and cell surface associated proteases, contributing extensively to regulation of homeostasis, as well as to dysfunctional responses required for progression of a number of diseases. This review examines common and distinguishing structural features of PARs, mechanisms of receptor activation, trafficking and signal termination, and discusses the physiological and pathological roles of these receptors and emerging approaches for modulating PAR-mediated signaling in disease.

Synthesis of benzodiazepine beta-turn mimetics by an Ugi 4CC/Staudinger/aza-Wittig sequence. Solving the conformational behavior of the Ugi 4CC adducts

5-Oxobenzo[e][1,4]diazepine-3-carboxamides were synthesized by sequential Ugi reaction-Staudinger/aza-Wittig cyclization. The pseudopeptidic backbone of the new benzodiazepine derivatives superimposed well with type I, I', II, and II' beta-turn motifs. The intermediate Ugi adducts were characterized as two conformers of the enol form by the correlation between (1)H NMR spectra and X-ray diffraction structures of model compounds.

Nonpeptide ligands for peptidergic G protein-coupled receptors

Neuropeptides play essential roles in many physiological systems in vertebrates and invertebrates. Peptides per se are difficult to use as therapeutic agents, as they are generally very unstable in biological fluid environments and cross biological membranes poorly. Recognition that nonpeptide ligands for peptide receptors have clinical utility came from the discovery that opiates (such as morphine) act by binding to G protein-coupled receptors (GPCRs) for which the endogenous ligands are a family of neuropeptides (enkephalins and endorphins). Basic research has revealed a very large number of distinct neuropeptides that influence virtually every aspect of mammalian physiology and considerable effort has been expended in the pursuit of new drugs that act through peptidergic signaling systems. Although useful drugs have been found to affect various aspects ofneuropeptide biology, most work has been devoted to the discovery of nonpeptide ligands that act as agonists or antagonists at peptidergic GPCRs. Similar opportunities are apparent for the discovery of nonpeptide ligands that act on invertebrate GPCRs. A consideration of the knowledge gained from the process as conducted for mammalian peptidergic systems can inform and illuminate promising strategies for the discovery of new drugs for the treatment and control of pests and parasites.

A solution NMR approach to the measurement of amphiphile immersion depth and orientation in membrane model systems

Oxygen and Ni(II) are ideal paramagnetic species for NMR studies of immersion depth since they establish prominent concentration gradients across the membrane-water interface of either bilayers or micelles. Corresponding gradients of paramagnetic shifts and relaxation rates are observed by NMR for membrane embedded amphiphiles. Specifically, upon dissolution of oxygen at a partial pressure of 20 bar or more, (13)C NMR spectra of membrane embedded amphiphiles reveal chemical shift perturbations which depend sensitively on average immersion depth in the membrane. Similarly, depth-dependent enhancements of spin-lattice relaxation rates can be detected by (1)H NMR. Generally, such paramagnetic effects depend both on steric or accessibility factors and on the local concentration of the paramagnet. The steric terms can be factored out by combining paramagnetic rates arising from O(2) and Ni, in the form of a ratio, R(1P)(O(2))/R(1P)(Ni). The natural logarithm of this ratio is shown to depend linearly on immersion depth in a micelle. The analysis is verified using molecular dynamics simulations of dodecylphosphocholine in a detergent micelle, while thorough consideration of the paramagnetic rate data also allows for the determination of the orientation of imipramine in the micelle. Thus, a complete picture of topology arises from this approach which is readily applicable to studies of drugs and amphiphiles in fast-tumbling bicelles, small unilamellar vesicles, and micelles.

The design and discovery of novel amide CCR5 antagonists

The synthesis of a range of novel amine-containing structures and their primary potency as inhibitors of HIV-1 fusion via blocking of the CCR5 receptor is described. The development of the medicinal chemistry strategy and SAR's which led to the identification of the piperidine amide compounds 33 and 36 as excellent leads for further evaluation is described, along with key physicochemical data which highlighted their lead potential.

Biaryl construction via Ni-catalyzed C-O activation of phenolic carboxylates

Biaryl scaffolds were constructed via Ni-catalyzed aryl C-O activation by avoiding cleavage of the more reactive acyl C-O bond of aryl carboxylates. Now aryl esters, in general, can be successfully employed in cross-coupling reactions for the first time. The substrate scope and synthetic utility of the chemistry were demonstrated by the syntheses of more than 40 biaryls and by constructing complex organic molecules. Water was observed to play an important role in facilitating this transformation.

Constitutive activation of G protein-coupled receptors and diseases: insights into mechanisms of activation and therapeutics

The existence of constitutive activity for G protein-coupled receptors (GPCRs) was first described in 1980s. In 1991, the first naturally occurring constitutively active mutations in GPCRs that cause diseases were reported in rhodopsin. Since then, numerous constitutively active mutations that cause human diseases were reported in several additional receptors. More recently, loss of constitutive activity was postulated to also cause diseases. Animal models expressing some of these mutants confirmed the roles of these mutations in the pathogenesis of the diseases. Detailed functional studies of these naturally occurring mutations, combined with homology modeling using rhodopsin crystal structure as the template, lead to important insights into the mechanism of activation in the absence of crystal structure of GPCRs in active state. Search for inverse agonists on these receptors will be critical for correcting the diseases cause by activating mutations in GPCRs. Theoretically, these inverse agonists are better therapeutics than neutral antagonists in treating genetic diseases caused by constitutively activating mutations in GPCRs.

Structural basis of cholecystokinin receptor binding and regulation

Two structurally-related guanine nucleotide-binding protein-coupled receptors for two related peptides, cholecystokinin (CCK) and gastrin, have evolved to exhibit substantial diversity in specificity of ligand recognition, in their molecular basis of binding these ligands, and in their mechanisms of biochemical and cellular regulation. Consistent with this, the CCK1 and CCK2 receptors also play unique and distinct roles in physiology and pathophysiology. The paradigms for ligand recognition and receptor regulation and function are reviewed in this article, and should be broadly applicable to many members of this remarkable receptor superfamily. This degree of specialization is instructive and provides an encouraging basis for the diversity of potential drugs targeting these receptors and their actions that can be developed.

Nonpeptide Urotensin-II receptor agonists and antagonists: review and structure-activity relationships

Human Urotensin-II (hU-II) is a cyclic 11-amino acid peptide that plays a role in cardiovascular homeostasis. Its receptor is a member of the class A of G-protein-coupled receptors, called GPR14. In recent years, several nonpeptide ligands have been reported in the literature. Most were identified by high-throughput screening and optimized by medicinal chemistry methods. Other nonpeptide ligands were discovered starting from the 3D structure of hU-II or other ligands. They were identified by a virtual screening approach based on a 3D pharmacophore or by structural similarity with others cyclic peptides. In this review, nonpeptide agonists and antagonists are presented in relation to structure-activity relationships.

'Clean' or 'Dirty' – Just How Selective Do Drugs Need To Be?

Chemotherapy has developed largely on the basis of searching for chemicals with selective toxicity, targeting a specific step or receptor in a disease process without negatively impacting on normal physiology. The desire for ‘clean’ drugs that act on a single target and thus avoid side effects has led to ever-increasing timeframes for introducing new drugs to humans. This has led to reappraisal of how selective drugs need to be. Examples here of compounds from common drug classes (kinase inhibitors, protease inhibitors, G protein coupled receptors ligands, non-steroidal anti-inflammatory drugs, statins, antibodies) highlight current debate on the merits of target selectivity versus target promiscuity in the development of drugs for inflammation, cancer, cardiovascular, central nervous system and infectious diseases.