2,7-Dioxo-2,3,4,5,6,7-hexahydro-1H-benzo[h][1,4]diazonine as a new template for the design of CCK(2) receptor antagonists

Neuroendocrine mechanism of gastric acid secretion: Historical perspectives and recent developments in physiology and pharmacology

The physiology of gastric acid secretion is one of the earliest subjects in medical literature and has been continuously studied since 1833. Starting with the notion that neural stimulation alone drives acid secretion, progress in understanding the physiology and pathophysiology of this process has led to the development of therapeutic strategies for patients with acid-related diseases. For instance, understanding the physiology of parietal cells led to the developments of histamine 2 receptor blockers, proton pump inhibitors (PPIs), and recently, potassium-competitive acid blockers. Furthermore, understanding the physiology and pathophysiology of gastrin has led to the development of gastrin/CCK2 receptor (CCK2 R) antagonists. The need for refinement of existing drugs in patients have led to second and third generation drugs with better efficacy at blocking acid secretion. Further understanding of the mechanism of acid secretion by gene targeting in mice has enabled us to dissect the unique role for each regulator to leverage and justify the development of new targeted therapeutics for acid-related disorders. Further research on the mechanism of stimulation of gastric acid secretion and the physiological significances of gastric acidity in gut microbiome is needed in the future.

Copper-Catalyzed Cycloadditions of Diazo Compounds with Imidazolidines/Hexahydropyrimidines for the Syntheses of N-Heterocycles

Reported herein are the unprecedented copper-catalyzed formal [n + 1]/[n + 3] (n = 5, 6) cycloadditions of diazo compounds with imidazolidines/hexahydropyrimidines, thus providing a general, economical, and efficient route to construct different sized (six- to nine-membered) diaza-heterocycles in moderate to excellent yields under mild reaction conditions. This strategy features the use of copper catalyst to accomplish such diverse annulations and the utilization of imidazolidines/hexahydropyrimidines as stable 1,5-/1,6-dipoles.

Construction of nine-membered N,N,O-heterocycles via Pd-catalyzed [6+3] dipolar cycloaddition

A new approach for the synthesis of 9-membered N,N,O-heterocycles by Pd-catalyzed [6+3] dipolar cycloaddition of N-iminoisoquinolinium ylides and 2-vinyl oxetanes has been developed.

1,3-Dipolar cycloaddition of nitrones: synthesis of multisubstituted, diverse range of heterocyclic compounds

The 1,3-dipolar cycloaddition reaction of nitrone is one of the most important methods for the synthesis of different sizes of heterocycles which have enormous applications in natural products, biologically active molecules and pharmaceuticals.

Arylacetylenes as two-carbon synthons: synthesis of eight-membered rings via C[triple bond, length as m-dash]C bond cleavage

The first synthesis of eight-membered N-containing heterocycles by oxidative bicyclization/ring extension of arylacetylenes and aryl amines has been achieved. This protocol uses arylacetylene as an unusual two-carbon synthon by incorporating the two parts of the cracked C[triple bond, length as m-dash]C bond into the final product, which provides a new method for using arylacetylenes as two-carbon synthons and further enriches C[triple bond, length as m-dash]C bond cleavage methodology. Moreover, this multi-component reaction can provide diverse fused elegant eight-membered N-heterocycles under mild conditions with wide substrate scopes.

Access to oxoquinoline heterocycles by N-heterocyclic carbene catalyzed ester activation for selective reaction with an enone

Organocatalytic ester activation is developed for a highly selective cascade reaction between saturated esters and amino enones. The reaction involves activation of the β-carbon atom of the ester as a key step. This method allows a single-step access to multicyclic oxoquinoline-type heterocycles with high enantiomeric ratios.

Synthesis of alpha-helix mimetics with four side-chains

The synthesis of a heterocyclic piperazine-based scaffold that mimics the i, i+4, i+8, i+11 side-chain projections of an alpha-helix is described. The synthesis is designed to be modular to allow the targeting of a range of protein-protein interactions involving alpha-helices.

Rationalizing the activities of diverse cholecystokinin 2 receptor antagonists using molecular field points

Cholecystokinin 2 receptor antagonists encompass a wide range of structures. This makes them unsuitable candidates for existing 3D-QSAR methods and has led us to develop an alternative approach to account for their observed biological activities. A diverse set of 21 antagonists was subjected to a novel molecular field-based similarity analysis. The hypothesis is that compounds with similar field patterns will bind at the same target site regardless of their underlying structure. This initial report demonstrates a linear correlation between ligand similarity and biological activity for this challenging data set. A model generated with three molecules was used to predict the activity of 18 test compounds, with different chemotypes, with a root-mean-square error of 0.68 pKB units. The ability to automatically derive a molecular alignment without knowledge of the protein structure represents an improvement over existing pharmacophore methods and makes the method particularly suitable for scaffold-hopping.

Molecular Field Extrema as Descriptors of Biological Activity: Definition and Validation

The paper describes the generation of four types of three-dimensional molecular field descriptors or 'field points' as extrema of electrostatic, steric, and hydrophobic fields. These field points are used to define the properties necessary for a molecule to bind in a characteristic way into a specified active site. The hypothesis is that compounds showing a similar field point pattern are likely to bind at the same target site regardless of structure. The methodology to test this idea is illustrated using HIV NNRTI and thrombin ligands and validated across seven other targets. From the in silico comparisons of field point overlays, the experimentally observed binding poses of these ligands in their respective sites can be reproduced from pairwise comparisons.

Scaffold hopping with molecular field points: identification of a cholecystokinin-2 (CCK2) receptor pharmacophore and its use in the design of a prototypical series of pyrrole- and imidazole-based CCK2 antagonists

A new molecular modeling approach has been used to derive a pharmacophore of the potent and selective cholecystokinin-2 (CCK(2)) receptor antagonist 5 (JB93182), based on features shared with two related series. The technique uses "field points" as simple and effective descriptions of the electrostatic and van der Waals maxima and minima surrounding a molecule equipped with XED (extended electron distribution) charges. Problems associated with the high levels of biliary elimination of 5 in vivo required us to design a compound with significantly lower molecular weight without sacrificing its nanomolar levels of in vitro activity. Two new series of compounds were designed to mimic the arrangement of field points present in the pharmacophore rather than its structural elements. In a formal sense, two of the three amides in 5 were replaced with either a simple pyrrole or imidazole, while some features thought to be essential for the high levels of in vitro activity of the parent compounds were retained and others deleted. These compounds maintained activity and selectivity for this receptor over CCK(1). In addition, the reduction in molecular weight coupled with lower polarities greatly reduced levels of biliary elimination associated with 5. This makes them good lead compounds for development of drug candidates whose structures are not obviously related to those of the parents and represents the first example of scaffold hopping using molecular field points.

Ligand-Based Molecular Modeling Study on a Chemically Diverse Series of Cholecystokinin-B/Gastrin Receptor Antagonists: Generation of Predictive Model

Pharmacophore hypotheses were developed for six structurally diverse series of cholecystokinin-B/gastrin receptor (CCK-BR) antagonists. A training set consisting of 33 compounds was carefully selected. The activity spread of the training set molecules was from 0.1 to 2100 nM. The most predictive pharmacophore model (hypothesis 1), consisting of four features, namely, two hydrogen bond donors, one hydrophobic aliphatic, and one hydrophobic aromatic feature, had a correlation (r) of 0.884 and a root-mean-square deviation of 1.1526, and the cost difference between null cost and fixed cost was 81.5 bits. The model was validated on a test set consisting of six different series of 27 structurally diverse compounds and performed well in classifying active and inactive molecules correctly. This validation approach provides confidence in the utility of the predictive pharmacophore model developed in this work as a 3D query tool in the virtual screening of drug-like molecules to retrieve new chemical entities as potent CCK-BR antagonists. The model can also be used to predict the biological activities of compounds prior to their costly and time-consuming synthesis.

Pharmacological analysis of CCK2 receptors up-regulated using engineered transcription factors

Designed zinc finger proteins (ZFPs) regulate expression of target genes when coupled to activator or repressor domains. Transfection of ZFPs into cell lines can create expression systems where the targeted endogenous gene is transcribed and the protein of interest can be investigated in its own cellular context. Here we describe the pharmacological investigation of an expression system generated using CCK2 receptor-selective ZFPs transfected into human embryonic kidney cells (HEKZFP system). The receptors expressed in this system, in response to ZFP expression, were functional in calcium mobilization studies and the potency of the agonists investigated was consistent with their action at CCK2 receptors (CCK-8S pA50 = 9.05+/-0.11, pentagastrin pA50 = 9.11+/-0.13). In addition, binding studies were conducted using [125I]-BH-CCK-8S as radioligand. The saturation binding analysis of this radioligand was consistent with a single population of high affinity CCK receptors (pK(D) = 10.24). Competition studies were also conducted using a number of previously well-characterized CCK-receptor selective ligands; JB93182, YF476, PD-134,308, SR27897, dexloxiglumide, L-365,260 and L-364,718. Overall, the estimated affinity values for these ligands were consistent with their interaction at CCK2 receptors. Therefore, CCK2 receptors up-regulated using zinc finger protein technology can provide an alternative to standard transfection techniques for the pharmacological analysis of compounds.

Short and novel stereospecific synthesis of trisubstituted 2,5-diketopiperazines

Novel syntheses of chiral trisubstituted 2,5-diketopiperazines using multicomponent Ugi reactions were developed.

Cholecystokinin antagonists: pharmacological and therapeutic potential

Cholecystokinin (CCK) is a regulatory peptide hormone, predominantly found in the gastrointestinal tract, and a neurotransmitter present throughout the nervous system. In the gastrointestinal system CCK regulates motility, pancreatic enzyme secretion, gastric emptying, and gastric acid secretion. In the nervous system CCK is involved in anxiogenesis, satiety, nociception, and memory and learning processes. Moreover, CCK interacts with other neurotransmitters in some areas of the CNS. The biological effects of CCK are mediated by two specific G protein coupled receptor subtypes, termed CCK(1) and CCK(2). Over the past fifteen years the search of CCK receptor ligands has evolved from the initial CCK structure derived peptides towards peptidomimetic or non-peptide agonists and antagonists with improved pharmacokinetic profile. This research has provided a broad assortment of potent and selective CCK(1) and CCK(2) antagonists of diverse chemical structure. These antagonists have been discovered through optimization programs of lead compounds which were designed based on the structures of the C-terminal tetrapeptide, CCK-4, or the non-peptide natural compound, asperlicin, or derived from random screening programs. This review covers the main pharmacological and therapeutic aspects of these CCK(1) and CCK(2) antagonist. CCK(1) antagonists might have therapeutic potential for the treatment of pancreatic disorders and as prokinetics for the treatment of gastroesophageal reflux disease, bowel disorders, and gastroparesis. On the other hand, CCK(2) antagonists might have application for the treatment of gastric acid secretion and anxiety disorders.

Peptide hormone binding to G-protein-coupled receptors: structural characterization via NMR techniques

G-protein-coupled receptors (GPCRs) allow cells to respond to calcium, hormones, and neurotransmitters. Not surprisingly, they currently make up the largest family of validated drug targets. Rational drug design for molecular regulators targeting GPCRs has been limited to theoretical-based computational approaches. X-ray crystallography of intact GPCRs has provided the topological orientation of the seven transmembrane helices, but limited structural information of the extracellular and intracellular loops and protein termini. In this review we detail an NMR-based approach which provides the high-resolution structural features on the extracellular domains of GPCRs and the ligand/receptor complexes formed upon titration of the peptide hormone. The results provide important contact points and a high-resolution description of the ligand/receptor interactions, which may be useful for the rational design of therapeutic agents targeting GPCRs. Recent results from our investigation of the cholecystokinin peptide hormone system are used to highlight this approach.