Structure-antigastrin activity relationships of new (R)-4-benzamido-5-oxopentanoic acid derivatives

Electrochemical selenylative ipso-annulation of N-benzylacrylamides to construct seleno-azaspiro[4.5]decadienones

Herein, we present the electrochemical synthesis of selenylated azaspiro[4.5]decadienones through domino selenylation/ipso-annulation of N-benzylacrylamides with diselenides. The method showed a wide substrate scope under mild and external oxidant-free reaction conditions, involving the construction of C-Se and C-C bonds. Gram-scale synthesis and further functional group conversion of the product are also demonstrated.

CAN-Promoted Thiolative ipso-Annulation of Unactivated N-Benzyl Acrylamides: Access to SCN/SCF3/SO2Ar Containing Azaspirocycles

A variety of acrylamides holding an unactivated N-benzyl group underwent dearomative ipso-cyclization induced by sulfur-centered radicals (SCN/ SCF₃/ SO₂Ar) in the presence of ceric ammonium nitrate (CAN) as the oxidant to furnish azaspirocycles in good yields. This is the first report on ipso-dearomatization of N-benzyl acrylamides that proceeds without a substituent at the para-position of the aromatic ring. The developed conditions are also found to be suitable for substrates holding substituents such as F, NO₂, OMe, OH, and OAc at the para-position. The reaction features water as the source of oxygen, is compatible with a variety of functional groups, and proceeds in a short time.

Synthesis of 2-azaspiro[4.6]undec-7-enes from N-tosyl-N-(3-arylpropargyl)-tethered 3-methylcyclohex-2-en-1-ols

The FeCl(3)-promoted synthesis of 2-azaspiro[4.6]undec-7-ene rings proceeds via ring expansion/cyclization/chlorination of N-tosyl-N-(3-arylpropargyl)-tethered 6-methylbicyclo[4.1.0]heptan-2-ols. This azaspirocyclic ring skeleton can also be obtained in one pot from the tert-butyldimethylsilyl-protected N-tosyl-N-(3-arylpropargyl)-tethered 3-methylcyclohex-2-en-1-ols and diethylzinc/diiodomethane.

Synthesis and evaluation of Novel Benzimidazole derivative [Bz-Im] and its radio/biological studies

Two different benzimidazole analogues act as multimodal agent, first one as novel non-peptidic CCK-B receptor antagonist and similarly as potent anti-fungal agent, designated as [Bz-Im]. These compounds were synthesized and characterized by spectroscopic techniques such as FT-IR, NMR, EI-MS and also evaluated for specific radiopharmaceuticals. Preliminary radiolabeling results with (99m)Tc and biological evaluation studies showed promising results for further evaluation in vivo. The efficiency of labeling was more than 97% and complex was stable for about 12h at 30 degrees C in the presence of serum. Both ligands showed binding to most of the organs, known to express CCK receptors in biodistribution studies. Cholecystokinin (CCK(1) andCCK(2)) receptor binding affinities of these analogues are, IC(50), 0.942+/-0.107 for compound C and 0.665+/-0.211 for compound D in rat pancreatic acini. The anti-fungal activity has shown inhibitory activity against Aspergillus flavus and Aspergillus niger. These studies have provided a new template for further development of non-peptidic ligands for diagnostic and therapeutic purposes of diseases related with CCK receptors as well as anti-microbes.

Cholecystokinin and gastrin receptors

Cholecystokinin and gastrin receptors (CCK1R and CCK2R) are G protein-coupled receptors that have been the subject of intensive research in the last 10 years with corresponding advances in the understanding of their functioning and physiology. In this review, we first describe general properties of the receptors, such as the different signaling pathways used to exert short- and long-term effects and the structural data that explain their binding properties, activation, and regulation. We then focus on peripheral cholecystokinin receptors by describing their tissue distribution and physiological actions. Finally, pathophysiological peripheral actions of cholecystokinin receptors and their relevance in clinical disorders are reviewed.

Cholecystokinin-A receptor antagonists: therapies for gastrointestinal disorders

Cholecystokinin (CCK) is a peptide that exerts several regulatory functions in the periphery, as well as in the brain. The biological functions attributed to CCK are mediated by two receptor subtypes, termed CCKA and CCKB, located predominantly in the gastrointestinal (GI) tract and in the brain, respectively. Several selective and potent non-petide CCKA receptor antagonists have been synthesised and fully characterised in preclinical studies. A few of them have been, and continue to be tested in humans. This paper focuses on the data available on the effect of CCKA receptor antagonist administration in humans, and shows how, in addition to allowing a more exact definition of the role of CCK in the regulation of some GI functions, these drugs may also possess therapeutic potential in GI disorders.

Anthranilic acid based CCK1 receptor antagonists: preliminary investigation on their second “touch point”

In this phase of structure-affinity relationship study of VL-0395, a new anthranilic acid based CCK1 selective antagonist, we propose a series of unnatural aminoacidic derivatives. The result of this work is the identification of a new CCK ligand, which possesses an affinity (IC50 = 35 nm) one order of magnitude greater than the lead and, as a general rule, it points out how the hypothesized receptorial pocket which accommodates the Phe residue allows much more structural modification than that interacting with the N-terminal group. Hence, the modification of the C-terminal pharmacophoric group of our lead VL-0395 can not only enhance the affinity of anthranilic acid derivatives but can modulate the selectivity for one CCK receptor subtype or afford mixed antagonists.

Ligand identification for G-protein-coupled receptors: a lead generation perspective

This review addresses strategies for the generation of ligands for G-protein-coupled receptors outside classical high-throughput screening and literature based approaches. These range from the chemical intuition-based strategies of endogenous ligand elaboration and privileged structure decoration to the in silico approaches of virtual screening and de novo design. Examples are cited where supporting pharmacological data has been presented.

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.

Anthranilic acid derivatives: a new class of non-peptide CCK1 receptor antagonists

Having successfully obtained new CCK(1) ligands holding appropriate groups on the anthranilic acid dimer used as molecular scaffold we were interested in increasing their micromolar affinity for the CCK(1) receptors by modifying the spatial relationship of the main pharmacophoric groups. Since, we have proposed simplified analogues reducing the anthranilic acid dimer to a monomer. In this stage of our research program we have prepared and tested on CCK receptors a series of N-substituted anthranilic acid derivatives keeping a Phe residue at the C-terminal site. The indole-2-carbonyl group imparts the best CCK(1) receptor binding affinity (compound 1: IC(50)=197.5 nM) while a sharp decrease in binding affinity is observed for the other indole containing derivatives. Moreover, in order to support the different binding behaviour observed for the synthesized compounds, a conformational investigation was carried out. Finally, on the basis of the main pharmacophoric groups of the obtained new lead compound (1) (coded VL-0395) a receptor binding hypothesis has been provided.

1,4-dibenzylpiperazines possess anticocaine activity

N,N-dibenzylpiperazines have high affinity for sigma receptors, and we aimed to increase their anticocaine activity by introducing substituents known to enhance such activity in other sigma ligands. Ligands with high affinity for sigma-1 receptors resulted, but their activity in attenuating cocaine-induced convulsions did not correlate with sigma-1 binding affinity, and may be more closely related to their sigma-2 binding affinities.

Cholecystokinin increases cytosolic calcium in a subpopulation of cultured vagal afferent neurons

Imaging fluorescent measurements with fura 2 were used to examine cytosolic calcium signals induced by sulfated CCK octapeptide (CCK-8) in dissociated vagal afferent neurons from adult rat nodose ganglia. We found that 40% (184/465) of the neurons responded to CCK-8 with a transient increase in cytosolic calcium. The threshold concentration of CCK-8 for inducing the response varied from 0.01 to 100 nM. In most neurons (13/16) the response was eliminated by removing extracellular calcium. Depleting intracellular calcium stores with thapsigargin slightly augmented the response. Most neurons were unresponsive to nonsulfated CCK-8. The response was eliminated by the CCK-A receptor antagonist lorglumide. Low concentrations of JMV-180 had no effect; however, high concentrations of JMV-180 reduced responses to CCK-8. These results demonstrate that CCK acts at the low-affinity site of the CCK-A receptor to trigger the entry of extracellular calcium into vagal afferent neurons. Increased cytosolic calcium may participate in acute activation of vagal afferent neurons, or it may initiate long-term changes, which modulate future neuronal responses to sensory stimuli.

Therapeutic and chemical developments of cholecystokinin receptor ligands

Cholecystokinin (CCK) is an important 'brain-gut' hormone located both in the gastrointestinal (GI) system and in the CNS. At least two different G-coupled high affinity receptors have been identified: the CCK-A and the CCK-B receptors. Although the complex biological role of CCK is, as yet, not fully understood, its connection with many different physiological processes both at the GI level and at the CNS level is now well established. There is much potential for therapeutic use of CCK receptor ligands, however, clear investigations have yet to be completed. Several chemical families have been investigated over the last 20 years to find potent, subtype selective and stable CCK receptor agonists and antagonists. The main goal was to discover new therapeutic drugs acting on GI and/or on CNS diseases and also, to obtain powerful pharmacological tools that could permit a better understanding of the biological role of CCK. Despite promising results from investigations into medicinal chemistry of CCK receptor ligands, the therapeutical applications of these ligands still remains to be defined. This article reviews the main biological role of CCK, the therapeutic potential of CCK-A and CCK-B receptor agonists and antagonists and the common compounds from the different families of ligands.

Effects of spiroglumide, a gastrin receptor antagonist, on acid secretion in humans

BACKGROUND

A gastrin receptor antagonist, CR2194 (spiroglumide), was used to explore the physiological role of gastrin in regulating gastric acid secretion in humans.

MATERIALS AND METHODS

The effect of CR2194 on inhibition of gastrin-stimulated acid output was evaluated in a four-period crossover study. Each subject received intravenous doses of 1, 2.5 or 7.5 mg kg-1 h-1 CR2194 or saline (control) followed by graded increasing doses of gastrin (6.4-800 pmol kg-1 h-1). Secondly, the effect of CR2194 on meal-stimulated intragastric acidity was evaluated by infusing either saline (control) or CR2194 (7.5 mg kg-1 h-1) before and after food ingestion.

RESULTS

Acid secretion was dose-dependently inhibited by CR2194. With CR2194, acidity was significantly reduced in the pre-meal and post-prandial period (P < 0.01 and 0.002 respectively), and the integrated gastrin response was augmented to 8.0 +/- 1.4 ng mL-1 240 min compared with 1.5 +/- 0.8 ng mL-1 240 min in the control experiment (P < 0.01). Finally, acid secretion in response to sham feeding was significantly reduced: 15.9 +/- 0.9 mmol 90 min-1 in the control experiment compared with 2.8 +/- 0.9 mmol 90 min-1 during CR2194 infusion (P < 0.05).

CONCLUSION

Gastrin receptor blockade with CR2194 alters gastric acid secretion in response to food ingestion or to sham feeding. The results support a physiological role for gastrin in regulating acid secretion in humans.

CCK receptor antagonists

1. The peptide hormone and neurotransmitter, cholecystokinin, is widely distributed throughout the gastrointestinal tract and central nervous system and mediates a diverse number of biological functions. 2. Two receptor subtypes, CCK-A and CCK-B, have been identified by both pharmacological characterization and molecular cloning. The CCK-A receptor is the predominant peripheral CCK receptor subtype and the CCK-B receptor is the predominant central CCK receptor. In addition, there are discrete populations of CCK-A receptors in the brain and CCK-B receptors are present in gastric mucosa. 3. Subtype selective antagonists have been developed which discriminate between the two receptor subtypes. One of the major chemical classes has exploited a benzodiazepine template present in asperlicin which was initially discovered in a natural product screen for CCK receptor antagonists. 4. The structurally related benzodiazepines L-365,260, L-740,093, and YM022 are selective antagonists of the CCK-B receptor subtype. Their in vitro pharmacological profiles have been characterized using the human CCK-B receptor expressed in CHO cells. 5. L-365,260 behaves in a manner consistent with that of a competitive antagonist and both L-740,093 and YM022 behave as insurmountable CCK-B receptor antagonists in vitro.

Effect of a new CCK-A receptor antagonist, dexloxiglumide, on the exocrine pancreas in the rat

The effect of dexloxiglumide, a new potent cholecystokinin (CCK) antagonist, on pancreatic enzyme secretion and growth was studied in the rat. Pancreatic exocrine secretion was studied both in vitro (isolated and perfused pancreatic segments) and in vivo (anaesthetized animals with cannulation of the common bile duct) whereas the trophic effect was investigated after short-term (7 days) administration of the CCK-agonist, caerulein, or camostate (a potent trypsin inhibitor), with or without dexloxiglumide. CCK-8 stimulated amylase release from in vitro pancreatic segments in a concentration-dependent manner. Dexloxiglumide displaced the concentration response curves to CCK-8 to the right without affecting the maximum response, suggesting a competitive antagonism. The Schild plot analysis of data gave a straight line with a slope (0.90 +/- 0.36) not significantly different from unity. The calculated pA2 for dexloxiglumide was 6.41 +/- 0.38. In vivo experiments confirmed results from in vitro studies since intravenous dexloxiglumide reduced pancreatic exocrine secretion induced by submaximal CCK-8 stimulation (0.5 nmol/kg/h) in a dose-dependent manner, the ID50 being 0.64 mg/kg. Both exogenous and endogenous (released by camostate) CCK increased the weight of the pancreas, the total pancreatic protein and DNA, trypsin and amylase content. Dexloxiglumide (25 mg/kg), administered together with caerulein (1 microgram/kg), reduced the peptide-induced increase in pancreatic weight, protein and enzyme content. Similarly, when dexloxiglumide was given together with camostate (200 mg/kg), all the observed changes were reduced by concomitant administration of the antagonist. These results demonstrate the ability of dexloxiglumide to antagonize the effects of CCK on pancreatic secretion and growth, suggesting that this compound is a potent and selective antagonist of CCK-A-receptors in the pancreas.

Analysis of the variation in the action of L-365,260 at CCKB/gastrin receptors in rat, guinea-pig and mouse isolated gastric tissue assays

1. Since L-365,260 was first described as a selective antagonist at cholecystokinin (CCK)B/gastrin receptors, we have used it periodically as a reference compound in isolated tissue assays of guinea-pig gastric muscle and lumen-perfused stomachs from mouse and immature rat. L-365,260 behaved as a surmountable antagonist and produced parallel rightward shifts of pentagastrin concentration-effect curves' in each of the replicate experiments. The experiments were performed by several different experimenters in the same laboratories over a five year period. 2. In the isolated, lumen-perfused, immature rat stomach assay, L-365,260 behaved as a simple competitive antagonist (Schild plot slope = 1.00 +/- 0.10, pKB = 7.54 +/- 0.03 from a global analysis of the data) acting at a homogeneous population of receptors in five separate, highly-reproducible, experiments. In contrast, the replicate data sets obtained from the interaction in the isolated, lumen-perfused mouse stomach and guinea-pig gastric muscle assays, over the same period, were not consistent with the presence of a single receptor population. The guinea-pig gastric muscle data were relatively reproducible between experiments but some individual Schild plot slopes and the slope estimated from a global analysis of all the data were significantly less than unity (slope = 0.80 +/- 0.07, pA2 = 8.56 +/- 0.05 from the global analysis). The data obtained in the mouse stomach were significantly more variable than that obtained in the same assay, during the same period, from the interaction between histamine and the H2-receptor antagonist, famotidine. The individual Schild plot slopes ranged from being very flat (0.20) to being not significantly different from unity (1.23) and the pA2 values ranged from 7.68 to 8.70. 3. Overall, the data could be accounted for by assuming the variable expression of two receptor subtypes across the assays. The rat stomach appeared to express a single receptor characterized by a low affinity constant for L-365,260 (pKB approximately 7.5). The guinea-pig gastric muscle and mouse stomach data could be explained by the presence of this receptor and a second one characterized by a high affinity constant for L-365,260 (pKB approximately 8.6). The activity of the two proposed receptor subtypes was consistent between experiments in the guinea-pig and the high affinity receptor appeared to be predominant. In contrast, the mouse stomach data could only be simulated by assuming that the proportion and absolute number of each subtype varied significantly between the replicate experiments. 4. The L-365,260 affinity estimates at the inferred receptor subtypes were indistinguishable from those obtained in a corresponding analysis of the behaviour of L-365,260 in CCKB/gastrin receptor radioligand binding experiments in guinea-pig gastric gland and mouse and rat cerebral cortex preparations.

Cytosolic Ca2+ evaluation in rabbit parietal cells: a novel method to screen gastrin receptor antagonists

We have evaluated the application of the fura-2 method to detect cytosolic Ca2+ increase in gastric cells expressing CCKB/gastrin receptors, in order to screen gastrin receptor antagonists, as an alternative to functional studies. We have characterized the receptors on parietal cell suspension from rabbit gastric mucosa and validated the method using both the CCKB and CCKA receptor agonists and antagonists. Human gastrin I (gastrin) (0.1 nM-4 microM) and sulfated cholecystokinin 26-33 (CCK-8) (0.01 nM-2 microM) dose-dependently augmented cytosolic Ca2+. The efficacies of the two agonists were similar, but the potency of CCK-8 (EC50 1.03 nM) was about 10-fold greater than that of gastrin (11 nM). Response to a submaximal dose of gastrin (50 nM) was dose-dependently blocked by the CCKB-receptor antagonists CAM-1028 (4-[[2-[[3-(1 H-indol-3-yl)-2-methyl-1-oxo-2-[[[1,7,7-trimethylbicyclo[2, 2,1]hept-2-yl)oxy]carbonyl]amino]propyl]amino]-1-phenylethyl]amino-4-oxo -[1 S-1 alpha, 2 beta [S'(S')4 alpha]]-butanoate-N-methyl-D-glucamine) (IC50 1.9 nM), L-365,260 (3 R(+)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1 H-1, 4-benzodiazepin-3-yl)-N'-(3-methylphenyl)urea) (IC50 10 nM) and spiroglumide ((R)-4-(3,5-dichlorobenzamido)-5-(8-azaspiro[4.5]decan -8-yl)-5-oxopentanoic acid) (IC50 2 microM). The results were in agreement with those obtained from binding studies in guinea-pig cortical membranes. The model was employed to optimize the synthesis of a new class of spiroglumide analogues which led to a new molecule, (S)-4-¿(R)-4'-(3,5-dichlorobenzoylamino)-5'-(8-azaspiro[4.5] decan-8-yl)-5'-oxo)-pentanoylamino-5-(1-naphthylamino)-5-oxo pentanoic acid (CR 2622), whose potency was about 100-fold greater than that of spiroglumide. CR 2622, as well as the other CCKB receptor antagonists tested, exhibited no effect on basal [Ca2+]i. The simplicity and the reproducibility of this method suggest that it is a useful model to screen gastrin and antigastrin activity in parallel or as an alternative to binding studies.

Effect of CCK and its antagonists on gastric emptying

Cholecystokinin (CCK) belongs to the group of substances known as brain-gut peptides: it functions both as a neuropeptide and a gut hormone. The peptide and its synthetic derivatives (like for instance CCK-8 and the amphibian counterpart caerulein) significantly delay emptying of gastric contents in both animals and humans. The fact that CCK, in doses mimicking postprandial plasma levels, strongly affects emptying rate suggests the peptide to be a physiologic regulator of gastric emptying. Unfortunately, clear definition of the role of CCK in the physiology of gastric motor activity has long been hampered by the lack of specific and potent non-peptide antagonists of CCK-receptors. The availability of such compounds has stimulated a broad array of investigations into the physiological actions of this hormone and examination of its putative role in certain diseases. This paper summarizes the available data concerning the effect of CCK and its antagonists on gastric emptying. The use of selective CCK-antagonists has allowed to establish that the gastric motor effect of the peptide is direct and mediated through the stimulation of CCK-A receptors. As a consequence, CCK-A antagonism results in acceleration of emptying rate under certain experimental and clinical conditions. This peculiar pharmacologic effect of CCK-A antagonists, which could be useful in the treatment of functional dyspepsia (idiopathic or diabetic), gastroparesis and gastro-esophageal reflux disease (where patients often display a delayed emptying rate of solid food) needs to be further investigated, in order to fully explore their potential as gastrokinetic drugs.