Synthesis and X-ray crystallographic analysis of quinazolinone cholecystokinin/gastrin receptor ligands

Crystal structure of 6-iodo-3-phenyl-2-propylquinazolin-4(3H)-one, C17H15IN2O

C17H15IN2O, monoclinic, C2 (no. 5), a = 23.6958(12) Å, b = 5.5334(2) Å, c = 15.9712(9) Å, β = 132.329(3)°, V = 1548.16(13) Å3, Z = 4, R gt(F) = 0.046, wR ref(F 2) = 0.093, T = 296(2) K.

Synthesis and evaluation of a fluorescent non-peptidic cholecystokinin-B/gastrin receptor specific antagonist for cancer cell imaging

Fluorescent labeling has enabled a better understanding of the relationships between receptor location, function, and life cycle. Each of these perspectives contributes new insights into drug action, particularly for G protein-coupled receptors (GPCRs). The aim of this study was to develop a fluorescein derivative, FLUO-QUIN-a novel antagonist of the cholecystokinin-B/gastrin receptor. A radioligand-binding experiment revealed an IC(50) of 4.79 nm, and the antagonist inhibited gastric acid secretion in an isolated lumen-perfused mouse stomach assay (up to 51 % at 100 nm). The fluorescence properties altered upon binding to the receptor, and the fluorophore was quenched to a greater extent when free than in the bound form. FLUO-QUIN specifically bound to human pancreatic carcinoma cells, MiaPaca-2, which are known to express the receptor, as evidenced by rapid clustering followed by time-dependent receptor internalization. This proves the stability of FLUO-QUIN and its ability to penetrate vesicular membranes and reach various cell targets. Hence it might be used as an agent for the detection of CCK-B-receptor-positive tumors by fluorescence imaging.

Synthesis and structure-activity relationship of new 1,5-dialkyl-1,5-benzodiazepines as cholecystokinin-2 receptor antagonists

This article deals with the synthesis and the activities of some 1,5-dialkyl-3-arylureido-1,5-benzodiazepin-2,4-diones which were prepared as potential CCK2 antagonists, with the intention to find a possible follow up of our lead compound GV150013, showing an improved pharmacokinetic profile. The phenyl ring at N-5 was replaced with more hydrophilic substituents, like alkyl groups bearing basic functions. In some cases, the resolution of the racemic key intermediates 3-amino-benzodiazepines was also accomplished. Among the compounds synthesized and characterised so far in this class, the 5-morpholinoethyl derivative 54, was selected as potential follow up of GV150013 and submitted for further evaluation.

2-Methyl-2-phenyl-1,2-dihydro-quinazolin-4(3H)-one

In the mol­ecule of the title compound, C₁₅H₁₄N₂O, the six-membered 1,3-diaza ring assumes an envelope conformation. The two benzene ring planes are almost perpendicular to each other, making a dihedral angle of 85.53 (5)°. Supra­molecular aggregation is mainly effected by N—H⋯O hydrogen bonding.

Novel 99mTcradiolabeled quinazolinone derivative [Qn-In]: synthesis, evaluation and biodistribution studies in mice and rabbit

A quinazolinone derivative as a novel non-peptidic CCK-B receptor antagonist designated as Qn-In, was synthesized, characterized by spectroscopic techniques and evaluated for radiopharmaceutical potential. The efficiency of labeling with (99m)Tc was greater than 98% and the complex was stable for about 7 hours at 37 degrees C in presence of serum. Affinity of Qn-In was determined to be in nanomolar range by competitive binding studies on cancer cell line MDA-MB-468. Bio-distribution of (99m)Tc labeled Qn-In in mice was examined by intravenous administration and time-activity curves were generated. The ligand showed binding to most of the organs, known to express CCK-B receptor. The lack of uptake in brain may be due to the inability of the complex to cross the blood-brain barrier. Our results show that (99m)Tc labeled Qn-In ligand provides a new template for further development of non-peptidic ligands for diagnosis and therapy of diseases related with CCK-B receptor.

Liquid chromatographic enantiomer separations of novel quinazolone derivatives on quinine carbamate based chiral stationary phases using hydro-organic mobile phases

Quinine carbamate-type weak chiral anion-exchange selectors (SOs) and the respective chiral stationary phases (CSPs) have been used for the direct liquid chromatographic enantiomer separation of a wide range of chiral acids. In the present work, we demonstrate that these CSPs can also be extended to chiral discrimination of a set of neutral polar potential NMDA (N-methyl-D-aspartic acid) and/or AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) antagonist imidazo-quinazoline-dione derivatives (selectands, SAs) using acetonitrile and methanol containing hydro-organic and buffered mobile phases. The influence of mobile phase composition, column temperature and structure variation of the SAs and SOs on retention and enantioselectivity was systematically investigated to gain insight into the overall chiral recognition mechanism. As was expected for the reversed-phase mode, acetonitrile has a stronger eluotropic effect compared to methanol. Except for two analytes, the acetonitrile containing mobile phases provided baseline resolution (R(S)) of the enantiomers with R(S) values ranging between 1.68 and 2.76. Using methanol as the organic modifier enhanced the enantioselectivity. The enthalpic and entropic terms for the SO-SA association were calculated from the linear van't Hoff plots. Data reveal that the enantiomer separations are predominantly enthalpically driven.

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.

Palladium-catalyzed cyclocarbonylation of o-iodoanilines with heterocumulenes: regioselective preparation of 4(3H)-quinazolinone derivatives

A catalyst system comprising palladium acetate-bidentate phosphine is effective for the cyclocarbonylation of o-iodoanilines with heterocumulenes at 70-100 degrees C for 12-24 h to give the corresponding 4(3H)-quinazolinone derivatives in good yields. Utilizing o-iodoaniline with isocyanates, carbodiimides, and ketenimines for the reaction, 2,4-(1H,3H)-quinazolinediones, 2-amino-4(3H)-quinazolinones and 2-alkyl-4(3H)-quinazolinones were obtained, respectively. The nature of the substrates including the electrophilicity of the carbon center of the carbodiimide, and the stability of the ketenimine, influence the product yields of this reaction. Urea-type intermediates are believed to be generated first in situ from the reaction of o-iodoanilines with heterocumulenes, followed by palladium-catalyzed carbonylation and cyclization to yield the products.

Characterization of potential NMDA and cholecystokinin antagonists I. acid-base properties of 2-methyl-4-oxo-3H-quinazoline-3-alkyl-carboxylic acids at the molecular and submolecular levels

The protonation macroconstants (log K) of 4(3H)-quinazolone (1) and two 2-methyl-4-oxo-3H-alkyl-quinazoline-3-carboxylic acid derivatives (2,3) were determined by pH-potentiometry. The acid-base chemistry of compounds 2 and 3, where proton-bindings take place in an overlapping fashion, was described in terms of protonation microconstants as well. Microspeciation was carried out by two means: UV-pH titration (selective, pH-dependent monitoring of the N1-binding site), and deductively (using a derivative compound as covalently fixed model of one of the protonation isomers). The microconstant values obtained by the two different methods are in agreement within 0.05 log K units. Microspeciation revealed remarkable differences between the two homologue compounds (2 and 3). The microconstant values show that insertion of a second methylene moiety into the aliphatic acid side-chain (1) increases the electron-density and most basicity parameters of both functional groups; (2) significantly modifies the extent of site-site interactions in the molecule; (3) opens new conformational preferences by N1 ring nitrogen-carboxylic group intramolecular hydrogen bond formation and (4) reverses the predominantly zwitterion-involved protonation pathway into a neutral form-involved pathway. These molecules exemplify that microconstant values allow the comparative prediction and quantitative evaluation of pharmacokinetic behaviour, and signify the fact that microspeciation is a powerful tool in the process of drug development.

Characterization of potential NMDA and cholecystokinin antagonists. II. Lipophilicity studies on 2-methyl-4-oxo-3H-quinazoline-3-alkyl-carboxylic acid derivatives

The lipophilicity of 17 newly synthesized potential NMDA and cholecystokinin antagonist 2-methyl-4-oxo-3H-quinazoline-3-alkyl-carboxylic acid derivatives has been investigated. The apparent partition coefficients of two amphoteric compounds of overlapping protonation (Q1 and Q2) were determined by shake-flask method and converted into true log P values using the protonation microconstants. The difference between their lipophilicity expressed with the true partition coefficients was less, than it could be expected from the 2D structures and was explained with conformational preferences and formation of intramolecular interactions. Out of the other 15 monoprotic quinazolone compounds the lipophilicity of ten molecules (Q8-Q17, experimental set) was determined by TLC method with the help of a calibration set consisting of 12 standard molecules, five quinazolones (Q3-Q7) and seven pyrido[1,2-a]pyrimidines (PP1-PP7). In order to justify the suitability of pyrido-pyrimidines as standards for the chromatographic log P determination of quinazolones, first Q3-Q7 were examined by TLC and HPLC using PP1-PP7 for calibration. Data showed good agreement of results obtained by shake-flask and two different chromatographic methods indicating the similar chromatographic behavior of the two bicyclic systems and the relevance of PP1-PP7 to extend the calibration set of quinazolones. The obtained log P values proved mostly the expected structure-activity relationships. Some findings, however, have revealed specific partition behavior of the compounds providing useful information in the estimation of their pharmacokinetics, and these are discussed in the paper.

Pyridothiadiazinedioxides structurally related to quinazolinones cholecystokinin/gastrin receptor ligands: synthesis and biological evaluation

The synthesis of 3-aralkyl-4-aryl-4H-, 3-aralkylamino-4-aryl-4H- and 3-aralkylsulfanyl-4-aryl-4H-pyrido[4,3-e]-1,2,4-thiadiazine 1, 1-dioxides is described. Moreover, the affinity of the different compounds towards the cholecystokinin CCK-A and CCK-B receptors was evaluated. For selected compounds, affinity on the two receptor subtypes was expressed in the micromolar range. This was comparable to the affinity observed with the naturally occurring CCK receptor antagonist asperlicin.

Novel nonpeptide CCK-B antagonists: design and development of quinazolinone derivatives as potent, selective, and orally active CCK-B antagonists

We have designed a novel series of CCK-B receptor antagonists by combining key pharmacophores, an arylurea moiety of 1 and a quinazolinone ring of 3, from two known series. Our earlier studies showed that compounds with methylene linkers in our "target" produced moderate binding affinity and selectivity for CCK-B receptors, whereas its higher and lower homologues resulted in loss of affinity. Introduction of -NH- as a linker dramatically enhanced binding affinity and selectivity for CCK-B receptors, thus providing several compounds with single-digit nanomolar binding affinity and excellent selectivity. Analogous to the earlier studies of the series of quinazolinone derivatives 3, we also found 3-isopropoxyphenyl as a preferred substitution on the N-3 quinazolinone. Electron-withdrawing substitutions on the urea terminal phenyl ring enhanced the CCK-B potency. Representative compounds of this series were tested in the functional assay and showed pure antagonist profiles. Compounds 51 and 61 were orally active in the elevated rat X-maze test. These compounds were also evaluated for their pharmacokinetic profile. The absolute oral bioavailability of compound 61 was 22% in rats.

Synthesis and biological evaluation of new 3-aralkylamino-2-aryl-2H-1, 2,4-pyridothiadiazine 1,1-dioxides as potential CCK-receptor ligands

A series of 2-aralkyl-4H-pyridothiadiazine 1,1-dioxides and 3-aralkylamino-2-aryl-2H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides structurally related to quinazolinone CCK receptor antagonists were synthesized and evaluated as CCK-A and CCK-B receptor ligands. The compounds were effective as cholecystokinin-ligands in the micromolar range of concentration, c.f. the cholecystokinin receptor antagonists asperlicin, lorglumide or benzotript, and were thus less potent than the best quinazolinones previously reported. Although the compounds were unsuitable for drug use, the work contributed to our understanding of the chemistry of unusual 2,3-disubstituted pyridothiadiazinedioxides.

Role of N- and C-terminal substituents on the CCK-B agonist-antagonist pharmacological profile of Boc-Trp-Phg-Asp-Nal-NH2 derivatives

Among the CCK derivatives, the tetrapeptide Boc-Trp-Phg-Asp-Nal-NH2 (1) behaves as a short potent CCK-B agonist which led to the development of an efficient peptidase-resistant CCK-B antagonist by bismethylation of its terminal CONH2 group. Further modifications of the N- and C-terminal moieties of 1 have been performed and are described in this paper, together with the pharmacological profile of the novel synthetized compounds. Introduction of more bulky substituents than NalNH2 on the C-terminal part decreased the CCK-B receptor binding affinity. In the series of N-protected tetrapeptides X30-Phg31-Asp32-Nal33-N(CH3)2, the Boc-substituent was shown to be optimal among the N-protecting groups Boc, 2Adoc, propionyl or acetyl when X = Trp. On the other hand, when X = alpha MeTrp, its optimal N-protecting group was 2Adoc and its configuration was preferentially D. In the newly synthesized compounds, 13: 2Adoc-D-alpha MeTrp-Phg-Asp-NalN(CH3)2 and 16: 2Adoc-D-alpha MeTrp-Phg-Asp-NalNH2 had the best CCK-B receptor affinities (KI = 3.5 and 3.4 nM, respectively) and were selected for further biological evaluation. Interestingly, when tested for their capacity to influence inositol phosphate formation, induced by CCK8 in CHO cells transfected with the rat CCK-B receptor, compound 13 behaved as a full CCK-B antagonist with an IC50 value of 18 +/- 1 nM, being as potent as the antagonist L-365,260 and PD-134,308 (IC50 values respectively, 39 +/- 17 and 30 +/- 2 nM), whereas compound 16 was found to behave as a partial CCK-B agonist. Indeed 16 behaved as an antagonist on the firing rate of rat CA1 hippocampal neurons and acted as an agonist in the pentagastrin stimulated gastric acid secretion (EC50 = 12 nmol/kg) in anesthetized rats. Compound 13 in contrast, was found to inhibit the pentagastrin action at a dose (ID50 = 0.56 mumol/kg) similar to the potent antagonist PD-134,308 (ID50 = 0.4 mumol/kg). The antagonist/agonist properties of compounds 13 and 16 show that both N- and C-terminal substituents modulate the pharmacological properties in the Boc-CCK4 derivatives presented here.

Pharmacological properties of ureido-acetamides, new potent and selective non-peptide CCKB/gastrin receptor antagonists

We present here the pharmacological properties of 3 ureido-acetamide members of a novel family of non-peptide cholecystokinin-B (CCKB) receptor antagonists. RP 69758 (3-(3-[N-(N-methyl N-phenyl-carbamoylmethyl) N-phenyl-carbamoylmethyl] ureido)phenylacetic acid), RP 71483 ((E)-2-[3-(3-hydroxyiminomethyl phenyl) ureido] N-(8-quinolyl) N-[(1,2,3,4-tetrahydro 1-quinolyl)carbonylmethyl]acetamide) and RP 72540 ((RS)-2-[3-(3-[N-(3-methoxy phenyl) N-(N-methyl N-phenyl-carbamoylmethyl) carbamoylmethyl] ureido) phenyl] propionic acid) displayed nanomolar affinity for guinea-pig, rat and mouse CCKB receptors labelled with [3H]pCCK-8 or with the selective CCKB receptor ligand [3H]pBC264. RP 69758 and RP 72540 showed selectivity factors in express of 200 for CCKB versus CCKA receptors. All three compounds had also high affinity for gastrin binding sites in the stomach. The ureido-acetamides behaved as potent antagonists of CCK-8-induced neuronal firing in rat hippocampal slices in vitro, a functional model of brain CCKB receptor mediated responses. RP 69758 is also a potent gastrin receptor antagonist in vivo that dose dependently inhibits gastric acid secretion induced by i.v. injection of pentagastrin in the rat. None of the three ureido-acetamides, at concentrations up to 1 microM, significantly blocked CCK-8-evoked contractions of the guinea-pig ileum in vitro, a CCKA receptor bioassay. In ex vivo binding studies, i.p. administration of RP 69758 and RP 72540 resulted in a dose-dependent inhibition of [3H]pCCK-8 binding in mouse brain homogenate. However, the relative penetration of these ureido-acetamides into the forebrain after peripheral administration was below 0.01%. RP 71483 did not appear to cross the blood-brain barrier in quantities sufficient to prevent [3H]pCCK-8 binding at low doses, a property that makes it suitable for the exploration of the peripheral versus central origin of the behavioural effects observed following systemic administration of CCK. RP 69758, RP 71483 and RP 72540 are highly potent and selective non-peptide CCKB receptor antagonists which are useful tools to explore the physiological functions of CCKB receptors.