3,4-Dihydroquinazoline derivatives as novel selective T-type Ca2+ channel blockers

One-Pot Three-Component Reaction for the Synthesis of 3,4-Dihydroquinazolines and Quinazolin-4(3H)-ones

A highly efficient and straightforward one-pot synthesis of diversely substituted 3,4-dihydroquinazolines and quinazolin-4(3H)-ones has been achieved through a domino three-component assembly reaction of arenediazonium salts, nitriles, and bifunctional aniline derivatives. This new protocol involves three C-N bond formations through the initial formation of N-arylnitrilium intermediates from arenediazonium salts and nitriles, followed by the sequential nucleophilic addition and cyclization reactions with bifunctional anilines, leading to such N-heterocyclic compounds of biological and pharmacological importance. This method offers a simple, expedient, and robust approach with the use of amenable and easily accessible reactants/reagents under metal-free mild conditions, good functional group tolerance, and high efficiency. The synthetic applications were also demonstrated by derivatization of the products obtained from these processes and syntheses of a diverse range of valuable polycyclic N-heterocycles.

A Concise and Efficient CuI-catalyzed Synthesis of Diimino Dihydroquinazoline Derivatives from Isocyanides and Guanidines Derivatives Through Intramolecular C-H Activation

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A novel series of diimino dihydroquinazoline derivatives were synthesized from isocyanides and guanidine analogs in quantitative yields by applying an efficient, inexpensive, one-pot copper-catalyzed intramolecular C-H activation reaction under mild conditions. The structures were confirmed on the basis of IR, 1HNMR, 13C NMR, mass spectral and elemental analysis data. The protocol offers advantages like short reaction time, simple workup process, high yields, and an environmentally benign methodology. Interestingly, better results (yield = 82%) were observed in terms of the yield obtained by using a mixture of CuI, Cs2CO3 and acetonitrile as the catalyst, base and solvent, respectively. The data also suggested that compound 5i is produced with the highest yield (87%) from the corresponding diisopropyl carbon diimide, 4-nitroaniline and phenyl isocyanide. Finally, a mechanistic explanation for the reaction promoted by cuprous iodide (CuI) was proposed on the basis of previous investigations and our experimental observations.

A bifunctional iminophosphorane squaramide catalyzed enantioselective synthesis of hydroquinazolines via intramolecular aza-Michael reaction to α,β-unsaturated esters

An efficient synthesis of enantioenriched hydroquinazoline cores via a novel bifunctional iminophosphorane squaramide catalyzed intramolecular aza-Michael reaction of urea-linked α,β-unsaturated esters is described. The methodology exhibits a high degree of functional group tolerance around the forming hydroquinazoline aryl core and wide structural variance on the nucleophilic N atom of the urea moiety. Excellent yields (up to 99%) and high enantioselectivities (up to 97 : 3 er) using both aromatic and less acidic aliphatic ureas were realized. The potential industrial applicability of the transformation was demonstrated in a 20 mmol scale-up experiment using an adjusted catalyst loading of 2 mol%. The origin of enantioselectivity and reactivity enhancement provided by the squaramide motif has been uncovered computationally using density functional theory (DFT) calculations, combined with the activation strain model (ASM) and energy decomposition analysis (EDA).

The activation of both aromatic and aliphatic ureas as N-centered nucleophiles in intramolecular Michael addition reactions to α,β-unsaturated esters was achieved under bifunctional iminophosphorane squaramide superbase catalysis.

Friedel-Crafts synthesis of bis(trifluoromethylated)-4-aryl-3,4-dihydroquinazolines, bis(trifluoromethylated)-3,4-dihydroquinazoline-4-ols and trifluoromethyl arylketoimines using N-aryltrifluoroacetimidoyl chlorides and benzene derivatives

A simple and straightforward approach to access biologically important N-heterocycles, namely bis(trifluoromethylated)-4-aryl-3,4-dihydroquinazolines, bis(trifluoromethylated)-3,4-dihydroquinazoline-4-ols and trifluoromethyl arylketoimines, as a group of important frameworks or initial substance from N-aryltrifluoroacetimidoyl chlorides with benzene derivatives via Friedel-Crafts reaction has been described. This novel strategy provides synthesis of trifluoromethylated dihydroquinazolines and trifluoromethyl arylketoimines in good to excellent yields.

The Hard-To-Close Window of T-Type Calcium Channels

T-Type calcium channels (TTCCs) are key regulators of membrane excitability, which is the reason why TTCC pharmacology is subject to intensive research in the neurological and cardiovascular fields. TTCCs also play a role in cancer physiology, and pharmacological blockers such as tetralols and dihydroquinazolines (DHQs) reduce the viability of cancer cells in vitro and slow tumor growth in murine xenografts. However, the available compounds are better suited to blocking TTCCs in excitable membranes rather than TTCCs contributing window currents at steady potentials. Consistently, tetralols and dihydroquinazolines exhibit cytostatic/cytotoxic activities at higher concentrations than those required for TTCC blockade, which may involve off-target effects. Gene silencing experiments highlight the targetability of TTCCs, but further pharmacological research is required for TTCC blockade to become a chemotherapeutic option.

Synthesis of dihydroquinazolines from 2-aminobenzylamine: N 3 -aryl derivatives with electron-withdrawing groups

The sequential N-functionalization of 2-aminobenzylamine (2-ABA) followed by cyclodehydration allowed for a straightforward and efficient synthesis of 3,4-dihydroquinazolines with N-aryl substituents bearing electron-withdrawing groups. The sequence involves an initial S_NAr displacement, N-acylation and MW-assisted ring closure. Remarkably, the uncatalyzed N-arylation of 2-ABA led to the monosubstitution product using equimolar amounts of both reagents. The individual steps were optimized achieving good to excellent overall yields of the desired heterocycles, avoiding additional protection and deprotection steps. A mechanistic interpretation for the cyclodehydration reaction promoted by trimethylsilyl polyphosphate (PPSE) is also proposed on the basis of literature data and our experimental observations.

Synthesis of 1,2-Dihydroquinazolines via Rearrangement of Indazolium Salts

A convenient synthesis of 1,2-dihydroquinazolines via rearrangement of indazolium salts was described. A mechanistic study using isotope labeling experiment revealed that the rearrangement passes through cleavage of N-N bond/ring opening after basic deprotonation of 2-benzyl in indazolium salts to yield intermediate E, which proceeds in an intramolecular N-nucleophilic addition to form the observed product. Computational analyses imply that the pathway of the rearrangement is determined by the energy barriers of the ring-closing process and the stability of the product.

Palladium-catalyzed selective synthesis of 3,4-dihydroquinazolines from electron-rich arylamines, electron-poor arylamines and glyoxalates

Palladium-catalyzed selective synthesis of various 3,4-dihydroquinazolines from electron-rich arylamines, electron-poor arylamines and glyoxalates was developed.

Syntheses of 3,4- and 1,4-dihydroquinazolines from 2-aminobenzylamine

A straightforward strategy for the synthesis of dihydroquinazolines is presented, which allows for the preparation of 3,4- and 1,4-dihydroquinazolines with different substitution patterns from 2-aminobenzylamine (2-ABA) as common precursor. The required functionalization of both amino groups present in 2-ABA was achieved by different routes involving selective N-acylation and cesium carbonate-mediated N-alkylation reactions, avoiding protection/deprotection steps. The heterocycles were efficiently synthesized in short reaction times by microwave-assisted ring closure of the corresponding aminoamides promoted by ethyl polyphosphate (PPE).

In silico identification of T-type calcium channel blockers: A ligand-based pharmacophore mapping approach

Limited progress has been made in the quest to identify both selective and non-toxic T-type calcium channel blocking compounds. The present research work was directed toward slaking the same by identifying the selective three dimensional (3D) pharmacophore map for T-type calcium channel blockers (CCBs). Using HipHop module in the CATALYST 4.10 software, both selective and non-selective HipHop pharmacophore maps for T-type CCBs were developed to identify its important common pharmacophoric features. HipHop pharmacophore map of the selective T-type CCBs contained six different chemical features, namely ring aromatic (R), positive ionizable (P), two hydrophobic aromatic (Y), hydrophobic aliphatic (Z), hydrogen bond acceptor (H) and hydrogen bond donor (D). However, non-selective T-type CCBs contain all the above mentioned features except ring aromatic (R). The present ligand-based pharmacophore mapping approach could thus be utilized in classifying selective vs. non-selective T-type CCBs. Further, the model can be used for virtual screening of several small molecule databases.

Asymmetric hydrogenation of quinazolinium salts catalysed by halide-bridged dinuclear iridium complexes bearing chiral diphosphine ligands

Asymmetric hydrogenation of 4-substituted quinazolinium salts catalyzed by dinuclear Ir complexes is described.

Pd-catalyzed Heck-conjoined amidation and concomitant chemoselective Michael-addition: an efficient tandem approach to highly functionalized tetrahydroquinazolines from o-haloanilines

Efficient palladium-catalyzed tandem approach for the synthesis of highly functionalized tetrahydroquinazolines from o-haloanilines with acrylates and isothiocyanates/isocyanates via Heck-conjoined amidation/thioamidation and concomitant chemoselective Michael-addition is described.

Low-voltage-activated T-type Ca2+ channel inhibitors as new tools in the treatment of glioblastoma: the role of endostatin

Ca(2+) plays a key role in intracellular signaling and controls various cellular processes such as proliferation, differentiation, cell growth, death, and apoptosis. Aberrant changes in intracellular Ca(2+) levels can promote undesired cell proliferation and migration and are therefore associated with certain tumor types. Many research groups have suggested a potential role for voltage-gated Ca(2+) channels in the regulation of tumor growth and progression, particularly T-type channels due to their unique biophysical properties. T-type channels are expressed in normal tissues throughout the body and in different types of tumors such as breast carcinoma, retinoblastoma, neuroblastoma, and glioma. It has been demonstrated that increased functional expression of the α1 subunit of T-type channels plays a role in the abnormal proliferation of glioblastoma cells. As such, siRNA-mediated knockdown of the expression of the α1 subunit of T-type channels decreases the proliferation of these cells. Moreover, pharmacological blockade of T-type channels significantly decreases tumor growth. In this review, we focus on the use of T-type channel blockers for the potential treatment of cancers, particularly highly proliferative tumors such as glioblastoma. We conclude that T-type channel blockers such as endostatin can serve as a potential therapeutic tool for tumors whose proliferation depends on increased T-type channel expression.

Poly(4-vinylpyridine) supported acidic ionic liquid: a novel solid catalyst for the efficient synthesis of 2,3-dihydroquinazolin-4(1H)-ones under ultrasonic irradiation

A novel poly(4-vinylpyridine) supported acidic ionic liquid catalyst was synthesized by the reaction of 4-vinylpyridine with 1,3-propanesultone, followed by the polymerization and the addition of the heteropolyacid. Due to the combination of polymer features and ionic liquid, it acted as a heterogeneous catalyst to effectively catalyze the cyclocondensation reaction of anthranilamide with aldehydes under ultrasonic irradiation and afforded the corresponding 2,3-dihydro-4(1H)-quinazolinones compounds in good to excellent yields. In addition, the catalyst could be easily recovered by the filtration and reused six times without significant loss of catalytic activity. More importantly, the use of ultrasonic irradiation can obviously accelerate the reaction.

Copper-catalyzed activation of α-amino peroxy and hydroxy intermediates to iminium ion precursor: an access to C4-substituted 3,4-dihydroquinazolines via oxidative cross coupling strategy

A simple and straightforward approach to access C4-substituted-3,4-dihydroquinazolines has been achieved, where copper-catalyzed activation of α-amino peroxide and hydroxide intermediates to iminium ion precursors has been realized as an important step. Reactions of these intermediates with alkynes, indoles, pyrrole, and silylenol ether afforded the structurally diverse C4-substituted-3,4-dihydroquinazoline derivatives in good yields.

Synthesis and pharmacological evaluation of 1-alkyl-N-[(1R)-1-(4-fluorophenyl)-2-methylpropyl]piperidine-4-carboxamide derivatives as novel antihypertensive agents

We synthesized and evaluated inhibitory activity against T-type Ca(2+) channels for a series of 1-alkyl-N-[(1R)-1-(4-fluorophenyl)-2-methylpropyl]piperidine-4-carboxamide derivatives. Structure-activity relationship studies have revealed that the isopropyl substituent at the benzylic position plays an important role in exerting potent inhibitory activity, and the absolute configuration of the benzylic position was found to be opposite that of mibefradil, which was first launched as a new class of T-type Ca(2+) channel blocker. Oral administration of N-[(1R)-1-(4-fluorophenyl)-2-methylpropyl]-1-[2-(3-methoxyphenyl)ethyl]piperidine-4-carboxamide (17f) lowered blood pressure in spontaneously hypertensive rats without inducing reflex tachycardia, an adverse effect often caused by traditional L-type Ca(2+) channel blockers.

T-type calcium channels inhibitors: a patent review

IMPORTANCE OF THE FIELD

T-type calcium channels are transmembrane proteins that regulate calcium entry in the cell in a voltage-dependent manner. Intracellular calcium levels are the key to many physiological processes, ranging from neuron firing to cardiac pacemaking. Inhibition of T-type calcium channels is heralded as a potential treatment to peripheral and CNS disorders, including hypertension, heart failure, sleep, epilepsy, drug addiction and neuropathic pain.

AREAS COVERED IN THIS REVIEW

A comprehensive summary of patent literature disclosing T-type calcium channels inhibitors is provided.

WHAT THE READER WILL GAIN

In all, 46 patent applications including 15 chemical structure classes are reviewed. Available in vitro, in vivo and clinical results are also discussed.

TAKE HOME MESSAGE

Several selective T-type calcium channels inhibitors with demonstrated in vitro and in vivo effects, including one Phase I clinical candidate, are now available. While future clinical results will be paramount to assess target validity in patients, these novel inhibitors represent excellent tools to further investigate the role of T-type channels in pathophysiological conditions.

Synthesis and SAR study of T-type calcium channel blockers. Part II

3,4-Dihydroquinazoline derivatives have been known to be the novel and potent T-type calcium channel blockers. From a systematic variation of 3,4-dihydroquinazoline derivative 5c (KYS05043), plausible SAR results were established. It was revealed that a 5-(dimethylamino)pentylamino group at R(1), a biphenyl group at R(2), and a benzyl amido group at R(3)in the 3,4-dihydroquinazoline backbone are closely related with the channel selectivity (T/N-type) as well as the potency based on the discovery of 6k (KYS05090).

T-type Ca2+ channel blockers suppress the growth of human cancer cells

In order to further clarify the role of T-type Ca(2+) channels in cell proliferation, we have measured the growth inhibition of human cancer cells by using our potent T-type Ca(2+) channel blockers. As a result, KYS05090, a most potent T-type Ca(2+) channel blocker, was found to be as potent as doxorubicin against some human cancer cells without acute toxicity. Therefore, this letter provides the biological results that T-type calcium channel is important in regulating the important cellular phenotype transition leading to cell proliferation, and thus novel T-type Ca(2+) channel blocker presents new prospects for cancer treatment.

Discovery of potent T-type calcium channel blocker

The intensive SAR study of 3,4-dihydroquinazoline series led to the most potent compound 10 (KYS05090: IC(50)=41+/-1 nM) against T-type calcium channel and its potency is nearly comparable to that of Kurtoxin. As a small organic molecule, this compound showed the highest blocking activity reported to date.

Synthesis and biological evaluation of novel T-type calcium channel blockers

3,4-Dihydroquinazoline analogues substituted by N-methyl-N-(5-pyrrolidinopentyl)amine at the 2-position were synthesized and their blocking effects were evaluated for T- and N-type calcium channels. Compound 11b (KYS05080), compared to mibefradil (IC50=1.34+/-0.49 microM), was about 5-fold potent (IC50=0.26+/-0.01 microM) for T-type calcium channel (alpha1G) blocking and its selectivity of T/N-type was also improved (7.5 versus 1.4 of mibefradil).

3D pharmacophore based virtual screening of T-type calcium channel blockers

Virtual screening of the commercial databases was done by using a three dimensional pharmacophore previously developed for T-type calcium channel blockers using CATALYSTtrade mark program. Biological evaluation of 25 selected virtual hits resulted in the discovery of a highly potent compound VH04 with IC(50) value of 0.10 microM, eight times as potent as the known selective T-type calcium channel blocker, mibefradil. Search for similar compounds yielded several hits with micro-molar IC(50) values and high T-type calcium channel selectivity. Based on the structure of the virtual hits, small molecule libraries with novel scaffolds were designed, synthesis and biological evaluation of which are currently in progress. This result shows a successful example of ligand based drug discovery of potent T-type calcium channel blockers.

Growth inhibition of human cancer cells in vitro by T-type calcium channel blockers

This paper describes the preliminary biological results that novel T-type calcium channel blockers inhibit the growth of human cancer cells by blocking calcium influx into the cell, based on unknown mechanism on the cell cycle responsible for cellular proliferation. Among the selected compounds from compound library, compound 9c (KYS05041) was identified to be nearly equipotent with Cisplatin against some human cancers in the micromolar range.

Morpholin-2-one derivatives as novel selective T-type Ca2+ channel blockers

Morpholin-2-one-5-carboxamide derivatives were prepared by using the one-pot Ugi multicomponent reaction and evaluated for blocking effects on T- and N-type Ca(2+) channels. Among them, compound 5i produced the highest potency (IC(50)=0.45+/-0.02 microM), while compounds 5d, 5f, 5k, 5n, 5o, and 6m produced relatively high potency as well as selectivity on T-type Ca(2+) channels. These novel scaffolds showed potent and selective T-type Ca(2+) channel blocking activities.

Synthesis and SAR studies of a novel series of T-type calcium channel blockers

For the novel, potent, and selective T-type Ca2+ channel blockers, a series of sulfonamido-containing 3,4-dihydroquinazoline derivatives were prepared and evaluated for their blocking actions on T- and N-type Ca2+ channels. Among them, 9c (KYS05064, IC50 = 0.96 +/- 0.22 microM) was found to be as potent as Mibefradil and also showed the highest selectivity for T-type Ca2+ channel with no effect on N-type Ca2+ channel.

Towards selective antagonists of T-type calcium channels: design, characterization and potential applications of NNC 55-0396

NNC 55-0396 is a structural analog of mibefradil (Ro 40-5967) that inhibits both T-type and high-voltage-activated (HVA) Ca2+ channels with a higher selectivity for T-type Ca2+ channels. The inhibitory effect of mibefradil on HVA Ca2+ channels can be attributed to a hydrolyzed metabolite of the drug: the methoxy acetate side chain of mibefradil is removed by intracellular enzymes, thus it forms (1S,2S)-2-(2-(N-[(3-benzoimidazol-2-yl)propyl]-N-methylamino)ethyl)-6-fluoro-1,2,3,4-tetrahydro-1-isopropyl-2-naphtyl hydroxy dihydrochloride (dm-mibefradil), which causes potent inhibition of HVA Ca2+ currents. By replacing the methoxy acetate chain of mibefradil with cyclopropanecarboxylate, a more stable analog was developed (NNC 55-0396). The acute IC50 of NNC 55-0396 to block recombinant Cav3.1 T-type channels expressed in HEK293 cells is approximately 7 muM, whereas 100 microM NNC 55-0396 has no detectable effect on high voltage-activated currents in INS-1 cells. Block of T-type Ca2+ current was partially reduced by membrane hyperpolarization and was enhanced at high stimulus frequency. Washing NNC 55-0396 out of the recording chamber did not reverse the T-type Ca2+ current activity, suggesting that the compound dissolves in or passes through the plasma membrane to exert its effect; however, intracellular perfusion of the compound did not block T-type Ca2+ currents, arguing against a cytoplasmic route of action. We conclude that NNC 55-0396, by virtue of its modified structure, does not produce the metabolite that causes inhibition of L-type Ca2+ channel channels, thus rendering it more selective to T-type Ca2+ channels.

New insights in the pharmacological therapy of arterial hypertension

PURPOSE OF REVIEW

Despite the large number of antihypertensive drugs available, their usefulness is limited due to low efficacy, side effects, poor patient compliance and failure to reduce the cardiovascular risk to the level of the general population. These limitations have stimulated the research and development of new antihypertensive drugs, which we briefly review herein.

RECENT FINDINGS

Novel antihypertensive drugs under development include new oral renin inhibitors, brain aminopeptidase A inhibitors, angiotensin-converting enzyme 2 modulators, short-acting L-type Ca channel blockers, new T-type Ca channel blockers, inhibitors of vascular NAD(P)H oxidase, angiotensin-converting enzyme crosslink breakers, Rho kinase inhibitors, renal Na/K ATPase inhibitors, potassium channel openers and drugs combining different mechanisms of action.

SUMMARY

Essential hypertension is a multifactorial and multigenic disorder, which means that various mechanisms contribute to a greater or lesser extent to increasing blood pressure. Drugs combining several mechanisms of action or combinations of antihypertensive drugs with those targeting other risk factors may offer an alternative to reduce overall cardiovascular risk. As we improve our understanding of essential hypertension, it should be possible to develop safer and more effective antihypertensive drugs. The risk/benefit ratio of these new existing antihypertensive drugs will require long-term endpoint assessment studies.

Synthesis and biological activity of 3,4-dihydroquinazolines for selective T-type Ca2+ channel blockers

We have synthesized 3,4-dihydroquinazoline derivatives for the potent and selective T-type Ca(2+) channel blockers and evaluated for their inhibitory activities against two subtypes T-type Ca(2+) channels and N-type Ca(2+) channels. Among them, 5b (KYS05044, IC(50)=0.56+/-0.10 microM) was identified as potent T-type Ca(2+) channel blocker with in vitro selectivity profile at meaningful level (T/N-type, SI=>100).