Novel pyrimidine-pyridine hybrids: Synthesis,cyclooxygenase inhibition,anti-inflammatory activity and ulcerogenic liability

Some derivatives containing pyrido[2,3-d:6,5d′]dipyrimidine-4,5-diones (9a-f), tetrahydropyrido[2,3-d]pyrimidine-6-carbonitriles (11a-c) and 6-(4-acetylphenyl)-2-thioxo-2,3,5,6,7,8-hexahydro-1H-pyrimido[4,5-d]pyrimidin-4-one (12) were synthesized from 6-amino-2-thioxo-2,3-dihydro-1H-pyrimidin-4-one (8). The anti-inflammatory effect of these candidates was determined and the ulcer indices were calculated for active compounds. 7-Amino-5-(3,4,5-trimethoxyphenyl)-4-oxo-2-thioxo-1,2,3,4-tetrahydropyrido[2,3-d] pyrimidine-6-carbonitrile (11c) exhibited better edema inhibition than celecoxib. Moreover, compounds 9b, 9d and 11c revealed better COX-2 inhibitory activity in a range (IC₅₀ = 0.25–0.89 µM) than celecoxib (IC₅₀ = 1.11 µM). Regarding ulcerogenic liability, all of the compounds under the study were less ulcerogenic than indomethacin. Molecular docking studies had been carried on active candidates 9d and 11c to explore action mode of these candidates as leads for discovering other anti-inflammatory agents.     

Synthesis and cytokinin activity of N-acylaminodeazapurines

Three 7-acylaminoimidazo[4,5-b]pyridines, namely 7-pentanoylaminoimidazo[4,5-b]pyridine (1), 7-benzoylaminoimidazo[4,5-b]pyridine(2), and 7-(2-furoylamino)imidazo[4,5-b]pyridine(3), six 4-acylaminoimidazo[4,5-c]pyridines, namely 4-propionylaminoimidazo[4,5-c]pyridine(4), 4-butyryl-aminoimidazo[4,5-c]pyridine(5), 4-pentanoylaminoimidazo[4,5-c]pyridine(6) 4-hexanoylaminoimidazo[4,5-c]pyridine(7),4-benzoylaminoimidazo[4,5-c]pyridine(8), and 4-(2-furoylamino)imidazo[4,5-c]-pyridine(9), and seven 7-acylaminoimidazo[4,5-c]pyridines, namely 7-propionylaminoimidazo[4,5-c]-pyridine(10), 7-butyrylaminoimidazo[4,5-c]pyridine(11), 7-pentanoylaminoimidazo[4,5-c]pyridine(12), 7-hexanoylaminoimidazo[4,5-c]pyridine(13), 7-benzoylaminoimidazo[4,5-c]pyridine(14), 7-phenylacetylaminoimidazo[4,5-c]pyridine(15), and 7-(2-furoylamino)imidazo[4,5-c]pyridine(16) were synthesized and tested for their cytokinin activity with the tobacco callus bioassay. 2 showed a cytokinin activity at 1 × 10⁻⁸ M and gave a callus yield about 72% of that produced by kinetin at 1 × 10⁻⁶ M. 1, 3 and 8 showed the optimum growth responses in the range of 10⁻⁷−10⁻⁶ M. 4, 5, 7, 9–16 were slightly active. These results support previous reports that a nitrogen atom at the 3-position in the purine ring plays an important role in conferring high cytokinin activity.     

Synthesis of novel 2-amino-4-(5′-substituted 2′-phenyl-1H-indol-3′-yl)-6-aryl-4H-pyran-3-carbonitrile derivatives as antimicrobial and antioxidant agents

As a part of systematic investigation of synthesis and biological activities of indole analogues linked to various heterocyclic systems, we have synthesized new compounds viz., 2-amino-4-(5′-substituted 2′-phenyl-1H-indol-3′-yl)-6-aryl-4H-pyran-3-carbonitriles (2a–i), 4,5-diamino-6-(5′-substituted 2′-phenyl-1H-indol-3′-yl)-8-aryl-2-oxo-2,6-dihydrodipyrano [2,3-b:3,2-e]pyridine-3-carbonitriles (3a–i), 4-amino-5-(5′-substituted 2′-phenyl-1H-indol-3-yl)-7-aryl-1H-pyrano[2,3-d]pyrimidin-2(5H)-ones (4a–i), 4-amino-5-(5′-substituted 2′-phenyl-1H-indol-3′-yl)-7-aryl-1H-pyrano[2,3-d]pyrimidin-2(5H)-thiones (5a–i), 4-(5′-subtituted 2′-phenyl-1H-indol-3′-yl)-6-aryl-1,4-dihydropyrano[2,3-c]pyrazol-3-amines (6a–i) and 5-(5′-substituted 2′-phenyl-1H-indol-3′-yl)-7-aryl-3H-pyrano[2,3-d]pyrimidin-4(5H)-ones (7a–i). Antibacterial activity results revealed that, compound 6a showed promising activity versus Escherichia coli, Staphylococcus aureus and Klebsiella pneumoniae. Compound 6d exhibited good activity against S. aureus, K. pneumoniae and Pseudomonas aeruginosa. Antifungal activity results indicated that, compound 4d exhibited maximum zone of inhibition against Aspergillus oryzae and Aspergillus flavus. In case of antioxidant activity, compound 4a showed promising radical scavenging activity, ferric ions (Fe³⁺) reducing antioxidant power (FRAP) and metal chelating activity.     

Synthesis and biological evaluation of substituted 1,2,3-benzotriazines and pyrido[3,2-d]-1,2,3-triazines as inhibitors of vascular endothelial growth factor receptor-2

A novel series of substituted 1,2,3-benzotriazines and pyrido[3,2-d]-1,2,3-triazines were synthesized. The abilities of these compounds to inhibit the VEGFR-2 kinase activity and the proliferation of human microvascular endothelial cells (MVECs) were determined. 6-Methoxy-4-substituted-1,2,3-benzotriazines and 4-substituted-6-chloro-pyrido[3,2-d]-1,2,3-triazines have the abilities of inhibiting the VEGFR-2 kinase activity, but only the 4-substituted-6-chloro-pyrido[3,2-d]-1,2,3-triazines exhibit good growth inhibitory effects on MVECs. Compound 6-chloro-4-(3-trifluoromethylanilino)-pyrido[3,2-d][1,2,3]triazin (11d) is less half active than PTK787 to inhibit the VEGFR-2 kinase activity, but is more active than PTK787 to inhibit the growth of MVECs. The potential binding modes of 6d, 11d, and CTZ12 in complex with their putative intracellular target, VEGFR-2, were predicted using Surflex-Dock.     

Synthesis and biological evaluation of novel pyrazolopyrimidines derivatives as anticancer and anti-5-lipoxygenase agents

A novel series of 6-aryl-3-methyl-1-phenyl-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-ones 3a-h were synthesized in a single step via condensation of carboxamide 2 with some aromatic aldehydes (presence of iodine). Treatment of aminopyrazole 1a with acetic anhydride afforded pyrazolopyrimidines 4 which on treatment with ethyl chloroacetate in refluxing dry DMF furnished a single product identified as ethyl 2-(3,6-dimethyl-4-oxo-1-phenyl-1H-pyrazolo[3,4-d]pyrimidin-5(4H)-yl) acetate 5. On the other hand, esterification of compound 6 with different alcohol, led to the formation of new esters linked pyrazolo[3,4-d]pyrimidinones hybrids 7a-f. The reaction of compound 2 with 3-propargyl bromide gave the compound 8 used as a dipolarophile to access to triazoles (4- and 5-regioisomers (9a-e) and (10a-e), respectively) via the 1,3-dipoar cycloaddition reaction. Finally, condensation reaction of aminopyrazole 1b with α-cyanocinnamonitiles gave the new pyrazolo[1,5-a]pyrimidine-3,6-dicarbonitriles 11a-e. Structures of compounds were established on the basis of ¹H/¹³C NMR and ESI-HRMS. Compounds were screened for their cytotoxic (HCT-116 and MCF-7) and 5-lipoxygenase inhibition activities. The structure-activity relationship (SAR) was discussed.     

Synthesis of 4-substituted pyrido[2,3-d]pyrimidin-4(1H)-one as analgesic and anti-inflammatory agents

4-Substituted-pyrido[2,3-d]pyrimidin-4(1H)-ones 4a–c were synthesized by oxidation of 4-substituted-dihydropyrido[2,3-d]pyrimidin-4(1H)-ones 3a–c which were in turn prepared from arylidenemalononitriles 1a–c and 6-aminothiouracil 2. The reactivity of compounds 4a–c towards some reagents such as formamide, carbon disulfide, urea, thiourea, formic and acetic acids were studied. All the synthesized compounds were characterized by spectroscopic means and elemental analysis. Compound 4c exhibited 64% and 72% analgesic activity. Also, compound 4b showed 50% and 65% anti-inflammatory activity. Interestingly these compounds showed one-third of ulcer index of the reference aspirin and diclofenac.     

Synthesis of carbon-11-labeled CK1 inhibitors as new potential PET radiotracers for imaging of Alzheimer’s disease

The reference standards methyl 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoate (5a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-methoxybenzamide (5c), and their corresponding desmethylated precursors 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoic acid (6a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-hydroxybenzamide (6b), were synthesized from 5-amino-2,2-difluoro-1,3-benzodioxole and 3-substituted benzoic acids in 5 and 6 steps with 33% and 11%, 30% and 7% overall chemical yield, respectively. Carbon-11-labeled casein kinase 1 (CK1) inhibitors, [¹¹C]methyl 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoate ([¹¹C]5a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-[¹¹C]methoxybenzamide ([¹¹C]5c), were prepared from their O-desmethylated precursor 6a or 6b with [¹¹C]CH₃OTf through O-[¹¹C]methylation and isolated by HPLC combined with SPE in 40–45% radiochemical yield, based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the molar activity (MA) at EOB was 370–740?GBq/μmol with a total synthesis time of ～40-min from EOB.     

The synthesis and biological activity of a series of 2,4-diaminopyrido[2,3-D]pyrimidine based antifolates as antineoplastic and antiarthritic agents

A new series of 2,4-diaminopyrido[2,3-d]pyrimidine based antifolates 1–3 were synthesized through an efficient conversion of 2-pivaloyl-4-oxo-6-ethynylpyrido[2,3-d]pyrimidine 5 to the corresponding 4-amino analog 7 via the activated 1,2,4-triazole intermediate 6. Compound 7 was used as the key intermediate for the preparation of the final products. The detailed biological evaluation of these compounds both as antineoplastic and antiarthritic agents will be discussed.     

Design,synthesis and dopamine D4 receptor binding activities of new N-heteroaromatic 5/6-ring Mannich bases

A series of phenylpiperazine-methyl-substituted 1H-pyrrolo[2,3-c]pyridine, imidazo[1,2-c]-, pyrrolo[2,3-d]- and pyrrolo[3,2-d]pyrimidines were prepared as selective dopamine D4-ligands. The pyrrolo[2,3-d]pyrimidine derivatives 12d (K_i = 1,9 nM) and 34d (K_i = 2,4 nM) as well as the pyrrolo[3,2-d]pyrimidine Mannich base 49f (K_i = 2,8 nM) showed high dopamine D4 receptor activity superior to the atypical antipsychotic agent clozapine.     

Discovery of thieno[2,3-d]pyrimidin-4(3H)-one derivatives as a new class of ROCK inhibitors

Herein, we report the discovery of a series of thieno[2,3-d]pyrimidin-4(3H)-one derivatives as a new class of ROCK inhibitors. Structure-activity relationship studies of these compounds led to the identification of the most potent compound, 3-(3-methoxybenzyl)-6-(1H-pyrrolo[2,3-b]pyridin-4-yl)thieno[2,3-d]pyrimidin-4(3H)-one (8k), which showed IC₅₀ values of 0.004 μM and 0.001 μM against ROCK Ⅰ and ROCK Ⅱ, respectively. In vitro, 8k significantly reduced the phosphorylation level of ROCK downstream signaling protein and induce changes in cell morphology and migration. Overall, this study provides a promising lead compound for drug discovery targeting ROCKs.     

Imidazo[2′,1′:2,3]thiazolo[4,5-d]pyridazinone as a new scaffold of DHFR inhibitors: Synthesis,biological evaluation and molecular modeling study

New series of thiazolo[4,5-d]pyridazin and imidazo[2′,1′:2,3]thiazolo[4,5-d]pyridazin analogues were designed, synthesized and evaluated for their in vitro DHFR inhibition and antitumor activity. Compounds 13 and 43 proved to be DHFR inhibitors with IC₅₀ 0.05 and 0.06 μM, respectively. 43 proved lethal to OVCAR-3 Ovarian cancer and MDA-MB-435 Melanoma at IC₅₀ 0.32 and 0.46 μM, respectively. The active compounds formed hydrogen bond at DHFR binding site between N₁-nitrogen of the pyridazine ring with Glu30; the carbonyl group with Trp24, Arg70 or Lys64; π-cation interaction with Arg22 and π-π interaction with Phe31 residues. Ring annexation of the active 1,3-thiazole ring analogue 13 into the bicyclic thiazolo[4,5-d]pyridazine (18,19) or imidazo[2,1-b]thiazoles (23–25) decreased the DHFR inhibition activity; while the formation of the tricyclic imidazo[2′,1′:2,3]-thiazolo[4,5-d]pyridazine (43–54) increased potency. The obtained model could be useful for the development of new class of DHFR inhibitors.     

Novel 1H-pyrrolo[2,3-c]pyridines as acid pump antagonists (APAs)

A series of 1H-pyrrolo[2,3-c]pyridines as acid pump antagonists (APAs) was synthesized and the inhibitory activities against H⁺/K⁺ ATPase isolated from hog gastric mucosa were determined. After elaborating on substituents at N1, C5, and C7 position of 1H-pyrrolo[2,3-c]pyridine scaffold, we have observed that compounds 14f and 14g are potent APAs with H⁺/K⁺ ATPase IC₅₀ = 28 and 29 nM, respectively.     

Multisubstituted quinoxalines and pyrido[2,3-d]pyrimidines: Synthesis and SAR study as tyrosine kinase c-Met inhibitors

Two series of new analogues were designed by replacing the quinoline scaffold of our earlier lead 2 (zgwatinib) with quinoxaline and pyrido[2,3-d]pyrimidine frameworks. Moderate c-Met inhibitory activity was observed in the quinoxaline series. Among the pyrido[2,3-d]pyrimidine series, compounds 13a–c possessing an O-linkage were inactive, whilst the N-linked analogues 15a–c retained c-Met inhibitory potency. Highest activity was observed in the 3-nitrobenzyl analog 15b that showed an IC₅₀ value of 6.5 nM. Further structural modifications based on this compound were undergoing.     

Fluorescent cytokinins: Stretched-out analogs of N6-benzyladenine and N6-(Δ2-isopentenyl) adenine

We have synthesized and compared the cytokinin activities in the tobacco bioassay of a series of benzologs of 6-(3-methyl-2-butenylamino)purine (N⁶-(Δ²-isopentenyl)adenine) (1a) and 6-benzylaminopurine (N⁶-benzyl-adenine) (1c). The linear benzo analogs 8-(3-methyl-2-butenylamino)imidazo[4,5-g]quinazoline (2b) and 8-benzyla-minoimidazo[4,5-g]quinazoline (2c) are active, while 9-(3-methyl-2-butenylamino)imidazo[4,5-f]quinazoline (3b) and 6-(3-methyl-2-butenylamino)imidazo[4,5-h]quinazoline (4b) are slightly active and 9-benzylaminoimidazo[4,5-f]-quinazoline (3c) and 6-benzylaminoimidazo[4,5-h]quinazoline (4c) are inactive. Compounds 2b and 2c represent the first examples of active cytokinins containing a tri-heterocyclic moiety. The above series of compounds demonstrates structural factors that affect cytokinin activity. These compounds also have interesting fluorescence properties which could render them useful as probes to study the mechanism of cytokinin action.     

Synthesis and antitumor activity of substituted triazolo[4,3-a]pyrimidin-6-sulfonamide with an incorporated thiazolidinone moiety

Chlorosulfonation of 3-methyl[1,2,4]triazolo[4,3-a]pyrimidine with chlorosulfonic acid in the presence of thionyl chloride was studied. When triazolo[4,3-a]pyrimidines are used as substrates, the substitution occurs at C-6. Also the reactivity of the hydrazides (7) towards aldehydes, thioglycolic acid and amines were studies. The newly prepared compounds 10a,d and 11a,d demonstrated inhibitory effects on the growth of a wide range of cancer cell lines generally at 10^?5 M level and in some cases at 10^?7 M concentrations.     

Practical and efficient synthesis of pyrano[3,2-c]pyridone,pyrano[4,3-b]pyran and their hybrids with nucleoside as potential antiviral and antileishmanial agents

A highly practical and efficient preparation of pyrano[3,2-c]pyridone and pyrano[4,3-b]pyran derivatives was developed via an ionic liquid mediated and promoted multi-component reaction of aldehyde (1), 4-hydroxy-pyridin-2(1H)-one or 4-hydroxy-2-pyranone (2), and malononitrile (3). As an application, a series of pyrimidine nucleoside-pyrano[3,2-c]pyridone or pyrano[4,3-b]pyran hybrids were efficiently obtained. These hybrid compounds were evaluated as potential antiviral and antileishmanial agents and showed encouraging biological activities.     

Synthesis of novel hetero ring fused pyridine derivatives; Their anticancer activity,CoMFA and CoMSIA studies

A series of novel furo[2,3-b]pyridine-2-carboxamide 4a–h/pyrido[3′,2′:4,5]furo[3,2-d] pyrimidin-4(3H)-one derivatives 5a–p were prepared from pyridin 2(1H) one 1 via selective O-alkylation with α-bromoethylester followed by cyclization, then reaction with different aliphatic primary amines to obtain 4 and further reaction with triethyl orthoacetate/triethyl orthoformate. Also prepared novel furo[2,3-b]pyridine-2-carbohydrazide Schiff’s bases 7a–h and pyrido [3′,2′:4,5]furo[3,2-d]pyrimidin-4(3H)-one derivatives 8a–h starting from furo[2,3-b]pyridine carboxylate derivatives 3 by reaction with hydrazine hydrate to form 6 and reaction with diverse substituted aldehydes and cyclization. Products 4a–h, 5a–p, 7a–h and 8a–h were screened against four human cancer cell lines (HeLa, COLO205, Hep G2 and MCF 7) and one normal cell line (HEK 293). Compounds 4e, 4f, 4g, 5h, 7c, 7d, 7e and 7f showed significant anticancer activity against all the cell lines at micro molar concentration and found to be non-toxic to normal cell line. Studies for HeLa, COLO205 and MCF-7 using CoMFA and CoMSIA. Models from 3D-QSAR provided a strong basis for future rational design of more active and selective HeLa, COLO205 and MCF-7 cell line inhibitors.     

Nature-inspired pyrrolo[2,3-d]pyrimidines targeting the histamine H3 receptor

Inspired by marine compounds the derivatization of the natural pyrrolo[2,3-d]pyrimidine lead scaffold led to a series of novel compounds targeting the histamine H₃ receptor. The focus was set on improved binding towards the receptor and to establish an initial structure-activity relationship for this compound class based on the lead structure (compound V, K_i value of 126 nM). As highest binding affinities were found with 1,4-bipiperidines as basic part of the ligands, further optimization was focused on 4-([1,4′-bipiperidin]-1′-yl)-pyrrolo[2,3-d]pyrimidines. Related pyrrolo[2,3-d]pyrimidines that were isolated from marine sponges like 4-amino-5-bromopyrrolo[2,3-d]pyrimidine (compound III), showed variations in halogenation pattern, though in a next step the impact of halogenation at 2-position was evaluated. The chloro variations did not improve the affinity compared to the dehalogenated compounds. However, the simultaneous introduction of lipophilic cores with electron-withdrawing substitution patterns in 7-position and dehalogenation at 2-position (11b, 12b) resulted in compounds with significantly higher binding affinities (K_i values of 7 nM and 6 nM, respectively) than the initial lead structure compound V. The presented structures allow for a reasonable structure-activity relationship of pyrrolo[2,3-d]pyrimidines as histamine H₃ receptor ligands and yielded novel lead structures within the natural compound library against this target.     

Discovery of pyrrolo[2,3-d]pyrimidin-4-ones as corticotropin-releasing factor 1 receptor antagonists with a carbonyl-based hydrogen bonding acceptor

A new class of pyrrolo[2,3-d]pyrimidin-4-one corticotropin-releasing factor 1 (CRF₁) receptor antagonists has been designed and synthesized. In general, reported CRF₁ receptor antagonists possess a sp²-nitrogen atom as hydrogen bonding acceptor (HBA) on their core scaffolds. We proposed to use a carbonyl group of pyrrolo[2,3-d]pyrimidin-4-one derivatives as a replacement for the sp²-nitrogen atom as HBA in classical CRF₁ receptor antagonists. As a result, several pyrrolo[2,3-d]pyrimidin-4-one derivatives showed CRF₁ receptor binding affinity with IC₅₀ values in the submicromolar range. Ex vivo ¹²⁵I-sauvagine binding studies showed that 2-(dipropylamino)-3,7-dimethyl-5-(2,4,6-trimethylphenyl)-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidin-4-one (16b) (30 mg/kg, po) was able to penetrate into the brain and inhibit radioligand binding to CRF₁ receptors (frontal cortex, olfactory bulb, and pituitary) in mice. We identified pyrrolo[2,3-d]pyrimidin-4-one derivatives as the first CRF₁ antagonists with a carbonyl-based HBA.     

Synthesis and biological activity of 1,4-dihydrobenzothiopyrano[4,3-c]pyrazole derivatives,novel pro-apoptotic mitochondrial targeted agents

This study reports the synthesis of a number of 1- and 2-phenyl derivatives of the 1,4-dihydrobenzothiopyrano[4,3-c]pyrazole nucleus, which were obtained by the reaction of the versatile 7-substituted 2,3-dihydro-3-hydroxymethylene-4H-1-benzothiopyran-4-ones with hydrazine and substituted phenylhydrazines. The antiproliferative activity of the synthesized compounds was evaluated by an in vitro assay on human tumor cell lines (HL-60 and HeLa) and showed a significant capacity of the 7-methoxy-substituted benzothiopyrano[4,3-c]pyrazoles 3b–d, carrying the pendant phenyl group in the 1-position, to inhibit cell growth. Investigation of the mechanism of action indicated the induction of the mitochondrial permeability transition (MPT) as the molecular event responsible for the inhibition of cell growth. This phenomenon is related to the ability of the test compounds to cause a rapid Ca²⁺-dependent and cyclosporin A-sensitive collapse of the transmembrane potential (ΔΨ) and matrix swelling. All this leads to the release of caspase activators, such as cytochrome c (cyt c) and apoptosis-inducing factor (AIF), which trigger the pro-apoptotic pathway leading to DNA fragmentation.