Synthesis,Characterization, and Screening for Analgesic and Anti‐Inflammatory Activities of Schiff Bases of 1,3,4‐Oxadiazoles Linked With Quinazolin‐4‐One

Sixteen Schiff bases of quinazolin‐4‐one‐linked 1,3,4‐oxadiazoles were synthesized by reaction with different aromatic aldehydes. Purity of newly synthesized derivatives was confirmed through thin‐layer chromatography, combustion analysis, and melting point. The structure of the derivatives was confirmed by determining infrared spectroscopy, nuclear magnetic resonance, and mass spectroscopy. All the synthesized derivatives were evaluated for their analgesic and anti‐inflammatory activities in mice and rats, respectively. In animal studies, the derivative (E )‐3‐(5‐(4‐(4‐methoxybenzylideneamino)phenyl)‐1,3,4‐oxadiazol‐2‐yl)‐2‐phenylquinazolin‐4(3H )‐one showed more potent analgesic activity and the derivative (Z )‐3‐(5‐(2‐(2‐hydroxybenzylideneamino)phenyl)‐1,3,4‐oxadiazol‐2‐yl)‐2‐phenylquinazolin‐4(3H )‐one showed more potent anti‐inflammatory activity as compared with other derivatives. The results of the present study indicate that reactions of 3‐(5‐(4‐aminophenyl)‐1,3,4‐oxadiazol‐2‐yl)‐2‐phenylquinazolin‐4(3H )‐one and 3‐(5‐(2‐aminophenyl)‐1,3,4‐oxadiazol‐2‐yl)‐2‐phenylquinazolin‐4(3H )‐one with different aromatic aldehydes produce Schiff bases of quinazolin‐4‐one‐linked 1,3,4‐oxadiazoles with potent analgesic and anti‐inflammatory activities.     

Synthesis and reactions of 3‐amino‐2‐methyl‐3H‐[1,2,4]triazolo[5,1‐b]‐quinazolin‐9‐one and 2‐hydrazino‐3‐phenylamino‐3H‐quinazolin‐4‐one

The reaction of 3‐N‐(2‐mercapto‐4‐oxo‐4H‐quinazolin‐3‐yl)acetamide ( 1 ) with hydrazine hydrate yielded 3‐amino‐2‐methyl‐3H‐[1,2,4]triazolo[5,1‐b]quinazolin‐9‐one ( 2 ). The reaction of 2 with o‐chlorobenzaldehyde and 2‐hydroxy‐naphthaldehyde gave the corresponding 3‐arylidene amino derivatives 3 and 4 , respectively. Condensation of 2 with 1‐nitroso‐2‐naphthol afforded the corresponding 3‐(2‐hydroxy‐naphthalen‐1‐yl‐diazenyl)‐2‐methyl‐3H‐[1,2,4]triazolo[5,1‐b]quinazolin‐9‐one ( 5 ), which on subsequent reduction by SnCl₂ and HCl gave the hydrazino derivative 6. Reaction of 2 with phenyl isothiocyanate in refluxing ethanol yielded thiourea derivative 7. Ring closure of 7 subsequently cyclized on refluxing with phencyl bromide, oxalyl dichloride and chloroacetic acid afforded the corresponding thiazolidine derivatives 8, 9 and 10 , respectively. Reaction of 2‐mercapto‐3‐phenylamino‐3H‐quinazolin‐4‐one ( 11 ) with hydrazine hydrate afforded 2‐hydrazino‐3‐phenylamino‐3H‐quinazolin‐4‐one ( 12 ). The reactivity 12 towards carbon disulphide, acetyl acetone and ethyl acetoacetate gave 13, 14 and 15 , respectively. Condensation of 12 with isatin afforded 2‐[N‐(2‐oxo‐1,2‐dihydroindol‐3‐ylidene)hydrazino]‐3‐phenylamino‐3H‐quinazolin‐4‐one ( 16 ). 2‐(4‐Oxo‐3‐phenylamino‐3,4‐dihydroquinazolin‐2‐ylamino)isoindole‐1,3‐dione ( 17 ) was synthesized by the reaction of 12 with phthalic anhydride. All isolated products were confirmed by their ir, ¹H nmr, ¹³C nmr and mass spectra.     

Synthesis,Characterization, and Biological Evaluation of Novel 3‐(4‐Chlorophenyl)‐2‐(substituted)quinazolin‐4(3H)‐one Derivatives as Multi‐target Anti‐inflammatory Agents

A novel class of 3‐(4‐chlorophenyl)‐2‐(substituted)quinazolin‐4(3H)‐one derivatives were synthesized, and the structure of synthesized compounds was characterized by IR, ¹H NMR, and mass spectroscopy. The newly synthesized compounds ( 4a–g and 6a–g ) were tested for their in vitro cyclooxygenase (COX) inhibition activity. The compounds have inhibitory profile against both COX‐1 and COX‐2, and some of the compounds are found to be selective against COX‐2. The compound 6g showed distinct inhibitory activity on COXs. The synthesized compounds were evaluated for their potential anti‐inflammatory activity as inhibitors of the proinflammatory cytokines IL‐6. Compounds 4d – g showed the highest level of inhibition among all the tested compounds. Thus, our data suggested that these compounds may represent a new class of potent anti‐inflammatory agents.     

Design and Synthesis of Novel 3‐(Phenyl)‐2‐(3‐substituted propylthio) Quinazolin‐4‐(3H)‐ones as a New Class of H1‐Antihistaminic Agents

A series of novel 3‐(phenyl)‐2‐(3‐substituted propylthio) quinazolin‐4‐(3H)‐ones were synthesized by the reaction of 2‐(3‐bromopropylthio)‐3‐(phenyl) quinazolin‐4‐(3H)‐one with various amines. The starting material, 2‐(3‐bromopropylthio)‐3‐(phenyl) quinazolin‐4‐(3H)‐one was synthesized from aniline. When tested for their in vivo H₁‐antihistaminic activity on conscious guinea pigs, all the test compounds protected the animals from histamine‐induced bronchospasm significantly. Compound 2‐(3‐(4‐methylpiperazin‐1‐yl) propylthiothio)‐3‐(phenyl) quinazolin‐4(3H)‐one ( Ph5 ) emerged as the most active compound (73.23% protection) of the series when compared with the reference standard chlorpheniramine maleate (70.09% protection). Compound Ph5 shows negligible sedation (5.01 %) compared with chlorpheniramine maleate (29.58%). Therefore, compound Ph5 can serve as the leading molecule for further development into a new class of H₁‐antihistaminic agents.     

Synthesis of a Novel Series of 2,3‐Disubstituted Quinazolin‐4(3H)‐ones as a Product of a Nucleophilic Attack at C(2) of the Corresponding 4H‐3,1‐Benzoxazin‐4‐one

A new series of 2,3‐disubstituted quinazolin‐4(3H)‐one derivatives was synthesized by nucleophilic attack at C(2) of the corresponding key starting material 2‐propyl‐4H‐3,1‐benzoxazin‐4‐one (Scheme 2). The reaction proceeded via amidinium salt formation (Scheme 3) rather than via an N‐acylanthranilimide. The structure of the prepared compounds were elucidated by physical and spectral data like FT‐IR, ¹H‐NMR, and mass spectroscopy.     

Synthesis and pharmacological investigation of novel 4‐(4‐Ethyl phenyl)‐1‐substituted‐4H‐[1,2,4]triazolo[4,3‐a]‐quinazolin‐5‐ones as new class of H1‐antihistaminic agents

A series of novel 4‐(4‐ethylphenyl)‐1‐substituted‐4H‐[1,2,4]triazolo[4,3‐a]quinazolin‐5‐ones were synthesized by the cyclization of 2‐hydrazino intermediate with various electrophile. The starting material 2‐hydrazino compound was synthesized from 2‐ethyl aniline by a new innovative route with improved yield. When tested for their in vivo H₁‐antihistaminic activity on conscious guinea pigs, all the test compounds significantly protected the animals from histamine induced bronchospasm. The compound II emerged as the most active compound of the series and it is more potent (73.93% protection) when compared to the reference standard, chlorpheniramine maleate (71% protection), it showed negligible sedation (10%) when compared to chlorpheniramine maleate (30%). Therefore compound II will serve as prototype molecule for further development as a new class of H₁‐antihistamines     

Synthesis and Antioxidant Evaluation of Quinoxalino[2′,3′:5,6][1,3,4]thiadiazino[2,3‐b]quinazolin‐15‐ones: Derivatives of a Novel Ring System

Quinoxalino[2′,3′:5,6][1,3,4]thiadiazino[2,3‐b]quinazolin‐15‐one, a novel fused heterocyclic system, was synthesized from a one‐pot condensation reaction of 2,3‐dichloroquinoxaline and 3‐amino‐2‐thioxo‐2,3‐dihydroquinazolin‐4(1H)‐one under mild condition. Derivatization was performed on treatment of the titled compound with several alkyl bromides. In vitro antioxidant activity of the synthesized compounds was evaluated.     

Synthesis and Characterization of Some Novel Phosphorylated 4‐Oxo‐2‐phenylquinazolines

Some novel phosphines, aminophosphines and their oxides, and derived phosphorus acids bearing 4‐oxo ‐ 2‐phenylquinazolin‐3‐yl moiety were synthesized. The methodology depended on the reaction of each 2‐phenylquinazolin‐4(3H)‐one ( 1 ) and 3‐amino‐2‐phenyl‐quinazolin‐4(3H)‐one ( 2 ) with (Ph)₂PCl, PhPCl₂, and PhP (O)Cl₂ in different ratios. The synthesized compounds were characterized by elemental analysis and spectral tools.     

Synthesis and Biological Evaluation of 2‐substituted‐6‐(morpholinyl/piperidinyl)pyridazin‐3(2H)‐ones as Potent and Safer Anti‐inflammatory and Analgesic Agents

A series of 2‐substituted‐6‐(morpholinyl/piperidinyl)pyridazin‐3(2H )‐ones was synthesized and the structures were established using various spectroscopic techniques. The target compounds were screened for anti‐inflammatory and analgesic activities at 20 and 40 mg/kg. The safety of the synthesized derivatives was evaluated by assessing anti‐platelet activity and ulcer index. The obtained pharmacological data revealed that 6‐morpholinyl derivatives 4a–12a were found to be somewhat more potent than 6‐piperidinyl derivatives 4b–6b. The 6‐morpholinyl substituted pyridazinone 12a exhibited maximum anti‐inflammatory and analgesic activities. Homoveratrylamine substituted compounds 6a and 6b emerged as promising leads in both the series with good anti‐inflammatory and analgesic activities without any ulcerogenicity. Anti‐platelet activity results of the compounds of both the series showed significantly low bleeding time in comparison with standard drug aspirin indicating the cardiovascular safety of new pyridazinones.     

Aromatization and ring cyclization: A better understanding on the ring cyclization mechanism of 3‐amino‐6‐hydrazino‐1,2,4‐triazin‐5(2H)‐one reacted with acetic acid in N,N‐dimethylformamide

In this paper we report that the title compound (3) reacts with excess N,N‐dimethylformamide (DMF) containing two equivalents of acetic acid to afford 6‐amino‐1,2,4‐triazolo[3,4‐f][1,2,4]triazin‐8(7H)‐one ( 1 ). When 3‐amino‐2‐benzyl‐6‐hydrazino‐1,2,4‐triazin‐5(2H)‐one ( 6 ), the N‐2 benzylated derivative of 3 , is treated under the same conditions, ring cyclization does not occur; instead, 3‐amino‐2‐benzyl‐6‐(2‐formyl‐hydrazino)‐1,2,4‐triazin‐5(2H)‐one ( 7 ) is formed. Single‐crystal X‐ray analysis of a 3‐ethyl derivative of compound 1 reveals the predominant tautomeric structure to be the 7H‐tautomer (7H‐ 1 ). From these results, we propose a reasonable cyclization mechanism that incorporates two important points: (1) the tautomerism of the N‐2 hydrogen with the C‐5 oxo group aromatizes the 1,2,4‐triazine ring, and (2) the DMF is proto‐nated by acetic acid on the nitrogen atom, then deamination occurs where DMF is attacked by the 6‐hydrazino group of 3 or 6 .     

Synthesis,Characterization and Biological Evaluation of a Novel Series of 1,2,4‐Triazolo‐[3,4‐b]‐1,3,4‐thiadiazines Containing an Amide Linkage

Two series of combinatorial library of 3,6‐disubstituted‐7H‐1,2,4‐triazolo‐[3,4‐b]‐1,3,4‐thiadiazines bearing an amide linkage were synthesized. All the newly synthesized compounds were characterized by spectral analyses. The newly synthesized compounds were screened for their cytotoxicity, anti‐inflammatory, and analgesic activities. Among the tested compounds, the compound 9g (Ar = 4‐(methoxybenzyl)piperazine) is the most promising molecule with half maximal inhibitory concentration (IC₅₀) value of 14.24 μM in (MCF‐7) cells. Compounds 9f (Ar = 4‐(chlorobenzyl)piperazine), 9g , and 9k (Ar = 2‐(fluorophenyl)piperazine) exhibited excellent anti‐inflammatory activity at a dose level of 50 mg/kg, almost comparable with the standard drug. In case of analgesic activity among the tested compounds, the compounds 9f , 9g , and 9k showed more potent and consistent activity in both 100 and 200 mg/kg/po doses with less ulcerogenic risk.     

Nickel boride mediated reductive desulfurization of 2‐thioxo‐4(3H)‐quinazolinones: A new synthesis of quinazolin‐4(3H)‐ones and 2,3‐dihydro‐4(1H)‐quinazolinones

A novel one‐pot approach for the synthesis of aryl substituted quinazolin‐4(3H)‐ones and 2,3‐dihydro‐4(1H)‐quinazolinones has been reported based on the reductive desulfurization of 3‐aryl‐2‐thioxo‐4(3H)‐quinazolinones with nickel boride in dry methanol at ambient temperature.     

Heterocyclic synthesis: A convenient route to some 2‐mercepto 1,3,4‐oxadiazole and green chemistry microwave‐induced one‐pot synthesis of 2‐aryl 1,3,4‐oxadiazole in quinazolone and their antibacterial and antifungal activity

Several 6‐substituted‐3‐[(5‐mercepto‐1,3,4‐oxadiazol‐2‐yl)methyl]‐2‐substituted quinazolin‐4(3H)‐one or 6‐substituted‐3‐[4‐(5‐mercepto‐1,3,4‐oxadiazol‐2‐yl)phenyl]‐2‐substituedquinazolin‐4(3H)‐one 2(a‐l) and 6‐substituted‐3‐[(5‐phenyl‐1,3,4‐oxadiazol‐2‐yl)methyl]‐2‐substitutedquinazolin‐4(3H)‐one or 6‐substi‐tuted‐3‐[4‐(5‐phenyl‐1,3,4‐oxadiazol‐2‐yl) phenyl]‐2‐substitutedquinazolin‐4(3H)‐one 3(a‐l) were synthesized using conventional and microwave techniques respectively and were screened for antibacterial and antifungal activity.     

Synthesis of Aldehydo Sugar (4‐oxoquinazolin‐2‐yl)hydrazones and their transformation into 1‐(alditol‐1‐yl)‐1,2,4‐triazolo‐[4,3‐a]quinazolin‐5(4H)‐ones

A series of the aldehydo‐sugar hydrazones 4a‐d and 5a‐d were prepared by the reaction of 2‐hydrazino‐quinazolin‐4(3H)‐one ( 1 ) and 3‐ethyl‐2‐hydrazinoquinazolin‐4(3H)‐one ( 2 ) with aldoses 3a‐d . Treatment of hydrazones 4a‐d and 5a‐d with acetic anhydride in pyridine gave hydrazone acetates 6a‐d and 7a‐d . Compounds 7a‐d were also prepared by ethylation of 6a‐d . Reaction of compounds 4a‐d and 5a‐d with hot ethanolic ferric chloride led to oxidative cyclization to angular ring systems 8a‐d and 9a‐d rather than to the linear system 10 . Acetylation of 8a‐d afforded the per‐O, N‐acetyl derivatives 11a‐d , which were converted into the corresponding ethyl derivatives 12a‐d . Compounds 12a‐d were identical with the acetylation products derived from 9a‐d .     

Synthesis and Hypolipidemic Activity of New 6,6‐Disubstituted 3‐R‐6,7‐Dihydro‐2H‐[1,2,4]triazino[2,3‐c]quinazolin‐2‐Ones

Presented article describes the synthesis and hypolipidemic activity of previously unknown 6,6‐disubstituted 3‐R‐6,7‐dihydro‐2H‐[1,2,4]triazino[2,3‐c]quinazolin‐2‐ones. It was shown, that interaction of 6‐R‐3‐(2‐aminophenyl)‐1,2,4‐triazin‐5(2Н)‐оnes with methylalkylketones in acetic acid resulted the single product, namely, the desired tricyclic derivatives. At the same time, after refluxing of 6‐R‐3‐(2‐aminophenyl)‐1,2,4‐triazin‐5(2Н)‐оnes with methylarylketones in acetic acid the mixture of target compound and insignificant amount of corresponding 3‐substituted 6‐methyl‐2H‐[1,2,4]triazino[2,3‐c]quinazolin‐2‐ones were isolated. The mechanism of above‐mentioned mixture formation was discussed. The structures of all synthesized compounds were proven using the appropriate physicochemical methods. The compounds with promising lipid‐lowering activity were identified and the «structure — hypolipidemic activity» correlations were discussed.     

Synthesis of New Triazole and Oxadiazole Derivatives of Quinazolin‐4(3H)‐one and Their Antimicrobial Activity

A series of new triazole derivatives of quinazolin‐4(3H)‐one and new oxadiazole derivatives of quinazolin‐4(3H)‐one were synthesized. The newly synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR and mass spectral data. All the newly synthesized compounds were screened for antibacterial activity against Staphylococcus aureus, Bacillus subtilis (gram‐positive bacteria), Escherichia coli, Pseudomonas aeruginosa (gram‐negative bacteria), and antifungal activity was carried out against Candida albicans and Aspergillus niger.     

CuBr/Et3N‐Promoted Reactions of 2‐Aminobenzamides and Isothiocyanates: Efficient Synthesis of Novel Quinazolin‐4(3H)‐ones

A series of novel quinazolin‐4(3H)‐one derivatives were efficiently synthesized starting from isatoic anhydride. First, reaction of isatoic anhydride and amines in H₂O at room temperature afforded 2‐aminobenzamides. Then, CuBr/Et₃N promoted reaction of 2‐aminobenzamides and different aryl isothiocyanates in DMF at 80° afforded the title compounds in good yield.     

Reinvestigation of the Synthesis of Ketanserin (5) and its Hydrochloride Salt (5.HCl) via 3‐(2‐Chloroethyl)‐2,4‐(1H,3H)‐quinazolinedione (2) or Dihydro‐5H‐oxazole(2,3‐b)quinazolin‐5‐one (1)

The synthesis of ketanserin ( 5 ) and its hydrochloride salt ( 5.HCl ) using respectively equimolar amounts of 3‐(2‐chloroethyl)‐2,4‐(1H,3H)‐quinazolinedione ( 2 ) with 4‐(parafluorobenzoyl)piperidine ( 3 ) and dihydro‐5H‐oxazole(2,3‐b)quinazolin‐5‐one ( 1 ) with hydrochloride salt of 4‐(parafluorobenzoyl)piperidine ( 3.HCl ) is reinvestigated. The one‐pot reaction of ethyl‐2‐aminobenzoate with ethyl chloroformate and ethanol amine has afforded 3‐(2‐chloroethyl)‐2,4‐(1H,3H)‐quinazolinedione ( 2 ) (86%) that was then refluxed with 4‐(parafluorobenzoyl)piperidine ( 3 ) in ethyl methyl ketone in the presence of sodium carbonate to obtain free base of ketanserin (87%). In another attempt, a very pure hydrochloride salt of ketanserin ( 5.HCl ) was synthesized using equimolar amounts of dihydro‐5H‐oxazole(2,3‐b)quinazolin‐5‐one ( 1 ) and hydrochloride salt of 4‐(parafluorobenzoyl)piperidine ( 3.HCl ) by a solvent‐less fusion method. Thus, under optimized conditions, 180°C and a reaction time of 30 min, the powder mixture was transformed into glassy crystals that were initially readily soluble in chloroform but were transformed afterwards over time (2 h) to white precipitates ( 5.HCl ) suspended in chloroform with a yield of 72%.     

Synthesis and In Vitro Antibacterial Activities of Novel 2‐Aryl‐3‐(phenylamino)‐2,3‐dihydroquinazolin‐4(1H)‐one Derivatives

An efficient synthesis of novel 2‐aryl‐3‐(phenylamino)‐2,3‐dihydroquinazolin‐4(1H)‐one derivatives using KAl(SO₄)₂.12H₂O (Alum) as a catalyst from an aldehyde and 2‐amino‐N‐phenylbenzohydrazine in ethanol is described. All synthesized derivatives were screened for anti‐bacterial activity. Some compounds exhibited promising anti‐bacterial activity with reference to standard antibiotics.     

Reactivity study on morpholine‐1‐carbothioic acid (2‐phenyl‐3H‐quinazolin‐4‐ylidene) amide

Regioselective reactions of morpholine‐1‐carbothioic acid (2‐phenyl‐3H‐quinazolin‐4‐ylidene) amide ( 1 ) with electrophiles and nucleophiles were studied. The compound ( 1 ) reacts with alkyl halides in basic medium to afford S‐substituted isothiourea derivatives, with amines to give 1,1‐disubstituted‐3‐(2‐phenyl‐3H‐quinazolin‐4‐ylidene) thioureas and l‐substituted‐3‐(2‐phenyl‐quinazolin‐4‐yl) thioureas via transami‐nation reaction. The reaction of ( 1 ) with amines in the presence of H₂O₂ provided N⁴‐disubstituted‐N'⁴‐(2‐phenylquinazolin‐4‐yl)morpholin‐4‐carboximidamide via oxidative desulfurization. Estimation of reactivity sites on ( 1 ) was supported using the ab initio (HF/6‐31G**) quantum chemistry calculations. The ir, ¹H nmr, ¹³C nmr, mass spectroscopy and x‐ray identified the isolated products.