Dipak K. Raval

Catalytic regioselective synthesis of pyrazole based pyrido[2,3-d]pyrimidine-diones and their biological evaluation

A new type of biopolymer-based heterogeneous catalyst, cellulose supported acidic ionic liquid (Cell-IL), which was developed earlier in our lab, has been found to be very effective for the regioselective synthesis of pyrazole based pyrido[2,3-d]pyrimidine-diones. Its regioselectivity was confirmed by (1)H NMR spectroscopy. All the newly synthesized compounds were characterized by LC-MS, (1)H NMR, (13)C NMR, IR spectroscopy and elemental analysis. The newly synthesized compounds were evaluated for their in vitro antimalarial activity against Plasmodium falciparum, in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv strain and also for their antibacterial activity against a panel of pathogenic strains of bacteria and fungi. Some of them exhibited excellent activity when compared with first line drugs.

A convenient and efficient protocol for the one pot synthesis of 3,4-Dihydropyrimidin-2-(1H)-ones catalyzed by ionic liquids under ultrasound irradiation

Derivados de 3,4-dihidropirimidin-2-(1H)-onas foram sintetizados via uma reacao one-pot de tres componentes, com excelentes rendimentos em curtos tempos reacionais, usando aldeidos, acetoacetato de etila e ureia (ou tioureia) em liquidos ionicos a temperatura ambiente (RTILs) sob radiacao de ultrassom, sem adicao de catalisador. Um mecanismo sintetico plausivel foi postulado levando em consideracao o papel catalitico dos liquidos ionicos em promover a reacao. Os liquidos ionicos puderam ser reciclados no minimo seis vezes com boa retencao de atividade. Derivatives of 3,4-dihydropyrimidin-2-(1H)-ones were synthesized in excellent yields in short reaction time by one pot, three component reaction of aldehydes, ethyl acetoacetate and urea (or thiourea) in room temperature ionic liquids (RTILs) under ultrasound irradiation without any added catalyst. A plausible mechanistic pathway has been postulated based on the catalytic role of the ionic liquid in promoting the reaction. The ionic liquids could be recycled at least six times with retention of their activity.

Synthesis, characterization and biological screening of novel 5-imidazopyrazole incorporated fused pyran motifs under microwave irradiation

A novel combinatorial library of fused pyran derivatives has been designed and synthesized under microwave irradiation by one-pot three-component cyclocondensation reaction of 5-(1H-imidazol-1-yl)-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde with two active methylene compounds and enolizable ketones/phenols in the presence of piperidine as a basic catalyst. All the newly synthesized compounds have been characterized by elemental analysis and various spectroscopic methods. All the final motifs have been screened for their preliminary in vitro antibacterial activity against a panel of pathogenic strains of bacteria and fungi, preliminary in vitro antituberculosis activity against Mycobacterium tuberculosis H37Rv and also for their antimalarial activity against Plasmodium falciparum.

Synthesis, identification and in vitro biological evaluation of some novel 5-imidazopyrazole incorporated pyrazoline and isoxazoline derivatives

In the present study, novel combinatorial libraries of substituted pyrazolines 6a–l and isoxazolines 7a–l have been synthesized via the reactions of chalcones with the hydrazine hydrate and hydroxylamine hydrochloride in ethanol. The title compounds were screened for their preliminary in vitro antibacterial activity against a panel of pathogenic strains, in vitro antituberculosis activity against Mycobacterium tuberculosis H37Rv, in vitro antimalarial activity against Plasmodium falciparum and in vitro antioxidant activity by the ferric-reducing antioxidant power method. Compounds 6k, 6l, 7h and 7k exhibited excellent antibacterial activity and a few of them exhibited moderate antituberculosis activity compared with the first line drugs. Half of the compounds exhibited terrific antimalarial activity and the majority of compounds showed highest antioxidant potency.

Acidic ionic liquid immobilized on cellulose: an efficient and recyclable heterogeneous catalyst for the solvent-free synthesis of hydroxylated trisubstituted pyridines

The synthesis of a novel cellulose supported acidic ionic liquid (Cell-IL) for the solvent-free synthesis of hydroxylated trisubstituted pyridines is reported. Cell-IL was prepared by immobilization of an acidic ionic liquid [1-butyl-3-(3-trimethoxypropyl)-1H-imidazol-3-ium hydrogen sulfate] on cellulose. The viability of this concept has been confirmed by FT-IR, TGA-DTG, 1H NMR and elemental analysis. The Cell-IL showed good thermal stability and exhibited a high catalytic activity in the synthesis of a series of hydroxylated trisubstituted pyridines. It was recovered and reused for the model reaction three times without an appreciable change in its activity.

A facile approach for the synthesis of 3,4-dihydropyrimidin-2-(1H)-ones using a microwave promoted Biginelli protocol in ionic liquid

AbstractCarboxy functionalized ionic liquid [cmmim][BF4] has been demonstrated to be an efficient and green catalyst for the one pot synthesis of 3,4-dihydropyrimidin-2-(1H)-ones heterocycles under microwave irradiation. The ionic liquid-microwave strategy represents an easy access to Biginelli compounds with high yields and purity. The protocol was found to be compatible with different structurally diverse aldehydes. The ionic liquid was recycled and reused in at least six subsequent reactions with consistent activity. Graphical AbstractCarboxy functionalized ionic liquid [cmmim][BF4] is shown to be an efficient and green catalyst for the one pot synthesis of 3,4-dihydropyrimidin-2-(1H)-ones heterocycles under microwave irradiation. This methodology represents an easy access to Biginelli compounds with high yields and purity. The ionic liquid was recycled and reused with consistent results.

1-Methylimidazolium trifluoroacetate [Hmim]Tfa: Mild and efficient Brønsted acidic ionic liquid for Hantzsch reaction under microwave irradiation

AbstractOne pot synthesis of 1,4-dihydropyridine derivatives was achieved via condensation of various β-ketoesters with aromatic/aliphatic aldehydes and ammonium acetate. The reaction was catalysed by a stable and reusable Brønsted acidic ionic liquid (IL), 1-methyl-imidazolium trifluoroacetate ([Hmim]Tfa), under microwave (MW) irradiation. The synergistic combination of MW with IL can potentially go a long way to meet the increasing demand for chemical processes. This homogeneous catalytic procedure is simple and efficient. The catalyst can be reused at least four times with almost complete retention in its activity. Graphical AbstractThe synthesis of 1,4- dihydropyridine derivatives via Hantzsch reaction induced by combination of microwave energy and ionic liquid is reported. This new protocol requires very mild reaction conditions with water as the only byproduct. The process proved to be simple, environmentally friendly, economic and high yielding.

Design, synthesis and characterization of fluoro substituted novel pyrazolylpyrazolines scaffold and their pharmacological screening

A novel series of fluoro substituted pyrazolylpyrazolines 7a-l was synthesized in good to excellent yield (77-88%) from pyrazole chalcones 5a-d and substituted phenyl hydrazine hydrochlorides 6a-c under microwave irradiation. The newly synthesized compounds were screened for their preliminary in vitro antibacterial activity against a panel of pathogenic stains of bacteria and fungi, antituberculosis activity against Mycobacterium tuberculosis H37Rv and antimalarial activity against Plasmodium falciparum. Compounds 7a, 7b, 7g, 7h, 7j and 7k displayed excellent activity against P. falciparum stain as compared to quinine IC50 0.268. Good antitubercular activity was exhibited by compounds 7a, 7e, 7h and 7k. Some of them also exhibited superior antibacterial activity as compared to the first line drugs.

Magnetically retrievable magnetite (Fe3O4) immobilized ionic liquid: an efficient catalyst for the preparation of 1-carbamatoalkyl-2-naphthols

A magnetite (Fe3O4) supported –SO3H functionalized benzimidazolium based ionic liquid has been synthesized via covalent grafting of benzimidazole on a (3-chloropropyl)triethoxysilane functionalized magnetic nanoparticle followed by quaternization reaction with 1,4-butane sultone. The obtained magnetic nanoparticle supported ionic liquid (IL@MNP) has been characterized by FT-IR, TGA, TEM, XRD, VSM, EDX and elemental analysis. The performance of the prepared catalyst was evaluated in the preparation of 1-carbamatoalkyl-2-naphthols. The magnetite supported catalyst showed excellent catalytic activity and the corresponding products were obtained in high yields in all the tested cases. The heterogeneous nature of the magnetite favoured easy recovery and recyclability of the catalyst through magnetic decantation making the protocol highly advantageous over conventional procedures.

Ionic liquid catalyzed convenient synthesis of imidazo[1,2-a]quinoline under sonic condition

An efficient protocol for the synthesis of imidazo[1,2-a]quinoline from aldehydes, enaminones, and malononitrile using 1,8-diazabicyclo[5.4.0]-undec-7-en-8-ium acetate ([DBU][Ac]) as a catalyst under ultrasound irradiation is described. Compared with other methods, this new method has the advantages of easier work-up, milder reaction conditions, high yields and environmentally benign procedure.