Microwave Assisted Regioselective Synthesis and Biological Evaluation of Pyrano[2,3-c]Pyridine Derivatives Utilizing DMAP as a Catalyst

E-mail: asmaamahmoud8521@hotmail.com asmaamahmoud8521@gmail.com Abstract: Regioselective facile production of pyrano[2,3-c]pyridine through multicomponent reaction of aromatic aldehydes, ethyl cyano acetate or malononitrile and C-H activated compound of 3-hydroxy picolinic acid in the occurrence of smaller amount of DMAP catalyst utilizing microwave apparatus, which is green and simple environmentally with high yield, recyclability catalyst. Totally the products were partitioned for antimicrobiogical action; it was detected that were active in contrast to S. pneumonia, E. coli and Candida albicans such as equated to typical drugs. Compounds of pyrano[2,3-c]pyridine-8-carboxylic acid derivatives 4i, 4e, 4p and 4p demonstrated effective development inhibitory activities. Additionally, the manufactured products were partitioned for in vitroantioxidant action by DPPH analysis. Products of pyrano[2,3-c]pyridine 4o and 4p were worthy free radical scavenging action through IC50 values of 252.52 and 223.2 μM; respectively.


Introduction
Multicomponent Reactions (MCR) have attempted extensive thought in combinatorial and biological chemistry (Thomas, 2017;Zhu, 2003;Zhu and Bienayme, 2005;Dömling, 2006;Dömling and Ugi, 2000). We established successfully numerous catalytic agent in organic synthesis exhausting MCR approach (Karnakar et al., 2015). The catalyst attractiveness is decrease of solvents ratios (Khan et al., 2008;2010a;Khan 2010b andKhan, 2011) and furthermore performance role in the yield of the product. This would be inexpensive, mild and environmentally friendly for attention to the synthetic organic researcher. Dimethyl Amino Pyridine (DMAP) is a catalyst of outstanding effectiveness in a variation group-transfer reactions and considered for applications in stereo selective catalysis (Armand et al., 2014).

General Instruments
Gallenkamp melting point apparatus were used for measuring the melting points. Furthermore the instrument Shimadzu FT-IR 8101 PC infrared spectrophotometer was used to record the IR spectrum. The 1 H-NMR and 13 C-NMR signals were evaluated in Deuterated Chloroform (CDCl 3 ) or DEUTERATED DIMETHYL SULFOXIDE (DMSO-d 6 ) at 300 MHz on a Varian Mercury-VX 300 NMR spectrometer ( 1 H at 300 MHz, 13 C at 75MHz) exhausting Trimethylsilane (TMS) as an interior signal. Shimadzu GCMS-QP 1000 EX mass spectrometer was used for detect the mass spectra at 70 eV. Elemental analyses were supported through Micro-analytical Center of Cairo University, Giza, Egypt. CEM Discover TM microwave instrument used for Microwave experiments.

Synthesis Thermal Method
Different of aromatic aldehydes (1mmol) and malononitrile, ethyl cyanoacetate (1mmol) in 4ml of ethanol was supplementary the catalyst DMAP (0.025g, 0.2mmol) and reserved magnificent at room tempeture. The obtained participation was formed instantaneously take 30-45 min in case of ethyl cyanoacetate while in malononitrile take few minutes and checked via Thin Layer Chromatography (TLC) and formerly allowable to relax at ordinary temperature, then Recrystallization from suitable solvent.

Microwave Method
Solution of aromatic aldehydes (1mmol) and malononitrile, ethyl cyano-acetate (1mmol) in 4ml of ethanol was additional the catalyst DMAP (0.025g, 0.2mmol) were diversified in Plus process vessel HP-500. The vessel was persevered accurately and irradiated through microwave underneath under pressure environments (17.2 bar, 100°C) (Elham et al., 2014;Salem et al., 2015) assumed for 1-5 min with or without stirring After 5 min one-time the reaction mix was transformed to pure solution, the preceipted product approached out underneath hot condition at the required period mention in Table 2 (tested by TLC), The reaction mix was transported to typical temperature and formed precipitated was strained off to acquire the preferred products 4a-4p.   3c]Pyridine-8-Carboxylic Acid (4b)

Results and Discussion
Chemistry Green synthesis one-pot of pyrano[2,3-c]pyridine annulated heterocyclic compound via threeconstituent condensation mixture reaction of aldehydes, ethyl cyanoacetate or malononitrile and 3hydroxy picolinic acid have been accomplished by microwave irradiation (Mady et al., 2015) and thermal heating utilizing 4-Dimethylaminopyridine (DMAP) as displayed in Scheme 1. For this study, an intermixture of aromatic benzaldehydes (1mmol) and ethyl cyanoacetate or malononitrile (1mmol) in ethyl alcohol was preserved with DMAP (0.1mmol) at typical temperature. Subsequently ingesting of initial aldehyde as examined via thin layer chromatography, 3-hydroxy picolinic acid was supplementary to the response combination and reserved for magnificent further down the heat for 1min in microwave instrument. Subsequently the accomplishment of the reaction examined via thin layer chromatography, the reaction combination was acquired to typical temperature and the formed precipitate was riddled off. Product 4a, was achieved in 85% yield in microwave irradiation, which was characterized by 1 HNMR, 13 C NMR, besides through elemental examination as displayed in Figure 1.

Scheme 1: Prepration of pyrano-fused heterocycles
The optimized reaction was exhausting different accelerator for attaining the excellent concern of 4a are summarized in Table 1. That one was distinguished that (20%) mol of DMAP in ethanol consequences from the greatest yield and time, the income obtained about (71%) in thermal heating. Subsequently the reaction optimization condition was comprehensive to a variability of aromatic aldehydes with dissimilar components.
The compounds 4a-4p were associated with those of conventional heating and microwave irradiation. It was demonstrated high yield properties of microwave compounds than thermal performance. The microwave was high yield and in a few minutes as shown in Table 2.
The formation of pyrano[2,3-c]pyridine-8-carboxylic acid derivatives can be reorganized as tracks. Initially, the Knovengel condensation of an aldehyde and alkyl nitrile to form acrylonitrile derivative I using DMAP catalyst, which responded to produce carbonian from activated 3-hydroxypicinolic acid to give the intermediate II, which cyclized to IV in the occurrence of DMAP. As a final point, IV tautomerized to provide preferred product 4 as presented in Scheme 2.

Biological Activity
In vitro Cytotoxic Activity Antimicrobial activity was accomplished at The Regional Center for Mycology and Biotechnology (RCMB), Al-Azhar University, Cairo, Egypt. Inhibition zones of bacterial evolution premeditated for the manufactured products and standard drugs utilizing Hole-plate dispersal procedure. Six intermediate (1 cm diameter) holes were finished consuming sterile cork borer in (MHA) Mullere Hinton agar sterile plates (16×16 cm), which remained before establishing bacterial separates. Holes were occupied with 100 ml of the established product concentration (100mmol disbanded in 1 ml DMSO) (Sunita and Mahendra, 2008;Andrews, 2001;Abdou et al., 2014). Subsequently, the dish protected for 24 h at 37°C. Subsequently maturation, the antimicrobiogical action of every regular product was estimated through determining the inhibition region diameters in contrast to examine bacteria and associated with typical region ranges of their standard sulfa medication. The experimentation was accomplished in triplicate and the regular region of inhibition was premeditated. Primarily, totally manufactured products and standard drugs Amphotericin B, Ampicillin and Gentamicin were estimated in vitro for their antimicrobiogical action, through the inhibition region procedure, exhausting three Gram(+) bacteria: S. pneumonia (RCMB 010010), Enterococcus faecalis (RCMB 010068) and S. aureus (RCMB 010028) through the accumulation of three Gram(-) bacteria: E. coli (RCMB 010052) and Salmonella typhimurium (RCMB 010072) and Pseudomonas aeruginosa (RCMB 010043), also were estimated in vitro for their antifungial action through the inhibition region procedure in contrast to Candida albicans (RCMB 05079) and Aspergillus fumigatus (RCMB 02568).

Free Radical Scavenging Action
The radical scavenging action of the manufactured products was confirmed by DPPH technique. Free radical (DPPH) is admitted one electron or hydrogen radical to come to be established diamagnetic fragment. DPPH in methanol appearances a characteristic band at 517 nm (dependent of PH beginning 5.0 to 6.5) and the solution performs to be bottomless violet color. For instance, DPPH radical is going through the donation hydrogen from the antioxidant, the point of staining designates the searching potential of the antioxidant products. Temporarily, different solution concentration (100, 200, 300, 400, 500 µg ml -1 ) of the examine products and ascorbic acid (standard) were organized in methanol and supplementary (1.5 ml) to the methanolic solution of DPPH (1.5 ml, 200 µM) (Abu-Hashem et al., 2011;Mohamed et al., 2012 andShu et.al 2007). The mix was stunned forcefully and permitted to attitude for 30 min in the dark. Subsequently, this, the absorbance was tested at 517 nm. Methanol (1.5 ml) was diversified with DPPH solution (1.5 ml, 200 µM). The scavenging action percentage was designed exhausting formulation: Where, the Ac = observance control (1.5 ml of each of methanol and the 200µM DPPH solution), At = absorption test compound/ascorbic acid. The inhibition percentage (%) curvatures for ascorbic acid and compounds were strategized in contrast to the concentration, from which IC 50 values of the inhibition percentage of DPPH via ascorbic acid and samples were considered exhausting regression equation.
The synthesized samples were selected for in-vitro antioxidant action by DPPH technique. The data achieved are represented in Table 4 as IC 50 (µM) values and supplementary to those of ascorbic acid as typical.
Improved observance of the samples with concentration exposes that products retain the radical scavenging action. Analysis of the results in Table 4. The manufactured products were selected for in vitro antioxidant action through DPPH technique. The data acquired are represented in Table 4 as IC 50 (µM) values and paralleled with those of ascorbic acid as typical. Absorbance increasing of the products with concentration exposes that products retain radical scavenging action. Analysis of the results in Table 2 which indicated the insertion of electron donating CH 3 and OCH 3 groups, as 4c, 4d, 4i and 4j reduced the radical scavenging activity and the electron withdrawing Cl, Br and NO 2, as in 4e, 4f, 4g, 4h, 4k and 4l increase the radical scavenging, moreover, pyrano[2,3-c]pyridine group of 4m, 4n ,4o, 4p encourages an growth in the antioxidant property. Among the products experienced 4o and 4p demonstrated effective free radical scavenging action with IC 50 standards of 252.52 and 223.2 µM, respectively (Morimoto et al., 1995).
The indication of the data obtained in Table 3 and 4 exposed that, generally pyrano[2,3-c]pyridine accompanying to heterocyclic were further active than those enclosing aromatic rings. Further studies are desirable to be supported out to invention association between IC 50 of the evaluated pyrano[2,3-c]pyridine and their molecular descripts, for instance electronic, lipophilic and steric parameters.

Conclusion
We require conceived a green and effective simple technique for the production pyrano[2,3-c]pyridine derivatives beneath DMAP catalyst exhausting microwave and conventional irradiation. The investigational ease, short reaction periods, extraordinary incomes, easy workup procedures, prevention of organic solvents and consumption of an expensive and freely obtainable and wastefully smart to synthesis these compounds. The improvement of DMAP in contrast to recognized catalyst is (i) cheap, (ii) eco-friendly and (iii) no essential chromatographic separation. The manufactured compounds exhibited moderate to good in vitro antimicrobial and antioxidant activities when associated with standard drugs. Compounds 4e, 4o and 4p demonstrated high potency against antimicrobial or antioxidant due to incorporated two heterocyclic moieties.