One-pot three component synthesis of substituted dihydropyrimidinones using fruit juices as biocatalyst and their biological studies

New and facile one-pot three component approach for the synthesis of substituted dihydropyrimidinones derivatives (4a-4h) from reaction of equimolar substituted aldehydes (1a-1h), methyl acetoacetate (2a) and urea (3a) in presence of nature derived catalyst viz. Cocos nucifera L. juice, Solanum lycopersicum L. juice and Citrus limetta juice, commonly known as coconut juice, tomato juice and musambi juice respectively, at room temperature has been carried out. All synthesized compounds were evaluated for in vitro herbicidal activity against Raphanus sativus L. (Radish seeds). The compounds (4a-4h) were also screened for their antifungal activity against Rhizoctonia solani and Colletotrichum gloeosporioides by poisoned food techniques method. Antibacterial activity was also studied against Erwinia cartovora and Xanthomonas citri by inhibition zone method. From activity data, it was found that compounds 4g and 4d were most active against Raphanus sativus L. (root) and Raphanus sativus L. (shoot) respectively. Compounds 4f and 4c was found most active against Rhizoctonia solani and Colletotrichum gloeosporioides fungus respectively at highest concentration. Compound 4g has shown maximum inhibition zone i.e. 1.00–5.50 mm against Erwinia cartovora at 2000 μg/mL concentration. Maximum Xanthomonas citrii growth was inhibited by compounds 4f showing inhibition zone 4.00–12.00 mm at highest concentration. Short reaction time, high yields, mild reaction condition and simple work-up are some merits of present methodology.


Introduction
Dihyropyrimidinones and its derivatives are found in a large family of natural products with wide biological activities, due to which they become important class of heterocyclic compounds. They generally possess therapeutic and pharmacological properties [1] and several derivatives of dihydropyrimidinone acts as calcium channel modulators [2], Ca-antagonists and vasodilative and antihypertensive [3]. In  dihyropyrimidinones, which is one-pot three component reaction between an substituted aldehydes, β-ketoester and urea. The major drawbacks of this procedure are lower yields and longer reaction time [4]. Therefore, we need to perform a very mild, simple, cost-effective, commercially beneficial and eco-friendly procedure for synthesis of dihydropyrimidinone derivatives for the academia and pharmaceutical industries [5]. Recently an efficient and facile green method has been developed for synthesizing substituted dihydropyrimidinones via Biginelli reaction at room temperature in presence of fruit juices viz amla, orange and lime juice [6]. Fruit juice is also acts as natural acids which were used as biocatalyst in organic synthesis. Now a day's fruit juice used in organic synthesis as homogeneous catalysts for various selective transformations of simple and complex molecules. The growing interest in fruit juice is mainly because of its biocatalysts, eco-friendly nature, non-toxic, non-hazardous and cost effective [7]. Therefore, in this paper we reported one-pot three components clean and facile synthesis of dihydropyrimidinone derivative in presence of fruit juices viz. Cocos nucifera L., Solanum lycopersicum L., Citrus limetta respectively. Some biologically and pharmacologically active dihydropyrimidinones derivatives are shown in Fig 1.

Materials and methods
All the chemicals were purchased from CDH (Central Drug House), SRL (Sisco Research Laboratory) and Sigma-Aldrich. Reaction were performed in oven-dried glassware and monitored by thin layer chromatography (TLC) silica gel plates using ethylacetate in hexane and other solvents combinations as the mobile phase. Melting points were determined in open capillaries on a Ganson electric melting point apparatus and are uncorrected. The 1 HNMR spectra were recorded in CDCl 3 or DMSO-d 6 using tetra methyl silane (TMS) as internal reference on "Brucker Ac 400 F"(400MHz) nuclear magnetic resonance spectrometer. The chemical shifts values are quoted in delta (parts per million, ppm). Infrared spectra (4000-350 cm -1 ) of the synthesized compounds were recorded in KBr pellets on Perkin Elmer FTIR-R2X spectrophotometer and frequency is expressed in cm -1 .
sterilized potato dextrose agar cooled at 45˚C after brief shaking. Each lot of medium was poured into Petri dishes and allowed to solidify. DMSO was used as negative control. Each dish was inoculated centrally with a 5 mm mycelial disc cut from the periphery of 2-3 days old fungal colonies. Inoculated Petri plates were incubated in the dark 25±2˚C for 48-72 h and colony diameters were measured periodically till the control dishes were nearly completely covered with fungus growth. All observations were made in triplicate. The degree of inhibition of growth was calculated from the mean differences between treatments and the control as percentage of latter by using the formula.
Control = mycelial growth in control dish Treated = mycelial growth in treated dish Antibacterial activity. Bacterial species Erwinia cartovora and Xanthomonas citri were grown on Luria-Bertani medium in laboratory. Antibacterial activity was evaluating using inhibition zone method [10]. 250, 500, 1000 and 2000 μg/ mL concentrations of synthesized compounds were prepared from the stock solution by taking appropriate amount and diluting with DMSO. DMSO was used as negative control. The circular paper discs of 10 mm diameter were prepared from Whatman's Filter paper No. 1. The disc were kept in Petri plate and autoclaved at 15 lbs pressure 20 minutes. Two paper discs were used for each concentration of the synthesized compounds. The excess of solution absorbed by paper discs was removed by holding them vertically by sterile forecep. Such soaked discs were transferred aseptically to Petri plates containing media and bacterial suspension spread over the surface. The Petri plates were kept in an incubator at 25±2˚C overnight and then examined for inhibition zone at these different concentrations of compounds. The experiment was performed in triplicate and activity was determined on the basis of inhibition zone (in mm).
Statistical analysis. The experiments were performed in triplicates for each treatment and the mean value were recorded and expressed as mean ± S.D. The descriptive statistics in form of box-and-whisker diagram were also presented in this paper. The spacing between the different parts of the box indicates the degree of dispersion and skewness in the data.
Preparation of biocatalyst. Extraction of Cocos nucifera L. juice. The coconut juice was obtained by perforating the fruit with a knife. The coconut juice was filtered using filter paper whatman no 1 for the elimination of residues to get clear juice which was used as a catalyst [11].
Preparation of Solanum lycopersicum L. juice. Fresh tomatoes were purchased from the local market. Then washed thoroughly under running tap water followed by rinsing thrice with double distilled water. Tomatoes were squeezed and juice were strained initially through a muslin cloth then passed through Whatman filter paper No. 1 [12].
Preparation of Citrus limetta juice. First of all wash the sweet limes and pat them dry. Cut them into two halves. Then using a citrus juice squeezer, extract the juice. Then the juice was filtered through cotton and then through whatman filter paper no 1 to remove solid material and to get clear juice which as used as a catalyst [13].
General procedure for the synthesis of substituted dihydropyrimidinones derivatives (4a-4h). By Cocos nucifera L. juice (Method A). The mixture of 20 mmol of substituted aldehydes (1a-1h), 20 mmol of methyl acetoacetate (2a), 20 mmol of urea (3a) and 2.5 mL of Cocos nucifera L. juice was stirring at room temperature. The completion of reaction was monitored by TLC. Then the reaction mixture was filtered, washed with water and pure yellow crystalline solid (4a-4h) recovered by recrystallized with methanol. All synthesized compounds were confirmed by FTIR and NMR and its melting point.
By Solanum lycopersicum L. juice (Method B). A mixture of substituted aldehydes (20 mmol) (1a-1h), methyl acetoacetate (20 mmol) (2a), urea (20 mmol) (3a) and Solanum lycopersicum L. juice (10 mL) was taken in round-bottom flask and stirring at room temperature. The progress of reaction was monitored using thin layer chromatography. Then the reaction mixture was filtered, washed with water and pure yellow crystalline solid (4a-4h) recovered by recrystallized with methanol. All synthesized compounds were confirmed by FTIR and NMR and its melting point.
By Citrus limetta juice (Method C). In 50 mL round bottom flask, substituted aldehydes (20 mmol) (1a-1h), methyl acetoacetate (20 mmol) (2a), urea (20 mmol) (3a) and Citrus limetta juice (10 mL) was stirred till the completion of reaction as indicated by thin layer chromatography. Then the reaction mixture was filtered, washed with water and pure yellow crystalline solid (4a-4h) recovered by recrystallized with methanol. All synthesized compounds were confirmed by FTIR and NMR and its melting point.
All the dihydropyrimidinone derivatives (4a-4h) were prepared according to Method A, B and C.
The reaction conditions were optimized by performing the reaction between 4-Hydroxy-3-methoxybenzaldehyde (20 mmol), methyl acetoacetate (20 mmol) and urea (20 mmol) in presence of catalyst viz. Cocos nucifera L. juice, Solanum lycopersicum L. juice and Citrus limetta juice at room temperature. Initially, the reaction was attempted between 4-Hydroxy-3-methoxybenzaldehyde (20 mmol), methyl acetoacetate (20 mmol) and urea (20 mmol) in presence of Cocos nucifera L. juice at room temperature. It was found that excellent yield (86%) of product was obtained when amount of Cocos nucifera L. juice was 2.5 mL and reaction time was also reduced ( Table 1, Entry 4). These results indicated that 2.5 mL of Cocos nucifera L. juice gives high yield of product over the completion of the reaction. Further the reaction was also optimized in presence of Solanum lycopersicum L. juice and Citrus limetta juice respectively. When the concentration of Solanum lycopersicum L. juice in the reaction mixture was 10.0 mL than yield of reaction was maximum (91%) and reaction completed in 5h ( Table 2, Entry 4). Hence 10.0 mL of Solanum lycopersicum L. juice under aqueous conditions at room temperature is the optimal condition for this reaction. The same reaction was also screened under aqueous conditions at room temperature in presence of Citrus limetta juice and maximum yield 93% (Table 2, Entry 4) was obtained when the amount of Citrus limetta juice was 10.0 mL in reaction mixture. The physical data of this study are presented in Table 3. After completion of the reaction, the solid products was collected by simple filtration and then recrystallized in methanol to afford pure dihydropyrimidinone derivatives (4a-4h). The structure of synthesized compounds was confirmed by 1  comparison of their melting points with those of reported compounds. The comparison of activity of different catalysts with respect to time and yield of reaction as shown in Table 4. All synthesized substituted dihydropyrimidinones derivatives (4a-4h) were shown in    The catalyst used in present study is nature derived, easily available and cost effective which makes this procedure is eco-friendly. In summary, we have reported a facile one-pot three component synthesis of substituted dihydropyrimidinones derivatives by condensation of substituted aldehyde, methyl acetoacetate and urea at room temperature in presence of Cocos nucifera L. juice, Solanum lycopersicum L. juice and Citrus limetta juice in excellent yields. The current procedure offers many advantages such as simple and efficient catalytic system, simple work-up, no use of hazardous solvents, cheap and products are obtained in good to excellent yields. Moreover, all products were obtained through simple filtration with no need for column chromatography, which reduces the waste as well as environmental pollution. We also conclude that current protocol will provide great utility in the synthesis of other heterocyclic compounds in the near future. The proposed mechanism for the formation of substituted dihydropyrimidinones is shown in Scheme 2. The first mechanism via the iminium route involves condensation between aldehyde and urea to form iminium intermediate (D), which undergoes nucleophillic addition with a β-keto ester leading to DHPMs. The second mechanism via enamine route (E) involves condensation reaction between urea and β-keto ester form protonated enamine intermediate, which reacts with aldehyde to give DHPMs. The third mechanism involves Knoevenagel condensation reaction (F) between aldehyde and β-keto ester results in the formation of carbenium ion intermediate, which further react with urea to give DHPMs [14]. It was also found that iminium mechanism is the most favourable route, both kinetically and thermodynamically to form DHPMs derivatives. Thus both experimental and theoretical results support the mechanism via iminium route as most plausible one for Biginelli reaction.

Herbicidal activity
All compounds (4a-4h) were tested for herbicidal activity against Raphanus sativus L. at 200, 150, 100 and 50 μg/mL concentrations as shown in Table 5. Results were shown in the form of primary screening. All compounds were diluted to 1000 μg/mL concentration as a stock solution. Herbicidal activities of compounds were evaluated against Raphanus sativus L. by inhibitory effect of compounds on the growth of weed roots and shoots. The percentage of inhibition growth was calculated from mean differences between treated and control. From the herbicidal activity results, we observed that compound 4g was exhibited maximum percentage growth inhibition i.e. 93.33 against Raphanus sativus L. (root) whereas compound 4d was exhibited maximum percentage growth inhibition i.e. 87.50 against Raphanus sativus L. (shoot) respectively at 200 μg/mL concentrations. The compounds 4g and 4d showed broadspectrum herbicidal activity because of presence of chloro substitution at phenyl ring. The herbicidal activity of compounds is given in Fig 3. The box plot and graphical representation of herbicidal activity of all compounds against Raphanus sativus L. were shown in Figs 4-7.

Antifungal activity
All synthesized compounds (4a-4h) were screened for their antifungal activity against 2 fungal strains viz. Rhizoctonia solani and Colletotrichum gloeosporioides by poisoned food technique method. DMSO was used as negative control against fungal strains. The result of antibacterial activity of tested compounds is shown in

Antibacterial activity
The optimistic antifungal activity of synthesized compounds (4a-4h) has influenced authors to test further for antibacterial activity. All synthesized compounds (4a-4h) were tested for their in vitro antibacterial activity against two bacterial strains Erwinia cartovora and Xanthomonas

Conclusions
We have reported a facile one-pot three component synthesis of substituted dihydropyrimidinones derivatives (4a-4h) by condensation of substituted aldehyde, methyl acetoacetate and

PLOS ONE
One-Pot Three Component Synthesis of Substituted Dihydropyrimidinones urea at room temperature in presence of Cocos nucifera L. juice, Solanum lycopersicum L. juice and Citrus limetta juice in excellent yields. The current procedure offers many advantages such as simple and efficient catalytic system, simple work-up, no use of hazardous solvents, cheap and products were obtained in good to excellent yields. Moreover, all products were obtained through simple filtration with no need for column chromatography, which reduces the waste as well as environmental pollution. All synthesized compounds (4a-4h) were also evaluated for their bioevaluation in terms of herbicidal activity against Raphanus sativus L. (Radish) seeds, antifungal activity against Rhizoctonia solani &Colletotrichum gloeosporioides and antibacterial activity against Erwinia cartovora and Xanthomonas citri. Based on activity data, it can be concluded that some of synthesized compounds exhibited good activity due to substitution of chloro, hydroxy and methoxy substitution on phenyl ring. We also conclude that current protocol will provide great utility in the synthesis of other heterocyclic compounds in the near future.