Design and Synthesis of Some Chromone derivatives of biological importance: A Greener Approach

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ScienceDirect Materials Today: Proceedings 4 (2017) 11894–11901

www.materialstoday.com/proceedings

ICNANO 2016

Design and Synthesis of Some Chromone derivatives of biological importance: A Greener Approach Jyothi H. Kinia*, Vasatakumar K. Paia, Yadav D.Bodkea a

Department of P.G.Studies and Research in Industrial Chemistry, Jnana Sahyadri, Kuvempu University, Shankaraghatta, Shivamogga– 577451, Karnataka, India.

Abstract Green synthesis and a healthy environment are now on the frontier of all material sciences. Green and sustainable chemistry is the motto of Chemists all over the World. Chemists are considered as the major contributors of the non-green environment. To prove it wrong and to change the views of the world, the chemists all over the world are trying to incorporate the greener ways in synthesis, processing techniques and disposal of the waste. In this paper, the authors made a greener attempt to synthesize some biologically important Chromones like 8-Formyl-7-hydroxy-2-phenyl chromones by using Microwave technology. Also, the designing of the bioactive molecules was done by the study of their Quantitative physicochemical characteristics. The in-silico study of prediction of bio-diffusion and crossing of the molecule, through the Blood-brain barrier, was done by using different physicochemical parameters like logP, Polar surface area, Molecular weight and Molecular refractivity etc. A brief comparison of the synthesis of bio-active compounds by conventional and MW method was done. An attempt was made for the designing of drug-like molecules using physicochemical methods. © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of INTERNATIONAL CONFERENCE ON NANOTECHNOLOGY (ICNANO2016). Keywords: Green synthesis, Chromones, Microwave method, Physicochemical parameters, 8-Formyl chromones, biologically active

1.

Introduction

Green synthesis and a healthy environment are now on the frontier of all material sciences. Keeping in view of the need to protect the environment from the unnecessary and unscientific way of synthesis and usage of chemicals, which make contributions to the crisis in a non-negligible account. Nowadays the chemists are not sticking to the * Corresponding author. E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of INTERNATIONAL CONFERENCE ON NANOTECHNOLOGY (ICNANO-2016).

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dependence of conventional methods of heating and using a lot of solvents which make the environment hazardous day by day. Instead, they use the smart techniques like microwave, ultrasonic, solvent-free mechanical methods etc., which helps in saving the time and also the environment. The greener approaches in designing the synthetic schemes are being adopted. As on today, maximum pollution to the environment is caused by numerous chemical industries. The cost involved in the disposal of the waste products is also enormous. The twelve principles of Green Chemistry can be applied to almost every part of chemistry, which includes synthesis of molecules with a desired structure and property, catalysis of a process, less polluting reaction conditions etc.[1] Nowadays, the Microwave assisted synthesis is gaining importance. Since the time required is less compared to the conventional method of heating and the solvents required were less and non-hazardous and the purity of the compound is also high as there are fewer issues of separation and purification. Chromones (benzo-γ-pyrone) and related compounds are widely distributed in nature and have been found to play an important role in a number of biological processes. Chromones have versatile biological activities like anticancer shown by Agullo et al.,[2]antioxidant, anti-inflammatory, antibiotic, anti-HIV by Xu et al., [3] and also as good vasodilators Middleton et al.[4] and were preferred due to their low mammalian toxicity as per the study by Gabor, in 1991.[5] Many natural chromones and flavones like Quercetin, Christen, Kaempferol, Myricetin, Apigenin, Luteolin etc., mainly present in apple, tomato, onion etc., found to have the property of inhibiting autooxidation reactions and scavenging of free radicals as spotted by Bors et al.; Miean and Mohamed.[6,7] This property delays the decaying of these natural fruits and vegetables. They play a key role in the prevention of cancer.[8-10] They also have “Anti-aging” properties as substantiated by Jones and Hughes.[11] The natural chromones were studied for their SAR (Structure Activity Relationships) [12] and many synthetic chromones related to the structure of natural chromones which are having similar structures, are found to possess similar activities. The automation of the study of the SAR of some natural and synthetic chromones as compiled by Kini et.al., assists to choose and design the most biologically potent chromones.[13] The present work involves automated devising of the novel compounds with the effective combination of Quantitative physicochemical characteristics of the designed compounds and the synthesis of only the potent compounds which are guaranteed to show lead like characteristics. Chromones which are having less mammalian toxicity with formyl (CHO) functional group [14]i.e. 8-Formyl-7-hydroxy-3-methyl-2-phenyl-chromones were very potent biologically active agents and were used as precursors for other more versatile derivatives of chromones.[15] An attempt was made to synchronize some physicochemical parameters in the path of search for lead molecules. The conventional method of synthesis of 8-Formyl-7-hydroxy-3-methyl-2-phenyl-chromones involves 4-5 synthetic steps with low yields. Also, the compounds need rigorous purification in each step to get the pure compound. The authors observed the wrench for the need to synthesize these biologically active chromone precursors with the easy and affordable method. The resultant method was the synthesis by using Microwave method,[16] which effectively reduced the time and also helped to get rid of the tedious purification procedures. 2.

Experimental 2.1 Materials and methods

All reagents and solvents used were of AR grade purchased from commercial sources like Sigma-Aldrich, Merck and Himedia. ONIDA Power solo 20 digital domestic Microwave oven was used for the synthesis with high MW compatible glasswares like tubes and conical flasks. Melting points were determined in open capillary tubes and were uncorrected. Chromatographic purification was done by the column chromatography using Merck silica gel (60 -120meshes). FTIR spectra (KBr) were run on Alpha Brucker-T spectrometer. NMR spectra were recorded on a Bruker-400 MHz spectrometer 1H-NMR 400 MHz, 13C-NMR 100 MHz in CDCl3 solvent using TMS as an internal standard. Chemical shifts (δ) were reported in parts per million (ppm) downfield from TMS. Mass spectra were obtained on a Bruker Compass esquire 6000. Elemental analyses were run on a Thermo Finnigan Flash EA1112 series. Reactions were monitored by thin-layer chromatography plates coated with 0.2-mm silica gel 60 F254 (Merck). TLC plates and were visualized under the UV light.

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2.2 Physico-chemical approach Many synthesized compounds, which showed the good in-vitro potency of biological activity seldom clear all the stages of clinical trials and emerge as potent lead molecules. This is mainly because of the failure of the potent invitro molecules to diffuse into the biological system.The interaction between the drug and receptor involves the formation of drug-receptor complex followed by the initiation of the biological effect. The study of the affinity of the ligand for the receptor and the efficacy of the biological activity reveals that these are not actually linearly related. But an agonist has an optimum affinity to effect maximum biological activity. A drug molecule has to cross both the aqueous and lipid barriers of the cell membrane to successfully reach the receptor or target site.[17] For a ligand to cross the cell membrane, it must have both the hydrophilic and hydrophobic nature. The lipophilicity and the hydrophilicity of the ligand can be calculated by calculating the partition coefficient P of the ligand in n-octanol/water system.[18] Again, the binding of the ligand to the receptor was usually by the hydrogen bonding. The number of hydrogen bond donor and the hydrogen bond acceptors helps in the prediction of the binding of the ligand with the receptor if the nature of the receptor is known. The size of the lead molecule also makes a difference in the diffusion of the molecule to cross the cell membrane barrier to enter into the biological system. The molecules with molecular weights between 100-500 are able to cross the barrier with much permeability. But for the molecules with high molecular weight >700, they may find much impermeability due to their large size. [19] Molecular refractivity is another important parameter which gives an idea about the electronic polarization of the ions (polarizability) of the molecule in the bio-fluids.[20] This accounts for the bio-absorption of the drug and the ability of the drug to form drug-receptor complex. The polar surface area(PSA) of the drug molecule helps in the determination of the surface volume of overall polar atoms including hydrogen atoms attached to them. PSA is a commonly used medicinal chemistry metric for the optimization of a drug's ability to permeate cells. For molecules to penetrate the blood–brain barrier (and thus act on receptors in the central nervous system), a PSA less than 90 Ao2 is usually needed.[21,22]Prediction of logP was done by the software HYPERCHEMIE 8.0 with rigorous optimization of more than 3hrs.the same was repeated 5 times to get concordant values. 2.3 Synthesis The derivatives of 8-Formyl-7-hydroxy-2-phenyl-3-methyl chromones, 6-Chloro, 8-formyl-7-hydroxy-2-phenyl chromones, 6-Bromo 8-Formyl-7-hydroxy-2-phenyl chromones, 8-Formyl-7-hydroxy-6-methyl -2-phenyl, chromones were synthesized using Microwave irradiation method. The substituted (Shown in Scheme 1) Resacetophenone were reacted with benzoyl chloride. The solvents used were Chlorobenzene and water was irradiated with MW irradiation for 5 mins. The resulting compounds were characterized by IR, 1H NMR and Mass spectrometry. The Microwave acts as the greener way compared to the conventional heating method. The synthesis was done using Microwave and the products obtained were >95% pure. The synthetic scheme was as in scheme 1. Step1: Synthesis of 1-(2,4 dihydroxy phenyl)-3-phenyl-1,3-dione:2(a-d) The Respropiophenone 1a (1mmol) was taken in a 100mL Benzoyl chloride (1mmol) was taken and 2mL Chlorobenzene was added to this, NaOH about (2mmol ) finely crushed was added in a glass tube kept in a microwave oven and irradiated with Microwave(2450MHz) for 5 mins. The completion of the reaction was tested with TLC , the tube was cooled, opened and acidified with hydrochloric acid and extracted with ethyl acetate (2X5mL). Ethyl acetate was removed under reduced pressure to give the solid which was purified by column chromatography to form 2a. The same method was adopted for the synthesis of 2b, 2c and 2d by the use of 1b,1c,1d respectively. Step 2: Synthesis of 7-Hydroxy-2-phenyl-chromen-4-one:3(a-d) Compound 2a (1mmol) was taken in a glass tube was dissolved in 2mL ethanol then catalytic amount of CuCl2 in ethanol was added and the tube was irradiated with MW for 3min. The glass was cooled and the contents were

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cooled in ice. The solid obtained was filtrated and washed with 1:1 cold HCl and recrystallized with ethanol to afford 3a. Similar procedure was adopted to synthesize 3b,3c and 3d by employing 2b, 2c and 2d respectively. Scheme 1:

Compd 1a 1b 1c 1d

R Compd R H 2a H Cl 2b Cl Br 2c Br 2d CH3 CH3

Compd 3a 3b 3c 3d

R H Cl Br CH3

Compd 4a 4b 4c 4d

R H Cl Br CH3

Step3: Synthesis of 8-Formyl-7-hydroxy-2-phenyl chromen-4-one (4a):4(a-d) 7-Hydroxy 2-phenyl chromone 3a (1mmol)was dissolved in 2mL Tri Methyl Acetic acid(TMAA) was taken in a glass tube (1mmol) HMT(Hexamethylenetetramine) was added and the glass tube was closed and irradiated with MW for 3mins. The glass tube was cooled and neutralized with saturated sodium bicarbonate. The solid separated was filtered and solid was extracted with ethyl acetate. The ethyl acetate was removed under reduced pressure and the residual solid was purified by column and recrystallized in methanol to afford 4a. Similar procedure was adopted for the synthesis of 6-Chloro derivative by using 3b, 6-bromo derivative by 3c and 6-methyl-8-Formyl-7-hydroxy-2phenyl chromone by using 3d to get respectively the compounds 4b, 4c and 4d. 3.

Characterization

1-(2,4 dihydroxy phenyl)-3-phenyl-1,3-dione (2a): Orange solid, (MeOH), yield 90%, mp 99-101oC;IR (KBr,cm-1) νmax 3014(C-H), 1706, 1680,1560, 1392,1238(-OH), 1011, 478, 818(Ar); 1H NMR(CDCl3,400MHz,) δ= 10.42 (2H,s,OH), 3.83(2H,s,H-C), 6.35(1H,s,H-1) 6.38(1H,d,J=6Hz,H-4), 6.39(1H,d,J=8Hz,H-5), 7.12 -7.78 ( 6 Ar protons), 1-(2,4 dihydroxy phenyl) -3-phenyl-5-chloro-1,3-dione (2b): Dull red solid, (MeOH), yield 87%, mp 132-134oC;IR (KBr,cm-1) νmax 3014(C-H), 1706, 1680,1560, 1392,1238(-OH), 1011, 476,818(Ar); 1H NMR(CDCl3,400MHz,) δ= 10.42 (1H,s,OH), 3.83(2H,s,H-C), 6.35(1H,s,H-1) 7.38(1H,s ,H-4), 7.12 -7.78 ( 6 Ar protons),

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1-(2,4 dihydroxy phenyl) -3-phenyl-5-bromo-1,3-dione (2c): Pale brown solid, (MeOH), yield 89%, mp 140-142oC;IR (KBr,cm-1) νmax 3014(C-H), 1706, 1680,1560, 1392,1238(O-H), 1011,574, 818(Ar); 1H NMR(CDCl3,400MHz,) δ= 10.42 (1H,s,OH), 3.83(2H,s,H-C), 6.35(1H,s,H-1) 7.90(1H,s ,H-4), 7.12 -7.78 ( 6 Ar protons), 1-(2,4 dihydroxy phenyl) -3-phenyl-5-methyl-1,3-dione (2d): Off white solid, (MeOH), yield 84%, mp 111-112oC;IR (KBr,cm-1) νmax 3014(C-H), 1706, 1680,1560, 1392,1238(O-H), 1011,120, 818(Ar); 1H NMR(CDCl3,400MHz,) δ= 10.42 (1H,s,OH), 3.83(2H,s,H-C), 6.35(1H,s,H-1) 7.90(1H,dd,J=4,J=8Hz,H-4), 2.8 (3H,d,J=10Hz,CH3-5) 7.12 -7.78 ( 6 Ar protons), 7-Hydroxy-2-phenyl-1H-chromene-4-one (3a): Brownish solid, (MeOH), yield 80%, mp 157-159oC;IR (KBr,cm-1) νmax 3014(C-H), 1706(C=O), 1560, 1392, 1238(O-H), 1011, 799, 818(Ar); 1H NMR(CDCl3,400MHz,) δ= 10.45 (1H,s,OH), 6.48(1H,s,H-5), 6.72(1H,d,J=6,H-6), 7.12 -7.78 ( Ar protons), 8.02(1H,d, J =10Hz,H-5) 7-Hydroxy-6-chloro-2-phenyl-1H-chromene-4-one (3b): Pale brown solid, (MeOH), yield 76%, mp 175-177oC;IR (KBr,cm-1) νmax 3014(C-H), 1706(C=O), 1560, 1392, 1238(-O-H), 1011, 476,818(Ar); 1H NMR(CDCl3,400MHz,) δ= 10.45 (1H,s,OH), 6.48(1H,s,H-5), 7.12 -7.78 (Ar protons), 7.92(1H,d, J =10Hz,H-5) 7-Hydroxy-6-bromo-2-phenyl-1H-chromene-4-one (3c): Pale brown solid, (MeOH), yield 76%, mp 175-177oC;IR (KBr,cm-1) νmax 3014(C-H), 1706(C=O), 1560, 1392, 1238(-O-H), 1011, 576,818(Ar); 1H NMR(CDCl3,400MHz,) δ= 10.45 (1H,s,OH), 6.56 (1H,s,H-5), 2.72(3H,d,J=6,H-6), 7.12 -7.78 (Ar protons), 8.02(1H,d, J =10Hz,H-5) 7-Hydroxy-6-methyl-2-phenyl-1H-chromene-4-one (3d): White solid, (MeOH), yield 86%, mp 144-146oC;IR (KBr,cm-1) νmax 3014(C-H), 1706(C=O), 1560, 1392, 1238(-OH), 1011, 120,818(Ar); 1H NMR(CDCl3,400MHz,) δ= 10.45 (1H,s,OH), 6.56 (1H,m,H-5), 7.12 -7.78 (Ar protons), 8.02(1H,d, J =10Hz,H-5) 8-Formyl-7-hydroxy-2-phenyl chromen-4-one (4a): Light Yellow solid, (MeOH), yield 85%, mp 120-122oC;IR (KBr,cm-1) νmax 3014(C-H), 1706, 1560, 1392(C-O-), 1238(-O-H),1374(C-CH3)1011, 818(Ar); 1H NMR(CDCl3,400MHz,) δ= 10.45 (1H,s,OH), 10.41(1H,s,HC=O), 6.85(1H,d,J=8,H-6), 7.12 -7.78 ( Ar protons), 7.52(1H,d, J =9.2Hz,H-5) 8-Formyl-7-hydroxy6-chloro-2-phenyl-chromen-4-one (4b): Yellow solid, (MeOH), yield 88%, mp 132-134oC;IR (KBr,cm-1) νmax 3014(C-H), 1706, 1560, 1392(C-O-), 1238(O-H),1374(C-CH3)1011,478,818(Ar); 1H NMR(CDCl3,400MHz,) δ= 10.45 (1H,s,OH), 10.41(1H,s,HC=O), 7.12 7.78 ( Ar protons),7. 8(1H,s ,H-5) 8-Formyl-7-hydroxy6-bromo-2-phenyl-chromen-4-one (4c): Dull brown solid, (MeOH), yield 85%, mp 139-141oC;IR (KBr,cm-1) νmax 3014(C-H), 1706, 1560, 1392(C-O-), 1238(-O-H),1374(C-CH3)1011,564,818(Ar); 1H NMR(CDCl3,400MHz,) δ= 10.45 (1H,s,OH), 10.41(1H,s,HC=O), 7.12 -7.78 ( Ar protons),8.28(1H,s ,H-5) 8-Formyl-7-hydroxy6-methyl-2-phenyl-chromen-4-one (4d): White solid, (MeOH), yield 90%, mp 124-126oC;IR (KBr,cm-1) νmax 3014(C-H), 1706, 1560, 1392(C-O-), 1238(-OH),1374(C-CH3)1011,124,818(Ar); 1H NMR(CDCl3,400MHz,) δ= 10.45 (1H,s,OH), 10.41(1H,s,HC=O), 7.12 -7.78 ( Ar protons), 2.56(3H,d,J=8,H-6), 7. 8(1H,q, J=2Hz,H-5)

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All these compounds were already synthesized by conventional methods and are not new compounds. So the 1H NMR was analyzed for the confirmation of the compounds synthesized using MW method. 4.

Results and Discussion

4.1 Physicochemical Properties Quantitative physicochemical properties data were shown in Table1. The CLogP value of the compound is the measure of their lipophilicity that helps them to enter into the cell. The degree of an antagonistic property of the analogs with the receptor/microbic protein reveals that the compounds having optimum CLogP values (3-4.1) showed good antimicrobial activities. The molecular refractivity (CMR) lying between (9-12) are expected to be lead like molecules. Also, the molecular mass lies between 290-490daltons. This holds good with the work of Ghose et.al.22 [22] Further, for the compounds having CLogP greater than 3 and calculated topological surface area of the compounds (tPSA) less than 74Ao2 are six times more likely to elicit in vivo effects at concentrations below 10µM of total drug compared to the compounds that have CLogP >3 and tPSA> 74Ao2 are more likely to have increased propensity for off-target pharmacology.[23] Table 1: Some Physicochemical properties of Chromone compounds.

Compd 1a 1b 1c 1d 2a 2b 2c 2d 3a 3b 3c 3d 4a 4b 4c 4d

CLogP 1.4298 1.9346 2.2146 2.1265 2.4653 2.9902 2.1923 2.9243 3.2109 3.4654 3.8973 3.9871 3.3394 3.7712 3.9717 3.7889

CMR 4.021 4.4532 4.6743 4.5343 6.9688 7.4602 7.7458 7.5430 6.8279 7.3187 7.6911 7.5437 7.3268 7.8185 8.1038 7.7906

Mol.Wt. 152.15 186.59 231.04 167.15 256.05 290.70 335.15 370.28 238.34 272.68 317.13 252.26 266.25 300.69 345.14 280.27

tPSA(Ao2) 57.53 57.53 57.53 57.53 74.6 74.6 74.6 74.6 46.53 46.53 46.53 46.53 63.6 63.6 63.6 63.6

4.2 Comparison of the conventional method to the Microwave method In the conventional method of synthesis of 8-Formyl-7-hydroxy 2-phenyl chromones, step 1 is the Synthesis of 7hydroxy-2phenyl-4H-chromene-4-one was done by two steps. As shown in Scheme2 The first step involves the reaction of res acetophenone with benzoyl chloride, which is refluxed for about 8hrs. to form the intermediate which upon neutralization, the solid formed is filtered and acidified with dilute 1:1 HCl and filtered to afford the 7Hydroxy chromone. The third step again involves the heating of the chromone with HMT in glacial acetic acid and refluxed for 6 hrs. on a water bath. Thus, it requires including the workup and reaction durations, about 36-72 hrs. to get the precursor 8-Formyl-7-hydroxy chromones for further reaction. Each step required common purification procedures like extraction and column chromatography. While if we compare this method with the Microwave assisted method, the time taken for the same synthesis was hardly 1-2 hrs. including the workup procedures. Also,

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the yield obtained was more compared to the conventional method and purity was also far better compared to the conventional method. The usage of solvent was also less.The scheme for the conventional method of synthesis of 8Formyl-7-hydroxy-2-phenyl chromone derivatives is as shown in Scheme 2. By comparing the physicochemical assay as shown in Table 1, The molecules 4a-4d showed ClogP values more than 3 and tPSA value <74Ao2. Also, the molecular weight and tPSA values lied within the permeability limit, which makes the molecule more active in vivo conditions.[24] Scheme2

Scheme 2: showing the scheme of synthesis of 8-Formyl-7-hydroxy-2-phenyl chromones by conventional method

5.

Conclusion

Thus, the Microwave assisted method has proven to be the most convenient method for the synthesis of the 8Formyl-7-hydroxy-2-phenyl chromones. These biologically active compounds were also confirmed by the study of their physicochemical parameters which are used extensively as the precursors for the synthesis of Schiff bases of chromones, which are very potent biologically active scaffolds. The 8-formyl chromones obey Lipinski's RO5, [25]Hansch’s property of logP and also the level of toxicity fulfills all the criterion to be drug-like or lead-like molecules. Acknowledgments One of the Authors (Kini Jyothi H.), sincerely thankful to the Government of Karnataka, Department of Collegiate Education and University Grants Commission for awarding Teacher Fellowship for Research. Also, the authors extend their gratitude towards the Research Centre, Department of Industrial Chemistry, Kuvempu University, for providing the lab facilities.

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