SYNTHESIS AND IN VITRO ANTIPLAQUE ACTIVITY OF CHALCONE, FLAVONOL AND FLAVANOL DERIVATIVES

SYNTHESIS AND IN VITRO ANTIPLAQUE ACTIVITY OF CHALCONE, FLAVONOL AND FLAVANOL DERIVATIVES

Vijayalaxmi Chavan Patil

Government College of Pharmacy, Aurangabad-431005, Maharashtra, India

ABSTRACT

Synthesis of chalcone derivatives was carried out by aldol condensation, these 2’-hydroxychalcones were cyclized to 3-hydroxyflavone and 2, 3- dihydroflavan-3-ol derivatives and we also report here there in vitro antiplaque activity. Most of the synthesized compounds were found to be active against Streptococcus mutans. Activity of two 3-hydroxyflavones was found to be higher than that of their corresponding 2, 3- dihydroflavan-3-ol derivatives and chalcone analogues. Investigated compounds having hydroxy group substituents in ring-B exhibited enhanced activity and the presence of electronegative groups in the studied compounds showed a direct relationship to the antiplaque activity.

Chalcone, Hydroxyflavones, Flavonols, Antiplaque, Streptococcus mutans

INTRODUCTION: Flavonoids are yellow color pigments and being named so as in Latin Flavus  means yellow colour. Structurally, flavonoids are derivatives of benzopyrone, a group of aromatic oxygen-bearing heterocyclic compounds. Flavonoids are chromene which has basic ring system of benzo-4-pyranone ¹.

All these Flavonoid derivatives are associated with free radical scavenging activity through various mechanisms like Direct radical scavenging, Inhibition of nitric oxide synthesis, Xanthine oxidase inhibition, Leukocyte immobilization inhibition, Direct inhibition of lipid peroxidation etc ².

Flavonoid derivatives shows cardioprotective, gastroprotective, anti-inflammatory activity, Anti-tumor, Antithrombogenic, Antiviral, Anti-osteoporotic, Antimicrobial, Antiprotozoal, Antiplaque activities & also prevents dementia ^3-11.

Chalcones are yellow pigments known as precursors of many naturally occurring pigments such as flavones. Chalcones are substituted benzalacetophenone derivatives, due to the presence of the reactive keto vinylenic group, chalcones and their analogues have been reported to be  antiulcerative, anti-inflammatory, anti-angiogenic, analgesic, anticancer and antioxidant ^{12, 13}.

The micro-organism responsible for tooth decay is Streptococcus mutans, it is gram positive anaerobic bacteria. It causes yellow plaque deposition on teeth, and further deteriorate the condition by causing gingivial inflammation i.e. Gingivitis, it is an inflammation of gums i.e. Gingiva around the teeth. In general terms the gingivitis is refered to the inflammation induced by bacterial biofilms adhered to tooth surface known as Plaques.

Green tea has been extensively examined, as a useful plant that contains flavonoids, in the control of plaque-related diseases. With respect to dental caries, extracts have been shown to kill Streptococcus mutans and Streptococcus sobrinus.

Inhibition of bacterial adherence, acid production, and glucosyl transferase activity (which is involved in extracellular polysaccharide formation), have all been demonstrated. Animal and human trials also support the use of green tea in the control of dental caries ¹⁴.

Literature states that plant flavonoids in toothpastes are responsible for antiplaque action and works against tooth decay. Plaque-related diseases are probably the most common bacterial diseases occurring in man. Flavonoid derivatives which posses hydroxylated phenolic nucleus where the C6-C3 unit is linked to an aromatic ring, demonstrates a broad range of antimicrobial activity. For example, catechins as found in green tea ¹⁵. Guaijaverin isolated from Psidium guajava Linn. Shows anti- Streptococcus mutans activity ¹⁶.

In nature, flavonoids are available but their use as drug is limited by high cost of processing. There are some marketed products of natural flavonoids from plant sources except a few for various activities like antiinflammatory, anticancer, antiviral, antimicrobial, muscle relxant, antiageing, antialzimer’s and other neurodegenerative diseases. Widespread use of flavonoids is hindered because of its limited availability, lengthy, tedious, time consuming and uneconomic isolation, separation, purification, and structural modification techniques.

Thus, goal of this work is to synthesize flavonoid derivatives starting from commonly available raw materials and its evaluation for Antiplaque activity.

In present investigation, 2’-hydroxychalcone  derivatives were synthesized by Aldol condensation, in this reaction hydroxy-acetophenone derivatives were treated with aromatic aldehyde in presence of strong base like NaOH.

Further, flavonol derivatives were synthesized by Algar Flynn Oyamada  reaction, the 2’-hydroxy chalcones were converted to 3-hydroxy flavones (flavonol) and 2,3-dihydroflavan-3-ol (flavanol) by cyclization. All the reactions are shown in Figure 1-3.

FIG. 1: SYNTHESIS OF 2'-HYDROXYCHALCONE DERIVATIVES

FIG. 2: SYNTHESIS OF 3-HYDROXY FLAVONES (FLAVONOL) DERIVATIVES

FIG. 3: SYNTHESIS OF 2,3-DIHYDROFLAVAN-3-OL (FLAVANOL) DERIVATIVES

2’-hydroxychalcone derivatives (C1-C5) were synthesized by following procedure ¹⁷. Equimolar quantities of aromatic aldehyde derivatives (0.01 mol) and acetophenone derivatives (0.01 mol) as shown in Table 1 were dissolved in minimum amount of alcohol.  Sodium hydroxide solution (0.02 mol) was added slowly and the  mixture stirred for 2hr until the entire mixture becomes very cloud. Then the mixture  was poured slowly into 400 ml of water with constant stirring and  kept in refrigerator  for 24 hours. The precipitate obtained was filtered, washed and recrystallized from ethanol. The completion of the reaction was monitored by TLC. Yields, melting points & Rf values of C1-C5 are reported in Table 2 .

TABLE 1: RAW MATERIAL USED FOR SYNTHESIS OF  2’-HYDROXYCHALCONE DERIVATIVES

TABLE 2: PHYSICAL CHARACTERISATION DATA OF SYNTHESIZED 2’-HYDROXYCHALCONE DERIVATIVES

C1= C₁₅O₂H_12, IR (KBr cm^-1) 1644(C=O), 3028(O-H), 1300-1400(C=C), 600-900(C-H aromatic), UV λmax (nm) 373(1.284), 249(0.612), MS (GC-MS) m/z 223(M+), 147(C₉O₂H₆⁺), 207 (C₁₅H₁₂O), 120 (C₆H₅O₂), 103 (C₈H₇⁺)

C2 = C₁₆H₁₄O_3,  IR (KBr cm^-1) 1774 (C=O), 3069 (O-H), 1300-1400(C=C), 600-900(C-H aromatic), UV λmax (nm) 317 (0.644), 251(0.559), MS (GC-MS) M/Z 268(M), 253 (C₁₅H₉O₄), 85(C₃H₂O₃⁺)

C3 = C₁₇H₁₇O₂N,  IR (KBr cm^-1) 1604 (C=O), 3074 (O-H), 3301( C-N), 1300-1400(C=C), 600-900(C-H aromatic), UV λmax (nm) 346 (1.276), 247(0.479)

C4 = C₁₇H₁₇O₃N, _, IR (KBr cm^-1)  1662 (C=O), 3092 (O-H), 1300-1400(C=C), 600-900(C-H aromatic), UV λmax (nm) 360 (2.004), 232(0.779)

C5 = C₁₇H₁₄O_{2 ,} IR (KBr cm^-1) 1634 (C=O), 3065 (O-H), 1300-1400(C=C), 600-900(C-H aromatic), UV λmax (nm) 346 (1.276), 247(0.479)

Flavonol derivatives (F1-F5) were synthesized by following procedure ¹⁸. To a suspension of chalcone (0.01mole) in 85ml ethanol was added to 10 ml 20% aqueous sodium hydroxide with stirring, followed by careful addition of 18ml 20% hydrogen peroxide over a period of 0.5hr. The reaction mixture was stirred for 3 hrs. at 30^oC and poured onto crushed ice containing 5N HCl. The precipitate was filtered, washed, dried and crystallized from chloroform: methanol [9:1] . Yields, melting points & Rf values of F1-F5 are reported in Table 3.

TABLE 3: PHYSICAL CHARACTERIZATION DATA OF SYNTHESIZED 3-HYDROXY FLAVONES DERIVATIVES

F1= C₁₅H₁₀O_3, IR (KBr cm^-1) 1605 (C=O), 3193 (OH), 1300-1400 (C=C), 600-900  (C-H aromatic), UV λmax (nm) 351 (2.146), 249(1.955), MS (GC-MS) M/Z 237(M+), 77(C₆H₆)

F2= C₁₆H₁₂O₄, IR (KBr cm^-1) 1606 (C=O), 3225 (OH), 1300-1400 (C=C), 600-900  (C-H aromatic), UV λmax (nm) 360 (1.902), 259(1.234)

F3 = C₁₇H₁₅O₃ N, IR (KBr cm^-1) 1603 (C=O), 3305 (OH), 1300-1400 (C=C), 600-900  (C-H aromatic), MS (GC-MS) M/Z 281(M), 105(C₇H₅O⁺)

F4 = C₁₇H₁₅O₄N, IR (KBr cm^-1) 1678 (C=O), 3049 (OH), 1300-1400 (C=C), 600-900  (C-H aromatic), UV λmax (nm) 338 (1.796), 240(0.427)

F5 = C₁₇H₁₂O_3, IR (KBr cm^-1) 1590 (C=O), 3060 (OH), 1300-1400 (C=C), 600-900  (C-H aromatic), UV λmax (nm) 437(0.962), 256(1.582)

2’-hydroxy chalcone derivatives (C1-C5) were cyclised to 2,3-dihydroflavan-3-ol derivatives (S1-S5) by following procedure. A suspension of a mixture of powdered 2’-hydroxychalcone (0.45 mmol), an aq. NaOH solution (8 M, 1.0 ml) and a 30% hydrogen peroxide solution (0.25 ml) was stirred at room temperature for 2 h. The crude product was filtered off, washed with water and dried in a desiccator to give flavanol. Recrystallization of the crude product from Methanol. Yields, melting points & Rf values of S1-S5 are reported in Table 4.

TABLE 4: PHYSICAL CHARACTERISATION DATA OF SYNTHESIZED 2, 3-DIHYDROFLAVAN-3-OL DERIVATIVES

S1= C₁₅H₁₂O_3, IR (KBr cm^-1) 1583 (C=O), 3070 (OH), 1300-1400 (C=C), 600-900  (C-H aromatic), UV λmax (nm) 322(1.469), 227(0.923),

S2= C₁₆H₁₄O_{4 ,} IR (KBr cm^-1) 1572 (C=O), 3051 (OH), 1300-1400 (C=C), 600-900  (C-H aromatic), UV λmax (nm) 339(1.313), 242(0.391)

S3= C₁₇H₁₇O₃ N _, IR (KBr cm^-1) 1601 (C=O), 3051 (OH), 1300-1400 (C=C), 600-900  (C-H aromatic), UV λmax (nm) 345(0.743), 250(0.177)

S4= C₁₇H₁₇O₄N _, IR (KBr cm^-1) 1664 (C=O), 3183 (OH), 1300-1400 (C=C), 600-900  (C-H aromatic), UV λmax (nm) 341(2.005), 241(0.419), MS (GC-MS)

S5= C₁₇H₁₄O_{3 ,} IR (KBr cm^-1) 1678 (C=O), 3049 (OH), 1300-1400 (C=C), 600-900  (C-H aromatic), UV λmax (nm) 353(1.70), 250(0.98)

Reactions and purity of compounds were monitored by thin layer chromatography (silica gel G60) using chloroform: methanol [9:1]  solvent system and the spots were identified by iodine vapor chamber. Melting points were determined in open capillary using paraffin bath and are uncorrected. Infra red spectra was recorded using FT-IR instrument in range 400-4000 cm^_1, Diffraction  reflectance scanning (DRS) technique was used to record the spectra. Mass spectral analysis was done in GC/MS Q2010 instrument by mass spectrometry technique using DI probe.¹⁹

Synthesized compounds were tested for their antibacterial activity by adopting agar well diffusion method. Using Streptococcus mutans Muller Hinton Agar (MHA) plates were used.  Wells were created in the medium with the help of a sterile metallic borer at appropriate distances.

Test samples of 1000 µg/ml were poured into each well and the plates were incubated at 37 ⁰C for 24 h. The results, in terms of inhibition zones, were noted and reported in Table 5 and shown in figure 4.

TABLE 5: ZONE OF INHIBITION

FIG. 4: PHOTOGRAPHS OF ZONE OF INHIBITION STUDY

On observation of positive results of antimicrobial activity, the Minimum Inhibitory Concentration of synthesized compounds were determined by tube dilution method and reported in Table 6.

Study indicated the requirement of highest concentration of 2'-hydroxy chalcone derivatives than 2’-hydroxy chalcone derivatives than 3-hydroxyflavone derivatives to inhibit the Streptococcus mutans. In other words MIC of 3-hydroxyflavone derivatives is lower than that of 2'-hydroxy chalcone derivatives. At the end of study it was concluded that C5 [1-(2-hydroxyphenyl)-5-phenylpenta-2,4-dien-1-one]; is inactive against Streptococcus mutans.

All 3-hydroxyflavone derivatives (F1-F5) showed their MIC in range of 250-125 µg/ml, 2'-hydroxy chalcone derivatives (C1-C5) showed inhibition at 250 µg/ml and 2,3-dihydro-flav-3-ol derivatives (S1-S5) showed inhibition at higher concentration of 500-1000 µg/ml. These results are compared in Figure 5-11.

TABLE 6: MIC OF CHALCONE AND FLAVONOID DERIVATIVES WITH STREPTOCOCCUS MUTANS

FIG. 5: PHOTOGRAPHS OF  MIC OF 2'-HYDROXY CHALCONE DERIVATIVES

FIG. 6: MIC OF 2'-HYDROXY CHALCONE DERIVATIVES

FIG. 7: PHOTOGRAPHS OF  MIC OF 3-HYDROXYFLAVONE DERIVATIVES

FIG. 8: MIC OF 3-HYDROXYFLAVONE DERIVATIVES

FIG. 9: PHOTOGRAPHS OF  MIC OF 2,3-DIHYDRO-FLAV-3-OL DERIVATIVES

FIG. 10: MIC OF 2,3-DIHYDRO-FLAV-3-OL DERIVATIVES

FIG. 11: COMPARATIVE ANTI STREPTOCOCCUS MUTANS ACTIVITY OF CHALCONES, FLAVONOLS AND FLAVANOLS.

2’-hydroxychalcone, 3-hydroxyflavone & 2,3-dihydro-flav-3-ol derivatives can be synthesized under available laboratory conditions and were confirmed by physicochemical and spectral analysis.

The result of antimicrobial study against plaque causing microorganism Streptococcus mutans shows that 3-hydroxy flavone derivatives are more active than corresponding 2-hydroxy chalcone & 2,3-dihydro-flav-3-ol derivatives.

Simple and feasible method of synthesis of flavonoid derivatives and evalution of antiplaque activity provided a path to explore the fascinating class of active compound.

These findings about the synthetic methods of flavonoids and their antiplaque activity is highly encouraging and many more flavonoids should be synthesized to obtain most useful once, and the work in this direction will be continued in future.

ACKNOWLEDGEMENT: The author wish to acknowledge Dr. V.K. Mourya, Principal, Government College of Pharmacy, Aurangabad for his idea of present research work, facilities provided for synthesis, analysis & activity evaluation.

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    How to cite this article:

    Patil VC: Synthesis and In-vitro Antiplaque Activity of Chalcone, Flavonol and Flavanol Derivatives. Int J Pharm Sci Res. 3(12); 5006-5014.

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