Research

, Volume: 14( 3)

Synthesis, Characterization, and Analgesic Activity of (E)-3-(2-amino-4,6dichloropyrimidin-5-yl)-1-(benzo[d][1,3]dioxol-5-yl)prop-2-en-1-one Mahapatra DK1*and Asati V2

*Correspondence:

Mahapatra DK , Department of Pharmaceutical Chemistry, Dadasaheb Balpande College of Pharmacy, Nagpur 440037, Maharashtra, India, Tel: 9172322500; E-Mail: dkmbsp@gmail.com

Abstract

Chalcone or 1,3-diphenyl-2E-propene-1-one or benzylideneacetophenone are low molecular weight ligands known to possess tremendous anti-inflammatory, analgesic, anti-gout, and anti-ulcer activities. From the literature, it was evidenced that chalcone with a number of substituents at B-ring (particularly, electron withdrawing groups) of the chalcone scaffold are well-known for expressing pronounced cycloxygenase (COX) and lipoxygenase (LOX) inhibitory potential. Inspiring from the fact, in the present research, a B-ring highly substituted chalcone was fabricated from 1-(benzo[d][1,3]dioxol-5-yl)ethanone and 2-amino-4,6-dichloropyrimidine-5-carbaldehyde using Claisen-Schmidt reaction and the structure was elucidated by sophisticated analytical techniques like FT-IR spectroscopy, 1H-NMR spectroscopy, mass spectroscopy, and elemental analysis. The analgesic activity was explored in Swiss albino rats by employing the acetic-acid induced writing model. The chalcone displayed noteworthy analgesic activity of 40.12% after 3 hrs. A significant reduction in the writing was observed in the Swiss albino rats. However, the degree of biological activity was found to be lower than that of the standard drug, diclofenac sodium. The study expressively indicated towards the analgesic potentials of the highly substituted chalcone which rejuvenated the importance of small molecules in modern pharmacotherapeutics. The study will motivate global researchers and will open new avenues in the rational development of natural products based NSAIDs.

Keywords

Chalcone; 1,3-diphenyl-2E-propene-1-one; Analgesic; Inflammation; Synthesis; Characterization

Introduction

Anti-inflammatory and analgesic effects are the most crucial pharmacological actions that find importance in everyday life. The non-steroidal anti-inflammatory drugs (NSAIDs) class is the most prominent for this application, along with some anti-pyretic relevance [1]. Over the years, the emergence, advancements, and implementation of the pharmacy practice subject thoroughly focused on the burning issues of patient compliance and side-effects and highlighted critical questions related with the prolonged administration of these medicines in the management of chronic conditions such as rheumatoid arthritis, etc [2]. While finding the most appropriate solution to these problems, several therapeutic approaches have been reported over the years by the global researchers [3]. Of which, natural products and its associated therapies or alternative medicines (like homeopathy, ayurvedic, naturopathy, etc.) are widely accepted among the masses. Walking through the similar path of research and new drug discovery, the NSAID perspective of the novel chalcone compounds have been explored [4].

Chalcone or 1,3-diphenyl-2E-propene-1-one or benzylideneacetophenone are Low-Molecular-Weight Ligand (LMWL) of natural origin having two aromatic nuclei connected with a three carbon α, β-unsaturated carbonyl bridge. They are the open chain intermediates in the aurones synthesis of flavones and are the precursors of flavonoids and isoflavonoids, having tremendous anti-cancer, anti-oxidant, anti-inflammatory, analgesic, antipyretic, anti-diabetes, anti-infective, anti-hypertensive, anti-hyperlipidemic, etc [5-9]. From the literature, it was evidenced that chalcone with a number of substituents at B-ring (particularly, electron withdrawing groups) of the chalcone scaffold are well-known for expressing pronounced cycloxygenase (COX) and lipoxygenase (LOX) inhibitory potential [5]. Inspiring from the fact, in the present research, a B-ring highly substituted chalcone was fabricated from 1-(benzo[d][1,3]dioxol-5-yl)ethanone and 2-amino-4,6-dichloropyrimidine-5-carbaldehyde, and analgesic activity was explored in Swiss albino rats by employing the acetic-acid induced writing model.

Materials and Methods

Chemicals and instrumentation

The starting material 1-(benzo[d][1,3]dioxol-5-yl)ethanone and the reactant 2-amino-4,6-dichloropyrimidine-5-carbaldehyde were purchased from Sigma Aldrich, Germany through a local vendor at Nagpur. The solvents employed in the chemical reaction were of analytical grade and procured from HiMedia Ltd., India. The formation of the prop-2-en-1-one compound was ascertained initially by monitoring the progress of the chemical reaction by utilizing the Merck® Silica gel-G pre-coated TLC plates. The final structure was completely confirmed by Fourier-transformed Infrared (FT-IR) Spectroscopy (Shimadzu® IR-Affinity-1), proton-NMR Spectroscopy (Bruker Avance-II), and Mass Spectroscopy (MICROMASS Q-TOF). Finally, CHN analysis was performed on an Elemental Analyzer of PerkinElmer 2400 model.

Animals

Synthesis of target compounds: The benzylideneacetophenone scaffold (E)-3-(2-amino-4,6-dichloropyrimidin-5-yl)-1-(benzo[d][1,3]dioxol-5-yl)prop-2-en-1-one (3) was fabricated by utilizing the aldol condensation mechanism where an aldehyde part of the substrate, 1-(benzo[d][1,3]dioxol-5-yl)ethanone (1) react with the acetyl portion of the reactant, 2-amino-4,6-dichloropyrimidine-5-carbaldehyde (2) in the presence of ethanolic sodium hydroxide solution to form a β-hydroxyketone function (SCHEME 1).

Synthetic protocol for (E)-3-(2-amino-4,6-dichloropyrimidin-5-yl)-1-(benzo[d][1,3]dioxol-5-yl)prop-2-en-1-one: An equal (0.01 M) concentration of substrate (1) and reactant (2) were made to react by refluxing in the presence of 20 mL aqueous sodium hydroxide solution, comprising of 90% ethanol (25 mL). Overnight, the reaction mixture was stand and the reaction content was poured over dilute HCl containing crushed ice with vigorous stirring using a glass rod. The product was separated by filtration with Whatman filter paper and further recrystallized.

77% yield; FTIR (KBr) υ (cm^-1): 3382 (-NH₂, stretching), 3115 (C-H, aromatic), 1730 (C=O), 1643 (-NH, bending), 1606 (C=C, aromatic), 1488 (-CH₂), 1332 (C-N), 1246 (C-O), 811 (C-Cl); 1H NMR (δ, ppm, CDCl₃): 8.21 (6, 1H), 7.29 (10, 2H), 7.1-7.8 (Aromatic, 3H), 6.19 (1, 2H). MS: M⁺ 337, M⁺ 2 339. Anal. Calcd. for C₁₄H₉Cl₂N₃O₃: C, 49.73; H, 2.68; N, 12.43. Found: C, 49.02; H, 2.19; N, 12.12.

Acute toxicity studies

Following the OECD guidelines, the acute toxicity and the in vivo safety profile of the chalcone compound were estimated through the estimation of the lethal dose (LD₅₀), based on the death of 50% animals, by gradually raising the dose ranging from 10 mg/kg to 300 mg/kg by i.p. route [10].

In vivo analgesic activity

By utilizing the acetic acid-induced writing method, the analgesic potential of the extract was screened in mice. The pain sensation was generated by intraperitoneal administration of acetic acid in mice. The Swiss Albino rats have fasted overnight and the chalcone was orally administered to at dose of 400 mg/kg b.w., 30 min prior to injection of 0.7% v/v acetic acid solution (0.1 mL/10 g). The positive control (diclofenac sodium) at a dose of 25 mg/kg b.w. was administered 15 minutes prior to the injection of acetic acid solution. The experimental animals were placed on the observation table and the number of writing made in 15 minutes was recorded. The half-writing was considered as incomplete writing and two half-writings are considered as one full writing. The number of writhes in the experimental group was compared with the control group and the positive control [11]. The % inhibition of writing was calculated according to the formula:

% inhibition=100–(Mc-Mt)/Mc × 100

Where Mc=Mean number of writing in the control group and Mt=Mean number of writing in the treated group.

Statistical treatment

The procured data were expressed in terms of Mean ± SEM and one-way ANOVA approach followed by Dunnett’s multiple comparisons test was applied as the statistical treatment. The obtained data were compared with the control group and value P<0.01 was considered as statistically significant.

Results and Discussion

Chemistry

The spectroscopic data focused on the formation of the prop-2-en-1-one compound. The amino group (-NH₂) was confirmed from the FT-IR spectra by the appearance of the peak at 3382 cm^-1 and also from the proton-NMR peak at 7.29 ppm. The above finding clearly supported the presence of the pyrimidine nucleus in the fabricated benzylideneacetophenone. Similarly, the part-A of the molecule containing 1,3-dioxole and phenyl ring were ascertained by both the spectroscopic tools. The FT-IR spectra demonstrated distinct peaks at 1488 cm^-1, which represented –CH₂ fragment of the 1,3-dioxole. Additionally, the 1H-NMR showed the presence of the 1,3-dioxole portion at 6.19 ppm. The existence of aromatic phenyl ring was established from the C-H and C=C stretching at 3115 cm^-1 and 1606 cm^-1, respectively. Likewise, the 1H-NMR presented the appearance of aromatic protons in the spectra in the range of 7.1-7.8 ppm. The presence of the bridge of the chalcone was found out from the analytical study at 8.21 ppm. The mass spectra recognized the formation of the compound from the base peak, which corresponds with the molecular mass (M⁺ 337). The high-intensity peak at molar mass 339 (M⁺²) signified the isotope of chlorine atoms, thereby, confirming the chlorine atoms in the molecule. Few fragment peaks of lower mass were observed in the mass spectra.

LD₅₀ value estimation

The safety studies in the administrated range of 10-300 mg/kg b.w. showed no such signs and symptoms of acute toxicity effects. The exploration of the analgesic activity of the chalcone molecule was performed at a dose of 200 mg/kg b.w.

Analgesic activity

The chalcone displayed noteworthy analgesic activity of 40.12% after 3 hrs. A significant reduction in the writing was observed in the Swiss albino rats. The heterocyclic portions, pyrimidine as well as 3′,4′-methylenedioxy moiety may found to play a pivotal role in mediating the analgesic effect [12,13]. However, the degree of biological activity was found to be lower than that of the standard drug, diclofenac sodium. The presence of the substituents in the chalcone scaffold may be believed to decrease the expression of cyclooxygenase-1/2 (COX-1/2), lipoxygenase (LOX), 15-Hydroxyprostaglandin dehydrogenase (15-PGDH), and other miscellaneous inflammatory mediators which play an imperative role in the mediation of algesia [14,15].

Comparison with previously synthesized chalcones

In a previous report by our research group, 3′,4′-methylenedioxy moiety containing murrayanine-based chalcone was synthesized which displayed anti-inflammatory potential of 59.41% after 3 hrs [13]. In another report, the B-ring substituted with hydroxyl group produced inhibition of inflammatory mediators to exhibit 48.33% edema control after 3 hrs [14]. Similarly, imidazole containing murrayanine-based chalcone presented edema reducing the potential of 40.13% after 3 hrs [16]. In a recent report, substitution of tert-butyl group in the Ring-B of murrayanine-chalcone resulted in a higher expression of anti-inflammatory activity with 64.69% reduction of edema after 3 hrs. These reports certainly indicated towards the NSAID perspectives of the chalcone scaffold and therefore, it might be predicted that due to diverse substitutions at specific regions produced significant algesia reduction in the experimental animals [17] (TABLE 1).

Table 1: In vivo analgesic activity of the fabricated chalcone compound.

Conclusion

The study expressively indicated towards the analgesic potentials of the highly substituted chalcone which rejuvenated the importance of small molecules in modern pharmacotherapeutics. The fabricated B-ring highly substituted chalcone molecule demonstrated noteworthy analgesic activity of 40.12% after 3 hrs which were quite lower than that of the standard drug, diclofenac sodium. The study will motivate global researchers and will open new avenues in the rational development of natural products based NSAIDs.

Conflict of Interest

None declared

References

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