SYNTHESIS OF PIPERAZINE NUCLEUS CONTAINING NOVEL CHALCONE DERIVATIVES AND THEIR ANTHISTAMINIC ACTIVITY
Field of the invention

The present invention relates to the application of Synthesis of Piperazine nucleus containing novel chalcone derivatives and their antihistaminic activity. More particularly the present invention relates to establish some of the synthetic processes leading to prepare chalcone derivatives by condensation of 4'-piperazinoacetophenone with different substituted aromatic aldehydes, their physicochemical characterization and evaluation for antihistaminic activity.

Background of the invention

Diaryl propene-2-ones, commonly called as Chalcones were reported to possess a wide range of biological activities, such as antibacterial, antiviral, antitubercular, anticancer, antihistaminic, anti-inflammatory and antihypertensive activities. The presence of a reactive a, P-unsaturated keto functional group in chalcone is found to be responsible for their broad spectrum activity, which may be altered depending on the type and position of substituent on the aromatic rings. It is evident from the literature that there is no work has been reported on 4'-piperazino aromatic nucleus containing chalcones and their application as antihistaminic agents.

The inventors of the present invention have endeavored to synthesize potential antihistaminic agents, novel chalcones with piperazine moiety and further characterize the compounds by elemental analysis and spectral data. The inventors also evaluated for their antihistaminic activity using mepiramine as a standard drug.

Objectives of the invention

Accordingly the main objective of the present invention is to synthesize Piperazine nucleus containing novel chalcone derivatives by condensation of 4'-piperazinoacetophenone with different substituted aromatic aldehydes. Yet another invention is to establish the physicochemical properties and chemical structural identification of synthesized chalcone derivatives. Yet another invention is to evaluate the synthesized compounds for the antihistaminic activity. The outcome of this invention will provide sufficient data for using the novel chalcone derivatives of piperazine moiety as potential drugs to use as antihistaminic agents.

Summary of the invention

Accordingly, the present invention provides synthetic routes of preparing eight (8) chalcone derivative compounds (coded as RCi to RCg) by condensation of 4'-piperazinoacetophenone with different substituted aromatic aldehydes in 40% alkali. The structures of the synthesized compounds were identified and established on the basis of elemental analysis, I.R., 1H NMR and mass spectral data. Since these compounds possessed piperazine moiety which is characteristic of many currently available antihistaminic agents, they were evaluated for their antihistaminic activity on guinea pig ileum using mepiramine as standard drug. Then different dilutions of standard solution were prepared to get concentrations of 0.1, 0.2, 0.4 and 0.8 μg/ml. Among the compounds tested, RC6 exhibited a much lower IC50 value than the standard drug (mepiramine) at 0.0033 ±0.0002 μM. Other compounds in this series also possessed dose dependent antihistaminic activity.

Detailed description of the invention

Many antihistaminic compounds contain the piperazine moiety. It is evident from the literature that mere is no work has been reported on 4'-piperazino aromatic nucleus containing chalcones and their application as antihistaminic agents.

The present invention will investigate to synthesize potential antihistaminic agents of novel chalcones with piperazine moiety (RC1 - RC8). Yet another invention is to characterize the structures of the synthesized compounds by elemental analysis, IR, 1H NMR and Mass spectral data. Yet another invention is to evaluate the synthesized compounds for their antihistaminic activity using mepiramine as a standard drug.

The outcome of this invention will provide sufficient data for using the novel chalcone derivatives of piperazine moiety as potential drugs to use as antihistaminic agents.

The present invention elaborates the reaction of a mixture of 4'-piperazinoacetophenone (0.01 M) and aryl aldehyde (0.01 M) (such as 3-bromo benzaldehyde, 4-nitro benzaldehyde, 3-anthracenyl aldehyde, 4-methyl benzaldehyde, 4-chloro benzaldehyde, 2,4-dichloro benzaldehyde, 2-chloro benzaldehyde and 4-fluoro benzaldehyde) by stirring in methanol (15 ml) and then adding an aqueous solution of 40% KOH (3.5 ml) it. The mixture was kept overnight at room temperature, poured into crushed ice, and then acidified with dil. HC1 (Scheme 1).

Yet another embodiment of the present invention is to process the solid separated by filtering and crystallizing from a mixture of ethyl acetate and methanol (8:2) and the melting point and % yield was calculated for the compounds synthesized (Table 1).

Table 1. Physical data of compounds (RC1-RC8)

Yet another embodiment of the present invention is to identify the synthesized chalcone derivatives l-[(4'-piperazino) phenyl]-3-phenyl-2-propene-l-one (RCi-RCg) by Wilson test and FeCl3 test. In Wilson test treatment of the synthesized chalcones with cone. H2SO4 showed a pink color where as in FeCl3 test, treatment of the same compounds showed violet color. All the melting points were determined by digital melting point apparatus.

Yet another embodiment of the present invention is to characterization which is done with the help of IR, 1H NMR and LC-MS spectral data. The IR spectra were recorded on Perkin-Elmer 377 spectrophotometer, the 1H NMR spectra on Bruker AV 400MHZ in CDCl3 using TMS as an internal standard and the mass spectra were obtained on LC-MS MDS Spiex API 2000 (Table 2).

The present invention elaborates the evaluation of antihistaminic activity of synthesized compounds (RC1-RC8) on guinea pig ileum. The animals were sacrificed after overnight fasting. The abdomen was opened; a required length of the long ileal portion was cut into small segments of 2-3 cm length, removed and immediately placed on the watch glass containing tyrode solution. One piece of ileum was taken and a thread was tied to top and bottom ends without closing the lumen and the tissue was mounted in the organ bath containing tyrode solution, maintained at 37°C and bubbled with oxygen air. A tension of 0.5 g was applied and the tissue was allowed to equilibrate for 30 minutes before adding drugs to the organ bath.

Yet another embodiment of present invention is to prepare the test and standard solutions for the study of antihistaminic activity. A l0mg of each test sample was dissolved in DMSO solvent. Different dilutions were made with dextrose normal saline (DNS) solution to get a concentration of 0.1, 0.2, 0.4 and 0.8 μg/ml. Similarly, the standard solution was prepared in the same concentrations as above in DNS solution.

The responses were recorded on a kymograph. The graph was plotted taking concentration of the test or standard on X-axis and % inhibition on Y axis.

where, a is height of histamine response and b is height of test or standard response in cm. A graph was plotted between the log dose of antagonist vs. percentage inhibition and the IC50 values were calculated by interpolation.

Claims:
1. The novel chalcones l-[(4'-piperazino) phenyl]-3-phenyl-2-propene-l-one (RC1-RC8) were synthesized successfully by condensation of 4'-piperazino acetophenone with different substituted aromatic aldehydes such as 3-bromo benzaldehyde, 4-nitro benzaldehyde, 3-anthracenyl aldehyde, 4-methyl benzaldehyde, 4-chloro benzaldehyde, 2,4-dichloro benzaldehyde, 2-chloro benzaldehyde and 4-fluoro benzaldehyde, in 40% alkali.

2. The compounds of claim 1 were purified either by crystallization and identified by TLC and qualitative tests such as Wilson test and FeCl3 test.

3. The yields of claim 1 were obtained between 66.6 and 80.7%.

4. The structures of the claim 1 were established on the basis of spectral data obtained from IR, 1H NMR and MS analysis which confirm the presence of piperazine nucleus in the synthesized chalcones.

5. The pharmacological study of claim 1 compounds revealed that all the chalcones possessed dose dependent antihistaminic activity. Among the compounds tested l-[(4'-piperazino) phenyl]-3-(2',4'-dichlorophenyl)-2-propene-l-one (compound RC6) exhibited the highest antihistaminic activity comparable with that of the standard drug mepiramine.

6. This antihistaminic activity of claim 1 was established on the basis of IC50 values (Figure 1). The calculated IC50 values in μM with ±SEM of novel chalcone derivatives were found to be 0.0945 ±0.0016 (RC1), 0.0141 ±0.0015 (RC5), 0.0033 ±0.0002 (RC6), 0.011 ±0.0013 (RC7), 0.0197 ±0.0024 (RC8) and 0.0053 ±0.0004 (mepiramine). The % inhibition of compounds RC2, RC3 and RC4 was < 40.7 therefore IC50 values were not obtained. The compound l-[(4'-piperazino) phenyl]- 3- (2',4'-dichlo-rophenyl)-2-propene-l-one (RC6) showed a much lower IC50 value than the standard drug (mepiramine) at 0.0033 ±0.0002 μM/ml.

7. Another interesting observation of claim 1 is that the compounds with halogen substituents have a favorable antihistaminic activity compared to those which do not have these halogens. This is evident from the highest antihistaminic activity of compound of RC6 due to the presence of two chlorine substituents at the ortho and para position of the aromatic ring.

8. The significant outcome of the study is the emergence of chalcones with piperazine nucleus as promising antihistaminic agents in general and compound RC6 as potent antihistaminic agent in particular.