INTRODUCTION:

Among the drugs interfering with Calcium-controlled cellular activities the so called Calcium antagonists have attracted particular attention in recent years. Calcium antagonists are compounds interfering with cellular Calcium homeostasis either by reducing the amount of intracellularly available activator Calcium or by inhibiting intracellular activator proteins. Calcium antagonists represent a large, structurally diverse group of chemicals that share the ability to inhibit calcium entry into muscle cells through actions on the calcium-sensitive ion channels. Given the widespread distribution of calcium channels within the cardiovascular system, it is not surprising that calcium channel antagonists have received considerable therapeutic interest^1-3. During the review of literature survey^4-9, it became evident that thiazolidin-4-ones, as a class, exhibited a wide range of pharmacological activity which includes:- CNS depressant activity, CVS activities, Antioxidant activity, Local anaesthetic activity, Antimicrobial activity, Insecticidal activities, Antitumor activity, Antiparkinsonian activity. In view of these observations and our interest in syntheses of biologically active thiazolidinones, the moiety was modified to explore its calcium antagonistic activity.

MATERIALS AND METHODS:

The melting points of the organic compounds were determined by open capillary tube method and are uncorrected. Synthesized compounds were subjected to Flash chromatography to obtain in its purest form and later they were subjected for NMR. IR spectra were recorded on spectrophotometer using KBr disc method. PMR spectra were recorded on sophisticated multinuclear FT-NMR Spectrometer model Avance-II (Bruker), using DMSO-d6 as internal standards. All the solvents used were analytical grade. A general procedure used for the synthesis of 2-(4-hydroxyphenyl)-3-(3-hydroxypropyl)thiazolidin-4oneis as follows^7-8: To a suspension of 4-hydroxy benzaldehyde(0.1 mol) in dry benzene(150 ml) was added 3-aminopropanol(0.1 mol) and the mixture was refluxed for 1.5 hr in a flask equipped with Dean- stark water separator. After cooling to room temperature, thioglycollic acid (0.1 mol) was added drop wise to the solution, and the resulting mixture was refluxed for 2 hrs. The progress of the reaction was monitored by TLC. It was then cooled and concentrated. The obtained residue was poured into water containing sodium bicarbonate (100ml) and extracted with chloroform. The extract was dried and concentrated. The residue was purified by flash chromatography.. It was recrystallised from alcohol. The solvent system used for TLC and Flash was 1:1:8 mixture of Acetone: Methanol: Benzene. The IR spectra showed bands at 3170 cm^-1(OH hydrogen bonded), 1671.52 cm^-1 (C=O stretch), 1215.74 cm^-1 (C-N stretch), 1156.17 cm^-1 (C-S stretch), 831.5 cm^-1 (substituted aro.), 1448.89 cm^-1 (methylene bending), 1283.43 cm^-1 (C-O alcohol).1H NMR spectra : δ(in ppm): 9.77(2H, OH alcoholic & phenolic), 6.92-7.75(4H, CH aromatic), 5.70 (1H, CH methine), 3.80(2H, CH₂ S-CH₂), 3.50-3.64(4H, CH₂ methylene), 1.71(2H, CH₂ β-methylene).

General procedure¹⁰ used for synthesis of 3-(2-(4-hydroxyphenyl)-4-oxothiazolidin-3-yl)propanoic acid is as follows: A mixture of (0.7 mol) of 2-(4-hydroxyphenyl)-3-(3-hydroxypropyl)thiazolidin-4one and a solution of 15 g sodium carbonate in 150 ml of water was placed in a 5 litre round-bottomed flask. A solution of 0.9 mol of potassium permanganate is added in 2750 ml of water, with vigorous stirring, during 3-4 hours, the mixture was cooled to 4-5 °C by immersion in a bath with ice-water. Then the reaction mixture was allowed to attain room temperature gradually. After 12 hours, the precipitated manganese dioxide was filtered off (or preferably centrifuged), the filtrate was concentrated to about 150 ml under reduced pressure and then cooled. The solution was covered with a layer of ether and acidified with dilute sulphuric acid. The ether layer was separated and aqueous layer was extracted two or three times with 50 ml portions of ether. The combined ethereal extracts were dried over anhydrous sodium sulphate, the ether was removed on a water bath and the residual liquid was fractionated. The dried crystals were collected. The yield, melting point and other physical characteristics are mentioned in Table 1. The IR spectra showed bands at 3209.4 cm^-1 OH(hydrogen bonded), 1666.4 cm^-1 C=O stretch, 1217.6 cm^-1 C-N stretch, 1161.0 cm^-1 C-S stretch, 835.9 cm^-1 Substituted Aro., 1453.2 cm^-1 Methylene bending, 1596.0 cm^-1 C-O(carboxylic acid). The method for syntheses is depicted in scheme 1. The physical data is computed in table 1.

Calcium antagonistic activity was carried out on the isolated aorta rings of albino rats¹¹. Albino rats of either sex weighing 100-120 g were sacrificed with an overdose of pentobarbital sodium. The chest cavity was opened and the descending thoracic aorta was rapidly removed and placed in a beaker of oxygenated Krebs bicarbonate buffer at 37°C. The tissue was then transferred to a dish containing fresh oxygenated, warmed Krebs solution. Fat and loose connective tissues were carefully removed while keeping the tissue moist with the solution. Eight rings of 4-5 mm width were obtained and each is mounted in a 20ml tissue bath which contains the oxygenated warmed Krebs solution. Initial tension was set at 1.0g. The tissue was allowed to incubate over a period of 2 hours, during which time the Krebs solution was changed every 15 min. Also during this time, tension was maintained at 1.0gm. Just prior to the end of the 2 hour equilibration period, the Krebs solution was changed again and the tissue was allowed to stabilize at 1.0gm tension. A sustained contraction was then generated by addition of either 40 mM KCl or 2.9x10^-3 mM norepinephrine. Twenty min after addition of the agonist, the test drug was added so that the final concentration in the bath is 1x10^-5 M. The percent relaxation reading was taken 30 min after addition of the test drug. If at least 30% relaxation occurs, an accumulative concentration-relaxation curve was established. There was a 30 min period of time between the addition of each concentration of the test compound. All the compounds were screened using diltiazem as standard drug at the concentration range of 1 x 10^-8 to 1 x 10^-4 M. The results are presented in table 2. The graphical representation of the calcium antagonistic activity of compounds in terms of % relaxation vs log M is presented in figure1.

Scheme 1: Synthetic scheme for syntheses of title compounds

Figure 1: % Relaxation by synthesized compounds

Table 1: Physical data of synthesized compounds

Comp.	Mol. Formula	Mol. Wt.	m.p/b.p (⁰C)	λ max	Yield (%)	Solvent system	Ratio	R_f value
HT	C₁₂H₁₅O₃SN	253	90-92	285	45	A:M:B	1:1:8	0.47
HAT	C₁₃H₁₇O₃SN	267	96-98	275	72	A:M:B	1:1:8	0.52
CT	C₁₂H₁₄O₂SNCl	272	120-122	226	76	EA:M	9:1	0.62
TT	C₁₃H₁₇O₂SN	251	102-104	223	76	C:M	9.5:0.5	0.59
AT	C₁₃H₁₇O₃SN	267	96-98	233	47	C:M	9.5:0.5	0.56
HTA	C₁₂H₁₃O₄SN	267	112-114	329	68	A:M:B	1:1:8	0.65
HATA	C₁₃H₁₅O₄SN	281	100-102	275	74	A:M:B	1:1:8	0.61
CA	C₁₂H₁₂O₃SNCl	286	104-106	225	65	EA:M	9:1	0.56
TA	C₁₃H₁₅O₃SN	265	110-112	225	67	C:M	9.5:0.5	0.62
AA	C₁₃H₁₅O₄SN	281	106-108	243	54	C:M	9.5:0.5	0.52

Table 2: Calcium antagonistic activity of synthesized compounds

Conc. (M)	% Relaxation
Conc. (M)	Diltiazem	HAT	CA	AA	CT	HATA	AT
1х10^-8	0.00	8.98	6.76	8.90	0.00	0.00	0.00
3 х 10^-8	0.00	12.66	7.34	11.10	0.00	0.00	0.00
1 х 10^-7	1.72	18.78	8.82	13.27	0.00	0.00	0.00
3 х 10^-7	15.52	25.00	9.86	32.22	0.00	0.00	0.00
1 х 10^-6	39.65	25.51	15.49	36.65	0.00	0.00	0.00
3 х 10^-6	61.21	27.35	15.93	38.88	11.37	0.00	0.00
1 х 10^-5	76.72	33.37	30.64	40.00	20.46	0.00	0.00
3 х 10^-5	81.03	35.62	32.83	72.22	20.46	5.37	6.67
1 х 10^-4	93.10	46.53	54.76	72.22	31.83	48.22	21.90

The calcium antagonistic activity is measured in terms of % relaxation

RESULTS:

All the synthesized compounds were screened for calcium antagonistic activity using diltiazem as standard drug at the concentration range of 1 x 10^-8 to 1 x 10^-4 M. Compound AA has exhibited noteworthy calcium antagonistic activity with Emax 74.76 comparable to diltiazem with Emax 88.96. Compounds CA, HATA, HAT & CT also exhibited comparable calcium antagonistic activity in Emax range of 30-62. Compound AT also exhibited activity with Emax 21.90. Compounds HTA, TT, HT, TA exhibited no activity at the concentration range of 1 x 10^-8 to 1 x 10^-4 M.

CONCLUSION:

From the above result it is evident that suitable molecular manipulation can still bring about compounds which could prove equal or better activity compared to the standard drug.

ACKNOWLEDGEMETNS:

The authors are thankful to Prof. Dr. F.V. Manvi, Principal, K.L.E.S.’s college of Pharmacy, Belgaum for providing facilities and encouragement.

REFERENCES:

1) C. Melchiorre and M. Giannella, Recent Advances in Receptor Chemistry, Elseveir Science Publishers B.V., Amsterdam,1988, 147-168.

2) Burger’s Medicinal Chemistry and Drug Discovery.6^th edition. Vol-3, A John Wiley & Sons, Inc., Publication.New Jersey, 2003,7-8,168

3) Denis M. Bailey, Annual reports in Medicinal chemistry-21, Academic Press, 1986, 85-94.

4) Saurabh C.,J N Gadre, Smita Nair, “Synthesis of some new 4-thiazolidinones and thiazin-4-ones as biologically potent agents”,Ind. J. Chem.,46B,653-659(2007).

5) Chaudhari M., Parmar S.S., Chaudhari S.K., Chaturvedi A K, Ramasastry B V, J. Pharm. Sci., 1976, 65, 443.

6) Chaudhari S K, Verma M, Chaturvedi A K, Parmar S. S.,J. Pharm. Sci., 1975, 64, 614.

7) Tatsuya Kato, Tomokazu Ozaki, Kazuhiko Tamura, Yoshiyuki Suzuki, Michitaka Akima, and Nobuhiro Ohi, Am. Chem. Soc., 1998, 10.1021/jm980335f.

8) Tatsuya Kato, Tomokazu Ozaki, Kazuhiko Tamura, Yoshiyuki Suzuki, Michitaka Akima, and Nobuhiro Ohi, Am. Chem. Soc., 1999, 10.1021/jm9900927.

9) Surrey A R, J. Am. Chem. Soc., 1949, 71, 3105.

10) Brian S. Furniss, Antony J. Hannaford, Vogel’s textbook of Practical Organic Chemistry, Pearson Education Ltd., 2008, 668.

11) H. Gerald Vogel, Wolfgang H Vogel(Eds), Drug Discovery and Evaluation, Pharmacological Assays, Springer- Verlag Berlin Heidelberg,Germany, 1987.96-103.

Received on 15.03.2010 Modified on 01.04.2010

Asian J. Research Chem. 3(3): July- Sept. 2010; Page 685-687