Comparison Study of CNS Depressant Study of Synthesized Schiff Bases of Mannich Bases of Resacetophenone Having Variable Electronegative Atoms (:O:/:S:/:NH)

Arpit D. Shah, Devanshi J. Raval, Nisha D. Pandya, Sunita J. Panchal, Viraj P. Jatakiya and

Dr. Dhrubo Jyoti Sen

Department of Pharmaceutical Chemistry, Shri Sarvajanik Pharmacy College, Gujarat Technological University, Arvind Baug, Mehsana-384001, Gujarat, India

*Corresponding Author E-mail: dhrubosen69@yahoo.com

ABSTRACT:

Three Schiff bases of Mannich bases of resacetophenone have been synthesised by using three variable electronegative atoms (X=O/S/NH) of urea/thiourea/guanidine and tested for CNS depressant activity. It has been found that Compound-3c (X=NH) showed maximum CNS depressant effect in the Albino mice and producing more sedative effect and more sleeping time, Compound-3a (X=O) showed less sleeping time than guanidine derivative. There is very less effect compared to both very less sedative effect in the case of Compound-3b (X=S). CNS depressant activity profile of three compounds is as follows: Compounds: 3c (X=NH) > 3a (X=O) > 3b (X=S). LogP values of three compounds were found to be X=O: 4.03, X=S: 4.63 and X=NH: 3.79. So, the partition coefficient is in this order: X=S: 4.63 > X=O: 4.03 > X=NH: 3.79. Partition coefficient of X=S is 4.63 which is greater than X=O (4.03) and X=NH (3.79). Electronegativity of S is 2.58 which is in between O=3.44 and NH=3.04. Electronegative atoms O and S both have two lone pair of electrons but electronegativity for O: 3.44 > N: 3.04 > S: 2.58. The electronegativity of N is 3.04 so the NH compound (guanidine) showed maximum CNS depression, electronegativity of O is 3.44 so the O compound (urea) showed medium CNS depression and the electronegativity of S is 2.58 so the S compound (thiourea) showed minimum CNS depression. The log P values of NH compound (guanidine) is 3.79 which is minimum but showed maximum CNS depression, log P value of O compound (urea) is 4.03 which showed medium CNS depression and log P value of S compound (thiourea) is 4.63 which showed minimum CNS depression. Oxygen and Sulfur both have two lone pairs of electrons so the CNS depression has been found lesser than NH group which has one lone pair of electrons and the potency of CNS depression is due to the difference in electronegativity: O: 3.44, S: 2.58 and NH: 3.79.

Keywords: Schiff base, Mannich base, cut off, sleeping time

INTRODUCTION:

The proposed planning has been designed to incorporate Schiff base and Mannich base together in single compound with variable electronegative atoms O/S/NH by using urea, thiourea and guanidine for X. All the three derivatives of resacetophenone have been tested for antimicrobial as well as antifungal activity with MIC and antioxidant property by logP values (Table-1). All the compounds were characterized by UV, IR analysis with N%.

Molecular skeleton X=O: Urea

X=S: Thiourea X=NH: Guanidine

Desired molecules

Synthesis of Mannich bases:

1 mole benzaldehyde was treated with 1 mole piperidine dissolved aqueous solution of 1 mole of urea/thiourea/guanidine and heated on water bath until the entire product solidified. It was placed in ice and filtered, washed with cold water to remove unreacted benzaldehyde and piperidine. It was then recrystallised with charcoal in aqueous ethanol.^1-3

1a: 1-[phenyl (piperidin-1-yl)-methyl]-urea X=O: C₁₃H₁₉N₃O

1b: 1-[phenyl (piperidin-1-yl)-methyl]-thiourea X=S: C₁₃H₁₉N₃S

1c: 1-[phenyl (piperidin-1-yl)-methyl]-guanidine X-NH: C₁₃H₂₀N₄

Synthesis of Resacetophenone: (Hoesch reaction)

1.2 moles of anhydrous zinc chloride was dissolved with the aid of heat in 2.7 moles of glacial acetic acid, which has been placed in a 1-l. beaker. To this hot mixture (about 140°C), 1 mole of resorcinol was added with constant stirring. The solution was heated on a sand bath until it just begins to boil (about 152°C). The flame was then removed and the reaction allowed completing itself at a temperature not in excess of 159°C. After standing on the sand bath without further heating for 20 minutes, the solution is diluted with a mixture of 250 ml. of concentrated hydrochloric acid and 250 ml. of water. The dark red solution was placed in an ice bath and cooled at 5°C. The resulting precipitate was collected on a filter and washed free from zinc salts with 1 l. of dilute (1:3) hydrochloric acid in 200-ml. portions. This orange-red product, after drying, weighs 104–110 g. and melts at 141–143°C. It was distilled under reduced pressure, and boils at 180–181°C at 10 mm. (147–152°C at 3–4 mm.). After most of the product has distilled, the temperature rises sharply and the operation was discontinued when the temperature reaches 190°C. The light-yellow distillate was removed from the receiver with hot ethanol and the ethanol is evaporated. This product weighs 100–106 g. It was further purified as follows: the substance was dissolved in 1.8 l. of hot dilute (1:11) hydrochloric acid, filtered hot and cooled to 5°C. The crystals were removed by filtration, washed with two 200-ml. portions of ice water and dried. The yield of tan-colored resacetophenone, melting at 142–144°C, is 93–99 g. (61–65%).^4-6

3a 3b 3c

Table-1. Physicochemical Parameters:-

Compounds	% Yield	M.P.ºC	Polarity	Solubility	Molecular Formula	Molecular Weight	N% Calculated	N% Found
3a	42.00	140-145	Non-polar	Ethanol, CHCl₃, CCl₄	C₂₁H₂₅N₃O₃	367	11.44	11.22
3b	40.52	155-160	Non-polar	Ethanol, CHCl₃, CCl₄	C₂₁H₂₅N₃O₂S	383	10.96	10.88
3c	50.00	190-194	Non-polar	Ethanol, CHCl₃, CCl₄	C₂₁H₂₆N₄O₂	366	15.29	15.23

Table-2

Compounds	Molecular Formula: Molecular weight	logP
3a	C₂₁H₂₅N₃O₃: 367	4.03
3b	C₂₁H₂₅N₃O₂S: 383	4.63
3c	C₂₁H₂₆N₄O₂: 366	3.79
Diazepam	C₁₆H₁₃ClN₂O: 287	2.91

Histogram of Log P

Table-3 U.V. Spectras

Compounds	l_max (nm)
3a	290
3b	326
3c	280

I.R. Spectras:-

Phenolic –OH stretch 3900-3000 cm^-1 very strong due to hydrogen bond formation and may obscures other band. In thus region particularly of –NH stretch. C-H stretching 3150-2700 cm^-1 complex region due to many no. of hydrocarbons skeleton. C=C conjugated gives very stronger absorption around the region 1500-1400 cm^-1. N-H bend often obscured by stronger C=C absorption with polar substitution otherwise it observed at around 1500 cm^-1. Aromatic overtone region around 1800-1940 cm^-1. N-H stretch at 3305.78 cm^-1 is quite clear seen on the top of the broad O-H stretch. C=O stretch not observed due to amide-amidol tautomerism so instead of it C-O bend observed at 1238.21 cm^-1. C-H bending observed at 950-700 cm^-1. N-C=S stretching at around 2250-1900 cm^-1here it is observed at 1907.47 cm^-1. C-N bending observed around 1300-1000 cm^-1and give complex region.

I.R. Spectras

Compound 3a: υ (KBr, cm^-1): 3940.30, 3139.90 (Phenolic –OH), 3150-2700 (-C-H, stretching), 1238.21 (-C-O), 1947.97, 1861.18 (-C₆H₅), 1450.37, 1413.72 (-C-H, bending), 744.47 (-C₆H₅, ortho), 821.62, 877.55 (-C₆H₅, para), Aromatic out of plane bending observed at 950-700 (-C₆H₅)

Compound 3b: υ (KBr, cm^-1): 3305.78 (-N-H, stretching), 3150-2700 (-C-H, stretching), 1600-1303 (C-C), 1500 (C=C), 1660 (C=N)^,1300-1000 (C-N), 1907.47 (N-C=S, stretching), 744.47 (-C₆H₅, ortho), 821.62, 877.55 (-C₆H₅, para), 950-700 (-C₆H₅, bending)

Compound 3c: υ (KBr, cm^-1): 3660.64, 3612.42, 3596.99, 3577.71, 3500.58 (Phenolic –OH, stretching)^,3379.05 (-N-H, stretching), 3407.96, 3417.63, 3442.70, 3454.27 (O-H, stretching), 3186.18 (-C₆H₅, stretching), 1301.86-1031.85 (C-N) and C-O)

Biological Screening of Synthesized Compounds (3a-3c)

CNS Depressant activity:

The synthesized compounds (3a-3c) were tested for their CNS depressant activities by following actophotometer (Janki Impex Pvt. Ltd) on the Albino mice (approved from CPCSEA and Institutional Animal Ethics Committee (IAEC):

The CNS depression study of all the synthesized compound were carried out by administering intraperitoneally the various doses of the test compounds in mg/kg dose in 18 hours fasting male albino mice using propylene glycol as an inert vehicle.

Compound 3c

The loss of writhing reflex and regaining of it was noted for each compound to determine the sleeping time for the compounds having urea/thiourea/guanidine linkage. Sleeping time potentiation effect was studied for the test compounds by using diazepam on male albino mice. All the observations were noted for four groups of mice and the bioassay result was tabulated for pharmacological screening.¹⁰

Our compounds which contain urea open chain while in case of diazepam which contain close ring of urea (Benzodiazepines) which shows the CNS depressant activity due to urea group so our compound also contain urea. It might be chance of CNS depressant activity.

Species : Wistar Albino Mice

Sex : Male

Age /weight : 20-25g

Environmental condition: Temperature of 25±2ºC and a relative humidity of 70±5%

Housing : 9 days

Feed /water : Standard animal pellets and RO water

Experimental Groups: 4 Groups (5 animals in each group)

Dose level : Standard: 4mg/kg of Diazepam

Test: 1 mg/kg of synthesized compounds3a, 3b and 3c.

Route of administration : Intraperitoneal

Duration of treatment : 1 day

Parameters to be studied : Decrease in no. of cut off after administration of synthesized compound in actophotometer.

Working principle of actophotometer:

Most of the CNS acting drug influences the locomotation activities in man and animals. The CNS depressant drugs like barbiturates and diazepam decrease motor activity while stimulants such as caffeine and amphetamine increase the activity. In another word locomotation activities can be an index of wakefulness (alertness) of mental activity. The locomotor activity can be easily measured using actophotometer which operates on photoelectrical cells which are connected in circuit which are counter. When beam of light falling on the photocell is cutoff by an animal, the count is recorded. An actophotometer could have either circular/square area in which the animal moves both rats and mice may be used for testing in this equipment.^11,12

§ Methodology: 4 groups of mice (each group contain 5 mice)

§ Group 1: control ( propylene glycol)

§ Group 2: test (3a , 3b, 3c)

§ Group 3: standard (diazepam)

§ Group 4: test + standard

Procedure for experiment:

· Weight the mice accurately on weight balance for the accurate dose calculation.

· Divide the mice in to 4 different groups as mentioned in the methodology. Calculate the dose of test samples and standards as per the weight.

· Put the mice in the photoactometer without administration of the any sample and observe the no. of cut off for 10 min.

· Then administered control in one group and measure the no. of cut off till 1 hour.

· Then administered test and standard in to the groups of it and observe the no. of cut off till the maximum effect of the drug observed.

· Then calculate the change in activity.^13,14

Table – 4. No. of cut off of individual compound:

NO.	Time	Control	Standard	Test compounds
NO.	Time	Control	Standard	3a	3b	3c
1	0 min	56	46	45	52	38
2	30 min	50	24	25	35	7
3	60 min	45	1	18	24	0
4	90 min	51	0	7	20	0
5	120 min	62	0	0	18	0

Table – 5. Change in activity:

Test compounds	Total no of cut off	Change in activity
Control	264	100
Standard	71	26.89
Test 3a	95	35.84
Test 3b	149	56.44
Test 3c	45	17.04

CONCLUSION:

Three Schiff bases of Mannich bases of resacetophenone have been synthesised by using three variable electronegative atoms (X=O/S/NH) of urea/thiourea/ guanidine and tested for CNS depressant activity. From the data of the Table 4 and 5, Compound 3c (X=NH) shows the more change in to locomotation activity 17.04 when Compound 3a (X=O) shows the change in the activity less than Compound 3c it means less depressant effect than that Compound 3c. While Compound 3b (X=S) shows less effect than both of compound. It has been found that Compound-3c (X=NH) showed maximum CNS depressant effect in the Albino mice and producing more sedative effect and more sleeping time, Compound-3a (X=O) showed less sleeping time than guanidine derivative Compound 3c (X=NH). There is very less effect compared to both Compound 3a and Compound 3c so very less sedative effect in the case of Compound-3b (X=S). CNS depressant activity profile of three compounds is as follows:

COMPOUND: 3c (X=NH) > 3a (X=O) > 3b (X=S).

Diazepam Compound: 3c

Diazepam has closed ring amide linkage –CO-NH- having benzodiazepine nucleus whereas the test compounds have open chain amide linkage –C(X)-NH- [X=O/S/NH]. The sedative activity of benzodiazepines occur due to blocking of GABA receptor which has also amide chain which is also present in the Compound 3c which showed maximum CNS depression activity due to same mechanism.

Log p values of three compounds were found to be X=O: 4.03, X=S: 4.63 and X=NH: 3.79. So, the partition coefficient is in this order: X=S: 4.63 > X=O: 4.03 > X=NH: 3.79. Partition coefficient of X=S is 4.63 which is greater than X=O (4.03) and X=NH (3.79). Electronegativity of S is 2.58 which is in between O=3.44 and NH=3.04. Electronegative atoms O and S both have two lone pair of electrons but electronegativity for O: 3.44 > N: 3.04 > S: 2.58. The electronegativity of N is 3.04 so the NH compound (guanidine) showed maximum CNS depression, electronegativity of O is 3.44 so the O compound (urea) showed medium CNS depression and the electronegativity of S is 2.58 so the S compound (thiourea) showed minimum CNS depression. The log P values of NH compound (guanidine) is 3.79 which is minimum but showed maximum CNS depression, log P value of O compound (urea) is 4.03 which showed medium CNS depression and log P value of S compound (thiourea) is 4.63 which showed minimum CNS depression. Oxygen and Sulfur both have two lone pairs of electrons so the CNS depression has been found lesser than NH group which has one lone pair of electrons and the potency of CNS depression is due to the difference in electronegativity: O: 3.44, S: 2.58 and NH: 3.79.

ACKNOWLEDGEMENT:

The authors (Arpit D. Shah: B. Pharm.-VIII, Devanshi J. Raval: B. Pharm.-VIII Nisha D. Pandya: B. Pharm – VIII, Sunita J. Panchal: B.Pharm-VIII and Viraj P. Jatakiya M.Pharm.-II) are thankful to the Department of Quality Assurance of Shri Sarvajanik Pharmacy College, Mehsana for UV & IR datas, also special thankful to the Department of Pharmacology of Shri Sarvajanik Pharmacy College, Mehsana to perform animal study and Department of Pharmaceutical Chemistry of Shri Sarvajanik Pharmacy College, Mehsana, Gujarat, India to perform the research work successfully with the expertise of project guide Dr. Dhrubo Jyoti Sen.

REFERENCES:

1. Kaumil Navnitbhai Modi, Sanjay D. Panchal and Prof. Dr. Dhrubo Jyoti Sen; Structure activity relationship studies of substituted Mannich bases of 2-oxo-4,6-diphenyl-2,6-dihydropyrazolo-[1,5-a][1,3,5]-triazine-7-carbonyl ring system with variable electronegative atoms (urea/thiourea/guanidine) for antimicrobial and antifungal activity: International Journal of Drug Development and Research: 3(2), 334-343, 2011.

2. Hiren R. Patel, Parth K. Patel, Dhrubo Jyoti Sen and Amit H. Patel; Growth inhibition of microorganism by bioisosterism: International Journal of Drug Development and Research; 2(1), 190-196, 2010.

3. S. R. Cooper Organic Syntheses Coll. Vol. 3, 761, 1955; Vol. 21, 103, 1941. Coll. Vol. 2, 522, 1943; Vol. 15, 70, 1935.

4. Yatri R. Shah, Dhrubo Jyoti Sen and C.N. Patel; Schiff’s bases of piperidone derivative as microbial growth inhibitors: Journal of Chemical and Pharmaceutical Research; 2(2), 581-589, 2010.

5. Yatri R. Shah and Prof. Dr. Dhrubo Jyoti Sen; Schiff’s bases of piperidone derivatives as fungal growth inhibitors: The Manufacturing Pharmacist; 02(09), 37-44, 2010.

6. Ravi Natvarlal Patel, Urviben Yashodharbhai Patel, Ripal R. Chaudhari and Prof. Dr. Dhrubo Jyoti Sen; Synthesis and antibacterial study of some new Schiff’s bases of 2-hydrazinyl-1-(1H-imidazole-1-yl)-ethanone: Asian Journal of Research in Chemistry; 4(1), 55-57, 2011.

7. Dhrubo Jyoti Sen, Palakben K. Parikh, Julee P. Soni, Kaumil N. Modi, Hiren M. Marvaniya, Priya R. Modiya, Apexa D. Patel, Dilip R. Chavda, Deepa R. Parmar, Sanjay D. Panchal and Vidhi R. Patel; Lead identification by structure activity relationship study of Schiff bases of 3-amino-2-methyl quinazolin 4-(3H)-one for antimicrobial and antifungal activity; International Journal of Pharmacology and Technology; 2(1), 37-43, 2010.

8. Hardik Arvindbhai Patel, Kiran Manubhai Patel, Dhrubo Jyoti Sen and Dilipkumar Ramjibhai Chavda; Structure activity relationship studies of conjugated diamides of variable atomic electronegativity for sleeping time synergistic activity: International Journal of Drug Development and Research: 1(1), 126-135, 2009.

9. Ankit B. Shah, Dhrubo Jyoti Sen and Jigna S. Shah; Comparison of pharmacological screening of CNS depressant action of fused ring heterocyclic adduct with fused ring aromatic with benzodiazepine as standard: International Journal of Drug Development and Research: 2(1), 20-26, 2010.

10. Vikramkumar Vishnubhai Patel and Prof Dr Dhrubo Jyoti Sen; Synthesis of substituted triazolo-pyrrole fused ring adduct with benzylidene piperidyl urea/thiourea bridge and screening for CNS depression: International Journal of Drug Development and Research: 2(1), 203-210, 2010.

11. Nidhi J. Kapadiya and Dhrubo Jyoti Sen; Structure activity relationship studies of synthesized diamides on CNS depression and sleeping time potentiation effect: Asian Journal of Research in Chemistry: 3(4), 249-254, 2010.

12. Ravikumar V. Modi and Prof Dr Dhrubo Jyoti Sen; Structure activity relationship studies of synthesized urea diamides on CNS depression and sleeping time potentiation effect: International Journal of Drug Development and Research: 2(3), 512-528, 2010.

13. S. K. Kulkarni, Hand book of Experimental Pharmacology, 3^rd edition, Vallabh Prakashan, page no: 117-119.

14. R. K. Goyal, Practicals in Pharmacology, 6^th edition, B. S. Shah Prakashan, Ahmedabad, page no: 121-122.

Received on 22.03.2012 Modified on 30.03.2012

Asian J. Research Chem. 5(4): April 2012; Page 556-562