Synthesis of Valproic acid derivatives and their evaluation for anticonvulsant activity
N Upmanyu, S Gupta, J Grover, P Mishra
Keywords
anticonvulsant, derivatives of valproic acid, epilepsy, valproic acid, valpromide
Citation
N Upmanyu, S Gupta, J Grover, P Mishra. Synthesis of Valproic acid derivatives and their evaluation for anticonvulsant activity. The Internet Journal of Alternative Medicine. 2008 Volume 7 Number 1.
Abstract
Valproic acid is simple branched chain carboxylic acid used in epilepsy. Valproic acid derivatives like acid chloride and amide were prepared by the reaction of valproic acid with thionyl chloride and ammonia. These acid chloride derivatives were reacted with hydrazine hydrate to give the corresponding hydrazides. These hydrazides were reacted with formaldehyde and different secondary amines to give substituted derivatives. The structures of the newly synthesized compounds were elucidated on the basis of analytical and spectral data. The compounds synthesized were then screened for anticonvulsant activity. Various studies were conducted on development of various prodrugs and derivatives of valproic acid. The present study showed that all synthesized amide derivatives (RDG1…RDG8) except RDG2 were more active than sodium valproate in chemical induced model as well as MES model. Amongst all the derivatives RDG3 was found to be more effective than even valpromide.
Introduction
Valproic acid is simple branched chain carboxylic acid used in epilepsy. Valproic acid increases GABA (γ-amino butric acid) synthesis and release and potentiates by this mechanism GABAergic transmission in specific brain regions (Kadam, Mahadik and Bothra, 1998). Valproic acid also reduces the release of excitatory amino acid β-hydroxy butyric acid and to attenuate neuronal excitation mediated by activation of N-methyl-D- aspartate glutamate receptors. (Mclean and Macdonald, 1986). Valproic acid is a broad-spectrum antiepileptic drug effective against all seizure types.
Various studies were conducted on development of various prodrugs and derivatives of valproic acid (Mergen etal) and other drugs, which shows anticonvulsant activity and reported in literature (Patil, Shyam and Dimmock, 1991) Valproic acid is reacted with thionyl chloride to give acid chloride of it and ammonia reacted with valproic acid to give Valpromide(Furniss etal, 1989) [2].This valpromide, reacted with formaldehyde to give N-(Hydroxymethyl) valpromide (Mishra , Agrawal and Shakya , 1991) [3]. This acid chloride is reacted with hydrazine- hydrate to give hydrazide of valproic acid (4). This hydrazide is reacted with formaldehyde and different secondary amine in ethanol to give N (N’N’-Dialkylamino) methyl valpromide (Singh, Bindal and Dixit, 1975) (5a-f). The scheme of these reactions is shown in scheme 1. Newly synthesized compounds were characterized by IR, NMR and elemental analysis. These compounds were screened for better anticonvulsant property.
Materials and Methods
Purity of the compounds was checked by TLC. Melting points were determined in open capillaries and are uncorrected. IR spectra (KBr) are recorded on the JASCO FT/ IR- 470 Spectrophotometer.1H NMR spectra was recorded on Burker AC-300 MHz Spectrophotometer by using CDCl3 as solvent and quantitative elemental analysis of nitrogen by using Perkin Elmer-2400 elemental analyser. For anticonvulsant activity wistar rats of either sex, weighing between 150-250g were used. All the animals were maintained under standard conditions and had access to pelleted animal feed and water.
N-Hydroxy Methyl Derivatives of valpromide
Valpromide (2) (0.04M), formalin (0.25M) and aqueous potassium carbonate solution 6-7 ml(20% w/v) were taken in a round bottom flask fitted with reflux condenser and refluxed for 2 hours. After cooling, the flask was placed in refrigerator overnight. The crystals of N-hydroxy methyl compound (3), which separated out were washed with cold distilled water to remove potassium carbonate and excess of formaldehyde. The product was recrystallized from ethanol (90%w/v) and dried. The I.R. spectrum of this compound exhibited peaks at 3600 cm-1(OH) and 3305.9cm-1(NH) indicating free hydroxyl and amide group. The NMR spectrum of this compound exhibited signals at 6.7 ð (s, 1H, amide NH) and 4.09 ð (t, 1H, of hydroxyl). The physical and elemental analysis data of the compounds given in Table 1.
Figure 1
Preparation of Hydrazine Derivatives of Valproic Acid
Hydrazine derivative was synthesized by taking hydrazine hydrate and acid chloride. Acid chloride was synthesized by taking 8 ml valproic acid (7.2g, 0.05 M) was taken in chloroform 25mL in a round-bottomed flask equipped with reflux condenser and an outlet. Thionyl chloride (7.5 ml, 0.085 M) was added drop wise and the reaction mixture was refluxed for 4 hours. The excess of chloroform and thionyl chloride was removed under reduced pressure to produce acid chloride.
Flat-bottomed flask equipped with two-way assembly fitted with dropping funnel and an outlet. The acid chloride as prepared above was taken in the flask and the hydrazine hydrate 2.4mL (0.05 M) was taken in dropping funnel. This hydrazine hydrate was added drop-wise to the acid chloride with constant stirring. Crystals of hydrazine derivative (4) formed were recrystallized with dehydrated alcohol. The I.R. spectrum of this hydrazide exhibited peaks at 3400 cm-1 of N-H(s) and at 1704.7cm-1(NH) indicating free hydroxyl and amide group. The NMR spectrum of this compound exhibited signals at 6.7 ð (s, 1H, amide NH) and 4.09 ð (t, 1H, of hydroxyl). The physical and elemental analysis data of the compounds given in Table 1.
Synthesis of N (N’N’-Dialkylamino) Methyl Valpromide
To a solution of valpromide 4g(0.028 M) in ethanol 19-20 ml, was added formalin 2.24mL(37%w/v, 0.028 M) followed by the addition of dialkyl (0.028 M) under constant stirring. Solvent was distilled off under reduced pressure to obtain product. It was recrystallized from hot water.
Anticonvulsant Activity
Anticonvulsant activity of synthesized compounds by using phenylenetetrazole (PTZ) induced and maximal electroshock seizure (MES) model of epilepsy. (Vogel, 2002)
Pentylenetetrazole induced convulsions
Pentylenetetrazole is an convulsive agent used for the induction of epilepsy in test animal.Wistar rats of either sex (150-250 g) were used in studies and divided into control and other groups. Control group received only the vehicle (propylene glycol) and other groups were administered each compounds. A 20 min after injecting the animals were administered pentylenetetraole (60 mg/kg i.p.). Animals were observed for convulsions, sedation and death for 1 hour. The observations are recorded in table 2 and table 3.
Figure 2
Total no of animals used for each group=6,
Intensity of sedation: + animals stopped moving but responded to physical stimuli, ++ animals had ataxia on moving, +++ animals did not respond to physical stimuli but responded to painful stimuli, ++++ absence of wrighting reflex as well as no response to painful stimuli.
Figure 3
Total no of animals used for each group=6,
Intensity of sedation: + animals stopped moving but responded to physical stimuli, ++ animals had ataxia on moving, +++ animals did not respond to physical stimuli but responded to painful stimuli, ++++ absence of wrighting reflex as well as no response to painful stimuli.
Maximal electroshock convulsions
To induce convulsions current of 150 mA was delivered through the electrodes dipped in normal saline at 50 Hz for 0.2 sec (Srivastava and Gupta, 2001). In this method only those rats were selected who responded to electroshock as mentioned above. The selected rats were administered either the vehicle or test compounds (i.p.) and 20 mins after injection, convulsions were induced. The rats were observed for presence or absence of hind limb extension and also for any sedation and mortality for next one hour. All the observations are represented in table 4.
Figure 4
Total no of animals used for each group=6,
Intensity of sedation: + animals stopped moving but responded to physical stimuli, ++ animals had ataxia on moving, +++ animals did not respond to physical stimuli but responded to painful stimuli, ++++ absence of wrighting reflex as well as no response to painful stimuli.
Results and discussion
Among the compounds tested for anticonvulsant activity only the compound 5a was proved to possess more efficacy, being considerably more active than sodium valproate in MES and PT2 induced seizure and was also more active than compound 2 in MES seizure. However the present study also pointed out that compound 5a was also slightly more sedative than compound 2.
Figure 5
Acknowledgements
The authors thank AIIMS, New Delhi for granting permission to perform pharmacological screening of synthesized compounds and Dr. H.S. Gour Vishwavidyalaya for providing necessary facilities. One of the authors thanks AICTE for providing financial assistance for the project.
Correspondence to
E-mail: suryatony@yahoo.co.in Surya Prakash B.N Gupta C/o Amrit Bandhu, Jawahar Chowk, Satna (M.P.)- 485001- INDIA