WO1994006758A1

WO1994006758A1 - Aryl semicarbazone anticonvulsants

Info

Publication number: WO1994006758A1
Application number: PCT/CA1993/000386
Authority: WO
Inventors: Jonathan R. Dimmock
Original assignee: University Of Saskatchewan
Priority date: 1992-09-21
Filing date: 1993-09-21
Publication date: 1994-03-31

Abstract

A number of aryl semicarbazones were prepared as candidate anticonvulsants. When administered orally to rats, significant activity was noted in the maximal electroshock (MES) screen and since neurotoxicity was either absent or reduced (as compared to intraperitoneal injection in mice), high protection indices were found in the majority of the compounds. The semicarbazones displayed little or no activity in the subcutaneous pentylenetetrazol screen. These observations support the theory that one large hydrophobic group (in this case the aryl ring) are requirements for protection in the MES screen. In general, the semicarbazones had rapid onsets of action and the most common mechanism of action was interaction with chloride channels. Empirical and semi-empirical conformational calculations indicated that certain molecular fragments and hydrophobicity of these molecules affect bioactivity.

Description

ARYL SEMICARBAZONE ANTICONVULSANTS

FIELD OF THE INVENTION

This invention relates to a novel class of semicarbazone compounds and their use on central nervous system activity. The compounds are particularly useful as anticonvulsants.

BACKGROUND OF THE INVENTION

The cause of epilepsy is only poorly understood, but it is thought to be due to the activity of faulty neurons in the brain which give sudden and excessive bursts of electrical activity. These aberrant neutrons in turn can affect neurons far from the original site which then behave in a similar way to the original abnormal neurons. The five major classification types of epilepsy are: 1° generalized seizures which involve the entire brain, 2° unilateral seizures which involve one side of the body, 3° focal seizures originating at one place in the body, 4° seizures of the new born, and 5° unclassified seizures, which are severe and often fatal. Two principal types of generalized seizures are grand mal and petit mal.

There is a need for new antiepileptic agents since complete control of epilepsy is found in only approximately 60% of patients with this malady.

Medication is available to treat generalized tonic-clonic (GTC) seizures (grand mal). An example of such medication is phenytoin. An experimental model to uncover drugs useful against this type of epilepsy is the maximal electroshock (MES) screen. Structural requirements for activity in the MES test have been stated to be the presence of at least one phenyl or similar aromatic group on a carbon atom in close proximity to two electron donor functions.

Other drugs such as ethosuximide, which are ineffective against GTC seizures, are useful in treating absence seizures (petit mal). Compounds with this activity may be detected in the subcutaneous pentylenetetrazol seizure threshold (scPTZ) test. The structural requirements for activity in this screen are claimed to be alkyl substitution close to two electron donor atoms. In other words, the hydrophobic moiety should be smaller in size than compounds effective in the MES test.

Synthetic anticonvulsants which incorporated the molecular features referred to in the previous paragraphs and yet were structurally dissimilar from many common monocyclic anticonvulsants containing the dicarboximide function which may contribute to toxic side effects have been prepared. A series of thiosemicarbazones and semicarbazones of arylidene methyl ketones were synthesized and evaluated in the MES, scPTZ and neurotoxicity screens. Approximately 75% of the compounds were active in the MES and/or scPTZ screens when given by the intraperitoneal route in mice. Although neurotoxicity and lethality in mice were higher in the thiosemicarbazones than the semicarbazones, the two most active compounds were both thiosemicarbazones. Hence, developments of this series of compounds rather than the corresponding semicarbazones were considered more likely to produce potent anticonvulsants.

Another study involved principally variation of the alkyl groups of some thiosemicarbazones of arylidene ketones and aldehydes. Activity was found in half of the compounds when screened. In addition, removal of the olefinic double bond led to the formation of aryl alkyl ketone semicarbazones and in certain instances, these compounds displayed activity in the MES test not only by the intraperitoneal route in mice but also when give orally to rats. However, a third study revealed that approximately 90% of various aryl alkyl ketones, thiosemicarbazones and related compounds were active in this screen but that when given orally, no protection was afforded by the compounds against seizures induced in the scPTZ screen in rats.

Hence, even though some structural requirements have been identified in order to obtain active anticonvulsants, most of the compounds proposed so far present drawbacks such as unwanted side effects or high toxicity.

SUMMARY OF THE INVENTION

In accordance with the present invention, a novel class of anticonvulsant semicarbazones is provided. The invention therefore relates to a compound having the following formula

wherein

R¹ is

or

a 5 to 7 member heterocycle having between 1 and 3 heteroatoms selected from the group consisting of O, S and N,

said heterocycle being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl,

wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and lower alkoxy;

R ² and R³ are the same or different and are selected from hydrogen, halogen, lower alkylamino, dilower alkylamino, amino, straight chain or branched, lower alkyl, lower alkoxy, lower alkylidene and lower arylidene,

said lower alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and aryl,

wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of hydrogen, halogen, straight chain or branched lower alkyl, lower alkoxy, amino, lower alkylamino and dilower alkylamino,

said lower alkoxy, lower alkylidene and lower arylidene being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl,

R ⁴ is hydrogen, strai.ght chai.n or branched alkyl or alkylidene,

said alkyl or alkylidene having between 1 and 10 carbon atoms and being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl. wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and lower alkoxy, with the proviso that when R⁵ is CH=CH

and R¹ is

with R ² and R³ being the same or different and representing H, Cl, CH₃, OCH₃ or OH, R ⁴ is not methyl;

R⁵ is a single bond between R¹ and R⁶, a straight chain or branched alkyl having between 1 and 10 carbon atoms or an alkylidene having between 2 and 20 carbon atoms, said alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl,

wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and lower alkoxy, said alkylidene being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and aryl,

wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of hydrogen, halogen, straight chain or branched lower alkyl, lower alkoxy, amino, lower alkylamino and dilower alkylamino, with the proviso that when R¹ is

with R ² and R³ bei.ng the same or different and representing hydrogen, halogen or alkyl having 1 to 3 carbon atoms, R ⁵ is not alkylidene having between 2 and

3 carbon atoms; and

R ⁶ is carbon;

and pharmaceutically effective salts thereof.

Preferred are compounds of formula I in which:

R¹ is

R ² and R³ are the same or different and are selected from hydrogen, fluorine, chlorine, bromine, iodine, lower alkoxy and straight chain or branched lower alkyl;

R⁴ is hydrogen;

R ⁵ is a single bond between R¹ and R⁶, a straight chain or branched lower alkyl or a substituted or unsubstituted alkylidene having between 2 and 20 carbon atoms; and

R⁶ is carbcon;

and pharmaceutically effective salts thereof. Also within the scope of the present invention is a pharmaceutical composition having anticonvulsant activity in mammals. This pharmaceutical composition comprises as an active ingredient an effective amount of a compound having the following formula

wherein

R¹ is

or

a 5 to 7 member heterocycle having between 1 and 3 heteroatoms selected from the group consisting of O, S and N;

R ² and R³ are the same or different and are selected from hydrogen, halogen, straight chain or branched. substituted or unsubstituted lower alkyl, amino, nitro, lower alkoxy, lower alkylidene and lower arylidene; said lower alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and aryl,

R⁴ is aryl or a 5 to 7 member heterocycle having between 1 and 3 heteroatoms selected from the group consisting of O, S and N, hydrogen, straight chain or branched alkyl or alkylidene,

said heterocycle being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl, wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and lower alkoxy;

said alkyl or alkylidene having between 1 and 10 carbon atoms and being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl,

wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and lower alkoxy,

with the proviso that when R ⁵ is CH=CH

and R ¹ is

wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of hydrogen, halogen, straight chain or branched lower alkyl, lower alkoxy, amino, lower alkylamino and dilower alkylamino; and

R⁶ is carbon;

and pharmaceutically effective salts thereof,

in admixture with a pharmaceutically acceptable carrier or adjuvant.

Preferred are those compounds of formula I in which:

R¹ is

R ⁴ is hydrogen;

R ⁵ is a single bond between R ¹ and R ⁶, a straight chain or branched lower alkyl having between 1 and 10 carbon atoms or an alkylidene having between 2 and 20 carbon atoms; and

R ² is carbcon;

and pharmaceutically effective salts thereof. The present invention also relates to a method for the treatment or prevention of convulsions in mammals. The method comprises administering to a patient in need thereof a pharmaceutically effective amount of a compound having the following formula:

wherein

R ¹ is

or

wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and lower alkoxy; R² and R³ are the same or different and are selected from hydrogen, halogen, straight chain or branched, substituted or unsubstituted lower alkyl, amino, nitro, lower alkoxy, lower alkylidene and lower arylidene; said lower alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and aryl,

R ⁴ is aryl or a 5 to 7 member heterocycle having between 1 and 3 heteroatoms selected from the group consisting of O, S and N, hydrogen, straight chain or branched alkyl or alkylidene,

with the proviso that when R ⁵ is CH=CH

and R ¹ is

with R ² and R³ being the same or different and representing H, Cl, CH₃, OCH₃ or OH, R⁴ is not methyl; R⁵ is a single bond between R¹ and R⁶, a straight chain or branched alkyl having between 1 and 10 carbon atoms or an alkylidene having between 2 and 20 carbon atoms, said alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl. wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and lower alkoxy, said alkylidene being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and aryl,

R is carbon;

and pharmaceutically effective salts thereof.

Also within the scope of the present invention is a commercial package for the treatment or prevention of convulsions in mammals. The package comprises a pharmaceutical agent therapeutically effective for the treatment of convulsions in mammals, together with instructions to use this pharmaceutical agent in the treatment or prevention of convulsions. The pharmaceutical agent used in the commercial package of the present invention is an effective amount of a compound of the following formula:

wherein R¹ is

or

R ² and R³ are the same or different and are selected from hydrogen, halogen, straight chain or branched, substituted or unsubstituted lower alkyl, amino, nitro, lower alkoxy, lower alkylidene and lower arylidene; said lower alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and aryl,

with the proviso that when R ⁵ is CH=CH and R¹ is

with R ² and R³ being the same or different and representing H, Cl, CH₃, OCH₃ or OH, R ⁴ is not methyl; R ⁴ is a single bond between R ¹ and R⁶, a straight chain or branched alkyl having between 1 and 10 carbon atoms or an alkylidene having between 2 and 20 carbon atoms, said alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl,

R ⁶ is carbon;

and pharmaceutically effective salts thereof,

The compounds described above are particularly useful in the prevention and treatment of epilepsy. Effective dosages can be administered orally. The present invention will be more readily illustrated by referring to the following description. IN THE DRAWINGS

Figure 1 represents the numbering scheme of semicarbazones used in molecular modelling and X-ray studies.

Figure 2 represents the ORTEP diagram of compound 2b.

Figure 3 represents the ORTEP diagram of compound 2d.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a novel class of semicarbazone compounds useful as anticonvulsants.

Members of this class that have been synthesized and tested demonstrated unusually valuable anticonvulsant properties that translate into high activity and excellent protection indices (TD₅₀/ED₅₀). It has been noted that structural modifications such as the passage from a semicarbazide structure to a semicarbazone structure or the passage from a thiosemicarbazone structure to a semicarbazone structure or the substitution of CH₃ by hydrogen at position R ⁴ in the compound of formula I are sufficient to impart substantial differences in anticonvulsant activity.

The compounds of interest that fall within the scope of the present invention have the following general formula:

wherein R¹ is

or

with the proviso that when R ⁵ is CH=CH and R¹ is

R ⁵ is a single bond between R¹ and R⁶, a strai.ght chain or branched alkyl having between 1 and 10 carbon atoms or an alkylidene having between 2 and 20 carbon atoms, said alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl,

R ⁶ is carbon;

and pharmaceutically effective salts thereof.

Preferred are compounds of formula I in which: R¹ is

R ⁴ is hydrogen;

R ⁵ is a single bond between R¹ and R⁶, a straight chain or branched lower alkyl having between 1 and 10 carbon atoms or an alkylidene having between 2 and 20 carbon atoms; and

R⁶ is carbon;

and pharmaceutically effective salts thereof.

Specific preferred compounds include those having the following structures:

General synthesis and testing procedures

The compounds of the present invention can be prepared by condensation of the appropriate aryl aldehyde, aryl alkyl ketone or aralkyl aldehyde or ketone with semi-carbazide in a suitable solvent. The product of the reaction is collected, recrystallized from appropriate solvents and identified by elemental analysis and NMR spectroscopy. After syntheses, the compounds are assayed for anticonvulsant properties.

The anticonvulsant properties of the compounds of the present invention have been measured by evaluating their ability to prevent the spread of seizures and/or increase the minimal seizure threshold. The procedures used to perform initial testing of candidate anticonvulsants are well-established procedures. Essentially, the testing was three-fold. It included the maximal electroshock seizure test (MES), the subcutaneous pentylenetetrazol test (scPTZ) as well as a toxicity screen used to detect minimal neurological deficit.

The MES test is described in detail in Swinyard et al., J. Pharmacol. Exp. Ther. 106. 319, 1952, hereby incorporated by reference. Detailed information on the scPTZ screen is provided in Swinyard E.A. in: Anticonvulsant drugs. International Encyclopedia of Pharmacology and Therapeutics, Section 19, Vol. 1, Ed.: J. Mercier, Pergamon Press, New York, pp. 47-65, 1972, also incorporated by reference. With regard to the toxicity screen, it is disclosed in Dunham and Miya., J. Am. Pharm. Assoc. 46, 208, 1957, also incorporated by reference.

The tests conducted with the compounds of the present invention demonstrate that semicarbazones are less neurotoxic than their corresponding thiosemicarbazones. Semicarbazones are also less toxic than their corresponding guanylhydrazones, which cause respiratory depression. The semicarbazones of the present invention have also been shown to be more active in vivo than their corresponding semicarbazides. One tentative explanation for this would be that the amino function of the semicarbazide moiety could confer more neurotoxicity to these compounds than the C=N double bond on the semicarbazone moiety. In fact, it appears that this double bond could have a direct influence on the overall anticonvulsant properties of the semicarbazones of the present invention.

Another important property of at least one of the preferred compounds of the present invention is their potential of maintained efficiency as anticonvulsants even when administered orally. This is important in the development of efficient and practical medication that, in the case of epilepsy for example, has to be taken daily by patients suffering from this ailment. In comparison, a wide variety of thiosemicarbazones and related compounds afford no protection against seizures induced in the scPTZ screen when given orally to rats.

The compounds of the present invention appear to be stable in vivo. A stability study, whereby the compounds were incubated at 37°C in deuterated dimethylsulfoxide, revealed that, at the time of peak effects of oral dosage in rats, no decomposition occurred. This is important and provides an advantage over most existing anticonvulsants compounds that tend to decompose relatively quickly after having been administered to mammals.

When comparing the protection indices of the semicarbazones of the present invention to those of mephenytoin (4.73) and phenobarbital (6.71), two antiepileptic drugs currently on the market, the figures are exceeded by fifteen of the nineteen compounds tested in the examples. In fact , five of the tested semicarbazones have protection indices greater than 20. Thus, these specific compounds demonstrate that the class of semicarbazones of the present invention represent a template providing potent anticonvulsant drugs in which the differential between doses which are effective therapeutically and those causing neurotoxicity is greater than is found with most currently available medication.

Molecular modelling calculations suggest that the activity of the semicarbazone anticonvulsants of the present invention is dependent on both pharmacokinetic and pharmacodynamic considerations. First the molecule must reach the receptor microenvironment (significance of log P); next, it must interact with its receptor. The receptor may have a lipophilic pocket and a hydrogen bonding surface to interact with the lipophilic and hydrogen bonding moieties of the semicarbazone, respectively. The separation and orientation of the lipophilic pocket and hydrogen bonding surface can both influence activity.

The semicarbazones disclosed and claimed in the present application have significant activity in protecting convulsions in the MES screen when administered orally to rats. High protection indices were found in the majority of compounds tested. In fact, no neurotoxicity was displayed at the maximum doses administered in many compounds. The presence of a large hydrophobic group (aryl ring) near four electron donor atoms (in the semicarbazo group) fulfills the structural requirements for activity in the MES screen which may account for the selective protection in this test in contrast to the scPTZ screen when the compounds were given orally. In general these semicarbazones are rapidly acting compounds and the most common mechanism of action is by interaction with chloride channels. The fragments of the semicarbazone molecules associated with oral activity in rats in the MES screen were obtained using empirical and semi- empirical conformational calculations which also suggest that the lipophilicity of the molecules was an important feature.

As the present invention also relates to pharmaceutical compositions comprising at least one of the semicarbazones described above, information is provided on appropriate formulation and dosage requirements.

To prepare the pharmaceutical compositions of the present invention, any suitable carrier known in the art can be used. The choice of the carrier, which should be a non-toxic carrier, is within the knowledge of the person skilled in the art. The carrier may be a solid, a liquid or mixture of a solid and a liquid. Solid form compositions include powders, tablets and capsules. If a liquid composition is prepared, a suspension of an aqueous material is necessary, due to the lack of aqueous solubility of the semicarbazones used as one of the pharmaceutical agents of the composition. The choice of the aqueous material is within the realm of the skilled artisan.

The pharmaceutical composition is preferably provided in unit dosage form. In such form, the composition is subdivided in unit doses containing appropriate quantities of the pharmaceutical agent. The quantity of pharmaceutical agent in a unit dose of composition can be varied or adjusted according to the particular need of the patient and the anticonvulsant activity of the particular compound used. Preferably, the compositions of the present invention are to be administered orally 4 times daily and have a pharmaceutical agent concentration ranging from 10 to 25 mg/kg.

In the following examples, which are provided to illustrate rather than limit the scope of the present invention, reference is made to compounds of series 1 to 4, the chemical structures of which are listed below. Data on the compounds of series 1 is provided to demonstrate differences in activity and toxicity between the semicarbazones of the present invention and corresponding thiosemicarbazones.

a: R¹=R²=H a: R¹=R²=H f: R¹=2-Cl; R²=4-Cl b: R¹=H; R²=CH₃ b: R¹=2-Cl; R²=H g: R¹=2-Cl; R²=6-Cl c: R¹=Cl; R²=CH₃ c: R¹=3-Cl; R²=H h: R¹ =3-Cl; R²=4-Cl d: R¹=OCH₃; R²=CH₃ d: R¹=4-Cl; R²=H i: R¹=4-OCH₃; R²=H e: R¹=2-Cl; R²=3-Cl

a: R=CH₃ d: R = (CH₂)₃CH₃ a: X=CH₂

b: R = CH₂CH₃ e: R=(CH₂)₄CH₃ b: X=CH₂CH₂

c: R=CH(CH₃)₂ f: R = C₆H₅ c: X=CH=CH Example 1

a) Synthesis of compounds of series 1-4

The preparation of compounds 1a-d, 3a has been described by Dimmock et al. in Eur. J. Med. Chem. 1991 26, 529-534. The method for the preparation of semicarbazones 2b-j, 3b-f and 4a-c is as follows. A solution of the appropriate aldehyde (0.01 mol) in methanol (10 ml) was added to a solution of semicarbazide hydrochloride (0.01 mol) and sodium acetate (0.01 mol) in water (10 ml). The mixture was stirred at room temperature for 1 h, the precipitate was collected, dried and recrystallized from 95% ethanol (2a.d.i. 3b,f), absolute ethanol (2b,c,j, 3c-e, 4a,b), 1-propanol (2e-q), 1-butanol (2h) or acetic acid (4c).

Minor modifications to this general procedure were as follows. In the preparation of 3c, e solutions of the reactants were stirred at room temperature for 3.5 and 2 h respectively followed by refrigeration overnight and 1 h respectively. The synthesis of 3f entailed heating the reaction mixture under reflux for 25.5 h and on cooling it was refrigerated overnight. The average yield was 62%, ranging from 78% in the synthesis of 3a to 14% in preparing 3c.

b) Analysis of compounds of series 1-4

Elemental analyses (C,H,N) undertaken on 2a- j, 3b-f, 4a-c were within 0.4% of the calculated values except for 3d (calcd. for C₁₂H₁₇N₃O:C:65.72%. Found:C:66.21%). The melting points (°C) and yields (%) of 2 e - h, j are as follows: 2e : 260,77; 2f: 252,60; 2g : 228-229,77; 2h: 238-239.75;2j:236.5-237.79.

X-ray crystallography revealed that compounds with either a halogen atom in the ortho position (2b) or no ortho substituents (2d) had the E configuration, and it is likely that all of the compounds in series 2. possess this stereochemistry. Since the time of peak effect (TPE) of 3a-d was 0.25 h, only one spectrum was recorded for each, as rapidly as possible after dissolution. Observations of the methyl, methylene and methine protons revealed the presence of only one isomer which, on the basis of previous experience, was assigned the E configuration. It is likely therefore that the anticonvulsant compounds of the present invention possess this stereochemistry when isomerism is possible.

The H NMR studies were undertaken using a

Bruker AM 300FT NMR instrument equipped with an Aspect 3000 Computer. H NMR spectra of 10mM solutions of 2a- h, 3a-d in deuterated dimethylsulfoxide at 37°C were also obtained. Acquisition of the spectra was obtained with 16K TD and 16K SI and the resolution was 0.513 Hz/Pt. The pulse angle was about 30° giving 1.95 sec acquisition and the relaxation delay was 2 sec. The total number of scans were 128. Chemical shifts were reported in ppm using tetramethylsilane as the internal standard. The absorption of the methine protons were as follows: 2a : 7.84; 2b:: 8.24; 2c: 7.89; 2d: 7.82; 2e: 8.25; 2f: 8.18; 2g: 8.09 and 2h: 7.80. The alkyl absorptions for 3a-d were as follows: 3a: 2.18 (CH₃); 3b: 2.73 (CH₂, J = 7.6 HZ), 1.01(CH₃, J = 7.6 Hz);3c: 3.31(CH, J = 7.1 HZ), 1.10 [(CH₃)₂, J = 7.1 Hz] and 3d: 2.73 (CH₂), 1.37(CH₂CH₂), 0.88(CH₃).

Example 2

Anticonvulsant studies.

The evaluation of the compounds for anticonvulsant activity was undertaken by the National Institute of Neurological Disorders and Stroke, National Institutes of Health using the procedure described in Porter et al. in Cleve. Clin. 51, 293, 1984, hereby incorporated by reference. Phase I screening

Phase I screening consisted of administering doses of 30, 100 and 300 mg/kg of the compounds in series 1-4 to mice by the intraperitoneal route and at the end of 0.5 and 4 hours evaluating whether protection in the MES and scPTZ screens occurred and also whether neurotoxicity was demonstrated. Compounds 1a-d. 2a,c,d,h, 3a-f, 4a-c were active in the MES screen while compounds 1a-c, 2a,c,d, 3a,c,e, 4c afforded protection in the scPTZ test.

A report outlining the Phase I screening of 26 thiosemicarbazones including 1a-d indicated that while anticonvulsant activities was found in 23 compounds, 77% of the derivatives prevented mice remaining on a circulating rotorod (toxicity screen). In addition, all of the compounds in series 1 demonstrated other neurotoxic symptoms such as continuous seizure activity.

The semicarbazones 2-4 displayed anticonvulsant activity and toxicity in 72 and 61% of the compounds respectively; however in contrast to the thiosemicarbazones, no other neurotoxic symptoms were noted except in the cases of 4a, b. In general therefore, anticonvulsant activity is retained in the semicarbazones while toxicity is diminished relative to the related thiosemicarbazones.

Phase II screening

In the Phase II screen, quantitation of representative compounds was undertaken in mice and rats in order to have precise potency indications for both intraperitoneal and oral administration routes.

The Phase II screening is carried out by first injecting compounds by the intraperitoneal route into mice. The first experiment is to determine the time of peak effect for both the neurotoxicity and MES screens. After this has been accomplished, four to five doses are administered to eight mice to obtain the TD₅₀ and ED₅₀ values. The scPTZ screen is undertaken at the time of peak effect found in the MES screen.

Table I experimental data outlines the quantitative Phase II screening in mice of selected compounds in all three screens.

The results shown in Table I indicate that the protection indices of the semicarbazones were greater than that of the thiosemicarbazone 1C and for each compound the figure obtained in the MES screen was approximately twice that found in the scPTZ test. In the MES screen, the most promising compounds in regard to the separation of activity and neurotoxicity were 2c,d with P.I. values greater than or comparable to phenobarbital (P.I. = 3.17). The P.I. of ethosuximide is 3.39, hence only 2c has a protection index comparable to this established drug.

In addition to the results shown in Table I, compounds 2b. f were given to mice at a dose of 100 mg/kg by both the intraperitoneal and oral routes. No protection in the MES screen was observed by these two compounds except that half of the mice were protected when 2f was given intraperitoneally. When administered orally to mice, the ED₅₀ values for compounds 2a, 2b and 4c in the MES test were 40.27, 57.74 and 77.85 mg/kg respectively and 54.86, 68.67 and 147.22 mg/kg in the scPTZ screen. The TD₅₀ figures for 2a, 2d and 4c were 87.67, 252.66 and 377.18 mg/kg respectively.

In the MES, scPTZ and toxicity screens, the times of peak effect were initially determined by oral dosage of various quantities of the compounds into 4 to 8 rats and examining them at one or more of the following time periods, namely 0.25, 0.5, 1, 2, 4, 6, 8 and 24 hours. Quantification of the response was achieved at the times of peak effect using a minimum of 4 doses and 4 to 8 animals per dose were employed.

The time of peak effect (TPE) determinations revealed that for seven of the ten semicarbazones tested, the TPE was 0.25 hour which indicates that in general the compounds are rapidly acting anticonvulsants. Phenobarbital, a drug used in treating generalized tonic-clonic seizures, has an ED_gn value in the Phase II MES screen in mice of 21.8 mg/kg. The semicarbazones tested range in potency from 62% (3a) to 15% (2h) that of the reference drug in this screen. In the scPTZ test, the semicarbazones had ED₅₀ values which were higher than the figures obtained in the MES screen. However, in comparison with ethosuximide which has an ED₅₀ value of 130 mg/kg in this screen, 3a and 4b were more potent and 2a,c,d, 3d,f, 4a, c were equipotent with this drug.

The anticonvulsant activity displayed by many of the semicarbazones 2-4 in the MES screen when administered orally to rats is of considerable interest. In addition, their low neurotoxicity resulted in high protection indices. This information is presented in Table II along with the data for four thiosemicarbazones in series 1.

Footnotes for Table II a Data taken from Dimmock et al., Eur. J. Med. Chem.

1991, 26 , 529-534.

b Data taken from Dimmock et al., Eur. J. Med. Chem.

1990, 25, 581-588.

c At a dose of 300 mg/kg, 1/2 animals was protected 0.5 h after administration but after 0.25, 1, 2 and 4 h, no anticonvulsant activity was demonstrated. At this dose, no neurotoxicity was noted in 0/2 animals 0.25, 0.5, 1, 2 and 4 h after oral dosage.

d At a dose of 500 mg/kg, the number of animals (out of four) protected at the end of 0.25, 1, 4, 6 and 8 h were 0, 0, 1, 2 and 1 respectively. Using these time intervals and the same number of animals and dose of the compound, no neurotoxicity was noted.

e Administration of 300 mg/kg of 2 i revealed protection in 1/2, 2/2, 2/2, 2/2 and 2/2 rats but no neurotoxicity at the end of 0.25, 0.5, 1, 2 and 4 h respectively. No activity or neurotoxicity was noted at these times when a dose of 50 mg/kg was employed.

Table II reveals that in series 1 , 1a-c have the same potency and are clearly superior to id while the thiosemicarbazone derived from an aryl aldehyde namely 1a had the highest P.I. Series 2 comprising a number of semicarbazones of various aryl aldehydes revealed that high potency was retained in this group of compounds and in general, protection indices comparable to or greater than 1a were obtained. Compounds 2c.d.h were equipotent with .la while 2j had a considerably higher P.I. than 1a but in the case of these four semicarbazones, no neurotoxicity was noted at a dose of 500 mg/kg. The presence of a 4-methoxy group in the aryl ring (2i), like the analogous thiosemicarbazone id, had relatively low activity. The ED₅₀ values in series 2 appear to be influenced by the positions of the substituents in the aryl ring rather than their electronic and hydrophobic properties. Thus greater anticonvulsant properties were noted with both the unsubstituted semicarbazone .2a and also compounds containing a 3-chloro and/or 4-chloro or 4-bromo substituents (2c,d,h,j) rather than derivatives with a 2-chloro atom (2b, f,g,e). This ortho substitution would cause a large interplanar angle (θ) to be formed between the aryl ring and the adjacent azomethine bond and it is conceivable therefore that small θ values are associated with marked oral activity in the MES screen.

The potencies in the oral MES screen in series 2 and 3 were similar being 32.4 and 35.2 mg/kg respectively using the data of the compounds for which ED₅₀ values were computed. However neurotoxicity was noted at lower doses in series 3. Thus while eight of the ten compounds in series 2 had TD₅₀ figures in excess of 500 mg/kg, only two of the six semicarbazones in series 3 were free from neurological deficit at this dose. This phenomenon contributed to protection indices being somewhat lower in series 3 than 2. In series 3 , variation in the nature of the R group had an effect on the hydrophobicity of the molecules which is reflected in changes in bioactivity. Furthermore, variation in the E_S values of the R group may affect the percentage of E and Z isomers in solution which in turn could alter the anticonvulsant properties of the molecules. Hence, in general, alkyl groups attached to the azomethine group are disadvantageous. The most promising lead compound in series 3 is 3e with a P.I. of greater than 15. In series 4, the different spacer groups employed indicate the variations of both the distance between the phenyl ring and the carbimino (C=N) group and the nature of the spacer group itself can have an influence in confering anticonvulsant activity.

In addition to the results provided in Table II, at the maximum doses administered (* 250 mg/kg), 1a-c, 2a-d,f-h, 3a-f, 4a-c were inactive in the scPTZ screen while 1d. 2i protected one in four animals at a dose of 300 mg/kg. Thus a noteworthy MES-selective protection was demonstrated by these compounds when given orally. A comparison of the data in Tables I and II indicate that in general, potency in the MES screen was increased and neurotoxicity decreased when the compounds were given orally to rats rather than by intraperitoneal injection into mice. Also, intraperitoneal injection of 1c, 3a and 4c to rats produced neurotoxicity at lower doses than when the compounds were given orally and the ED₅ value in the MES screen of 1c was reduced. In addition, a dose of 100 mg/kg of 2e given intraperitoneally into rats gave protection in half of the animals in the MES screen.

Administration of three representative compounds namely 2a,d and 4c to both rats and mice by the oral route indicated that while 2a had the same ED ₅₀ value in the MES screen whether given orally to either mice or rats, both 2d and 4c displayed greater potency in rats. The ED ₅₀ figures of all three compounds were higher in rats and hence higher P.I. figures were obtained by oral dosing in rats. The route of administration appears unimportant in mice since lower ED₅₀ and TD₅₀ figures were recorded for 2a when given orally and for 4c when given by the intraperitoneal route while 2d had the same bioactivity when given by either route of administration.

Hence, intraperitoneal injection gave higher bioactivities than when the compounds were administered orally to rats. This phenomenon is likely due to differences in species of animals and routes of administration. However, once the anticonvulsant properties of the semicarbazones of the present invention have been established, determination of the most efficient mode of administration for a given animal species is within the knowledge of the person skilled in the art.

The ED₅₀ values (95% C.I.) of phenobarbital, phenytoin and ethosuximide in the MES test when administered by the intraperitoneal route to mice are as follows: 21.8(15.0-25.5), 9.50(8.13-10.4) and > 1000 mg/kg respectively. The figures in the scPTZ screen are 13.2(5.87-15.9), inactive and 130(111-150) mg/kg respectively. In the neurotoxicity screen, the figures for these three drugs are 69.0(62.8-72.9), 65.5(52.5- 72.1) and 441(383-485) mg/kg respectively. After oral administration to rats, the ED₅₀ values for phenobarbital and mephenytoin in the MES screen are 9.1(7.58-11.86) and 18.1(14.07-24.91) mg/kg respectively and the TD₅₀ figures for these two compounds are 61.1(43.72-95.85) and 85.7(69.88-93.70) mg/kg respectively.

In comparison, the 95% confidence intervals for a number of derivatives mentioned in the text are as follows namely compound (route of administration and animals), screen, ED₅₀ or TD₅₀ values (mg/kg); 1c (intraperitoneal injections to mice): MES, 7.46(4.14-13.58); TD₅₀, 20.45(11.57-33.41); 2a (oral administration to mice): MES, 40.27(31.04-53.08); SCPTZ, 54.86(39.50-87.10); TD₅₀, 87.67(72.00-101.92); 2d (oral administration to mice): MES, 57.74(52.16-65.79); scPTZ, 68.67(54.61-94.96); TD₅₀, 252.66(95% C.I. is unavailable since slope for the compound is very flat); 4c (oral administration to mice): MES, 77.85(66.45-95.23); SCPTZ, 147.22 (103.10-202.86); TD₅₀, 377.18(261.92-558.25). Example 3

Evaluation of 2a,d, 3b, e in benzodiazepine and γ- aminobutyric acid receptor binding assays using synaptic membranes.

In the benzodiazepine receptor binding assay, which is described by Braestrup and Squires in Proc. Natl. Acad. Sci., 1977, 74, 3805-3809, hereby incorporated by reference, concentrations of 3,10,30 and 100 μM of 2a gave percentage increases (p value) in the binding of [ ³H]flunitrazepam to membranes isolated as a P₂ fraction from mouse whole brain homogenates of

11.8(<0.05), 13.8(<0.05), 16.4(<0.01) and 23.0(<0.01).

In the case of 2d, a significant increase of 9.1%

(p<0.01) in [ ³H]flunitrazepam binding to the receptor at a concentration of 100 μM was noted. No significant effect (p>0.05) on the displacement of the labelled ligand to the receptors was obtained using concentrations up to an including 100 μM of 3b, e.

Since none of these derivatives displaced the radioligand from the homogenate, no interaction of 2a , d , 3b , e with the benzodiazepine receptor site occurs. The ability of 2a,d, 3b, e to displace radiolabelled flunitrazepam and γ-aminobutyric acid from their respective receptors was examined. At the maximum concentrations of compounds employed, 2a,d caused small but statistically significant increases in the binding of [ ³H]flunitrazepam to its receptors rather than lowering the amount of bound ligand.

Compounds 3b, e had no effect in this assay.

Compounds 2a, 3e inhibited the binding of [ ³H]γ-aminobutyric acid to GABA receptors in mouse whole brain P₂ pellets by 20.7-28.7% (p<0.05) and 22.8-24.1% (p<0.05) using concentrations of 0.05-10 μM and 0.1-10 μM of 2a, 3e respectively. The test is described by Zukin et al. in Proc. Natl. Sci. USA 1974, 71, 4802-4870 and by Enna, S.J. and Snyder S.H. in Brain Res. 1975, 100. 81-97. No significant effect (p>0.05) was observed with 2d, 3b using concentrations up to and including 10 μM. Both 2a and 3e inhibited the binding of [³]γ-aminobutyric acid to GABA receptors while 2d and 3b were inactive in this test.

Example 4

Effect of 2a,d, 3b, e on adenosine uptake into synaptosomes.

Use of the procedure described by Phyllis et al. in Gen. Pharmacol. 1981, 12, 67-70, hereby incorporated by reference, revealed that 2a inhibited the uptake of [³H] adenosine into mouse whole brain synaptosomes by

15.5% (p<0.05) at a concentration of 100 μM. Since adenosine is thought to be involved in the central actions of benzodiazepines, a number of compounds binding at the benzodiazepine receptor inhibit the uptake of adenosine into synaptosomes.

Compound 3e caused percentage enhancement of binding of 3.6 (p<0.05), 8.7 (p<0.01), 9.4 (p<0.01) and 7.7 (p<0.01) at concentrations of 0.3, 1, 10 and 30 μM respectively while there was no significant effect at 3 and 100 μM. No inhibition of adenosine uptake (p>0.05) was obtained using concentrations up to and including 100 μM with 2d, 3b. In an assay measuring the alteration in the uptake of [ ³H] adenosine into mouse whole brain synaptosomes, 2a inhibited the uptake of the ligand, 3e gave erratic results and 2d, 3b had no effect. Example 5

Evaluation of 2a,d, 3b,e in the timed intravenous pentylenetetrazol test.

The compounds in methylcellulose solution (0.5%) were administered by the intraperitoneal route to mice using ten animals per dose (nine animals for the 135 mg/kg dose of 2d). After 0.25 h, a solution of 0.5% pentylenetetrazol in heparinized 0.9% sodium chloride solution was infused into the tail veins of mice and the times of the first appearance of both the focal seizure and also clonic seizure were recorded. These times were compared to values obtained using ten control animals (nine in the case of 2d).

The times of the first focal seizures (dose in mg/kg, time in seconds, p value) were as follows: 2a: 50 , 33.9 , 0.10; 100 , 38.4 , 0. 0004 ; 2 d: 75 , 37.4 , 0.04 ; 135 , 42.6 , 0. 002 ; 3b: 50 , 38. 1 , 0. 003 ; 100 , 37.7 , 0. 03 ; 3e : 50,33.1,0.33;100, 35.8, 0.02. The times of the clonic seizures (dose in mg/kg, time in seconds, p value) were as follows: 2a: 50,47.3,0.008;100,53.5,0.0002; 2d: 75 , 62.4 , 0.004 ; 135 , 60.5 , 0.001; 3b: 50, 46.8 , 0.008 ; 100, 50.5 , 0. 002 ; 3e: 50,40.5,0.26;100,45.7,0.005. Hence, the semicarbazones 2a,d, 3b, e increased the times prior to the first focal seizures and also chronic convulsions induced by the intravenous administration of pentylenetrazol.

Certain anticonvulsants have proconvulsant properties. In order to determine the likelihood of the compounds prepared in this invention having convulsant activities, pentylenetetrazol was infused into the tail veins of mice and the time taken for the appearances of the first local seizures and also clonic seizures were recorded. The experiment was repeated using varying concentrations of 2a,d, 3b, e and in each case the times prior to seizures occurring were increased and hence they appear to be bereft of proconvulsant properties.

Example 6

Protection of 2a, d, 3e against seizures induced by N-methyl-D-aspartate.

Various doses of compounds 2a,d, 3e in 0.5% methyl cellulose were injected by the intraperitoneal route into mice. After 0.25 h (2a, 3e) or 1 h (2d) and intracerebroventricular injection of N-methyl-D- aspartate (0.2 μg/μl) was administered and the number of animals protected was noted. Five to ten animals per dose were utilized. The ED₅₀ values (95% C.I., slope, SE) for the protection against clonic seizures were as follows: 2a: 64.86 mg/kg (39.37- 99.41,3.20,0.94); 3e: 208.6 mg/kg (125.8- 332.5,2.9,0.93). The protection afforded by 2d at doses of 5, 10, 20, 40 and 80 mg/kg was 1/5, 2/6, 3/10, 4/6 and 6/10 animals and an ED₅₀ was unable to be calculated. The experiment was repeated using a concentration of 3.0 μg/5 μl of N-methyl-D-aspartate and protection against forelimb tonic extensions in mice by 2a,d, 3e expressed as ED₅₀ values (95% C.I., slope, SE) was as follows: 2a: 28.62 mg/kg (17.92- 44.68,2.20,0.51); 2d: 12.9 mg/kg (8.6-18.4,4.65,1.36); 3e: 59.67 (30.5-172.08), 1.38, 0.42.

A number of common antiepileptics inhibit clonic seizures and forelimb tonic extension (FTE) in mice induced by the excitory amino acid N-methyl-D-aspartate

(NMDA). Compounds 2a,d, 3e afforded protection in both tests. In contrast to valproic acid, the semicarbazones 2a, 3e were more active in protecting against clonic seizures while in the FTE screen, 2d was more potent and 2a, 3e were equipotent with this antiepileptic drug. In both tests, the three compounds were less active than phenytoin and phenobarbital.

The ED₅₀ values (95% C.I.) of phenobarbitone, phenytoin and ethosuximide in protecting against clonic seizures in this test are 2.75(0.17-4.90), 8.59(6.64-14.10) and 408.09(341.68-487.96) mg/kg respectively. The same drugs have ED₅₀ values in protecting against forelimb tonic extension of 3.09 (1.44-4.67), 0.60 (0.34-0.95) and 82.58(30.94-131.87) mg/kg respectively. Example 7

Evaluation of 2a,c,d,h, 3a,b,e,f, 4a, b for protection against seizures induced by bicuculline, picrotoxin and strychnine.

Various doses of the compounds were administered by the intraperitoneal route to mice. Bicuculline (2.7 mg/kg), picrotoxin (2.5 mg/kg) or strychnine (1.8 mg/kg) were administered subcutaneously and the protection afforded by the semicarbazones noted. Where ED₅₀ values were obtained, eight animals per dose were used and in the remaining cases two, seven or eight mice per dose were employed. Compounds which block seizures induced by bicuculline, picrotoxin and strychnine do so by acting on γ-aminobutyric acid (GABA) receptors, chloride channels and glycine receptors respectively.

The results of this evaluation using bicuculline and picrotoxin are presented in Table III; at the maximum doses employed, that is 80 (4b), 100(3a, f) , 150(4a), 200(3b), 300(2a,d) and 500(2c,h, 3e), no protection against seizures induced by strychnine was noted except for marginal activity in the case of 4a.

Table III indicates that a site of action of 2a,

3e, 4a is GABA receptors while six of the ten compounds acted on chloride channels. No significant protection was noted by any of the compounds listed in Table III against seizures induced by strychnine. Thus the most common site of action of the anticonvulsant semicarbazones appears to be chloride channels. The

ED_S0 values for mephenytoin, valproic acid and phenobarbital in the bicuculline test are 124.1, 360.0 and 37.7 mg/kg respectively and in the sc picrotoxin screen the figures are 101.0, 387.2 and 27.5 mg/kg respectively.

Example 8

Evaluation of physicochemical constants.

In order to seek correlations between the potencies of 2a, 3a-f and variations in the hydrophobic, steric and electronic properties of the hydrogen atom (in 2a) or group R (in 3) attached to the azomethine bond, linear plots of the ED₅₀ figures versus the fragment constant (f), molar refractivity

(MR), resonance (r) and field (g) constants were made.

The f, MR, r and g constants were taken from the literature (Hansch, C. and Leo, A.J., Substituent constants for correlation analysis in chemistry and biology, 1979, John Wiley and Sons Inc., N.Y.). The fragment constants were calculated using f

_H, f_C, , f^θ _H and f^θ _cl figures of 0.23, 0.20, 1.90, 0.23 an

d 0.94 respectively. The f values for the ethyl, isopropyl, n-butyl and n-pentyl groups were obtained using a bond factor (F_b) of -0.12 applied n-1 times where n is the number of bonds in the group. In the case of the isopropyl function, a one time chain branch factor (FcBr) of -0.13 was used. The olefinic group in the styryl function of 4c required the use of a double bond factor (f^θ=) of -0.44. Using the test for zero correlation (Bolton, S . Pharmaceutical Statistics, Dekker, New York, 1984, p. 207), anticonvulsant potency was significantly correlated with f and r values (p<0.05) as well as the g constants (p<0.10) but not with the MR figures (p>0.10).

The average times of peak effects in series 2-4 were approximately 2, 0.25 and 0.6 hours respectively. The time required for maximum penetration to a site of action may be influenced by the hydrophobic properties of the molecules. Hence, a linear plot of the TPE values of the rat oral MES screen of the compounds in series 2-4 (except 2e, i) versus the fragment constants (f) of the variable atoms and/or groups on the carbon atom on the carbimino function i.e. the non-carbon aryl substituents and either a proton (series 2 , 4) or a R group (series 3) was performed. No correlation was observed (r = 0.00).

The semicarbazones 4b, c possessing two carbon atom spacer groups between the aryl ring and azomethine carbon atom had similar and greater potencies respectively than 2a. All three compounds are more active than 4a in which a methylene group insulates the phenyl ring from the azomethine linkage. However 4a is less neurotoxic than 2a resulting in a higher protection index (>11.69) than is found in 2a (P.I. = 11.30). Of the two compounds possessing two carbon atom spacer groups, an unsaturated linkage is preferable both in terms of potency and P.I. In fact, the P.I. of 4c is singularly noteworthy and the marked difference to Phase II screening is of interest.

Example 9.

Molecular modelling calculations.

For molecular mechanics calculations, two force field equations were employed: Dreiding as implemented in BIOGRAF 3.0, and MM2 (85). Semi-empirical molecular orbital quantum mechanics calculations were performed using the AM1 Hamiltonian as implemented in MOPAC 5.01. For statistical calculations the SAS package of statistical programs, vesion 6.06, was used. Molecular mechanics and semi-empirical molecular orbital conformational calculations were performed on IBM RS/6000550 and 32OH RISC computers operating under AIX in the Queen's University/IBM Molecular Modelling Laboratory, Kingston, Ontario, Canada; statistical calculations were performed on an IBM ES/9129 computer operating under VM/CMS.

To ascertain the conformation of a given molecule, the following calculational strategy was used. First, for each analog, fifty different starting conformations were fully optimized using the Dreiding force field and a first derivative minimization procedure. These analogs were selected by varying dihedral angles. Next, the ten lowest energy conformations from the Dreiding calculations were optimized using the MM2(85) force field and a second- derivative Newton-Raphson minimization procedure. The lowest energy conformer from the MM2 calculations was then mimized using the AMI semi-empirical molecular orbital Hamiltonian. The AMI optimized conformation and geometries were used for the structure-activity relationship studies.

For structure-activity studies, each analog was described by four series of descriptors: (i) geometric descriptors to represent three-dimensional properties and to reflect aspects of molecular size and shape (e.g. bond lengths, torsional angles, interatomic distances, substituent volumes); (ii) electronic descriptors to represent variable electron distribution throughout the molecular framework (e.g. atomic charge densities, molecular dipole); (iii) topological descriptors encoding aspects of molecular composition and connectivity (e.g. Randic Indices, Keir-Hall Indices); and (iv) physicochemical descriptors describing molecular lipophilicity (e.g. log P). The geometric and electronic descriptors were obtained from the optimized AMI calculational results. Topological descriptors were divided into two groups: graph theory descriptors and ad hoc. The graph theory topological descriptors were determined from graph theory calculations. The physicochemical descriptor was calculated using the approach of Ghose and Crippen. Descriptors are listed in Table IV.

Each compound was described by thirty-nine descriptors. Regression and discriminant statistical analyses were performed to establish a relationship between the molecular descriptors and biological activity and to ascertain the minimal number of descriptors for identifying optimal bioactivity.

The semicarbazone anticonvulsants of the present invention may be considered as bifunctional molecules, possessing a lipophilic moiety (substituted phenyl ring) and a hydrogen bonding moiety (the semicarbazono portion, N1-N2-C8 (O)-N3). Figure 1 indicates the numbering of these molecules. All analogues from series 2 , 3 and 4 were studied. Each analogue was described by 39 descriptors which are listed in Table IV.

A subset of descriptors which correlated with oral anticonvulsant activity (ED₅₀) in the MES test (Table II) was selected from the full descriptor array using stepwise and forward selective regression procedures at the 95% and 85% confidence levels. At the 95% level, none of the descriptors were significant. At the 85% level, eight descriptors were significant; these are listed in Table V.

TABLE V Significant descriptors at the

85% Confidence Level Molecular dipole

Log P

Atomic charge on N3

Atomic charge on C2

The C7-N1-N2-C8 torsional angle Randic-3 index

The C4-0 distance

The C7-N1-N2 angle

The eight statistically significant descriptors

(Table V) suggest that the geometric distance between the hydrogen bonding and lipophilic moieties is important for activity (C4-0 distance) and that the orientation between the lipophilic and hydrogen bonding moieties is important (C7-N1-N2-C8 torsional). The geometry of the hydrogen bonding moiety (C7-N1-N2 angle) is important as is the charge on the N3 atom. Activity is also influenced by the phenyl substitution pattern (charge on the C2 atom of the phenyl ring).

Claims

1. A compound having the following formula:

wherein

R¹ is

or

said heterocycle being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl ,

R ² and R³ are the same or different and are selected from hydrogen, halogen, lower alkylamino, dilower alkylamino, amino, straight chain or branched, lower alkyl, lower alkoxy, lower alkylidene and lower arylidene, said lower alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and aryl,

R ⁴ is hydrogen, strai.ght chain or branched alkyl or alkylidene,

wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and lower alkoxy, with the proviso that when R⁵ is CH=CH and R¹ is

R ⁵ is a single bond between R¹ and R⁶, a straight chain or branched alkyl having between 1 and 10 carbon atoms or an alkylidene having between 2 and 20 carbon atoms, said alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl,

with R ² and R³ being the same or different and representing hydrogen, halogen or alkyl having 1 to 3 carbon atoms, R ⁵ is not alkylidene having between 2 and

3 carbon atoms; and

R⁶ is carbon;

and pharmaceutically effective salts thereof.

2. A compound according to claim 1, wherein

R¹ is

R⁴ is hydrogen;

R ⁵ is a single bond between R¹ and R⁶, a straight chain or branched lower alkyl having between 1 and 10 carbon atoms or an alkylidene having between 2 and 20 carbon atoms; and R⁶ is carbon;

and pharmaceutically effective salts thereof.

3. A compound according to claim 1, wherein said compound has the following formula:

4. A compound according to claim 1, wherein said compound has the following formula:

5. A compound according to claim 1, wherein said compound has the following formula:

6. A compound according to claim 1, wherein said compound has the following formula:

7. A compound according to claim 1, wherein said compound has the following formula:

8. A compound according to claim 1, wherein said compound has the following formula:

9. A compound according to claim 1, wherein said compound has the following formula:

10. A compound according to claim 1, wherein said compound has the following formula:

11. A compound according to claim 1, wherein said compound has the following formula:

12. A compound according to claim 1, wherein said compound has the following formula:

13. A compound according to claim 1, wherein said compound has the following formula:

14. A compound according to claim 1, wherein said compound has the following formula:

15. A compound according to claim 1, wherein said compound has the following formula:

16. A compound according to claim 1, wherein said compound has the following formula:

17. A compound according to claim 1, wherein said compound has the following formula:

18. A compound according to claim 1, wherein said compound has the following formula:

19. A compound according to claim 1, wherein said compound has the following formula:

20. A compound according to claim 1, wherein said compound has the following formula:

21. A compound according to claim 1, wherein said compound has the following formula:

22. A pharmaceutical composition having anticonvulsant activity in mammals, said composition comprising an effective amount of a pharmaceutical agent comprising a compound having the following formula:

wherein

R¹ is

or

said heterocycle being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl. wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and lower alkoxy;

with the proviso that when R⁵ is CH=CH

and R¹ is

with R ² and R³ bei.ng the same or different and representing H, Cl, CH₃, OCH, or OH, R⁴ is not methyl; R⁵ is a single bond between R"i and R6, a straight chain or branched alkyl having between 1 and 10 carbon atoms or an alkylidene having between 2 and 20 carbon atoms, said alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl,

wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of haloqen, amino. lower alkvlamino. dilower alkylamino and lower alkoxy, said alkylidene being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and aryl,

R⁶ is carbon;

and pharmaceutically effective salts thereof,

in admixture with a pharmaceutically acceptable carrier or adjuvant.

23. A composition according to claim 22, wherein

R¹ is

R⁴ is hydrogen;

R⁶ is carbon;

and pharmaceutically effective salts thereof.

24. A pharmaceutical composition according to claim 22, wherein said pharmaceutical agent comprises an effective amount of at least one compound selected from the group selected from:

25. A method for the treatment or prevention of convulsions in mammals, said method comprising administering to a mammal a pharmaceutically effective amount of a pharmaceutical agent comprising a compound having the following formula:

wherein

R¹ is

or

R ² and R³ are the same or different and are selected from hydrogen, halogen, straight chain or branched, substituted or unsubstituted lower alkyl, amino, nitro, lower alkoxy, lower alkylidene and lower arylidene; said lower alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino and aryl, wherein said aryl is unsubstituted or substituted with at least one substituant selected from the group consisting of hydrogen, halogen, straight chain or branched lower alkyl, lower alkoxy, amino, lower alkylamino and dilower alkylamino,

with the proviso that when R ⁵ is CH=CH

and R ¹ is

with R ² and R³ being the same or different and representing H, Cl, CH₃, OCH₃ or OH, R⁴ is not methyl; R⁵ is a single bond between R¹ and R⁶, a straight chain or branched alkyl having between 1 and 10 carbon atoms or an alkylidene having between 2 and 20 carbon atoms, said alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl,

R⁶ is carbon;

and pharmaceutically effective salts thereof,

in admixture with a pharmaceutically acceptable carrier or adjuvant,

for the purpose of preventing or treating convulsions in said mammals.

26. A method according to claim 25, wherein in said compound of formula I:

R¹ is

R⁴ is hydrogen;

R⁵ is a single bond between R¹ and R⁶, a straight chain or branched lower alkyl having between 1 and 10 carbon atoms or an alkylidene having between 2 and 20 carbon atoms; and

R⁶ is carbon;

and pharmaceutically effective salts thereof.

27. A method according to claim 26, wherein said pharmaceutical agent comprises at least one compound selected from the group consisting of

28. A commercial package for the treatment or prevention of convulsions in mammals, said package comprising a pharmaceutical agent therapeutically active for the treatment or prevention of convulsions in mammals, together with instructions to use said pharmaceutical agent in the prevention or treatment of convulsions in mammals, and wherein said pharmaceutical agent comprises a compound having the following formula I:

wherein

R¹ is

or

with the proviso that when R ⁵ is CH=CH

and R ¹ is

with R² and R³ being the same or different and representing H, Cl, CH₃, OCH₃ or OH, R ⁴ is not methyl; R ⁵ is a single bond between R ¹ and R ⁶, a straight chain or branched alkyl having between 1 and 10 carbon atoms or an alkylidene having between 2 and 20 carbon atoms, said alkyl being unsubstituted or substituted with at least one substituant selected from the group consisting of halogen, amino, lower alkylamino, dilower alkylamino, lower alkoxy and aryl,

R ⁶ is carbon;

and pharmaceutically effective salts thereof.

29. A commercial package according to claim 28, wherein:

R¹ is

R² and R³ are the same or different and are selected from hydrogen, fluorine, chlorine, bromine, iodine, lower alkoxy and straight chain or branched lower alkyl;

R ⁷ is hydrogen;

R ⁶ is carbon;

and pharmaceutically effective salts thereof.

30. A commercial package according to claim 28, wherein said pharmaceutical agent comprises at least one compound selected from the group consisting of