Pharmaceutical Research, Vol. 6, No. 8, 1989
`
`Research Article
`
`Structure—Pharmacokinetic Relationships in a Series of
`Valpromide Derivatives with Antiepileptic Activity
`
`Abdulla Haj-Yehial and Meir Bialerm
`
`Received November 10, 1988; accepted March 8, 1989
`
`The following valpromide (VPD) derivatives were synthesized and their structure»-pharmacokinetic
`relationships explored: ethylbutylacetamide (EBD), methylpentylacetamide (MPD), propylisopro-
`pylacetamide (PID), and propylallylacetamide (PAD). In addition, the anticonvulsant activity of these
`compounds was evaluated and compared to that of VPD, valnoctamide (VCD), and valproic acid
`(VPA). MPD, the least-branched compound had the largest clearance and shortest hal.f—life of all the
`amides investigated and was the least active. All other amides had similar pharmacokinetic parame-
`ters. Unlike the other amides, PID and VCD did not metabolize to their respective homologous acids
`and were the most active compounds. Our study showed that these amides need an unsubstituted B
`position in their aliphatic side chain in order to biotransform to their homologous acids. An amide
`which is not metabolized is more potent as an anticonvulsant than its biotransformed isomer. All
`amides were more active than their respective homologous acids. In this particular series of aliphatic
`amides, which were derived from short-branched fatty acids, the anticonvulsant activity was affected
`by the pharmacokinetics in general and by the biotransformation of the amide to its homologous acid
`in particular. This amide—acid biotransformation appeared to be dependent upon the chemical struc-
`ture, especially upon the substitution at position B of the molecule.
`KEY WORDS: valpromide; valproic acid; antiepileptic activity; SAR; pharmacokinetics.
`
`Introduction
`
`Valpromide or dipropylacetamide (VPD-I; Fig. 1), a pri-
`mary amide of valproic acid, is widely used in several Eu-
`ropean countries, both as an antiepileptic and as an antipsy-
`chotic drug (1-3).
`Previous reports (3-5) have shown that, upon oral ad-
`ministration to humans, valpromide was biotransformed to
`valproic acid (VPA-II; Fig. 1), a well-known antiepileptic
`agent (6), before reaching the systemic circulation. Pharma-
`cokinetic analysis demonstrated that VPD is a prodrug of
`VPA (2—5,7,8) and that this may account for its antiepileptic
`activity.
`Loscher and Nau (9) reported that among a series of
`VPA analogues tested in mice for anticonvulsant activity,
`VPD was found to be the most potent, being two to five
`times more potent than VPA. However, VPD also exerted a
`more significant sedative side effect.
`Recent articles have reported that VPD also possesses
`specific properties of its own (unrelated to VPA), i.e., the
`induction of an elevation in the plasma levels of carbamaz-
`epine-10,11-epoxide, the active metabolite of carbamazepine
`(10-14).
`Following i.v. administration, VPD was shown to be
`rapidly and almost completely metabolized to VPA in hu-
`
`1 Department of Pharmacy, School of Pharmacy, Hebrew Univer-
`sity of Jerusalem, POB 12065, Jerusalem 91120, Israel.
`2 To whom correspondence should be addressed.
`
`mans, with an fm value of 80% (fm = the metabolized frac-
`tion of VPD to VPA) (8). In dogs, VPD’s biotransformation
`to VPA was only partial and was independent of the route of
`administration, the fm being in the range of 30-40% (15,16).
`Valnoctamide (VCD-III; Fig. 1; valmethamide or 2-
`ethyl-3-methylpentamide), an isomer of VPD, has also
`proven useful as a tranquilizer in the treatment of anxiety
`and tension (17-19). In a recent study in dogs,
`it was re-
`ported that VCD’s major pharmacokinetic parameters were
`similar to those of VPD (20), the main difference being that
`VCD was not a prodrug of its homologous acid (valnoctic
`acid; VCA-IV; Fig. 1). This pharmacokinetic (or metabolic)
`difference may explain the different pharmacological prop-
`erties of the two isomers. The extent of biotransformation of
`an aliphatic amide (such as VPD or VCD) to its homologous
`acid, therefore, appears to be a key issue in these com-
`pounds’ pharmacological activity.
`Another compound, similar to both VPD and VCD, is
`allylisopropylacetamide (AIA-V; Fig. 1). In contrast to VPD
`and VCD, which are used as drugs, AIA is defined as a
`“suicide substrate” (21,22). Despite the fact that VPD,
`VCD, and AIA are chemically similar, there are marked dif-
`ferences in their pharmacological properties.
`Keane et al. (23) and Loscher and Nau (9) have dem-
`onstrated that within a large series of branched monocarbox-
`ylic acids, VPA had the optimal chemical structure with re-
`gard to margins between its anticonvulsant effect and its
`sedative/hypnotic side effects. Since pharmacokinetics plays
`a major role in the pharmacological activity of these ali-
`
`683
`
`0724-8741/89/0800-0683$06.00/O e 1939 Plenum Publishing Corporation
`
`Par Pharm., Inc.
`Exhibit 1 054
`
`Par Pharm., Inc. v. Novartis AG
`Case lPR201 6-00084
`
`Ex. 1054-0001
`
`

`
`684
`
`CH5-CH2-CH
`
`CH
`
`/
`3-CH2-CH2
`
`CH-DDNH2
`
`CH3-CH2~EI1{ CH - COOH
`Z
`CH3-CH2~l.‘.H
`
`VALPRCMIDE - VPD (I)
`
`VALPROIC ACID - VPA (II)
`
`CH
`
`z"=
`‘Hz
`’
`3 -CH2-DH-CH-CONH2
`
`CH
`
`z"=
`CH3 N2
`-
`I
`CH3-CH2 H-CH-CDOH
`
`VALNOETAMIDE - vcn (III)
`
`vALNoc1’|I: ACID - VGA (Iv)
`
`3
`
`Cit, [CHCH
`
`CH2 I CH-CH2-0H-CONH2
`ALLVLISDPRDPYACETAMIDE - AIA (V)
`
`CH
`1 3
`[EH2
`O43-CH2-CH2-CH2-CH-CDNH2
`ETHVLBUTYLACETAMIDE - EBD (VI)
`
`CN
`3
`I
`CH3-CH2-CH2-CHz<CM2-GM-CEIM2
`METHVLPENTVLACETAMIDE - DPD (VII)
`
`:7":
`cu cu
`f”:
`, 3, 2
`CH3-CM-CH-CONM2
`PROPVLISOPRDPVLACETAMI as -
`Pl u (v: I I )
`
`9":
`9":
`F":
`CH2 I CH2-CH2-CH-CDNHI
`PROPVLALLYLACETAMIDE -
`PAD ( IX)
`Fig. 1. Chemical structures of the different aliphatic amides and
`acids discussed in the paper.
`
`phatic amides, we decided to explore the structure-
`pharmacokinetic relationships that may exist within a series
`of VPD (or VCD) isomers or derivatives which contain eight
`carbon atoms per molecule.
`The following aliphatic branched-chain amides were
`synthesized and their pharmacokinetics investigated in dogs
`(following i.v. administration): ethylbutylacetamide (EBD-
`VI), methylpentylacetamide (MPD-VII), propylisopropylac-
`etamide (PID-VIII), and propylallylacetamide (PAD-IX).
`The chemical structures of these amides are depicted in
`Fig. 1.
`In order to evaluate whether any relationships exist
`among chemical structure, pharmacokinetics, and anticon-
`vulsant activity in the above-mentioned compounds, we
`tested and evaluated the antiepileptic data of our compounds
`by using the anticonvulsant screening project of the NIH
`Epilepsy Branch (24).
`
`MATERIALS AND METHODS
`
`Materials
`
`Structure—Pharmacokinetics of Valpromide Derivatives
`
`appropriate alkyl halide (all chemicals were purchased from
`Aldrich, Milwaukee, Wis.). The acids were then obtained by
`decarboxylation (heating to 150—180°C until the elaboration
`of all of the CO2 stopped) of the condensation product and
`the amides (compounds VI to IX) by amidation of the acyl
`chloride with ammonia. The chemical structures were con-
`firmed by nuclear magnetic resonance (NMR) and elemen-
`tary microanalysis.
`
`Animals
`
`The experiments were carried out in six dogs (mon-
`grels), three males and three females, ranging in weight be-
`tween 18 and 23 kg. Although mice and rats are usually used
`for anticonvulsant screening (24), these animals are too small
`to be used in pharmacokinetic studies with a crossover de-
`sign. In addition, the disposition of drugs in dogs has the
`potential of being more similar to that in humans than the
`disposition of the same drugs in rodents. In a randomized
`crossover design, each dog was injected intravenously with
`400 mg (in 1.5 ml 70% alcohol) of the amide (into one of the
`cephalic veins). In cases where an amide was biotrans-
`formed into its homologous acid, the acid was also adminis-
`tered (i.v., 400 mg). Urine was collected systematically for
`16 hr from all dogs by means of an indwelling catheter. A
`washout period of 3 weeks was allowed between any two
`consecutive studies.
`
`Protocol
`
`Venous blood samples (6 ml) were collected via an in-
`dwelling catheter (the other cephalic vein) at specified inter-
`vals following injection (0, 2, 5, 10, 15, 20, 30, 40, and 50 min
`and 1, 1.25, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7,8, 9, and 10 hr,
`respectively). The plasma was then immediately separated
`by centrifugation at 7000 rpm for 15 min and stored at
`— 20°C. Before each assay, the plasma was allowed to reach
`room temperature, vortexed, and centrifuged, and the resid-
`ual clot removed. Plasma levels of the amide and its homol-
`ogous acid were assayed by gas—liquid chromatography
`(GLC), an assay which we have reported on for the deter-
`mination of VPD and VCD (25,26).
`As the acids of compounds VI to IX were considered, a
`priori, to be potential metabolites of the amides, they were
`also synthesized. In preliminary studies we verified the fact
`that the acids can also be detected and monitored, simulta-
`neously with the appropriate amide, in our GLC assay.
`
`Anticonvulsant Activity
`
`The amides VPD (I), VCD (III), EBD (VI), MPD (VII),
`PID (VIII), and PAD (IX) and their respective homologous
`acids were screened in mice for their anticonvulsant activity
`by the NIH Epilepsy Branch (24). The screening procedure
`involved the following: (i) the maximal electroshock (MES)
`test, which measures seizure spread; (ii) the subcutaneous
`pentylenetetrazol test (s.c. Met. test), which measures sei-
`zure threshold; and (iii) the rotorod ataxia test, which as-
`sesses neurotoxicity.
`
`The amides (compounds VI to IX) and their homologous
`acids were synthesized by means of the classical method of
`a condensation between the diethylmalonate ester and the
`
`Pharmacokinetic Analysis
`
`The linear terminal slope (B) of log C (amide or acid
`
`Ex. 1054-0002
`
`Ex. 1054-0002
`
`

`
`Haj-Yehia and Bialer
`
`plasma concentration) versus t (time) was calculated by the
`method of least squares. The terminal half-life of the com-
`pound (t.,,[3) was calculated from the quotient 0.69/terminal
`slope. The AUC (area under the C versus the t curve) was
`calculated by using the trapezoidal rule with extrapolation to
`infinity—by dividing the last experimental plasma concen-
`tration by the terminal slope (27).
`The total body clearance (CL) of the amides was calcu-
`lated by using the quotient of the i.v. dose (D) and the AUC.
`The volume of distribution (VB) was calculated using the
`quotient of the clearance and the linear terminal slope. The
`volume of distribution at steady state (V55) and the mean
`residence time (MRT) were calculated using Eqs. (1) and (2)
`(28-30).
`
`D - AUMC
`Vss = ——,——
`(AUC)
`AUMC
`AUC
`
`MRT =
`
`<1)
`
`(2)
`
`The AUMC is the area under the product of time (t) and the
`plasma drug concentration (C) versus (t), from time zero to
`infinity. The AUMC was calculated by the trapezoidal rule
`with extrapolation to infinity. The fraction metabolized of
`the amide to its respective homologous acid (fm) was calcu-
`lated using Eq. (3) (3l,32), where (AUCm)D is the AUC of
`the acid obtained as a metabolite of the amide after i.v. ad-
`ministration of the amide and (AUC),,, is the AUC of the acid
`obtained after i.v. administration of the acid to the same
`animal which previously received the parent amide. D and
`Dm are the i.v. doses and CL and CL(m) are the clearances
`of the amide and acid, respectively.
`
`f : (AUCm)D _ AUC", = (AUCm)D . CL (m)
`m
`D
`' Dm
`AUC
`CL
`
`(3)
`
`All of the pharmacokinetic parameters were calculated in a
`noncompartmental manner based on the statistical moment
`theory (30,33).
`
`Partition, Stability, Water Solubility, and Protein
`Binding Studies
`
`The blood—plasma concentration ratio (34,35) of the
`amides (partition study) was carried out at room temperature
`by spiking known amounts of the amides in seven samples of
`fresh blood taken from a dog prior to drug administration.
`The amides’ concentration ranged from 3 to 20 mg/liter.
`Each blood sample was centrifuged immediately after spik-
`ing and the separation of the plasma was carried out accord-
`ing to the procedure mentioned above. Plasma levels of the
`amides were determined by GLC.
`A blood stability study of the amides was carried out by
`incubating 400 ug of each compound in 20 ml of dog blood
`(placed in heparinized test tubes) at 37°C with continuous
`shaking. Blood samples (2 ml) were then collected at the
`following times: 0, 1, 2, 3, 4, 5, 6, and 7 hr. Plasma was
`immediately separated and the amide concentration in the
`plasma assayed by GLC.
`Protein binding of the amides was evaluated by using
`the ultrafiltration method. This was carried out in four amide
`
`685
`
`plasma samples at drug concentrations of 5, 10, 15, and 20
`mg/liter. The amides’ levels in the filtrate (plasma water)
`were assayed by GLC. The free fraction (fu) of the amides
`was calculated form the quotient of the drug concentration in
`the filtrate to the initial drug concentration in the plasma.
`The water solubility of each amide was determined by stir-
`ring 40 mg of the appropriate amide in 3 ml of distilled water
`for 2 hr. At the end of the 2-hr period, the sample was cen-
`trifuged and 3-p.l aliquots were taken for GLC assay.
`
`RESULTS
`
`The mean plasma levels of the amides EBD, MPD, PID,
`and PAD are presented in Figs. 2-5, respectively and Table
`I summarizes their mean pharmacokinetic parameters as
`compared to those of VCD. Unlike EBD, MPD, and PAD,
`PID was not biotransformed to its homologous acid. Table I
`also shows the mean pharmacokinetic parameters (obtained
`after i.v. administration to the same dogs) of the acids found
`to be metabolites of their homologous amide. These acids
`were ethylbutyl acetic acid (EBA), methylpentyl acetic acid
`(MPA), and propylallyl acetic acid (PAA). The fm (the frac-
`tion metabolized of the amide to its respective homologous
`acid) calculations showed that MPD and PAD were com-
`pletely biotransformed to their homologous acids, while
`EBD was only partially biotransformed, having an fm value
`
`rnq[L
`
`
`
`
`
`PLASMACONC.(mglL)
`
`TIME lman)
`
`Fig. 2. Mean plasma levels of ethylbutylacetamide (EBD) and eth-
`ylbutyl acetic acid (EBA) following i.v. administration (400 mg) of
`EBD to six dogs. The coefficient of variation of these mean data
`ranged between 20 and 40%.
`
`Ex. 1054-0003
`
`Ex. 1054-0003
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`

`
`686
`
`Structure—Pharmacokinetics of Valpromide Derivatives
`
`
`
`PLASMcoMcENTnAnou{mg[L)
`
`
`
`noPLASMACmlCENTRA1'IOl\l(mdl.\
`
`‘rlvIE(min)
`Fig. 3. Mean plasma levels of methylpentylacetamide (MPD) and
`methylpentyl acetic acid (MPA) following i.v. administration (400
`mg) of MPD to six dogs. The coefficient of variation of these mean
`data ranged between 20 and 50%.
`
`of only 16%. The individual fm calculations for MPD in two
`dogs gave a value greater than one. This may be due to (i) a
`deviation from the assumptions (such as linear kinetics) in-
`herent in Eq. (3) and/or (ii) a rapid and multisite metabolism,
`accounting for the quick conversion of MPD to MPA. MPD
`was rapidly metabolized to MPA, its peak plasma concen-
`tration being obtained 5 min after the i.v. administration of
`MPD. Analyzing the urine showed that less than 1% of the
`administered dose of the amides was excreted unchanged.
`Stability studies showed that, unlike MPD, which is un-
`stable, EBD, PID, and PAD are stable in dog blood. Assum-
`ing first-order kinetics, the half-life of degradation of MPD
`was 4.8 hr. After 7 hr, there was a 40% decrease in the MPD
`concentration and a proportional increase in the concentra-
`tion of its homologous acid (MPA). MPD was stable in
`plasma.
`The data of the partition, plasma protein binding, sta-
`
`YIME(min)
`Fig. 4. Mean plasma levels of propylisopropylacetamide (PID) fol-
`lowing i.v. administration (400 mg) to six dogs. The coefficient of
`variation of these mean data ranged between 20 and 35%.
`
`bility, and water solubility studies are summarized in Table
`II. The partition study indicated that EBD and MPD are
`taken up by blood cells, while PID and PAD showed little
`and balanced uptakes, respectively.
`In Phase 1 of the anticonvulsant screening project of the
`NIH Epilepsy Branch, all of the amides were found to be
`more active than their respective homologous acids. There-
`fore, for Phase 2 the amides were subsequently tested in
`order to determine their ED50’s, TD50’s, and protective in-
`dices (PI; the ratio between the TD50 and the ED50 values).
`The results are shown in Table III. Even though the PI val-
`ues of VCD and PID were not dramatically higher than those
`of VPA, VPD, PAD, and EBD (in the PI MES values), VCD
`and PID were the most active of all of the compounds tested.
`MPD was found to be the least active of all of the compounds
`tested.
`
`DISCUSSION
`
`Following i.v. administration the plasma levels of the
`investigated amides declined in a biphasic fashion. MPD
`(VII) had the shortest mean terminal half-life (0.4 hr), while
`both PID and PAD had a half-life of 2.5 hr, a value which
`was similar to that obtained previously for VPD and VCD
`(15,20). The mean volume of distribution of MPD was the
`
`Ex. 1054-0004
`
`Ex. 1054-0004
`
`

`
`Haj-Yehia and Bialer
`
`687
`
`Using Eq. (4), the following mean values of blood clearance
`(ml/min) were obtained: EBD, 244; MPD, 753; PID, 251; and
`PAD, 89. Dividing the blood clearance by the mean dog
`hepatic blood flow of 560 ml/min (36) gave the following
`extraction ratios (E): EBD, 43%; PID, 45%; and PAD, 16%
`(Table I). This means that the metabolic clearance of PAD,
`like that of VCD, was low and restrictive (37). Thus, PAD
`has a low extraction ratio (E) by the liver, which indicates
`that it is not susceptible to a first-pass effect upon oral ad-
`ministration. PAD’s low extraction ratio indicates that al-
`though its clearance will not be affected by changes in blood
`flow, it may be affected by changes in plasma protein binding
`(37). EBD and PID have intermediate metabolic clearances
`and, thus, they may be susceptible to a partial first-pass
`effect upon oral administration.
`The mean f“ values of the amides ranged between 0.46
`and 0.86. This indicated that these amides were not highly
`bound to plasma proteins. Therefore, plasma protein binding
`does not appear to be a major factor in the disposition and
`pharmacokinetics of these amides. The water solubility of
`the investigated amides were all of the same order of mag-
`nitude (3.5 to 9.5 mg/ml; Table II).
`Table I compares the major pharmacokinetic parame-
`ters of the four amides investigated in this study to those of
`VCD. The values for CL, V, and t,,2 were similar for VPD,
`VCD, PID, and PAD. However, MPD had a large clearance
`Value and, therefore,
`the shortest half—life. Unlike VPD,
`EBD, MPD, and PAD, PID and VCD did not biotransform to
`their homologous acids. They were eliminated from the body
`by metabolic pathways which did not include hydrolysis of
`their amide moiety. This may be due to the fact that, in these
`two compounds, one of the [3 positions in the molecule has
`an alkyl substituent. Thus, an amide in this series of com-
`pounds investigated needs a free (unsubstituted) B position
`in its aliphatic side chain in order to undergo metabolism to
`its homologous acid. The differences in the extent of
`biotransformation to the respective homologous acid may
`therefore account for the differences in the pharmacological
`activities of the investigated compounds. In addition, the
`two amides which did not biotransform to their homologous
`acids were the most potent in the anticonvulsant screen.
`Therefore, in this series of aliphatic amides derived from
`short-branched fatty acids, the biotransformation of the
`amide to its homologous acid depends upon the chemical
`structure of the compound, especially upon whether the [3
`position of the molecule is substituted or not.
`Results from other laboratories (9,23) also showed that,
`in a series of VPA derivatives evaluated, a branched chain
`was essential for anticonvulsant activity. This may explain
`why MPD (the least-branched compound) showed the least
`activity. Keane et al. reported that when a series of VPA
`homologoues and analogues was tested for their anticonvul-
`sant activity, a significant correlation existed between side-
`chain length and anticonvulsant potency (23). In the Keane
`study, no sedative or toxic effects were observed with VPA
`homologues containing seven or fewer carbon atoms or with
`VPA (which possesses eight carbon atoms). However, 2-
`ethylhexanoic acid (Which is an isomer of VPA) and three
`VPA analogues with 9 or 10 carbons all exhibited sedative
`and/or toxic properties. Thus, VPA appears to have the op-
`timal chemical structure in this series, as it possesses a very
`
`
`
`PLASMAcoMcsurnAnou(mg[L)
`
`
`
` 120 O 360
`
`um: (min)
`Fig. 5. Mean plasma levels of propylallylacetamide (PAD) and pro-
`pylallyl acetic acid (PAA) following i.v. administration (400 mg) of
`PAD to six dogs. The coefficient of variation of these mean data
`ranged between 20 and 35%.
`
`largest (VS: = 38 : 20 liters) and it also produced the largest
`interdog variability. The other three amides had similar vol-
`umes of distribution (20 liters), a value which was of the
`same order of magnitude as that of VPD and twice that of
`VCD.
`the total-body
`As reflected by its short half-life,
`(plasma) clearance of MPD (VII) was 10 times that of VPD,
`VCD, PID, and PAD and 3 times that of EBD. Since this
`Value is greater than the blood flow through any individual
`organ in the dog (36),
`it indicates that the metabolism of
`MPD,
`including its biotransformation to its homologous
`acid, may occur at several metabolic sites. In addition, the
`facts that MPD is unstable in blood and that its biotransfor-
`mation to MPA occurs in blood also contribute to this large
`clearance value.
`The other three amides (EBD, PID, and PAD) were
`taken up by blood cells and were found to be stable in blood.
`This indicates that blood cells and/or plasma are not among
`their metabolic sites. As very low amounts of the three
`amides were found in the urine and as they were stable in
`blood, it appears that these three, like VPD and VCD, are
`eliminated from the body by metabolic processes.
`In order to compare plasma clearance with hepatic
`blood flow, the amides’ blood clearance had to be calcu-
`lated. This was carried out by using Eq. (4) (34):
`
`plasma clearance
`blood clearance
`
`blood concentration
`plasma concentration
`
`(4)
`
`Ex. 1054-0005
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`

`
`688
`
`Structure-Pharmacokinetics of Valpromide Derivatives
`
`Table I. Comparison of the Mean Pharmacokinetic Parameters of EBD, EBA, MPD, MPA, PID, PAD, PAA, and VCD
` EBD EBA MPD MPA PID PAD PAA VCD“
`
`
`
`
`
`
`
`
`1.1:
`0.7:
`
`0.4
`0.2
`
`1.1: 0.6
`: 0.3
`
`2.1:
`0.4:
`
`0.8
`0.1
`
`2.4:
`0.4:
`
`1
`0.2
`
`0.31:
`2.4 :
`
`0.05
`0.6
`
`0.33: 0.20
`2.6 : 1.1
`
`: 0.3 0.4: 0.1
`1
`0.7: 0.3
`1.9: 0.5
`
`21
`
`:
`
`9
`
`40
`
`: 7
`
`6.5:
`
`2.4
`
`10
`
`:
`
`7
`
`28
`467
`
`: 18
`:300
`
`10
`171
`
`: 2
`:30
`
`70
`1167
`
`: 31
`:516
`
`63
`1056
`
`: 45
`:757
`
`11
`9
`49
`
`: 7
`: 3
`:11
`
`: 157
`43
`:
`25
`:
`25
`1.1:
`16
`:
`
`8
`7
`0.4
`5
`
`0.9:
`
`1.5:
`
`0.5
`
`0.7
`
`24
`25
`34
`
`: 10
`:
`7
`: 22
`
`753
`
`:332
`>100
`: 17
`35
`: 20
`38
`0.6:
`0.1
`124
`: 42
`
`0.4:
`
`0.6:
`
`0.2
`
`0.2
`
`73
`
`6
`100
`
`251
`
`20
`19
`3
`
`: 20
`
`2
`:
`: 30
`
`:154
`45
`:
`:
`:
`0
`
`7
`5
`1
`
`85
`
`6
`100
`
`89
`
`18
`22
`4
`100
`
`5
`
`8
`
`:30
`
`: 3
`:50
`
`:45
`16
`: 2
`: 6
`: 1
`:30
`
`: 3
`
`: 5
`
`54
`
`:19
`
`92
`
`:21
`
`9
`148
`
`: 3
`:54
`
`4.5: 0.5
`75
`:18
`
`9
`10
`1
`
`: 2.5
`: 2.5
`: 0.4
`
`74
`
`12
`13
`3
`
`: 18
`13
`: 3
`: 3
`: 0.8
`0
`
`B(hr“)
`t,/26 (hr)
`AUC
`(mg/L-
`hr)
`CL“
`LP/hr
`ml/min
`CL,,”
`(ml/min) 244
`E‘(%)
`VB(L)
`Vss(L)
`MRT(hr)
`f,,,(%)e
`t./ZB acid
`(hrY
`MRTacid
`(hr)f
`AUC
`(mg/I-~
`hr)’
`Cmax
`: 2
`9
`:
`26
`1.2
`:
`3
`(mg/L)’
`
`
`
`
`
`0.4: 0.2 0.8: 0tmax(hr)f 1.3 : 0.5
`" Plasma clearance.
`” Blood clearance.
`° Extraction ratio (MPD had a large E value due to its multisite metabolism).
`" VCD data are taken from Ref. 20.
`” The fraction metabolized of the amide to its respective homologous acid.
`f A parameter of the acid as a metabolite of its respective homologous amide.
`
`6
`
`:
`
`3
`
`12
`
`:
`
`5
`
`56
`
`:26
`
`good anticonvulsant activity without producing sedative side
`effects. Therefore, in our study, we also focused on amides
`and acids that were isomers or analogues of VPD or VPA
`which contained eight carbon atoms in their molecule.
`Our study showed that the amides were more active as
`anticonvulsants than their respective homologous acids.
`However, amides may possess other biological activities,
`such as antipsychotic (VPD) or anxiolytic (VCD). In the case
`of VCD and PID, the anticonvulsant activity appears to be
`due in the parent compounds. However, with amides which
`undergo biotransformation to their homologous acids, the
`acid also appears to contribute to the anticonvulsant activ-
`
`ity. Taking this into consideration, there may be a species
`difference in the extent of this biotransformation. This may
`then influence the anticonvulsant activity——a fact which
`should be taken into consideration when anticonvulsant ac-
`tivity studies in animals are being extrapolated to humans.
`ACKNOWLEDGMENTS
`
`The authors thank Dr. Harvey J. Kupferberg and Mr.
`James Stables of the NIH Epilepsy Branch for screening the
`compounds in their anticonvulsant screening project. Our
`thanks to Mr. Abu Salach Omar and Mr. Abed Lutef for
`their skillful technical assistance.
`
`Table II. Results of the Partition, Protein Binding, and Water Solubility Studies of the Four Investi-
`gated Amides
`
`EBD (VI)
`MPD (VII)
`PID (VIII)
`PAD (IX)
`VCD (IlI)”
`
`Cb/Cpa
`1.91 : 0.33
`1.55 : 0.18
`0.39 : 0.03
`1.12 : 0.05
`1.01 : 0.05
`
`fu (%)"
`46 : 3
`63 : 2
`86 : 4
`81 : 3
`68 : 2
`
`“ The blood/plasma ratio (mean : SD; N : 7).
`” The free (unbound) fraction in plasma (mean : SD; N = 4).
`'7 The data on VCD are taken from Ref. 20.
`
`Water solubility
`(mg/ml)
`4.4
`7.1
`3.5
`9.5
`8.7
`
`Ex. 1054-0006
`
`Ex. 1054-0006
`
`

`
`Haj-Yehia and Bialer
`
`689
`
`Table III. Results of Phase 2 of the NIH Anticonvulsant Screening Project: ED5o, TD50 (mg/kg), and
`PI (Mice i.p.)
`
`MES test ED50
`s.c. Met test ED”
`Neurotoxicity TD50
`PI, MES
`P1, s.c. Met
`
`VPA
`
`200
`146
`283
`1.4
`1.9
`
`EBD
`
`78
`103
`116
`1.5
`1.1
`
`MPD
`
`167
`268
`205
`1.2
`0.8
`
`PID
`
`58
`49
`99
`1.7
`2.0
`
`PAD
`
`VPD
`
`VCD
`
`67
`67
`96
`1.4
`1.4
`
`56
`55
`81
`1.4
`1.5
`
`58
`32
`81
`1.4
`2.5
`
`This work is abstracted in part from the doctoral disser-
`tation of Mr‘ Abduua Ha-i‘Yehia’ in partial fulfillment of the
`Ph.D. degree requirements of the Hebrew University of Je-
`rusalem.
`
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`Ex. 1054-0007
`
`Ex. 1054-0007