Anticonvulsant activity of novel derivatives of 2- and 3-piperidinecarboxylic acid in mice and rats.

The relative ability of derivatives of 2-piperidinecarboxylic acid (2-PC; pipecolic acid) and 3-piperidinecarboxylic acid (3-PC; nipecotic acid) to block maximal electroshock (MES)-induced seizures, elevate the threshold for electroshock-induced seizures and be neurotoxic in mice was investigated. Protective index (PI) values, based on the MES test and rotorod performance, ranged from 1.3 to 4.5 for 2-PC benzylamides and from < 1 to > 7.2 for 3-PC derivatives. PI values based on elevation of threshold for electroshock-induced seizures and rotorod performance ranged from > 1.6 to > 20 for both types of derivatives. Since preliminary data indicated that benzylamide derivatives of 2-PC displace [3H]1-[1-(2-thienyl)-cyclohexyl]piperidine (TCP) binding to the phencyclidine (PCP) site of the N-methyl-D-aspartate (NMDA) receptor in the micromolar range and such low affinity uncompetitive antagonists of the NMDA receptor-associated ionophore have been shown to be effective anticonvulsants with low neurological toxicity, the 2-PC derivatives were evaluated in rat brain homogenates for binding affinity to the PCP site. Although all compounds inhibited [3H]TCP binding, a clear correlation between pharmacological activity and binding affinity was not apparent. Select compounds demonstrated minimal ability to protect against pentylenetetrazol-, 4-aminopyridine- and NMDA-induced seizures in mice. Corneal and amygdala kindled rats exhibited different sensitivities to both valproic acid and the nonsubstituted 2-PC benzylamide, suggesting a difference in these two models. Enantiomers of the alpha-methyl substituted benzylamide of 2-PC showed some ability to reduce seizure severity in amygdala kindled rats.

Synthesis and CLOGP correlation of imidooxy anticonvulsants.

Continuing structure-activity studies on the anticonvulsant activity of analogs of N-(benzyloxy)-2-azaspiro[4.4]nonane-1,3-dione (2a), which displayed anti-electroshock seizure (MES) activity and a protective index (TD50/ED50) of > 4.5 are reported. An in-depth analysis of this moiety was studied employing the Topliss structure activity and the Craig plot analytical approaches as well as a semiempirical method. CLOG P analysis was also applied to this series after experimentally determining the NOR fragment. All compounds were minimized and these physicochemical parameters correlated to anticonvulsant activity. Several interesting substituted benzyloxy compounds emerged from this study: the 2',4'-dichloro (2b), 4'-(trifluoromethyl) (2c), 2'-bromo (2d), 3'-chloro (2o), 2'-chloro (2r), 2'-fluoro (2p), and 3'-fluoro (2w) analogs, all of which had comparable, or better activity than the parent unsubstituted analog (2a). X-ray crystal analysis of the active 2a versus inactive N-benzyl-2-azaspiro[4.4]nonane-1,3-dione (10) is discussed.

Synthesis and anticonvulsant activity of enaminones. 2. Further structure-activity correlations.

This report continues the in-depth evaluation of methyl 4-[(p-chlorophenyl)amino]-6-methyl-2-oxocyclohex-3-en-1-oate , 1 (ADD 196022), and methyl 4-(benzylamino)-6-methyl-2-oxocyclohex-3-en-1-oate, 2, two potent anticonvulsant enaminones. These compounds were evaluated employing the amygdala kindling model. Neither 1 nor 2 was active against amygdala kindled seizures, further supporting the corneal kindled model as a definitive tool for antielectroshock seizure evaluation as previously reported. Additional intraperitoneal (ip) data on 1 revealed toxicity at 24 h at 100 mg/kg. Several active analogs have been prepared with the view to minimizing toxicity. In a special ip rat screen developed by the Antiepileptic Drug Development (ADD) Program, these newer analogs were evaluated for protection against maximal electroshock seizures (MES) at 10 mg/kg and neurotoxicity at 100 mg/kg. From this screen, several compounds were shown to be safer alternatives, the most notable was methyl 4-[(p-bromophenyl)amino]-6-methyl-2-oxocyclohex-3-en-1-oate, 13. Compound 13 had an ip ED50 of 4 mg/kg in the rat and a TD50 of 269 mg/kg, providing a protective index (TD50/ED50) of > 67. By variation in the ring size, additional aromatic substitutions and the synthesis of acyclic analogs, these newer compounds provide a more definitive insight into the structure-activity correlation. CLOGP evaluation and molecular modeling studies are also provided to further elaborate the molecular characteristics of potential anticonvulsant enaminones.

Determination of m-nitrophenol and nipecotic acid in mouse tissues by high-performance liquid chromatography after administration of the anticonvulsant m-nitrophenyl-3-piperidinecarboxylate hydrochloride.

The nipecotic acid ester m-nitrophenyl-3-piperidinecarboxylate (MNPC) possesses anticonvulsant activity. In the present study, the metabolites m-nitrophenol and nipecotic acid were determined in mouse blood and brain tissue after administration of MNPC. This determination was used as an indication of the distribution of the parent compound MNPC and to provide information regarding the differences in distribution between the enantiomers of MNPC, the times of onset, and effectiveness when (+/-) MNPC was administered by subcutaneous (sc) and intraperitoneal (ip) routes. m-Nitrophenol was determined by a previously reported high-performance liquid chromatography (HPLC) method. There was no significant difference in m-nitrophenol distribution after sc administration of (+)MNPC and (-)MNPC (400 mg/kg each). This similar pattern of distribution is in agreement with the earlier reported equi-effectiveness of the enantiomers of anticonvulsants. Peak m-nitrophenol levels in blood, which occurred at 15 min, were three times greater when (+/-) MNPC was administered by ip injection as compared with sc injection. This significant difference is most likely due to enhanced absorption and the peripheral metabolism of MNPC by the liver when the ip route is employed. A novel HPLC assay for the determination of nipecotic acid in mouse brain was developed, based on a modification of a reported amino acid analysis procedure. The results of the brain distribution studies showed that nipecotic acid brain levels peaked at 30 min after sc administration of (-)MNPC.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and anticonvulsant activity of enaminones.

A new series of novel enaminones has been synthesized from cyclic beta-dicarbonyl precursors which were condensed with morpholine, pyrrolidine, phenethylamine, hydrazines, substituted benzyl amines, and substituted anilines. These compounds were subsequently evaluated for anticonvulsant activity in a variety of anticonvulsant models by the National Institute of Neurological and Communicative Disorders and Stroke and in our laboratory. Several of these compounds exhibited potent anticonvulsant activity with a remarkable lack of neurotoxicity. The most active analog, methyl 4-[(p-chlorophenyl)amino]-6-methyl-2-oxo-cyclohex-3-en-1-oate++ + (27), was protective in the maximal electroshock (MES) seizure test in the rat with an oral ED50 of 5.8 mg/kg with no toxicity noted at doses up to 380 mg/kg, thus providing a protective index (TD50/ED50) of greater than 65.5. A similar protective index for 27 was noted upon intraperitoneal (ip) administration in mice. The anticonvulsant effect of 27 occurred within 15 min of administration and the compound remained active beyond 4 h. Compound 27 was also active in the rat corneal kindled model. The application of Free-Wilson analysis to structure-activity correlation in this series is discussed.

The role of bicuculline, aminooxyacetic acid and gabaculine in the modulation of ethanol-induced motor impairment.

Ethanol's intoxicating effects may result from ethanol-induced changes in central gamma-aminobutyric acid (GABA) mechanisms. To further test this hypothesis, mice were pretreated with bicuculline (1 mg/kg s.c.), aminooxyacetic acid (15, 20, 25 or 30 mg/kg i.p.) or gabaculine (20 or 40 mg/kg i.p.). Following pretreatment, 20% ethanol (2.25 g/kg i.p.) was administered and rolling roller performance evaluated. All ethanol-treated control animals showed lack of rolling roller performance at 5 min post ethanol but regained rolling roller performance by 35 min. Only 42% of the bicuculline pretreated mice demonstrated lack of rolling roller performance at 5 min post ethanol and all regained rolling roller performance by 15 min. Impairment of rolling roller performance by ethanol was potentiated by aminooxyacetic acid in a dose-dependent manner. Aminooxyacetic acid (25 and 30 mg/kg doses) slowed blood ethanol disappearance although analysis of blood ethanol disappearance and motor impairment curves indicated that aminooxyacetic acid potentiation of ethanol-induced rolling roller performance impairment cannot be attributed solely to aminooxyacetic acid's effect on blood ethanol levels. Gabaculine also potentiated ethanol's impairment of rolling roller performance but was more effective than aminooxyacetic acid in slowing ethanol disappearance, suggesting that in comparison to aminooxyacetic acid, alteration of ethanol metabolism plays a greater role in gabaculine's potentiation of ethanol-induced motor impairment.

A comparison of prodrug esters of nipecotic acid.

The relative ability of the enantiomers of the ethyl and m-nitrophenyl esters of nipecotic acid to block convulsions induced by bicuculline and pentylenetetrazol, as well as to block the uptake of GABA into whole brain mini-slices, was studied in mice. Neither (+)ethyl nipecotate hydrogen tartrate [(+)E.Tartrate], which is hydrolyzed to (-)nipecotic acid, nor (-)ethyl nipecotate hydrogen tartrate [(-)E.Tartrate], which is hydrolyzed to (+)nipecotic acid, provided protection against challenge with bicuculline. Both (+)E.Tartrate and (-)ethyl nipecotate hydrochloride [(-)E.HCl], which are hydrolyzed to (-)nipecotic acid, blocked seizures induced by pentylenetetrazol. However, neither (-)E.Tartrate nor (+)ethyl nipecotate hydrochloride [(+)E.HCl], which are hydrolyzed to (+)nipecotic acid, provided significant protection against challenge with pentylenetetrazol. These results agree with the relative ability of these compounds to inhibit the uptake of GABA, where (-)nipecotic acid was more potent than (+)nipecotic acid and (+)E.Tartrate was more potent than (-)E.Tartrate. The enantiomers of m-nitrophenyl-3-piperidinecarboxylate hydrochloride, (+)MNPC.HCl and (-)MNPC.HCl, were almost equi-effective in preventing seizures induced by bicuculline. This lack of significant difference in anticonvulsant activity is in contrast with the ability to inhibit the uptake of GABA, where (-)MNPC.HCl was significantly more potent than (+)MNPC.HCl. Changing the route of administration from subcutaneous to intraperitoneal injection reduced the onset of time of the peak effect and the anticonvulsant potency of (+/-)MNPC.HCl. Cholinergic effects were observed with the administration of (+)E.Tartrate and (-)E.HCl, but not with (-)E.Tartrate, (+)E.HCl, (+)MNPC.HCl or (-)MNPC.HCl.(ABSTRACT TRUNCATED AT 250 WORDS)

Spiro[4.5] and spiro[4.6] carboxylic acids: cyclic analogues of valproic acid. Synthesis and anticonvulsant evaluation.

Spiro[4.5]decane-2-carboxylic acid (12a), spiro[4.5]decane-2,2-dicarboxylic acid (11a), spiro[4.6]undecane-2-carboxylic acid (12b), spiro[4.6]undecane- 2,2-dicarboxylic acid (11b), and spiro[4.6]undecane-2-acetic acid (13) were synthesized by an improved method and evaluated for anticonvulsant activity. These analogues were synthesized to evaluate the role of the carboxylic acid group as an essential substituent in valproic acid (di-n-propylacetic acid, 1). Carbocyclic spiranes are known to resist metabolic alteration so that any activity elicited by these compounds would be due to the carboxylic acid function and not to any metabolic change. Spiro[4.6]undecane-2-carboxylic acid (12b) was the most active analogue tested and the pentylenetetrazol and picrotoxin evaluations of 12b compared favorably to 1. However, 12b failed to provide adequate protection against maximal electroshock seizures, bicuculline, or strychnine in mice. Possible reasons for these results are discussed.

gamma-Aminobutyric acid uptake inhibition and anticonvulsant activity of nipecotic acid esters.

n-Alkyl esters of nipecotic acid were prepared by Fischer esterification, and the esters were evaluated against bicuculline-induced seizures in mice. Evaluation of the alkyl esters for inhibition of gamma-aminobutyric acid uptake into mouse whole brain mini-slices revealed that the order of potency was proportional to chain length. The octyl ester inhibited gamma-aminobutyric acid and beta-alanine uptakes by apparently nonspecific mechanisms. A variety of phenyl esters of nipecotic acid were also synthesized utilizing either dicyclohexylcarbodiimide or 1,1'-carbonyldiimidazole as the condensing agent. Most of the phenyl esters were potent inhibitors of gamma-aminobutyric acid uptake. The uptake inhibition appeared to involve specific and nonspecific (detergent-like) mechanisms. The m-nitrophenyl and p-nitrophenyl esters were particularly potent against bicuculline-induced seizures in mice.

Anticonvulsant activity of the nipecotic acid ester, (+/-)-m-nitrophenyl-3-piperidinecarboxylate.

The nipecotic acid ester, (+/-)-m-nitrophenyl-3-piperidinecarboxylate hydrochloride (MNPC) is a potent inhibitor of uptake of GABA in vitro and should be able to penetrate into the brain much more readily than the parent compound nipecotic acid. A study of the effects of MNPC on convulsions induced by chemicals which interfere with GABA-mediated neurotransmission was carried out in the mouse, with MNPC being administered by subcutaneous injection 30, 60 or 90 min prior to challenge with bicuculline. It was found that MNPC protected against convulsions induced by bicuculline with ED50 values for clonic and tonic convulsions of 157.8 and 138.8 mg/kg, respectively, at the time of peak effect of 60 min and MNPC abolished both the clonic and tonic components of isoniazid convulsions with respective ED50 values of 255.3 and 76.7 mg/kg at 1 hr. Picrotoxin and pentylenetrazol-induced seizures were also blocked with corresponding ED50 values for clonic convulsions of 224.9 and 235.9 mg/kg at 1 hr. No serious side effects were observed during the 90 min period after the administration of MNPC in doses up to 600 mg/kg.

Esters of nipecotic and isonipecotic acids as potential anticonvulsants.

A variety of esters of nipecotic and isonipecotic acids were synthesized and evaluated for anticonvulsant activity. The ester group was varied in terms of lipophilicity and reactivity toward hydrolysis. The esters were screened against seizures induced by electroshock, pentylenetetrazol, and the putative gamma-aminobutyric acid antagonist, bicuculline. The most significant activity was demonstrated by the p-nitrophenyl esters of nipecotic and isonipecotic acids against bicuculline-induced seizures. Esters of nipecotic acid were tested for in vitro inhibition of gamma-aminobutyric acid and L-proline uptakes into mouse whole brain minislices. The p-nitrophenyl, n-octyl, and succinimidyl esters were the most potent inhibitors of gamma-aminobutyric acid uptake. The uptake of gamma-aminobutyric acid by the ester derivatives appeared to involve specific and nonspecific mechanisms.