Design and synthesis of new transition-state analogue inhibitors of aspartate transcarbamylase

Six transition-state or bisubstrate analogue inhibitors (6-11) have been designed, synthesized, and tested against aspartate transcarbamoylase (ATCase). Several of these inhibitors, 7-9, were designed as analogues of N-(phosphonoacetyl)-L-aspartate (PALA, 5a) and incorporated a tetrahedral sulfur group (-S-, -SO-, -SO2-) alpha to a phosphonic acid moiety. Synthesis of 7-9 was accomplished with a new reagent, diethyl (mercaptomethyl)phosphonate (19). Thiol addition of 19 to diethyl itaconate or other olefins proves a new general synthetic route to (thiomethyl)-phosphonate analogues of acyl phosphates or diphosphate anhydrides. Analysis of the observed inhibition kinetics with ATCase and structural modeling studies indicate that increased steric size of the sulfur moieties in the sulfide 7, sulfoxide 8, sulfone 9, and sulfonamide 10 may cause these compounds to be less potent inhibitors of Escherichia coli ATCase than N-(phosphonoacetyl)-L-aspartate (PALA, 5a). The pKa of the carbonyl groups (or S-analogue thereof) may be a key factor in determining the affinity of ATCase for inhibitor. The distance from the alpha-carbon to the phosphorus atom was judged to be a less important factor in determining the tightness of inhibitor binding since no significant change in the inhibition constant (Ki) occurred upon elimination of the alpha-methylene group in sulfide 7 to give sulfide 11. The ester analogue of PALA (5a), O-(phosphonoacetyl)-L-malic acid (6), exhibited a Ki of 2 X 10(-6) M.     

(1-Amino-2-propenyl) phosphonic acid, an inhibitor of alanine racemase and D-alanine:D-alanine ligase

DL-(1-Amino-2-propenyl)phosphonic acid was synthesized through the sequential oxidation, sulfoxide elimination, and deprotection of diphenyl [1-[(benzyloxycarbonyl)amino]-3-(phenylthio)propyl] phosphonate. This analogue of vinylglycine is a strong inhibitor of the alanine racemases from Pseudomonas aeruginosa and Streptococcus faecalis and of the D-Ala:D-Ala ligase from this latter species. This molecule is ineffective against the whole bacterial cells. Unlike vinylglycine, this unsaturated phosphonate does not inhibit the following mammalian enzymes: aspartate aminotransferase, alanine aminotransferase, D-amino acid oxidase, which indicates its specificity. Thus, its incorporation in a peptide structure could induce interesting antimicrobial properties.     

New alpha-amino phosphonic acid derivatives of vinblastine: chemistry and antitumor activity

A series of new amino phosphonic acid derivatives of vinblastine (1, VLB) has been synthesized and tested in vitro and in vivo for antitumor activity. The compounds were obtained from O4-deacetyl-VLB azide. All of the new products studied were capable of inhibiting tubulin polymerization in vitro. The most potent antitumor compounds bore an alkyl substituent on the phosphonate. In these compounds, the anti-tumor activity strongly depended on the stereochemistry of the phosphonate. The phosphonate (1S)-[1-[( O4-deacetyl-3-de(methoxycarbonyl)vincaleukoblastin-3-yl] carbonyl]amino]-2-methylpropyl]phosphonic acid diethyl ester exhibited a remarkable activity against cancer cell lines both in vitro and in vivo.     

Synthesis and antiviral activity of certain nucleoside 5'-phosphonoformate derivatives

(Ethoxycarbonyl)phosphonic dichloride (3) was synthesized by chlorination of bis(trimethylsilyl) (ethoxycarbonyl)phosphonate with thionyl chloride. Adenosine 5'-(ethoxycarbonyl)phosphonate (4), guanosine 5'-(ethoxycarbonyl)phosphonate (5), 2'-deoxyadenosine 5'-(ethoxycarbonyl)phosphonate (18) and 2'-deoxyguanosine 5'-(ethoxycarbonyl)phosphonate (19) were synthesized by coupling of compound 3 with adenosine, guanosine, 2'-deoxyadenosine, and 2'-deoxyguanosine, respectively. Alkaline treatment of 4, 5, 18, and 19 gave the corresponding adenosine 5'-(hydroxycarbonyl)phosphonate (14), guanosine 5'-(hydroxycarbonyl) phosphonate (15), 2'-deoxyadenosine 5'-(hydroxycarbonyl)phosphonate (20), and 2'-deoxyguanosine 5'-(hydroxycarbonyl) phosphonate (21). Treatment of 4 and 5 with methanolic ammonia resulted in the production of adenosine 5'-(aminocarbonyl)phosphonate (12) and guanosine 5'-(aminocarbonyl)phosphonate (13), respectively. The nucleotide analogue 20 exhibited the most potent antiviral activity of this group of nucleotide tested in vitro and was most active against herpes viruses especially HSV-2. The nucleotide analogue 21 had lower, but significant, activity against HSV-2. All of the compounds tested were nontoxic to confluent Vero cells at concentrations as high as 5000 microM.     

Synthesis and biological activity of a series of aspartate transcarbamoylase inhibitors: N-substituted diethyl aspartates and N-substituted-3-oxo-1,4-piperazine-2-acetic acid esters

Series of N-substituted diethyl aspartates and N-substituted-3-oxo-1,4-piperazine-2-acetic acid esters were synthesized as potential inhibitors of aspartate transcarbamoylase. The aspartates were obtained by addition of substituted alkyl amines to diethyl maleate, or conversion of the hydroxy ethyl amino adduct to other functions. The 3-oxo-1,4-piperazine-2-acetic acid esters were prepared by addition of ethylene diamine to diethyl maleate, followed by cyclization. Addition of 1,2-diamino-2-methylpropane gave the corresponding 5,5-dimethyl-3-oxo-1,4-piperazine-2-acetic acid ester. N-Acyl derivatives in each series were obtained using the bromoacyl chlorides. A majority of the compounds in each series showed antimicrobial activity against five representative microorganisms, as well as significant activity against aspartate transcarbamoylase. Four of the compounds were found to have significant specificity against several tumor cell lines. A distance of two carbons between N and a reactive function was found to give the best activity for either antimicrobial, antienzyme, or tumor cell specificity activities, in either the open chain aspartates or cyclic piperazines. Little difference in anti-enzyme activity was found between the aspartates and piperazines, but introduction of the planar phenyl substituents lowered inhibitory activity.     

Synthesis and antiviral activity of phosphonoacetic and phosphonoformic acid esters of 5-bromo-2'-deoxyuridine and related pyrimidine nucleosides and acyclonucleosides

Phosphonoacetic acid (PAA, 1) was coupled with various acyclonucleosides, 2'-deoxyuridines, cytidines, and arabinosyluracils, with 2,4,6-triisopropylbenzenesulfonyl chloride (TPS) or dicyclohexylcarbodiimide (DCCI) as condensing agents, to give a range of phosphonate esters. The carboxylic ester linkage of PAA to the 5'-position of 5-bromo-2'-deoxyuridine (BUdR, 3) was achieved via the mixed anhydride formed from (diethylphosphono)acetic acid and trifluoroacetic anhydride. Phosphonoformic acid (PFA, 2) was coupled with BUdR by using the DCCI method to give the phosphonate ester. Of these compounds only phosphonate esters in the 2'-deoxyuridine series showed significant activity against herpes simplex virus types 1 and 2. The BUdR-PAA derivative and the BUdR-PFA derivative were highly active, especially the latter, which was more active than the parent nucleoside BUdR against the type 2 virus. The active compounds may exert their effects by extracellular or intracellular hydrolysis to the corresponding antiviral agents, but an intrinsic component of antiviral activity may also be involved.     

An in vivo insight to the toxicological profile of various organotellurides

In this study we have examined the in vivo toxic effects of various organochalcogens on hepatic, renal, glycemic and lipid profile. Diorganotellurium dichloride phosphonate (C1) at all tested doses did not modify serum alanine aminotransferase (ALT) activity in mice. While, 2-butyltellurium furan (C2) and dinaphthalene ditelluride (C3) at a dose of 0.75 and 0.125 mmol/kg caused an increase in aspartate aminotransferase (AST) and ALT activities. Our data showed that C1 caused an increase in urea content at different doses while treatment with C2 and C3 did not modify urea content. Treatment with C2 caused a significant alteration in serum glucose and fructosamine levels which explains the possible toxicity of these compounds. No significant changes were observed for cholesterol and triglycerides levels. These results suggest that organochalcogen compounds presented liver and renal toxicity and also altered glycemic profile which may leads to various clinical complications.     

一种选择性脱苄基方法在天然产物结构修饰中的应用

目的 研究路易斯酸三氟化硼乙醚在脱苄基时的选择性.方法 以天然活性成分丹参素、阿魏酸和水杨酸为原料,制备的化合物结构中既含有苄醚又含有苄酯,采用上述方法进行苄基保护的脱除.结果 三氟化硼乙醚只脱去苄醚上的苄基,而苄酯中的苄基不受影响.结论 三氟化硼乙醚在苄醚和苄酯同时存在的情况下,对苄醚上的苄基具有选择性脱除作用.     

Phosphonate O-deethylation of [4-(4-bromo-2-cyano-phenylcarbamoyl) benzyl]-phosphonic acid diethyl ester, a lipoprotein lipase-promoting agent, catalyzed by cytochrome P450 2C8 and 3A4 in human liver microsomes.

NO-1886 ([4-(4-bromo-2-cyano-phenylcarbamoyl) benzyl]-phosphonic acid diethyl ester) increases lipoprotein lipase activity, resulting in a reduction in plasma triglycerides and an increase in high-density lipoprotein cholesterol. The metabolism of NO-1886 in human liver was investigated in the present study. Ester cleavage of NO-1886 from diethyl phosphonate to monoethyl phosphonate was the major metabolic pathway catalyzed by cytochrome P450. In addition, the minor metabolic pathway in human liver was the hydrolysis of the amide bond of NO-1886 by a specific cytosolic esterase. Eadie-Hofstee plots of phosphonate O-deethylation of NO-1886 in human liver microsomes showed a biphasic curve, indicating low- and high-K(m) components. Inhibition experiments with chemical inhibitors and antibodies against various cytochrome P450 isoforms suggested the involvement of CYP2C8 and CYP3A in the phosphonate O-deethylation. Recombinant CYP3A4 and CYP2C8 expressed in baculovirus-infected insect cells and human lymphoblastoid cells exhibited a high activity for phosphonate O-deethylation of NO-1886. The recombinant cytochrome P450 enzymes indicated that CYP2C8 and CYP3A4 were responsible for the low- and high-K(m) components in human liver microsomes, respectively. The selectivity of CYP2C8 in catalyzing phosphonate O-deethylation indicates that coadministration of drugs that are metabolized by the same enzyme requires careful consideration.     

An approach to trapping gamma-glutamyl radical intermediates proposed for vitamin K dependent carboxylase: alpha,beta-methyleneglutamic acid

The vitamin K dependent carboxylase activates the glutamyl gamma-CH of substrate peptides for carboxylation by producing a gamma-glutamyl free radical, a gamma-glutamyl carbanion, or through a concerted carboxylation. We propose to intercept the putative gamma-glutamyl free radical by the intramolecular rearrangement of a substrate containing the alpha,beta-cyclopropane analogue of glutamic acid. The rearrangement of cyclopropylcarbinyl radicals into 2-butenyl radicals is rapid, exothermic, and considered diagnostic of free-radical formation. 1-Amino-2-(carboxymethyl)cyclopropane-1-carboxylate, the beta-cyclopropane analogue of glutamic acid, was synthesized starting from diethyl alpha-ketoglutarate. The alpha-keto ester was first treated with benzonitrile in sulfuric acid, to yield diethyl alpha,alpha-dibenzamidoglutarate. The alpha,alpha-dibenzamido acid was cleaved to produce the alpha,beta-dehydroamino acid and benzamide on treatment with p-toluenesulfonic acid in hot benzene. Diazomethane addition to the dehydroamino acid resulted in cycloaddition of diazomethane and production of the pyrazoline, which upon irradiation lost N2 to give the protected cyclopropane-containing amino acid analogue. Acidic hydrolysis of the N-benzoyl-alpha,beta-methyleneglutamate diethyl ester resulted in the production of the unprotected amino acid, alpha,beta-methyleneglutamic acid, in high yield. A single dehydroamino acid and a single methyleneglutamic acid isomer were produced in this synthesis; both are identified as the Z isomer, the former by NMR using the nuclear Overhauser effect and the latter through X-ray crystallographic analysis of N-benzoyl-alpha,beta-methyleneglutamate diethyl ester. Saponification of a N-protected methyleneglutamic acid dialkyl ester using limiting alkali was shown to selectively yield the alpha-alkyl ester gamma-acid. The reaction was used to produce alpha,beta-cyclopropane-containing analogues of the carboxylase substrates N-t-Boc-L-glutamic acid alpha-benzyl ester and N-benzoyl-L-glutamic acid alpha-ethyl ester. The cyclpropane-containing analogues were tested and found to be neither substrates for nor inhibitors of the rat liver microsomal vitamin K dependent carboxylase. The inability of the enzyme to recognize these substrate analogues is attributed to the alpha-alkyl substitution, which apparently abolishes substrate binding.     

钙拮抗剂拉西地平的合成新工艺

目的完成钙拮抗剂拉西地平合成的新工艺.方法以邻苯二甲醛、β-氨基巴豆酸乙酯、三苯基亚膦基乙酸叔丁酯为原料,采用常规的化学合成法合成.结果采用先形成二氢吡啶环,再通过Wittig反应制备烯烃双键的顺序,拓展了拉西地平合成的新工艺.结论新工艺与专利文献相比,具有收率高、操作简便的特点,更适于工业化生产.     

Analogues of carbamyl aspartate as inhibitors of dihydroorotase: preparation of boronic acid transition-state analogues and a zinc chelator carbamylhomocysteine

Dihydroorotase (DHO) catalyzes the conversion of carbamyl aspartate (CA) to dihydroorotate (DO) in the de novo pyrimidine biosynthetic pathway. Few effective inhibitors of DHO have been reported, and thus blockade of this reaction has not been widely pursued as a strategy for development of antitumor agents. Utilizing two mechanism-based strategies, we have designed and prepared potential DHO inhibitor analogues of CA. One strategy replaced the gamma-carboxyl moiety of CA with a boronic acid. This substitution yields compounds which form stable charged tetrahedral intermediates and mimic the enzyme-substrate transition state. Preparation of the boronic acid analogues of CA and its carboxylic acid esters focused on a Curtius rearrangement as a key step following a malonic ester synthesis. This was followed by carbamoylation of the free amine under nonaqueous neutral conditions with Si(NCO)4. The ethyl ester was a competitive inhibitor of DHO with an apparent Ki of 5.07 microM, while the nonesterified analogue and the methyl ester were not effective inhibitors. None of the compounds were cytotoxic against L1210 cells in culture. An active-site-directed sulfhydryl-containing zinc chelator was also prepared. This analogue irreversibly inhibited the enzyme, but it also was ineffective in L1210 growth inhibition.     

Folate analogues. 21. Synthesis and antifolate and antitumor activities of N10-(cyanomethyl)-5,8-dideazafolic acid

A close analogue of the antileukemic agent 5,8-dideaza-N10 propargylfolic acid (2) was synthesized by replacing the propargyl moiety of 2 with a cyanomethyl group. This compound, N10-(cyanomethyl)-5,8-dideazafolic acid (3), was evaluated for its antifolate and antitumor activities in several biological test systems. Alkylation of diethyl N-(4-aminobenzoyl)-L-glutamate with bromoacetonitrile gave diethyl N-[4-[(cyanomethyl)amino]benzoyl]-L-glutamate (7). Reaction of 7 with 2 amino-6-(bromomethyl)-4-hydroxyquinazoline (9) in dimethylacetamide gave the corresponding diethyl ester 11, which was hydrolyzed to the target compound 3. The known antileukemic agent 2 was also synthesized for comparative studies by employing a modified procedure, which resulted in a better yield of this product. Both compounds 2 and 3 were evaluated for their antifolate activities by using two folate-requiring microorganisms, Streptococcus faecium and Lactobacillus casei. They were further evaluated as inhibitors of thymidylate synthase and dihydrofolate reductase derived from the above organisms, as well as for their antitumor activity by using selected tumor cells in culture. Compound 2 was found to be as equally potent as methotrexate (MTX) against S. faecium, and it was an excellent inhibitor of L. casei thymidylate synthase. The cyanomethyl analogue 3 was less active than 2 in all the test systems, except the inhibition of dihydrofolate reductase.     

Synthesis and antifolate properties of 10-alkyl-5,10-dideaza analogues of methotrexate and tetrahydrofolic acid

Synthesis of the 10-methyl and 10-ethyl analogues of 5,10-dideazatetrahydrofolic acid (DDTHF), a potent inhibitor of glycinamide ribotide (GAR) formyltransferase, is reported. Key intermediates in the process were 10-methyl- and 10-ethyl-4-amino-4-deoxy-5,10-dideazapteroic acid. Condensation of the piperidine enamines of branched 4-(p-carbomethoxyphenyl)butyraldehydes with (acetoxymethylene)malononitrile afforded 1,1-dicyano-4-piperidinobutadiene 5a,b. Subsequent reaction with alcoholic ammonium hydroxide yielded the appropriately substituted 2-amino-3-cyanopyridines 6a,b. Ring closure with guanidine gave 10-methyl- and 10-ethyl-4-amino-4-deoxy-5,10-dideazapteroic acids (7a,b). Coupling with diethyl glutamate followed by ester hydrolysis afforded 10-alkyl-5,10-dideazaminopterin analogues 9a,b. Hydrolysis of the 4-amino group of 7a,b yielded the 10-alkylpteroic acids, which were coupled with diethyl glutamate, hydrogenated over PtO2, and saponified to afford 10-alkyl-5,10-dideazatetrahydrofolic acids 13a,b. Aminopterin analogues 9a,b were effective inhibitors of DHFR derived from L1210, but were less potent than methotrexate for inhibition of growth of L1210 in culture. The 10-ethyl (13b) analogue of 5,10-DDTHF was about twice as potent an inhibitor of L1210 cell growth as 5,10-DDTHF, but was only 1/7 as potent for inhibition of GAR formyltransferase. 10-Methyl analogue 13a was similar in potency to 5,10-DDTHF. All of the compounds showed moderately improved transport into L1210 cells relative to methotrexate.     

Metabolic properties of phosphonate esters

The object of the present work was to investigate the difference in the metabolism of the phosphonate derivatives of primary or secondary hydroxyl groups. To study the phosphorolytic cleavage of such P-O bonds, zidovudine (AZT) hexanoyloxymethyl-methylphosphonate (HOM-AZT-P), an ester of a primary OH functionality, and methyl-pivaloyloxymethyl-testosterylphosphonate (POM-T-P), an ester of a secondary OH functionality, were prepared. The actions of pure enzymes such as alkaline phosphatase and phosphodiesterase on the corresponding phosphonate compounds (AZT-P and T-P) were investigated at various pH values. The phosphonate derivative of the secondary hydroxyl group of testosterone proved completely resistant to such phosphorolytic attacks, and release of free testosterone could not be detected. The phosphonate derivative of the primary hydroxyl group of zidovudine proved resistant to phosphodiesterase, but not to alkaline phosphatase, and in this second case, release of free zidovudine could be detected.     

Synthesis of certain nucleoside methylenediphosphonate sugars as potential inhibitors of glycosyltransferases

The synthesis of alpha-D-glucopyranosyl 1-(methylenediphosphonate) (11), alpha-D-galactopyranosyl 1-(methylenediphosphonate) (14), and alpha-D-mannopyranosyl 1-(methylenediphosphonate) (17) has been accomplished. [(Di-phenoxyphosphinyl)methyl]phosphonic acid (diphenyl-MDP) (5), synthesized by two different procedures, was fused with beta-D-glucopyranose pentaacetate followed by catalytic hydrogenation to give 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl methylenediphosphonate (glucose-MDP) (10). The anomeric configuration of 10 was assigned on the basis of NMR spectral studies. Condensation of 10 with 2',3'-di-O-acetyladenosine was accomplished by using 1-(mesitylene-2-sulfonyl)-3-nitro-1,2,4-triazole (MSNT) as coupling agent, and removal of the blocking groups gave adenosine 5'-[(alpha-D-glucopyranosylhydroxyphosphinyl)methyl]phosphonate (20). Uridine 5'-[(alpha-D-galactopyranosylhydroxyphosphinyl)methyl] phosphonate (23) and guanosine 5'-[(alpha-D-mannopyranosylhydroxyphosphinyl)methyl]phosphonate (26) were similarly prepared. Using a specific glycoprotein galactosyltransferase (EC 2.4.1.38) assay, uridine 5'-[(alpha-D-galactopyranosylhydroxyphosphinyl)methyl]phosphonate (23) demonstrated competitive inhibition with an apparent Ki of 97 microM. The adenosine analogue did not inhibit the enzyme. None of the above compounds show any in vitro antitumor or antiviral activity. Such specific inhibitors of glycosyltransferases may serve as specific probes to study various glycosyltransferases that might be involved in the process of metastasis.     

Cardioactivity and solid-state structure of two 4-isoxazolyldihydropyridines related to the 4-aryldihydropyridine calcium-channel blockers

Diethyl 2,6-dimethyl-4-(5-ethyl-3-phenylisoxazol-4-yl)-1,4-dihydroyprid ine-3,5- dicarboxylate (5) and diethyl 2,6-dimethyl-4-(5-isopropyl-3-phenylisoxazol-4-yl)-1,4-dihydropyri dine-3,5- dicarboxylate (6) were synthesized, and their molecular structures were determined by X-ray crystallography. In compound 5, which has an ethyl group at the C5 position of the isoxazole ring, the deviation from planarity in the dihydropyridine (DHP) ring is the smallest of all known DHP derivatives. The dihedral angle between the aromatic ring (the isoxazole) and the DHP ring, which is approximately 90 degrees in similar biologically active dihydropyridines, is somewhat smaller (82.7 degrees and 85.2 degrees, respectively) in these two compounds. In both compounds, one of the ester groups is coplanar with the DHP ring while the other one is out of plane by 14.7 degrees (ethyl) and 18.8 degrees (isopropyl). Both 5 and 6 were found to be vasodilators in the Langendorff assay. The potency of 6 on cardiac flow was similar to that of nifedipine; however, that of 5 was considerably attenuated. Since isoxazolyl analogue 6 lacks the significant negative inotropic activity associated with nifedipine, 6 offers promise as an antihypertensive or antianginal agent.     

Isozyme-specific enzyme inhibitors. 11. L-homocysteine-ATP S-C5' covalent adducts as inhibitors of rat methionine adenosyltransferases

The title compounds (14a,b) were 5' epimers of a derivative of a phosphonate isostere of ATP in which the CH2OP alpha system of ATP was replaced by CH(R)CH2P alpha [R = L-S(CH2)2CH(NH2)CO2H]. They resisted synthesis via attempted S-alkylation of the corresponding epimeric 5'-mercapto derivatives. A practicable route to 14a,b commenced with Michael condensation of L-homocysteine with the diphenyl ester of the 5',6'-vinyl phosphonate analogue of 2',3'-O-isopropylideneadenosine 5'-phosphate. The resulting epimeric 5' thioethers were separated by reverse-phase HPLC. The two phenyl groups were replaced by benzyl groups, after which the alpha-amino acid residue was protected as an N-Boc methyl ester. Both benzyl groups were removed by hydrogenolysis, and the resulting phosphonic acid was converted into its pyrophosphoryl derivative. Blocking groups were then removed under conditions that furnished 14a and 14b without racemization of their L-amino acid residues. Also synthesized were the P beta-NH-P gamma imido analogue (15a) of 14a and the sulfoxide derivative (16a) of 14a. The structures of 14a and 16a were verified by FAB mass spectra, which revealed the protonated molecular ions of their sodium salts. All adducts appeared to function as dual substrate site inhibitors (competitive to ATP and to methionine) of the rat normal tissue (MAT-2) form of methionine adenosyltransferase (MAT); 14a and 15a [KM(ATP)/Ki = 4 and 9, respectively] were the most effective. Adduct 15a was the most effective inhibitor [KM(ATP)/Ki = 13] of the MAT-T form from rat hepatoma tissue; the kinetic data indicated dual-site inhibition by 15a with apparently complete coverage of the ATP site and incomplete coverage of the methionine site. The inhibition properties of the adducts indicated little preference in the order in which the two MAT forms bound ATP and methionine.     

Impaired motor coordination in mice induced by 2-amino-7-phosphonoheptanoic acid (APH), glutamic acid diethyl ester (GDEE), and other compounds

Impairment of motor coordination by the excitatory amino acid antagonists 2-amino-7-phosphonoheptanoic acid (APH) and glutamic acid diethyl ester (GDEE) was measured and compared to GABA agonists and anticonvulsants and other compounds by the Coughenour inverted screen test. The GABA agonists muscimol and imidazole acetic acid, and the GABA analogue gamma-hydroxybutyric acid were found to produce a marked impairment of motor coordination. The dosages of phenytoin and valproate which impaired motor coordination, on the other hand, were considerably above the dosages which have been reported to inhibit seizures. APH caused motor incoordination at a dosage of 125 mg/kg, and a prolonged motor impairment was present after administration of APH, 250 mg/kg. GDEE did not significantly impair motor coordination in any dosage tested up to 1920 mg/kg. These results further encourage development of more potent GDEE-like compounds as potential anticonvulsants.