When the concentration of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) diminishes below a threshold level in the brain, convulsions can arise. Increasing the GABA concentration terminates the convulsion. Recently, it also was found that increasing GABA levels decreases the sharp increase in dopamine levels found to be responsible for drug addiction. However, because GABA does not cross the blood-brain barrier, it cannot be used either as an anticonvulsant agent or in the treatment of substance abuse. An alternative approach to increase brain GABA levels has been to inhibit the enzyme that degrades GABA, namely, GABA aminotransferase (GABA-AT).
The specific aims of this proposal are (1) to design and synthesize new mechanism-based and structure-based inactivators and inhibitors of GABA-AT using a variety of techniques; (2) to study the mechanisms of inactivation of these compounds; (3) to use computer modeling to rationalize the activity and inactivity of our previously-studied potential inactivators of GABAAT; (4) to use computer modeling to design new inhibitors and new lead compounds based on the crystal structure coordinates of our collaborator and structure-based design software; and (5) to use the known human brain clone for mutagenesis experiments to try to determine which residues are important for inactivation. New compounds that are proposed for study include those related to the epilepsy drug vigabatrin: a series of exocyclic-methylene and exocyclic fluoromethylene analogues of 3-aminocyclopentanecarboxylate; 3-amino-4-cycloheptenecarboxylate and 3-amino-4-cyclooctenecarboxylate; 3-amino-3-(1-cyanocyclopropyl)propionate; and 4-amino-5(Z),7- octadienecarboxylate; and a series of isosteres of vigabatrin and beta-alanine-like vigabatrin analogue isosteres. Possible new carboxylate isosteres of GABA will be synthesized. A potential aromatization mechanism inactivator not related to vigabatrin is 4-amino-6,6-dichlorobicyclo[3.1.0]hexane-2-carboxylate. Potential inactivators not related to vigabatrin that may inactivate by an enamine mechanism include: 4-aminothiacyclopentanecarboxylate, the corresponding sulfone, 4-aminothiacyclohexanecarboxylate, and the corresponding sulfone. A potential inactivator that may proceed by a novel Favorskii mechanism also will be made. To get crystal structure snapshots of substrate and product complexes, will be synthesized, and structures of substrate-like and product-like, respectively, bound to GABA-AT will be obtained. The driving force of the proposal is the design of novel inactivators, the elucidation of inactivation mechanisms, and the design of new potent inhibitors.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Biochemistry Study Section (BIO)
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Ikeda, Richard A
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Northwestern University at Chicago
Schools of Arts and Sciences
United States
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Le, Hoang V; Hawker, Dustin D; Wu, Rui et al. (2015) Design and mechanism of tetrahydrothiophene-based ?-aminobutyric acid aminotransferase inactivators. J Am Chem Soc 137:4525-33
Lee, Hyunbeom; Le, Hoang V; Wu, Rui et al. (2015) Mechanism of Inactivation of GABA Aminotransferase by (E)- and (Z)-(1S,3S)-3-Amino-4-fluoromethylenyl-1-cyclopentanoic Acid. ACS Chem Biol 10:2087-98
Lee, Hyunbeom; Doud, Emma H; Wu, Rui et al. (2015) Mechanism of inactivation of ?-aminobutyric acid aminotransferase by (1S,3S)-3-amino-4-difluoromethylene-1-cyclopentanoic acid (CPP-115). J Am Chem Soc 137:2628-40
Juncosa Jr, Jose I; Groves, Andrew P; Xia, Guoyao et al. (2013) Probing the steric requirements of the ýý-aminobutyric acid aminotransferase active site with fluorinated analogues of vigabatrin. Bioorg Med Chem 21:903-11
Silverman, Richard B (2012) The 2011 E. B. Hershberg award for important discoveries in medicinally active substances: (1S,3S)-3-amino-4-difluoromethylenyl-1-cyclopentanoic acid (CPP-115), a GABA aminotransferase inactivator and new treatment for drug addiction and infantile spasms. J Med Chem 55:567-75
Hawker, Dustin D; Silverman, Richard B (2012) Synthesis and evaluation of novel heteroaromatic substrates of GABA aminotransferase. Bioorg Med Chem 20:5763-73
Pan, Yue; Gerasimov, Madina R; Kvist, Trine et al. (2012) (1S, 3S)-3-amino-4-difluoromethylenyl-1-cyclopentanoic acid (CPP-115), a potent ?-aminobutyric acid aminotransferase inactivator for the treatment of cocaine addiction. J Med Chem 55:357-66
Liu, Dali; Pozharski, Edwin; Fu, Mengmeng et al. (2010) Mechanism of inactivation of Escherichia coli aspartate aminotransferase by (S)-4-amino-4,5-dihydro-2-furancarboxylic acid . Biochemistry 49:10507-15
Clift, Michael D; Silverman, Richard B (2008) Synthesis and evaluation of novel aromatic substrates and competitive inhibitors of GABA aminotransferase. Bioorg Med Chem Lett 18:3122-5
Clift, Michael D; Ji, Haitao; Deniau, Gildas P et al. (2007) Enantiomers of 4-amino-3-fluorobutanoic acid as substrates for gamma-aminobutyric acid aminotransferase. Conformational probes for GABA binding. Biochemistry 46:13819-28

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