Mechanism-Based & Structure-Based Inhibitors of GABA-AT

描述（由申请人提供）： 当抑制性神经递质γ-氨基丁酸（GABA）的浓度降低到大脑中的阈值水平以下时，可能会出现惊厥。增加GABA浓度终止惊厥。最近，人们还发现，增加GABA水平降低了多巴胺水平的急剧增加，多巴胺水平被认为是导致药物成瘾的原因。然而，由于GABA不能穿过血脑屏障，因此不能用作抗惊厥剂或用于治疗药物滥用。增加脑GABA水平的另一种方法是抑制降解GABA的酶，即GABA氨基转移酶（GABA-AT）。本研究的具体目标是：（1）利用多种技术设计和合成新的基于机理和结构的GABA-AT失活剂和抑制剂;（2）研究这些化合物的失活机理;（3）利用计算机模拟来合理化我们先前研究的GABAAT潜在失活剂的活性和失活;（4）利用计算机建模，根据我们合作者的晶体结构坐标和基于结构的设计软件，设计新的抑制剂和新的先导化合物;（5）利用已知的人脑克隆进行诱变实验，试图确定哪些残基对失活很重要。提出用于研究的新化合物包括与癫痫药物氨己烯酸相关的那些化合物：3-氨基环戊烷羧酸酯的一系列环外亚甲基和环外氟亚甲基类似物; 3-氨基-4-环庚烯羧酸酯和3-氨基-4-环辛烯羧酸酯; 3-氨基-3-环己烯羧酸酯和3-氨基-4-环己烯羧酸酯。（1-氰基环丙基）丙酸酯;和4-氨基-5（Z），7-辛二烯羧酸酯;以及一系列氨己烯酸的电子等排体和β-丙氨酸样氨己烯酸类似物电子等排体。可能的新的羧酸电子等排体的GABA将被合成。 与氨己烯酸无关的潜在芳构化机理灭活剂是4-氨基-6，6-二氯双环[3.1.0]己烷-2-羧酸酯。与氨己烯酸无关的潜在灭活剂（可能通过烯胺机制进行灭活）包括：4-氨基硫代环戊烷羧酸酯、相应的砜、4-氨基硫代环己烷羧酸酯和相应的砜。一种潜在的灭活剂，可能会进行一个新的Favorskii机制也将。为了得到底物和产物复合物的晶体结构快照，将合成，并且将分别获得与GABA-AT结合的底物样和产物样的结构。该提案的驱动力是设计新的灭活剂，阐明灭活机制，并设计新的有效抑制剂。

DESCRIPTION (provided by applicant): 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.