A new generation of specific Tryponosoma cruzi trans-sialidase inhibitors
A new generation of specific Tryponosoma cruzi trans-sialidase inhibitors
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DOI：
10.1002/anie.200705435
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Withers, Stephen G.
中科院分区：
文献类型：
--
作者：
Buchini, Sabrina;Buschiazzo, Alejandro;Withers, Stephen G.
原生动物寄生虫克氏锥虫是人类锥虫病的病原体，也被称为恰加斯病，其慢性形式可导致严重衰弱并最终死亡。[1]据世界卫生组织(WHO)估计，2005年拉丁美洲有1600万至1800万人感染。目前只有两种被批准的药物(硝呋莫司和苯硝唑)用于治疗这种感染，但这两种药物的疗效都很低，而且与严重的不良副作用有关。[2]2005年完成的克氏锥虫全基因组序列预测包含编码近23000种蛋白质的基因。[3]这种寄生虫特有的基本蛋白质的鉴定有望提供有吸引力的新药物靶标。在这些靶标中，克氏锥虫的转唾液酸酶(TCTS)得到了广泛的研究。Tcts是一种糖基磷脂酰肌醇锚定的表面蛋白，在寄生虫的感染发育阶段差异表达。[4]它属于糖苷水解酶家族33(http://afmb.)。CNRS-MRS。FR/CAZY)，并催化唾液酸残基从宿主糖结合物α-(2，3)转移到寄生虫表面粘蛋白样糖蛋白的末端半乳糖单位。最近解决了TCTS的晶体结构，并证明了一种涉及共价唾液酸酶中间体的两步双置换机制(方案1)。[6]Tyr342以3-氟唾液酰氟1为底物类似物被鉴定为催化亲核剂，形成捕获的中间物种(方案1)。[7]C3上的氟原子诱导地破坏了带正电的氧卡宾离子类过渡态的稳定性，从而减缓了共价中间体的形成和水解。然而，C2上良好的离开基团的存在使糖基化反应迅速进行，并导致唾液酸酶中间体的捕获。因此，如果这类化合物对TCTS比人类唾液酸酶具有选择性，并且如果它们形成长寿的中间体，那么它们有可能作为抗锥虫的药物。根据方案2所示的动力学模型，3-氟唾液酰氟1以前被证明以时间依赖的方式失活野生型TCTS。然而，在去除多余的失活剂后，当与天然受体乳糖孵育时，该酶通过转糖基化迅速恢复了全部活性。如此快速的糖基化将使这些化合物失去抗锥虫药的作用。对TCTS和唯一的人类唾液酸酶的结晶学特征的检查，Neu2，[9]揭示了TCTS的位置在C9周围的区域更加宽敞和疏水。
The protozoan parasite Trypanosoma cruzi is the causative agent of human American trypanosomiasis, also known as Chagas disease, which in its chronic form can lead to severe debilitation and ultimately death.[1] According to World Health Organization (WHO) estimates, 16 to 18 million people were infected in Latin America in 2005. Only two approved drugs (nifurtimox and benznidazole) are currently used for the treatment of the infection, but both display low efficacy and are associated with severe undesired side effects.[2] The whole genome sequence of Trypanosoma cruzi, completed in 2005, contains genes predicted to encode almost 23000 proteins.[3] The identification of essential proteins specific to the parasite will hopefully provide attractive new drug targets. Among such targets, the Trypanosoma cruzi trans-sialidase (TcTS) has been extensively studied. TcTS is a glycosylphosphatidylinositol-anchored surface protein that is differentially expressed during the infective developmental stage of the parasite.[4] It belongs to the glycoside hydrolase family33 (http://afmb. cnrs-mrs. fr/CAZY) and catalyzes the α-(2, 3) transfer of sialic acid residues from host glycoconjugates to the terminal galactosyl units of mucin-like glycoproteins on the surface of the parasite.[5] Extensive sialylation of the T. cruzi surface is pivotal for the establishment of a chronic infection. The crystal structure of TcTS was recently solved, and a two-step, double-displacement mechanism involving a covalent sialyl–enzyme intermediate was demonstrated (Scheme 1).[6] Tyr342 was identified as the catalytic nucleophile by the use of 3-fluorosialyl fluoride 1 as a substrate analogue, which forms a trapped intermediate species (Scheme 1).[7] The fluorine atom at C3 inductively destabilizes the positively charged oxocarbenium ion like transition states, thereby slowing both the formation and the hydrolysis of the covalent intermediate. However, the presence of a good leaving group at C2 allows glycosylation to proceed rapidly and results in the trapping of the sialyl–enzyme intermediate. Compounds of this class therefore have the potential to act as anti-trypanosomal agents if they can be made selective for TcTS over human sialidases and if they form long-lived intermediates. 3-Fluorosialyl fluoride 1 was shown previously to inactivate wild-type TcTS in a time-dependent manner according to the kinetic model illustrated in Scheme 2.[8] However, after removal of excess inactivator, the enzyme rapidly recovered full activity by transglycosylation when incubated with the natural acceptor lactose. Such rapid transglycosylation would render these compounds useless as anti-trypanosomal agents. Inspection of the three-dimensional structures of TcTS and the only human sialidase as to yet be characterized crystallographically, Neu2,[9] revealed that the TcTS site is more spacious and hydrophobic in the region around C9 of