以結構與反應機轉設計岩藻醣轉移酶之抑制劑

Abstract

生物體中岩藻醣轉移酶常催化最後一個轉醣步驟，而形成如Lewis y與sialyl Lewis x含有岩藻醣的寡醣。由於這些寡醣的重要生理活性 (諸如與癌細胞轉移及細菌感染的關聯性)，使得這類酵素常被視為藥物開發的目標。此篇碩士論文即針對岩藻醣轉移酶抑制劑的設計、合成及其應用作探討。 根據先前所報導的X-ray晶體結構及其反應機轉，在抑制劑的設計上有三項特點。二磷酸鳥苷 (guanosine diphosphate) 在與岩藻醣轉移酶間的作用力上，扮演重要的角色；酵素反應的過渡態 (transition state)具有正電荷的特徵；醣受體結合部位附近之疏水區域。針對這些特點，設計出具有比咯啶 (pyrrolidine)、吡咯烷(piperidine)、嘧唑 (imidazole) 的二磷酸鳥苷衍生物為細菌及人類岩藻醣轉移酶抑制劑，並探討其分子結構與活性間的關係。 除此之外，本實驗室先前合成一系列具有二磷酸鳥苷的岩藻醣抑制劑，以篩選三唑環上不同衍生基團對生物活性的影響，將此結果中效果最好的衍生基團連結到比咯啶環抑制劑YCC-7 (化合物61)。此化合物對胃幽門桿菌的岩藻醣轉移酶抑制效果最好，IC50及Ki值分別為44.1 micromolar及29.5 micromolar，我們進一步以電腦模擬計算解釋抑制劑YCC-7與該酵素間的作用力。

α-Fucosyltransferases (FucTs) usually catalyze the final steps in the biosynthesis of fucose-containing oligosaccharides. Owing to the related biological significance (such as tumor metastasis and bacterial infection), these enzymes are considered as the targets for therapeutic intervention. This thesis is mainly focused on the design, synthesis and evaluation of FucT inhibitors. On the basis of the reported x-ray crystal structures and mechanistic studies, the molecules were designed to include guanosine diphosphate (GDP) that offers major binding affinity, a negative-containing group to mimic the positive-charge character of the transition state, and a hydrophobic group to acquire additional affinity. Several GDP-conjugated pyrrolidines, piperidines and imidazoles were prepared and evaluated as the inhibitors against the FucTs from Helicobacter pylori and human. The structure and activity relationship was also discussed. Furthermore, a series of GDP- and triazole-containing compounds were also developed as FucT inhibitors previously. Because 2’-(phenylsulfonyl-methyl)benzyl group was found to be the best hydrophobic group attached to the triazole, the same group was hens coupled with GDP-pyrrolidine to give YCC-7 (61). YCC-7 was found to be a potent inhibitor against H. pylori alpha-1,3-FucT. The corresponding IC50 abd Ki values are 44.1 and 29.5 micromolar, respectively. Computational modeling was further empoyled for the explanation at molecular basis.