有效合成亞胺醣類衍生物作為細菌β-葡萄糖醛酸苷酶的抑制劑

Abstract

已知腸道菌相於人體代謝機制中扮演重要的角色。其中，葡萄糖醛酸化為人體重要的化合物代謝機制之一，幫助體內疏水性之外源化合物增加親水性並代謝至體外。腸道菌表現之β-葡萄糖醛酸苷酶 (GUS) 可將接有葡萄糖醛酸的醣苷配基水解並重新釋出，因此該酵素是生物活性化合物的再活化與內源性分子的回收再利用的關鍵酵素，然而其中部分具有毒性的醣苷配基再釋出會導致腸道損傷。為針對該問題提出解決方案，本研究將細菌GUS作為欲抑制的標的物，以化學合成方式製備亞胺醣分子，實驗發現uronic isofagomine (UIFG) 在生理pH值下被質子化，可模擬GUS反應過渡態之電性特徵，為好的GUS抑制物。 為進一步開發選擇性抑制細菌GUS的抑制劑，合成UIFG C6與N位置之衍生物。初步實驗結果指出C6位置之衍生具有提升親和性與選擇性的決定效果，故本研究進一步開發並合成C6-aminomethyl UIFG，提供較有效率的合成策略，預期利用組合式化學，可快速合成一系列候選化合物，用以篩選更具潛力及選擇性之細菌GUS抑制劑。

Gastrointestinal microbiota plays an important role in shaping many metabolic pathways. One example is glucuronidation of xenobiotics, which occurs in the liver to conjugate hydrophobic compounds with glucuronic acid (a monosaccharide) to increase their solubility and then facilitate rapid excretion. Microbiome-encoded β-glucuronidases (GUSs) that catalyze the hydrolytic removal of glucuronic acid are known to be critical to regenerate bioactive compounds and recycle endogenous molecules. However, these enzymes also represent the main cause of xenobiotics-induced toxicity. To develop potent and selective inhibitors for gut bacterial GUSs, herein we report the chemical synthesis of several iminosugars that often display satisfying potency. Among them, uronic-type isofagomine (UIFG) can be protonated at physiological pH to be a good mimicry of the transition state in β-glucuronidase-catalyzed reactions. We designed and synthesized several UIFG derivatives according to previous structure-activity relationship studies of GUS inhibitors, including N- and C6-substituted UIFGs. The preliminary results indicated that the substitution at C6 increased the affinity and selectivity at the same time. Also, we developed an efficient synthesis of C6-aminomethyl UIFG which can be further diversified by combinatorial chemistry to search for more potent and selective inhibitors.