亞胺醣(iminosugar)是具有藥效潛力的糖苷酶抑制劑(glycosidase inhibitor)並能夠應用於許多疾病，例如:癌症、糖尿病、病毒、溶小體儲積症等等。由化學角度出發，質子化的亞胺醣被認為能夠模擬醣苷酶水解時的過渡態中間體(oxacarbenium ion)而達到抑制酵素的效果。苦馬豆素(swainsonine) 為一種廣為人知的吲哚里西汀類(indolizidine)天然雙環亞胺醣，因為其對於a-甘露糖苷酶(Golgi a-mannosidase II, hGMII)具有很強力的抑制作用，透過抑制a-甘露糖苷酶能夠影響癌症細胞表面醣蛋白(glycoprotein)的型態，進而抑制癌細胞的轉移，因此，長年以來，科學家對苦馬豆素深感興趣並發展出許多的合成方式。另一方面，苦馬豆素也對於細胞內另一個a-甘露糖苷酶(lysosomal a-mannosidase, hLM)有很強的抑制，因而造成細胞內受質堆積的嚴重副作用-溶小體儲積症，因此限制苦馬豆素在臨床上的應用，針對這兩個酵素發展具有選擇性的抑制劑將有潛力發展為癌症相關的藥物。
本論文之分為兩個章節，透過立體選擇性的反應快速製備一系列苦馬豆素類似物，並利用硝酮(nitrone)官能基製備胺基化之苦馬豆素 (章節一)。藉由先前實驗室的方法及經驗，我們設計、合成出一系列新的苦馬豆素骨架，經由初步生物活性測試篩選出候選分子(2-7b)，再經由快速的組合式化學(combinatorial chemistry)進行取代基修飾，製備以苦馬豆素為骨架的分子庫，並再次檢測其對於human Lysosomal mannosidase (hLM)和human Golgi mannosidase II (hGMII)的抑制能力及選擇性，參考當中具有較強抑制力或是選擇性的分子(2-7b-6C)之結構重新合成(resynthesis)一系列結構類似之新型抑制劑，經由生物活性測試得到結構活性關係及2-7b-6C為目前選擇性最佳之抑制劑，另外，我們設計之抑制劑對於hGMII為非競爭抑制劑 (non-competitive inhibitor)，加上此論文實驗使用之人造酶底物(enzyme substrate)和天然的酶底物具有結構上的差異，因此未來將使用天然的酶底物加上高效能液相層析儀(HPLC)進行更進一步的實驗，以期找出新穎hGMII選擇性抑制劑 (章節二)。

Iminosugars have received immense attention due to their broad-spectrum biological application, especially inhibitory activity against various sugar-processing enzymes related to many diseases such as diabetes, cancer, viral infections, and lysosomal storage disorders. The protonated iminosugar mimics the transition state of sugar during processing, the oxocarbenium ion. This similarity enables iminosugars to compete with natural substrates and act as the inhibitors of sugar processing enzyme. Swainsonine, a naturally occurring trihydroxylated indolizidine alkaloid, had been of long-standing interest due to its potent inhibitory activity against Golgi a-mannosidase II (GMII). Inhibition of GMII leads to alteration of the glycosylation pattern of glycoproteins present on the cancer cell surface which is associated with metastasis and disease progression. On the other hand, swainsonine is also associated with side effects such as unwanted co-inhibition of the lysosomal a-mannosidase (LM) causing the accumulation of high-mannose oligosaccharide in tissues, so-called mannosidosis, which limits its use in the clinical trials. Therefore, our goal was to develop selective inhibitors of GMII.
In this dissertation, we report a flexible, stereoselective and straightforward route to synthesize a series of swainsonine analogues bearing different ring size and C8 chirality. In addition, we also prepared amino-modified swainsonine derivatives using nitrone functional group. The structure-activity relationship of these swainsonine analogues was studied and the results revealed the importance of six-membered ring, C8 chirality and the hydroxyl group at C8 position (Chapter 1).
The novel swainsonine-based scaffolds, 3-aminomethyl swainsonines, were designed and synthesized according to the previous studies reported by our laboratory. After preliminary activity screening of these compounds against hLM and hGMII, candidate molecule (2-7b) showed its ability as an inhibitor against hLM (Ki = 413 nM, competitive) and hGMII (Ki = 0.65 uM, noncompetitive) and was selected for the further diversification via combinatorial chemistry to prepare (thio)urea type library. After screening, the molecule (2-7b-6C) was discovered as a noncompetitive inhibitor for hGMII with a good inhibition activity (Ki = 0.2 uM for hGMII) plus promising selectivity (40 fold for hGMII). Structural related analogues base on the structure of 2-7b-6C were also resynthesized and examined for inhibition study and the results showed 2-7b-6C was the best selective inhibitor. On the other hand, we will utilize tagged natural substrate of hLM and hGMII instead of artificial substrate plus HPLC assay for further bio-evaluation to investigate the hGMII inhibition study more thoroughly with the hope to find the lead compounds as the hGMII selective inhibitors bearing both selectivity and potency (Chapter 2)

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