摘要
Orotidine 5'-monophosphate decarboxylase (ODCase) 催化的orotidine 5'-monophosphate (OMP) 去羧基反應是生物體內合成pyrimidine類核酸化合物重要步驟。針對ODCase酵素及其受質的研究已發現，應用在抗病毒、抗瘧疾及抗癌等疾病上相當有發展的潛力。為了解ODCase催化機制，利用可能成為ODCase受質或抑制劑的化合物與該酵素反應後，觀察結果推測；因此，考慮在uridine鹼基上C6位置作官能基修飾及置換的可能性，設計並準備合成一系列的OMP類似物，其中包含有C-nucleoside及N-nucleoside的類似物。
OMP C-nucleoside的類似物包括有pseudouridine及其衍生物。利用文獻中的合成方法，可由5-bromouracil製備醣具保護的pseudouridine。我們亦嘗試利用合成pseudouridine的方法來製備6-methylpseudouridine，但因進行C-ribosylation時反應的位置是在鹼基環外C6的甲基上，而非預期中的環上C5位置，結果並沒有成功。
設計合成OMP類似物的N-nucleoside方面包含，在鹼基C6位置上的tetrazoles, amide oximes, imidates 及親核性取代基的置換；反應起始物6-cyanouridine的衍生物由文獻合成方法製備而成；6-(tetrazol-5-yl)uridine，從uridine開始製備，經形成6-cyanouridine後與sodium azide進行環化加成反應，經六個合成步驟後可以得到，總產率約29 %。Amide oxime官能基衍生物方面，經由6-cyanouridine的中間產物進行合成，但因醣上保護基移除時所產生的不穩定性，而無法得到。以親核性取代基對6-cyanouridine衍生物上cyano官能基直接進行取代反應也無法順利得到產物。在本篇論文中，我們已成功合成出6-(tetrazol-5-yl)uridine；此化合物是OMP的bioisostere，可用來作為探測ODCase反應機制的受質或抑制劑。

Abstract
Orotidine 5'-monophosphate decarboxylase (ODCase) catalyzes the decarboxylation of orotidine 5'-monophosphate (OMP), an essential step in pyrimidine nucleic acid biosynthesis. It has been identified as a potential target for antiviral, antiparasitic and antitumor therapies. In order to develop effective mechanistic probes to disclose the possible mechanisms for ODCase, a series of OMP analogs modified at the C6- position of uridine were designed and prepared to synthesize, including N-nucleoside and C-nucleoside analogs.
The C-nucleoside analogs of OMP / UMP included pseudouridine and its derivatives. The sugar protected pseudouridine was prepared based on literature procedures from 5-bromouracil. However, attempts to synthesize 6-methylpseudouridine based on the same approach were unsuccessful. The C-ribosylation occurred at the exocyclic methyl group, instead of the expected pyrimidine ring carbon.
The N-nucleoside analogs of OMP designed based on bioisosteric replacement of carboxylate including derivatives with tetrazoles, amide oximes, imidates and nucleophilic substituents on the C6 position of uridine. 6-Cyanouridine derivatives were prepared from uridine by literature procedures as starting materials. 6-(Tetrazol-5-yl)uridine was prepared from uridine through the cycloaddition of 6-cyanouridine intermediate with sodium azide in 6 steps with an over yield of 29 %. Amide oxime functional group was also obtain from the reaction of 6-cyanouridine with hydroxylamine. However, the removal of sugar protecting groups were unsuccessful. Direct substitutions of the cyano group of 6-cyanouridine derivatives with nucleophiles were unsuccessful. In this thesis, we have successfully synthesized 6-(tetrazol-5-yl)uridine. It is a bioisostere of OMP and potential mechanistic probe for ODCase.

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