腺嘌呤核、胞嘧啶核及石膽酸衍生物的合成及生物活性評估
Abstract
醣類於身體中不僅參與了細胞認知，訊息的傳遞，也和能量供應及組成細胞結構有關，而唾液酸（sialic acids）更是在許多生理機制上扮演重要角色。唾液酸轉移負責催化唾液酸和醣受體形成鍵結，而許多研究指出，唾液酸轉移的表現量和許多癌症有關，例如：乳癌，子宮頸癌，及腦癌，在病人的腫瘤細胞中，發現唾液酸轉移的活性顯著增加。所以我們實驗室嘗試合成唾液酸轉移的抑制劑，分別為以腺嘌呤核，胞嘧啶核及石膽酸做修飾的衍生物，並測試其對α(2→3)唾液酸轉移的生物活性，我們可以將結果分成三部分來討論。在第一部份成功的改良部分反應條件，經由11步的合成步驟，得到5´-去氧胞嘧啶核酸，總產率約為0.5 %，所合成出的5´-去氧胞嘧啶核酸於抑制效果上大不如天然物CMP，發現5´位置的氧原子可能擔任與酵素間產生氫鍵的角色，因此缺少氧原子極可能破壞了Ligand-enzyme間的結合力而降低抑制能力。第二部份以Ctyidine（胞嘧啶核）和Adenosine（腺嘌呤核）做修飾的衍生物的抑制效果在mM範圍左右，對於α(2→3)唾液酸轉移，發現核酸上的鹼基對（base）結構的變化似乎不是主要原因。第三部份，我們有效利用了K. Barry Sharpless所改良的方法來催化末端炔及azide反應，成功合成出六個具有活性的石膽酸（Lithocholic acid）衍生物， 以石膽酸為骨架所衍生具有triazole基團者,是目前所合成出來效果最好的抑制劑（IC50約為5~20 μM）而且尾端的羧基團是必須的，但含側鏈芳香基和末端羥基團則阻礙了抑制能力。
Carbohydrates not only involved in cell-cell recognition, message transfer but the energy supplement. Sialic acid is one of the carbohydrates and plays important roles in human physiology. Sialyltransferase can catalyze sialic acid(SA) transfer from SA donor to SA acceptor. In recent researches, we found that the expression of SA is correlated with cancer cells. In patients’tumor cell, there is a great increase in activities of sialyltransferases.We tried to synthesize the inhibitor of sialyltransferase ,and modified the substructure of adenosine , cytidine and lithocholic acid (LA) respectively. These compounds to were tested their inhibitory properties for α(2→3)sialyltransferase.For the first part, we were successful in synthesizing 5´-deoxy- cytidine monophosphate by 11 steps, and the total yield is about 0.5% .The activity of 5´-deoxy- cytidine monophosphate is lower than CMP, We found 5´-oxygen atom may serve as a role to produce hydrogen bonding with amino acid residue at the active site of the enzyme. The binding affinity between ligand-enzyme is probably terminated because it is absence of oxygen atom.This should result in the reduction of inhibitory potential of 5´-deoxy- cytidine monophosphate toward α(2→3)sialyltransferase. For the second part, the inhibition of derivatives from modified cytidine and adenosine is about mM range.The base in nucleosides may not be the major responsibility for inhibition. For the third part, we took K. Barry Sharpless’method to catalyze the reaction of terminal alkyne and azide ,then six derivatives from LA with good inhibition were successfully synthesized. We found that these triazole cpds. with a terminal carboxyl group have the best inhibition to α(2→3)sialyltransferase, the triazole compounds of LA . with a branched aromatic functional group or terminal hydroxyl group will decrease inhinition potential.
Carbohydrates not only involved in cell-cell recognition, message transfer but the energy supplement. Sialic acid is one of the carbohydrates and plays important roles in human physiology. Sialyltransferase can catalyze sialic acid(SA) transfer from SA donor to SA acceptor. In recent researches, we found that the expression of SA is correlated with cancer cells. In patients’tumor cell, there is a great increase in activities of sialyltransferases.We tried to synthesize the inhibitor of sialyltransferase ,and modified the substructure of adenosine , cytidine and lithocholic acid (LA) respectively. These compounds to were tested their inhibitory properties for α(2→3)sialyltransferase.For the first part, we were successful in synthesizing 5´-deoxy- cytidine monophosphate by 11 steps, and the total yield is about 0.5% .The activity of 5´-deoxy- cytidine monophosphate is lower than CMP, We found 5´-oxygen atom may serve as a role to produce hydrogen bonding with amino acid residue at the active site of the enzyme. The binding affinity between ligand-enzyme is probably terminated because it is absence of oxygen atom.This should result in the reduction of inhibitory potential of 5´-deoxy- cytidine monophosphate toward α(2→3)sialyltransferase. For the second part, the inhibition of derivatives from modified cytidine and adenosine is about mM range.The base in nucleosides may not be the major responsibility for inhibition. For the third part, we took K. Barry Sharpless’method to catalyze the reaction of terminal alkyne and azide ,then six derivatives from LA with good inhibition were successfully synthesized. We found that these triazole cpds. with a terminal carboxyl group have the best inhibition to α(2→3)sialyltransferase, the triazole compounds of LA . with a branched aromatic functional group or terminal hydroxyl group will decrease inhinition potential.
Description
Keywords
唾液酸, 核醣, 石膽酸, 核酸, 抑制劑