Lin C H, Lin C C
Institute of Biological Chemistry, Academia Sinica Nan-Kang, Taipei 11529, Taiwan.
Adv Exp Med Biol. 2001;491:215-30. doi: 10.1007/978-1-4615-1267-7_16.
In conclusion, either enzymatic or chemical approaches have their unique features and unavoidable disadvantages. Enzyme-catalyzed sialylations provide the desired sialo-glycosidic linkages in the two enzyme reactions (CMP-NeuAc synthetase and sialyltransferase) with exclusive stereoselectivity and high yield as long as the required sialyltransferase is available. High substrate specificity of the two enzymes is a limitation so that many unnatural glycoconjugates cannot be prepared enzymatically. As for chemical glycosylations of sialic acids, it is possible to introduce any modification in sialyl donor and acceptor, in addition to create special sugar linkages. Nevertheless, reducing the number of reaction steps (for preparing both donors and acceptors of glycosylation), and enhancing stereoselectivity, as well as reaction yield are still problems to be overcome.
总之，酶法或化学法都有其独特的特点和不可避免的缺点。只要有所需的唾液酸转移酶，酶催化的唾液酸化反应就能在两个酶促反应（CMP-唾液酸合成酶和唾液酸转移酶）中以独特的立体选择性和高产率提供所需的唾液酸糖苷键。这两种酶的高底物特异性是一个限制因素，因此许多非天然糖缀合物无法通过酶法制备。至于唾液酸的化学糖基化，除了生成特殊的糖键外，还可以在唾液酸供体和受体中引入任何修饰。然而，减少反应步骤的数量（用于制备糖基化的供体和受体）、提高立体选择性以及反应产率仍然是有待克服的问题。
