Cohen S B, Halcomb R L
Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA.
J Org Chem. 2000 Sep 22;65(19):6145-52. doi: 10.1021/jo000646+.
alpha-2,3-Sialyltransferase catalyzes the transfer of sialic acid from CMP-sialic acid (1) to a lactose acceptor. An analogue of 1 was synthesized in which the anomeric oxygen atom was replaced with a sulfur atom (1S). The key step in the synthesis of 1S was a tetrazole-promoted coupling of a cytidine-5'-phosphoramidite with a glycosyl thiol of a protected sialic acid. Compounds 1 and 1S were characterized for their activity in a sialyl transfer assay. The rate of solvolysis in aqueous buffer of analogue 1S was 50-fold slower than that of 1. Analogue 1S was found to be substrate for alpha-2,3-sialyltransferase. The K(m) of 1S was just 3-fold higher than that of 1, while the k(cat) of 1S was 2 orders of magnitude lower compared to 1.
α-2,3-唾液酸转移酶催化唾液酸从CMP-唾液酸（1）转移至乳糖受体。合成了1的一种类似物，其中异头氧原子被硫原子取代（1S）。1S合成中的关键步骤是胞苷-5'-亚磷酰胺与受保护唾液酸的糖基硫醇在四唑促进下的偶联。对化合物1和1S进行了唾液酸转移测定以表征其活性。类似物1S在水性缓冲液中的溶剂解速率比1慢50倍。发现类似物1S是α-2,3-唾液酸转移酶的底物。1S的K(m)仅比1高3倍，而1S的k(cat)与1相比低2个数量级。
