磷酰化丝氨酸六配位磷中间体的结构及其反应

The Structures and Reactivities of Hexa -coordinate Phosphorus Intermediate for the Phosphoserine

用 MNDO方法对磷酰化丝氨酸仿生化反应机理中所形成的六配位磷中间体 ( 3 )可能的 3个异构体的结构及其反应活性进行了研究 .在六配位磷中间体 3的 6根键中 ,丝氨酸的羧基氧 O3与磷之间的键最弱 ,最易断裂生成新的五配位磷中间体 4 ,4的 P_ N键断裂得到磷酰基的 N→ O转位反应产物 5.对于六配位磷中间体 3中的两个异丙氧基 ,位于丝氨酸侧链羟基 O6对面的异丙氧基较另一个易于离去 (约低 3 7k J/mol)并得到中间体 6,接着甲醇从 O6对面新产生的空隙进攻中间体 6中的磷 ,生成磷上酯交换产物 9.六配位磷中间体机理比较好地解释了实验中所发现的磷酰化丝。

The phosphoryl N→O migration reaction and ester exchange reaction on phosphorus of phosphoserine with methyl alcohol involving hexa coordinate phosphorus intermediate 3 had been studied by MNDO method. The three isomers structures of 3 were discussed in detail based on the calculation results. Among the six bonds in 3, the P_O bond between the phosphorus and carboxyl oxygen O3 was the weakest one, and could be easily broken to form a new penta coordinate intermediate 4 which could yield the phosphoryl N→O migration product 5 by breaking the weaker P_N bond. For these two iso propoxyl groups that bonded to phosphorus in 3, the one situated opposite to O6 of serine side chain, was easier to leave than the other one by about 37 kJ/mol to produce the intermediate 6. Then a methanol could attack phosphorus of 6 from this new formed vacancy position to yield the ester exchanged product. Thus, the hexa coordinate phosphorus intermediate mechanism could be used to explain various bio mimic reactions for phosphoserine. [WT5HZ]