磷酰化丝氨酸形成六配位磷中间体的理论研究

A Theoretical Study on the Formation of Hexa-coordinate Phosphorus Intermediate for Phosphoserine's Bio-mimic Reaction

用 MNDO方法对磷酰化丝氨酸仿生化反应机理中六配位磷中间体的形成过程进行了研究 .磷酰化丝氨酸 (1 )形成分子内磷酸 -羧酸分子内混酐的五配位磷中间体 (2 )后 ,其酸性质子解离 ,分子经过具有氢桥键结构的过渡态 ,使氨基酸侧链羟基上的氢通过氢键作用向磷上的 O1进行转移 ,然后再经过构型由三角双锥向八面体的转变 ,形成六配位磷中间体 (3) .氢桥键的存在使反应过渡态能量降低 ,其相对能量为 1 4 8.5k J/mol.

The mechanism of phosphoserines bio mimic reaction involving the formation of hexa coordinate intermediate was studied by MNDO method. From literature, the intramolecular carboxylic phosphoric mixed anhydride 2 could be formed from starting material phosphoserine 1 by a non synchronous concerted reaction pathway and the transition state energies were 172 kJ/mol. In this paper, it was showed that the penta coordinate phosphorus 2 could in turn be converted into hexa coordinate phosphorus 3 by two steps. In the first step, the acidic proton in the intermediate 2 dissociated from P_O_H bond to form 2, in which there is a weak hydrogen bond between O1 on phosphorus and the hydroxyl group on the serine side chain. Then the hydrogen of the hydroxyl group could be transfered to O1 on phosphorus through a hydrogen bond bridged transition state. In the second step, the oxygen O6 anion on the serine side chain could attack the phosphorus and the molecule geometry was changed into octahedral structure of hexa coordinate phosphorus intermediate 3. The hydrogen bond bridge structure lowered the transition state energy to 148. 5 kJ/mol. These results could be used to explain the formation of hexa coordinate phosphorus intermediate and the co participation of the carboxyl group and hydroxyl group of serine side chain during its bio mimic reaction.