【摘要】 采用量子化学计算研究了磷酰化氨基酸的反应性质 ,包括 N -磷酰氨基酸成肽反应、成酯反应、磷上酯交换反应和磷上的 N→ O迁移反应的机理以及计算模型和计算方法的选择 ,并从理论上解释了自然界选择 α-氨基酸而不是 β,γ-氨基酸的实验事实 .更多还原

【Abstract】 Some interesting phenomena such as peptide formation, ester formation, ester exchange on phosphorus and N→O migration occur at room temperature when the amino group of amino acid is associated with phosphoryl group. In this paper, quantum chemical calculation was used to discuss these reaction mechanisms. It is found that MNDO method is one of the best semiempirical method to be used in the calculation of penta-coordinate phosphoric intermediates qualitatively. Therefore, it can be used widely in the study of phosphorus chemistry. In ab initio and density functional calculations, the model in which isopropyl group on phosphorus atom is simplified by methyl group was reasonable. It was found that the stabilities of the penta-coordinate intermediates and transition states were affected by the strain energies, charges, hydrogen bond and steric hindrance. The penta-coordinate phosphoric intermediates with five-membered ring from α-carboxylic groups were the most stable, and then are those with six-membered ring from β-COOH, while those with seven-membered ring from γ-carboxylic groups were the most unstable. The energies of the corresponding transition states showed the same relative stability pattern. Meanwhile, the intermediates with six-membered or seven-membered ring in di-equatorial spanning arrangements are highly unstable than those in apical- equatorial spanning arrangements. The calculation results can be used to explain the facts that why N-phosphoryl amino acids with a polar side chain have higher activities. The energies of the transition states in gas phase and solutions showed that the peptide formation from α-COOH could take place in aqueous solution without any coupling reagents under a mild condition. Meanwhile, β-COOH and γ-COOH could not be involved in the reaction because of their high activation energies. Therefore, the calculation results and the experiments show that only α-COOH is selected to form peptides by N-phosphorylation under mild conditions. These might give some clue to the study on the origin of proteins, protein biosynthesis, and combinational peptide synthesis, and might help explain why nature chose α-amino acids as the protein backbone.更多还原