Study On The Synthesis Of Amino Acid Carboxylic Anhydride By DMC Method And Its Acid-base Synergistic Catalytic Mechanism

a-amino acids-N-carboxy anhydrides(NCAs)ring opening polymerization is one of the most effective and convenient methods for the synthesis of polypeptide.The development of NCAs synthesis from DMC is an important way to realize the green preparation of polypeptide and amino acid based chemicals.For the synthesis of NCAs from DMC,amino acids have the low carboxymethylation selectivity and efficiency,and the decarboxylation is the main factor to prevent NCAs synthesis from carboxymethylation intermediates.Herein,the metal ions and phosphorus based hybrid catalyst were prepared which can capture proton,award proton,catalyze selective carboxymethylation and promote precise cyclization.The modes of substrate adsorption,activation and transformation over catalysts were characterized by in situ FT-IR,in situ NMR and XRS,GC-MS and situ FT-IR were used to investigate the correlation between the proton award process and decarboxylation reaction during intermediate cyclization.According to the characterized results,the catalytic cyclization mechanism was studied.The influence of catalyst,solvent molecules,and substrates and activation temperature on carbonyl activation modes was studied to explore the catalytic mechanism of directional carboxymethylation and targeting cyclization.Firstly,the conversion form of amino acids,the activation of DMC and the hindered factors of intermediate synthesis in the "one-pot"reaction were explored.And also the effects of different temperatures,solvents,time and other factors on various products in the synthesis process were investigated.When the ratio of alanine and DMC was 1:2,the maximum yields of four products were 81.54%,53.47%,22.65%and 19.35%in DMF solvent,respectively.Secondly,the intermediate product was synthesized from benzyl glutamate and DMC though amino carbonylation,and then the carboxylic anhydride of glutamic acid benzyl ester was synthesized though cyclization reaction.And also the effects of different solvents,reaction temperatures and time on the yield of intermediate and cyclized product were investigated.When the ratio of benzyl glutamate and DMC was 1:2,the highest yields of intermediate and carboxylic anhydride reached 83.2%and 65.76%in DMF solvent at 100? for 5 h.Finally,a novel structure mesoporous catalyst NaZnPO4 was prepared.The catalytic efficiency of catalyst was investigated by studying the performance and structure of the catalyst.It was found that the catalytic yield could be increased to 68.59%.Based on the acid-base synergistic catalytic reaction,the possible catalytic mechanism of directed acylation and cyclization reactions was proposed.