On The Amide Isomerization Of Cephalosporins

Cephalosporins are β-lactam antibiotics, which belong to the 7- aminocephalosporin acid(7- ACA) derivative. So 7- ACA belongs to the mother nucleus of cephalosporin. The sterilization mechanism of cephalosporin is similar. Cephalosporin compound is a kind of more mature antibiotic drugs. Because the amide bond of 7- ACA existed as different configurations, this kind of drug molecules exist different isomer. At present, the study of its configurations was very few. So it is necessary to study the amide bond isomerization of cephalosporin compounds. In this article, five kinds of cephalosporin drugs such as cefathiamidine, cefoperazone, ceftazidime, cefotaxime and cephalothin were studied and the different configuration(Z/E isomer) generated by amide isomerization were found. The cis/trans configuration and protein spatial structure were docked together to predict the isomer activity. It is significant that a highly active space structure is produced by this method in the process of industrial production.Firstly, ultraviolet(UV) was used to test cephalosporin compounds in different solvents. We found that the maximum absorption wavelength was gradually disappearing in UV spectra when different equivalents of trifluoroacetic acid(TFA) were added to the cephalosporin solutions,. Then a certain amount of triethylamine was added to the protonated solution, the maximum absorption wavelength was gradually recovering. The result indicated that this kind of change of cephalosporin compounds was reversible. We also used the high performance liquid chromatography(HPLC) to determinate the two isomers in different solvents and study the influence of p H of mobile phase on the two configurations. The results showed that the solvent and the p H of mobile phase had remarkable effect on the propotion of two isomers. We also found two configurations could transform to each other in the certain conditions. The 13 C NMR spectra showed cephalosporin compounds existed as two isomers in the mixed solution of acetonitrile-D3 and trifluoroacetic acid-D/ acetonitrile-D3 and acetic acid-D3. Since amide group of 7 side chain was limited by p-? conjugation and cannot freely rotate, the chemical environment of carbon atoms around the amide bond were changed and the peak of them splited in the 13 C NMR spectra. It was further proved that the isomers existed. 2D NOESY were used to prove the spatial structure of cephalosporins in different solutions. cefathiamidine, cefoperazone, ceftazidime, cefotaxime and cephalothin existed as E configuration in the water and existed as Z configuration in the mixed solutions. When the Z-configuration existed, hydrogen atoms on the side chain amide bond may be relevant to the hydrogen atom on 7,6. Finally, the activity of two configurations was tested by molecular docking. We can determine the strength of the interaction between the protein and different configurations by scoring function. Then we could know which configuration had higher biological activity.