Structural Analysis and Protein Binding of Cephalosporins

Abstract

Cephalosporins are a widely used subclass of β-lactam antibiotics that demonstrate variable protein binding independent of generation or antibiotic coverage. Prior work analyzed carbon 3 (C3) and carbon 7 (C7) substituents (locations of R₂ and R₁ groups respectively) for protein binding interactions. This study builds upon these results with statistical analysis of additional agents of the class. Chemical structures of 23 cephalosporins were used to identify the presence of 40 functional groups, and correlative relationships were identified using established protein binding data. Four functional groups were significantly correlated with protein binding: tetrazole (positive association), pyridinium, primary amine, and quaternary amine (negative associations). Cephalosporins with a negative charge at physiological pH were associated with increased protein binding. Analysis of tetrazole-containing cephalosporins and ceftriaxone indicates the need for further study of the potential role in protein binding of neutral or negatively charged aromatic nitrogen heterocycles linked at the C3 position by a thiomethylene group.

Figure 1

Cephem pharmacophore and ceftriaxone (R₁ purple, R₂ blue).

Figure 2

Warfarin structure and bound to human serum albumin (negatively charged at physiological pH 7.4).

Figure 3

Cephalosporins containing tetrazole with similar groups at the R₂ position. Tetrazole groups blue, related groups at R₂ position red, thiomethylene linkage green.