Fig. 3

a Degradation hypothesis of cefadroxil (CX) after nucleophilic opening of betalactam ring by protein amino groups, leading to the cephalosporoyl intermediate, which degrades through dihydrotiazine fragmentation, and leading different functionality at carbon 6, hydroxyl and aldehyde respectively, and eventually resulting in the proposed antigenic determinants. Those equivalent synthetic structures for further immunological evaluation are represented in the square. b Synthesis of pyrazinone (molecule 2), pyrazin-2(1H)-one, proposed as CX determinant, through Ugi/Deprotect/Cyclize strategy