[Studies on ampicillin and amoxicillin derivatives. III. Synthesis of 6-[2-[(pyrido[2,3-d]pyrimidin-6-yl)methylamino]-2- phenylacetamido]-penicillanic acid derivatives, 6-[2-(4-pyrimidinylamino)-2-phenylacetamido]penicillanic acid derivatives and -cephalosporanic acid derivatives].