头孢菌素乃继青霉素之后在自然界发现的第二类型β-内酰胺抗生素。它在化学结构、生物学性质、以及由前体生物合成方面与青霉素有许多共同的特征。长期以来,人们一直认为青霉素和头孢菌素是唯一已知的分子中含有β-内酰胺环的抗生素,只是到最近,才知道有一个新型的β-内酰胺抗生素一硫霉素。头孢菌素的特点是分子中有一个由β-内酰胺和双氢噻嗪环构成的缩合双环系统(Ⅰ)。 Cephalosporins are the second type of β-lactam antibiotics found in nature after penicillin. It shares many characteristics with penicillin in terms of chemical structure, biological properties, and precursor biosynthesis. For a long time, penicillins and cephalosporins have long been considered the only known antibiotics with β-lactam rings in their molecules, and only recently have they discovered a novel β-lactam antibiotic, spiramycin. Cephalosporins are characterized by the presence of a condensed bicyclic ring system consisting of a β-lactam and a dihydrothiazine ring (Ⅰ).