The chemistry of antibiotics is so varied that a chemical classification is of limited value. Some similarities can be found, however, indicating that some antibiotics may be the products of similar mechanisms in different organisms and that these structurally similar products may exert their activities in a similar manner. For example, several important antibiotics have in common a macrolide structure (i.e., a large lactone ring). This group includes erythromycin and olean-domycin. The tetracycline family comprises a group of compounds very closely related chemically. Several compounds contain closely related amino sugar moieties, such as those found in streptomycins, kanamycins, neomycins, paro-momycins, and gentamicins. The antifungal antibiotics nys-tatin and the amphotericins (see Chapter 6) are examples of a group of conjugated polyene compounds. The bacitracins, tyrothricin, and polymyxin are among a large group of polypeptides that exhibit antibiotic action. The penicillins and cephalosporins are j-lactam ring-containing antibiotics derived from amino acids.
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