{'fraction_non_alphanumeric': 0.018656716417910446, 'fraction_numerical': 0.0, 'mean_word_length': 6.06140350877193, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Tetracyclines: chemistry, biochemistry, and structure-activity relations.

Tetracycline antibiotics continue to play an important role in human and veterinary medicine and in animal nutrition. The classical tetracyclines obtained by fermentation have been supplemented by products of partial synthesis which provide, in particular, the advantages of better pharmacokinetic properties and greater tolerance. Following a brief review of older work, the present article describes partial and total syntheses of tetracyclines, the influence of electronic, steric, and lipophilic factors and of complex formation on biological activity. The inhibition of biochemical systems invoked in interpretation of the mode of action of tetracyclines and problems involved in the development of resistance are discussed.