In recent years drug stereochemistry has become a significant issue for both the pharmaceutical industry and the regulatory authorities. The significance of stereoisomerism in antimicrobial agents is addressed in this review using examples drawn from the β-lactams, as being representative of semisynthetic agents, and the quinolones, as examples of synthetic agents. Within these two groups of compounds it is clear that stereochemical considerations are of significance for an understanding of concentration effect relationships, selectivity in both action and inactivation and for an appreciation of the mode of action at a molecular level.
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A French chemist, , was the first to prepare acetylsalicylic acid in 1853. In the course of his work on the synthesis and properties of various , he mixed with a salt of salicylic acid (). A vigorous reaction ensued, and the resulting melt soon solidified. Since no structural theory existed at that time, Gerhardt called the compound he obtained "salicylic-acetic anhydride" (wasserfreie Salicylsäure-Essigsäure). This preparation of aspirin ("salicylic-acetic anhydride") was one of the many reactions Gerhardt conducted for his paper on anhydrides and he did not pursue it further.
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As pointed out above many of the agents used in antimicrobial chemotherapy are natural or semisynthetic products and frequently single isomers are used. However, mixtures of diastereoisomers and enantiomers do occur and the remainder of this article will examine such cases using the β-lactams and quinolone derivatives as representative examples.
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Thus, the British Pharmacopoeia (1993) defines Ampicillin as 6R-6-(α-D-phenylglycylamino) penicillanic acid. The side chain chiral centre being denoted by the D/L system and only in the case of Ampicillin is the stereochemistry of the ring system indicated and then for only one of the three centres. Within the literature the two possible diastereoisomers arising from the introduction of the side chain in these two compounds are frequently referred to in terms of D and L.
The Journal of clinical psychiatry 60 Suppl 17: 9–13; discussion 46–8
A particular problem in the nomenclature and stereochemical designation of semisynthetic compounds occurs as both the above systems may be used to define the structure of a single molecule. For example, the absolute stereochemistry of the 6-aminopenicillanic acid and 7-aminocephalosporanic acid nucleii have been determined and defined using the R/S system but the addition of a side chain, e.g. Ampicillin, Cephalexin may result in the introduction of an additional chiral centre, which in the case of these two compounds is frequently defined in terms of the D/L system.
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A 2010 article in the Journal of Clinical Oncology has suggested that aspirin may reduce the risk of death from breast cancer. While the information has been well-circulated by the media, official health bodies and medical groups have expressed concern over the touting of aspirin as "miracle drug".
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In another 2009 article published by the Journal of the American Medical Association, it was found that men and women who regularly took aspirin after colorectal cancer diagnosis had lower risk of overall and colorectal cancer death compared to patients not using aspirin.