Page - (000052) - in Biomedical Chemistry: Current Trends and Developments

4. A retro-Claisen reaction cleaves the β-ketothioester yielding two thioesters, producing the initial acyl-CoA shortened by two carbons and acetyl-CoA (this proceeds to the citric acid cycle, ultimately being oxidized to CO2). The pathway is repeated until all of the fatty acid is oxidised. If, during the cleavage process, a cis-oriented unsaturation is encountered, the stereochemistry of the double bond is switched to trans by an isomerase and the reaction sequence continues as for saturated fatty acids, since the enoyl-CoA hydratase is stereospecific for a trans-configuration. 1.1.5.3 Penicillin ‒ a Strong Acylating Agent Historically, penicillin antibiotics are one of the most important classes of antibiotics and are worth studying since many different reactions in its synthesis and mode of action are involved. The essential feature in penicillin class antibiotic’s structure is shown in Fig. 1.1.8. Penicillins are part of the bigger class of β-lactam antibiotics, named because the β- lactam ring is the active site of the compound. A lactam is a cyclic amide, and the β means there are 2 carbons in between the O and N atoms in their structure.