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The Chemistry of Imidazole Dipeptides

Carnosine, anserine, balenine and homocarnosine are imidazole dipeptides found exclusively in animal tissue, especially in skeletal muscle and nerves. These compounds exist as an equilibrium of two tautomeric structures of their imidazole ring, known as Nτ–H and Nπ–H, usually shifted towards the former tautomer. While terrestrial mammals and amphibians contain mostly carnosine, anserine predominates in fish and birds, and balenine in reptiles and cetaceans. The imidazole ring of these peptides is fairly prone to electrophilic attack at the imine nitrogen, but it is much less likely to undergo a nucleophilic substitution reaction unless the ring is activated by strongly electron-withdrawing groups. Synthesis of imidazole peptides is usually done by chemical routes, but enzymatic approaches are being increasingly used, especially due to their higher specificity and lower environmental impact. Imidazole dipeptides play an important role as intracellular buffers in vertebrate muscle (up to 60% of buffering capacity) due to their pK values, which are close to physiological pH, a theory known as “alphastat regulation”. Moreover, carnosine and anserine show in vivo antioxidant activity through metal-chelating and free-radical scavenging mechanisms.

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13 Aug 2015
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