Epimerisaatiot

Epimerisaatiot are chemical reactions that alter the configuration of a stereogenic center in a molecule while leaving the rest of the structure unchanged. In contrast to general isomerization, epimerization specifically changes the spatial arrangement around a single chiral atom, converting one epimer into another. The term comes from the Greek words for "other" and "mirror," and is often used in carbohydrate chemistry where sugars frequently exist as epimers.

The most common example of epimerisaatiot is the conversion of glucose to its epimer glucose-1-phosphate in enzymatic pathways such as the Calvin cycle. In aqueous solutions, reducing sugars like lactulose can epimerize at their anomeric carbon, leading to equilibrium mixtures of α and β anomers. Another widely studied system is the interconversion of D-glucuronate and D-mannuronic acid by epimerases, enzymes that play a role in plant cell wall biosynthesis.

Mechanistically, epimerisation can proceed via an enol or enediol intermediate under basic or acidic conditions, or through enzyme-catalysed proton abstraction and re‑addition. In many biological systems, epimerases stabilize the transition state and enforce stereospecificity, ensuring the proper configuration of metabolic intermediates.

Epimerisaatiot are important in food chemistry, where they affect the sweetness and stability of sugars, and in drug development, where the activity of stereochemically distinct enantiomers can differ markedly. Because the overall molecular formula remains unchanged, epimerisation is often monitored by chiral chromatography, NMR spectroscopy, or mass spectrometry with chiral derivatizing agents.