‘D’ and ‘L’ notations in carbohydrate nomenclature indicate the relative configuration of a stereoisomer concerning the known configuration of glyceraldehyde. Compounds chemically correlated to the D isomer of glyceraldehyde are assigned D-configuration, and those correlated to the L isomer are assigned L-configuration.
How are ‘D’ and ‘L’ notations used in carbohydrate nomenclature, and what is their significance?
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The ‘D’ and ‘L’ notations in carbohydrate nomenclature refer to the configuration of the chiral carbon furthest from the carbonyl group. In a Fischer projection, ‘D’ signifies that the hydroxyl group on this chiral carbon is on the right, while ‘L’ indicates it is on the left. These notations are crucial for describing the absolute configuration of sugars. Despite the historical correlation between optical activity and ‘D’ or ‘L’ designation, today, it’s based on the absolute configuration. ‘D’ sugars are not always dextrorotatory, and ‘L’ sugars are not always levorotatory, but the nomenclature aids in conveying spatial arrangement in complex carbohydrate structures.