Lsugars

Lsugars, or L-sugars, are the enantiomeric forms of the more common D-sugars within the family of monosaccharides and related carbohydrates. They rotate plane-polarized light to the left (levorotatory) and have the opposite configuration at the chiral centers relative to their D-counterparts. The designation L follows the conventional reference to glyceraldehyde; D-sugars are the mirror images of their L-forms.

Most biological systems predominantly use D-sugars, but L-sugars occur in nature as components of certain polysaccharides and glycoconjugates. Examples include L-rhamnose and L-arabinose found in bacterial and plant polysaccharides, as well as L-fucose present in glycoproteins and mucins. Free L-sugars are less common and often metabolically less accessible to human enzymes.

In terms of metabolism, human enzymes and most glycolytic pathways are specific for D-sugars; as a result, many L-sugars are less readily digestible or have historically been considered non-nutritive. Some L-sugars, such as L-glucose, are not appreciably metabolized by humans and can serve as research tools or non-nutritive analogs.

Applications of L-sugars include serving as stereochemical building blocks in chemical synthesis, aiding studies of enzyme specificity and transport, and supporting investigations of glycan structures in microbiology and biochemistry. The distinction between L- and D-sugars is a fundamental concept in carbohydrates chemistry, glycoscience, and related fields. See also D-sugars and enantiomers.