Rare sugars: L-Rhamnose, D-Galactose and D-Mannose

Carbohydrates, or as they are more commonly called sugars, are one of the four most important biological macromolecules. These are the primary sources of energy for most organisms. From single-celled bacteria to multicellular human beings, almost all organisms are dependent on sugars.

Simple sugars, most prominently glucose, are abundant in nature. These are also the primary manner of storing energy. Both the availability and dependability has resulted in their frequent industrial use.

However, diabetes and other related ailments have driven the research to search for alternative sugar molecules which are not normally metabolized in body, or are present in only trace amounts.

Rare sugars provide an important niche for this research.

What are rare sugars

Simply put, these are sugars that are not abundantly present in nature. When found in nature, they are present only in trace amounts—too little to separate and process them for industrial, research or other applications.

Instead of extracting these trace amounts, rare sugars are often obtained through a combination of biological processes. These processes include fermentation (usually utilizing different bacterial species) and enzymatic conversions from similar compounds.

The enzymatic synthesis of rare sugars has been proved to be useful for various industrial applications. These are often used in artificial sugars as low-calorie sweeteners and in developing medicines with lower side effects.



This rare sugar is the L-isomer of methylpentose molecule. It is often found in plant glycosides and certain bacterial lipopolysaccharides from gram-negative species.

This 6-carbon sugar molecule is commonly used in either its monohydrate or pyranose form for numerous industrial and research applications. It is used in cardiac drugs, synthetic spices, food additives and to prepare several other biochemical reagents.


It is an aldohexose sugar, named because it carries a single aldehyde group (−CH=O). It is naturally found in D-configuration, similar to most of the other naturally occurring sugars.

Galactose is one of the three most important monosaccharides; the other two being glucose and fructose. However, it is comparatively less sweeter in taste.

It is widely used in baby food, other healthy food options, functional and soft drinks, and medicinal drugs. It is also often used as a raw material for studying carbohydrate synthesis and other aspects of glycobiology.



It is a fermentable hexose sugar, often found in ash Fraxinus ornus and other plant species. In human metabolism, it is important for glycosylation of certain proteins.

However, it is not an essential nutrient and is only produced rarely from sugar.

In industry, it is often used as a flavor enhancer, sweetener, pharmaceutical intermediate, nutrient supplement and other uses. Synthesis of carbohydrates, particularly rare sugars, requires streamlined processes to deliver high quality material. The purity of these reagents dictates their research and industrial applications.