What is the Difference Between Pyranose and Furanose

The main difference between pyranose and furanose is that pyranose has a six-membered ring with five carbon atoms and one oxygen atom, whereas furanose has a five-membered ring system with four carbon atoms and one oxygen atom.

Carbohydrates are biological molecules with carbon (C), hydrogen (H), and oxygen (O) in them. They have the general formula C₆H₁₂O₆. We can classify carbohydrates as monosaccharides, disaccharides, polysaccharides, and oligosaccharides. Monosaccharides are the simplest of all carbohydrates. They are also known as simple sugars, and they cannot be further hydrolyzed into small carbohydrates. Chemically, they are aldehydes or ketones with two or more hydroxyl groups. Furanose and pyranose are two types of monosaccharides that exist in cyclic forms.

Key Areas Covered

1. What is Pyranose 
      – Definition, Composition
2. What is Furanose
      – Definition, Composition
3. Difference Between Pyranose and Furanose
      – Comparison of Key Differences

Key Terms

Furanose, Pyranose 

What is Pyranose

Pyranose is a saccharide having a six-membered ring with five carbon atoms and one oxygen atom. Hence pyranose molecules are cyclic in nature. The name “pyranose” comes from the word “pyran” due to the similarity in their ring structure. However, when compared to the structure of pyran, pyranose does not have double bonds.

Pyranose is one of the forms of two cyclic monosaccharides. In aqueous solutions, the cyclic and chain form exists in equilibrium, but the most common form is the cyclic form. In the chain form, the carbonyl carbon is located at the end of the chain, while hydroxyl groups are bonded to other carbon atoms of the chain. The hemiacetal group forms when the hydroxyl group in the chain bonds with the carbonyl carbon atom of the molecule. Moreover, the hydroxyl group is responsible for the water solubility of the molecule. The carbonyl carbon, on the other hand, is responsible for the sweetness of the sugar. Pyranose is the most common type of cyclic sugar. In fact, glucose and mannose mostly occur in the pyranose form.

What is Furanose

Furanose is a carbohydrate having a five-membered ring consisting of four carbon atoms and one oxygen atom. The name furanose comes from the word “furan,” the oxygen heterocycle, which is similar to the furanose. However, furanose does not have double bonds in its structure.

The presence of D configuration and L configuration in furanose is determined by the highest numbered chiral carbon. The substitute on the highest numbered chiral carbon points downwards out of the plain in the L configuration of furanose. Moreover, in the D configuration, the highest-numbered chiral carbon faces upwards.

Furanose can exist in either alpha configuration or beta configuration. Depending on the direction the anomeric hydroxyl group is facing, the configuration is assigned. For example, in the alpha configuration of the D furanose configuration, the hydroxyl group points downwards. In the beta configuration, the hydroxyl group points in the upward direction.

Fructose mainly occurs in the furanose form. However, this is a less common group of cyclic sugar when compared to pyranose, which is more abundant.

Difference Between Pyranose and Furanose

Definition

Pyranose is a carbohydrate having a six-membered ring with five carbon atoms and one oxygen atom, while furanose is a carbohydrate having a five-membered ring with four carbon atoms and one oxygen atom.

Chemical Composition

Pyranose has 6-membered rings with 5 carbon atoms and 1 oxygen atom, whereas furanose has a system of 5-membered ring system with 4 carbon atoms and 1 oxygen atom.

Examples

Glucose and mannose mostly occur in the pyranose form, while fructose occurs in the furanose form.

Abundance

The pyranose group is the most common group of cyclic sugars, whereas furanose is a less common type of cyclic sugar.

Conclusion

Carbohydrates are a type of common molecule present in food. Carbohydrates have a variety of different subgroups according to the structural composition of molecules. In brief, pyranose and furanose are two types of carbohydrates. The main difference between pyranose and furanose is that pyranose has a six-membered ring with five carbon atoms and one oxygen atom, whereas furanose has a five-membered ring system of four carbon atoms and one oxygen atom.

Reference:

1. Krishnamurthy, R., Campbell, T., Kim, EK. “Furanose.” Encyclopedia of Astrobiology. Springer.
2. “Pyranose and Furanose Forms.” LibreTexts. Chemistry

Image Courtesy:

1. “Beta-D-Fructofuranose”  By Jü – Own work (CC0) via Commons Wikimedia
2. “TetrahydroPYRANE V.2” By NEUROtiker (talk · contribs) – Own work (Public Domain) via Commons Wikimedia