A furanose is a simple
sugarthat contains a five-membered furan-based ring structure and is a sub-terminal ketone which gives it reducing power.
The furanose ring is a cyclic
hemiacetalof an aldopentoseor a cyclic hemiketalof a ketohexose.
A furanose ring structure consists of four
carbonand one oxygenatom with the anomeric carbon to the right of the oxygen. The highest numbered chiral carbon (typically to the left of the oxygen in a Haworth projection) determines whether or not the structure has a D-configuration or L-configuration. In an L-configuration furanose, the substituent on the highest numbered chiral carbon is pointed downwards out of the plane, and in a D-configuration furanose, the highest numberd chiral carbon is facing upwards.
The furanose ring will have either alpha or beta configuration, depending on which direction the anomeric
hydroxygroup is pointing. In a D-configuration furanose, alpha configuration has the hydroxy pointing down, and beta has the hydroxy pointing up. It is the opposite in an L-configuration furanose. Typically, the anomeric carbon undergoes mutarotationin solution, and the alpha-beta configuration switches constantly--thus it is in an equilibrium state.
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