20. Carbohydrates

Draw a Haworth projection for α-D-altrose.

D-ribose is an aldopentose sugar that is found in the DNA. It commonly exists as a five-membered β anomer. Draw D‑ribose in its cyclic hemiacetal form.

In the monosaccharide hemiacetal shown below number all the carbon atoms, identify the anomeric carbon atom, and identify it as the α or β anomer.

The cyclic structure of D-idose, an aldohexose, is shown in the margin. Convert this to the straight-chain Fischer projection structure.

Identify the following as diastereomers, enantiomers, and/or anomers.

(a) β-D-fructose and β-D-fructose

(b) D-galactose and L-galactose

(c) L-allose and D-glucose (both aldohexoses)

D-Talose, a constituent of certain antibiotics, has the open-chain structure shown next. Draw d-talose in its cyclic hemiacetal form.