CHEM20018 Reactions and Synthesis
Tutorial 4 - Carbohydrate Chemistry
1. Consider the sugars drawn below. For (a) convert the Fischer projection to a Haworth projection; for (b) and (c) convert the Haworth projections to Fischer projections.
[Suggestion: 1. identify the configurational carbon (the furthest stereocentre from the most oxidized), this is on the right for a D- sugar; 2. identify the most oxidized carbon, this sits at the top; for the remaining stereocentres, use the rule LURD (left-up, right-down)]
2. D-Sorbose is a 2-ketohexose. Reduction of D-sorbose using sodium borohydride affords two polyhydroxylated derivatives, one of which is termed D-gulitol. By consulting the D-sugar family tree (see Lecture Notes):
(a) Draw a Fischer projection of the structure for D-gulitol and the other product (ie not D-gulitol) formed upon reduction of D-sorbose. Suggest an appropriate name for the other product.
(b) Draw a Fischer projection of the structure of D-sorbose.
Hint: D-Gulitol may also be formed by the reduction of D-gulose.
3. The following glycolipid has been isolated from Mycobacterium tuberculosis.
(a) Classify the linkages as α and/or β .
(b) Is the glycolipid a reducing sugar?
Additional Questions
AQ1. Starting with the open-chain form. of D-mannose, draw all the stable isomers that are likely to be formed in aqueous solution, and name them.
AQ2. The following equilibration between these two diastereoisomers (anomers) is catalyzed by acid or base. If isotope-labeled H218O water is used, a single 18O atom is eventually incorporated.
(a) Show how an atom of 18O can be incorporated
(b) Equilibration of the two diastereoisomers (anomers) catalyzed by acid, in labeled H218O, occurs 30 times faster than the incorporation of the 18O label. Discuss this data in terms of the equilibria present.
AQ3. Predict the outcomes of the following reactions (and name the products):