Lecture 22 Sugar Structures

Aldose (example too)

Aldehyde (R-CHO) at the end of a sugar ex: glucose

Ketose

Ketone (R-O-R) at the end of sugar ex: fructose

D/L chirality of sugars

L-configuration has alcohol (-OH) on the left side, whereas D-configuration has alcohol on the right side. Look at the last chiral carbon

Enantiomers

Mirror images of each other

Diastereomers

Isomers that are the same sugar, but not mirror images. Same chemical makeup.

Epimers

Diastereomers that only differ in chirality at a single carbon

How many sugars are in a monosaccharide?

1

How many sugars are in a disaccharide?

2

How many sugars are in a polysaccharide?

Many

How many C atoms are in triose?

3

How many C atoms are in tetrose?

4

How many C atoms are in pentose?

5

How many C atoms are in hexose?

6

How many C atoms are in heptose?

7

What are reducing sugars?

Able to act as reducing agents, monosaccharides are reducing sugars while polysaccharides are not all reducing sugars

What end of the sugar is the reducing end?

The end with the carbonyl

How are artificial sweeteners able to trigger sweet taste, but not able to trigger insulin response and subsequent/concomitant metabolic processes?

Sweet taste & insulin release are separate biological processes

What triggers insulin release?

Elevated blood glucose levels

How do cyclic sugars form?

Reaction of an alcohol group with aldehyde or ketone to generate hemiacetal, hemiketal (intramolecular)

What sugar has a 6-member ring?

Pyranose

What sugar has a 5-member ring?

Furanose

What is anomeric?

The carbon atom that carried the aldehyde or ketone carbonyl group in the open-chain sugar. When the sugar cyclizes, this carbon turns into a new chiral center (stereocenter)

Where is the reducing end in a Fischer Projection?

Reducing end at the top

Where is the reducing end in a Haworth Projection?

First sugar has reducing end on the right

α-conformation

The 1 and 6 positions are in the trans conformation above and below the ring

β-conformation

The 1 and 6 positions are in the cis conformation on the same side of the ring

Which confirmation is more favorable?

β-conformation

How do you determine the anomeric carbon in a Haworth Projection?

Locate the oxygen, anomeric carbon has to have another oxygen bonded to it, go around without passing through the oxygen in the ring

Equatorial vs. Axial substituent

Equatorial: aligned with the ring’s plane

Axial: points straight up or down