Biomolecules - Configuration of D-Ketoses

Slide 1:

• D-Ketoses are monosaccharides that contain a ketone functional group and an aldehyde functional group.
• The carbon atom next to the carbonyl carbon is referred to as the alpha carbon, while the carbon atom opposite to the carbonyl carbon is referred to as the beta carbon.
• D-Ketoses have the ketone functional group on the second carbon atom.

Slide 2:

• D-Ketoses have a chiral center at the alpha carbon due to the presence of four different groups attached to it.
• These four different groups can be arranged in two possible configurations: D or L.
• In D configuration, the -OH group on the penultimate carbon is on the right side.
• In L configuration, the -OH group on the penultimate carbon is on the left side.

Slide 3:

• Fischer projection is commonly used to represent the configuration of D-Ketoses.
• In Fischer projection, vertical lines represent bonds coming out of the plane, while horizontal lines represent bonds going into the plane.
• D-Ketoses are represented by drawing the molecule in the Fischer projection with the highest numbered chiral center on the top.

Slide 4:

• The configuration of D-Ketoses can also be determined using the R/S system.
• In this system, the groups attached to the chiral center are prioritized based on their atomic number.
• If the prioritized groups are arranged in a clockwise direction, it is assigned as R configuration.
• If the prioritized groups are arranged in a counterclockwise direction, it is assigned as S configuration.

Slide 5:

• Let’s consider an example of D-Ketose, D-Fructose.
• D-Fructose has a ketone functional group on the second carbon atom.
• The alpha carbon of D-Fructose is the carbon atom next to the carbonyl carbon.

Slide 6:

• In the Fischer projection of D-Fructose, the alpha carbon is at the top.
• The prioritized groups at the alpha carbon are -OH group, -CH2OH group, -H atom, and -CHO group.
• Let’s assign R and S configuration to D-Fructose based on the R/S system.

Slide 7:

• Let’s assign priorities to the groups attached to the alpha carbon in D-Fructose.
• The -OH group has the highest atomic number and is given the highest priority.
• The -CH2OH group is next in priority, followed by the -H atom, and finally the -CHO group.

Slide 8:

• In D-Fructose, the -OH group is directed towards the right side in Fischer projection.
• The -CH2OH group is directed towards the left side, the -H atom is directed towards the plane, and the -CHO group is directed towards the right side.
• The arrangement of the prioritized groups is counterclockwise, indicating that the alpha carbon has an S configuration in D-Fructose.

Slide 9:

• D-Fructose has an S configuration at the alpha carbon and is named as (2S,3R,4S,5R)-2,3,4,5-tetrahydroxyhexanal.
• The configuration of D-Fructose can also be represented using the D/L system.
• In the D/L system, the configuration is determined based on the -OH group on the penultimate carbon.

Slide 10:

• D-Fructose has the -OH group on the penultimate carbon on the right side.
• Therefore, it is assigned the D configuration in the D/L system.
• The full name of D-Fructose is D-(+)-Fructose.

# Biomolecules - Configuration of D-Ketoses

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**Slide 11:**

- D-Ketoses are monosaccharides that contain a ketone functional group and an aldehyde functional group.
- The carbon atom next to the carbonyl carbon is referred to as the alpha carbon, while the carbon atom opposite to the carbonyl carbon is referred to as the beta carbon.
- D-Ketoses have the ketone functional group on the second carbon atom.

**Slide 12:**

- D-Ketoses have a chiral center at the alpha carbon due to the presence of four different groups attached to it.
- These four different groups can be arranged in two possible configurations: D or L.
- In D configuration, the -OH group on the penultimate carbon is on the right side.
- In L configuration, the -OH group on the penultimate carbon is on the left side.

**Slide 13:**

- Fischer projection is commonly used to represent the configuration of D-Ketoses.
- In Fischer projection, vertical lines represent bonds coming out of the plane, while horizontal lines represent bonds going into the plane.
- D-Ketoses are represented by drawing the molecule in the Fischer projection with the highest numbered chiral center on the top.

**Slide 14:**

- The configuration of D-Ketoses can also be determined using the R/S system.
- In this system, the groups attached to the chiral center are prioritized based on their atomic number.
- If the prioritized groups are arranged in a clockwise direction, it is assigned as R configuration.
- If the prioritized groups are arranged in a counterclockwise direction, it is assigned as S configuration.

**Slide 15:**

- Let's consider an example of D-Ketose, D-Fructose.
- D-Fructose has a ketone functional group on the second carbon atom.
- The alpha carbon of D-Fructose is the carbon atom next to the carbonyl carbon.

**Slide 16:**

- In the Fischer projection of D-Fructose, the alpha carbon is at the top.
- The prioritized groups at the alpha carbon are -OH group, -CH2OH group, -H atom, and -CHO group.
- Let's assign R and S configuration to D-Fructose based on the R/S system.

**Slide 17:**

- Let's assign priorities to the groups attached to the alpha carbon in D-Fructose.
- The -OH group has the highest atomic number and is given the highest priority.
- The -CH2OH group is next in priority, followed by the -H atom, and finally the -CHO group.

**Slide 18:**

- In D-Fructose, the -OH group is directed towards the right side in the Fischer projection.
- The -CH2OH group is directed towards the left side, the -H atom is directed towards the plane, and the -CHO group is directed towards the right side.
- The arrangement of the prioritized groups is counterclockwise, indicating that the alpha carbon has an S configuration in D-Fructose.

**Slide 19:**

- D-Fructose has an S configuration at the alpha carbon and is named as (2S,3R,4S,5R)-2,3,4,5-tetrahydroxyhexanal.
- The configuration of D-Fructose can also be represented using the D/L system.
- In the D/L system, the configuration is determined based on the -OH group on the penultimate carbon.

**Slide 20:**

- D-Fructose has the -OH group on the penultimate carbon on the right side.
- Therefore, it is assigned the D configuration in the D/L system.
- The full name of D-Fructose is D-(+)-Fructose.

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Slide 21:

• D-Ketoses have an open-chain structure when in their linear form.
• They can undergo intramolecular reactions to form cyclic structures called hemiketals.
• Hemiketal formation occurs when the C1 carbonyl carbon reacts with a hydroxyl group on the same molecule.

Slide 22:

• In D-Ketoses, the hydroxyl group on the C5 carbon can react with the C2 carbonyl carbon to form a cyclic structure.
• This cyclic structure is known as a pyranose ring due to its resemblance to the pyran molecule.
• Pyranose rings can exist in either a chair or boat conformation.

Slide 23:

• In chair conformation, the ring is in a chair-like shape with alternating axial and equatorial positions.
• The axial positions are perpendicular to the plane of the ring, while the equatorial positions are parallel to the plane of the ring.
• The chair conformation is more stable than the boat conformation due to the reduced steric hindrance between groups.

Slide 24:

• The cyclic structure of D-Fructose is a pyranose ring.
• The hydroxyl group on the C5 carbon reacts with the C2 carbonyl carbon to form the ring structure.
• In the pyranose ring, the C1 carbon becomes a new chiral center.

Slide 25:

• The configuration of the chiral center in the pyranose ring can be determined using the R/S system.
• The prioritized groups at the chiral center are -OH group, -CH2OH group, -H atom, and -CHO group.
• Assigning R or S configuration to the chiral center follows the same rules as in the linear form.

Slide 26:

• The pyranose ring of D-Fructose can exist in different forms based on the configuration of the chiral center.
• The most common form is the alpha-D-fructopyranose, where the -OH group on the C1 carbon is on the same side as the -OCH2OH group.
• The beta-D-fructopyranose is the other form, where the -OH group on the C1 carbon is on the opposite side as the -OCH2OH group.

Slide 27:

• The cyclic structure of D-Fructose can also be represented using Haworth projection.
• Haworth projection is a two-dimensional representation of a cyclic molecule.
• In Haworth projection, the ring is depicted as a planar hexagon, with vertical lines indicating groups below the plane and horizontal lines indicating groups above the plane.

Slide 28:

• In Haworth projection, the alpha-D-fructopyranose is represented with the -OH group on the C1 carbon pointing downwards.
• The beta-D-fructopyranose is represented with the -OH group on the C1 carbon pointing upwards.

Slide 29:

• The cyclic structure of D-Fructose undergoes mutarotation.
• Mutarotation is the process of interconversion between the alpha and beta forms of a sugar.
• This interconversion involves the breaking and reforming of the glycosidic bond.

Slide 30:

• The equilibrium between the alpha-D-fructopyranose and beta-D-fructopyranose is known as the mutarotation equilibrium.
• In solution, the ratio of alpha to beta forms reaches an equilibrium that depends on factors such as temperature, pH, and concentration.

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