25.3 D,L Sugars
3 min read•may 7, 2024
Sugars come in two main flavors: D and L. These stereoisomers differ in their spatial arrangement, which we can see using Fischer projections. , like glucose, have their OH group on the right, while have it on the left.
Most natural sugars are D sugars, matching 's configuration. This stereochemistry is crucial for how enzymes recognize and interact with sugars in our bodies. Understanding these differences helps us grasp how sugars function in living systems.
Stereochemistry of D and L sugars
Differentiate between D and L sugars based on their stereochemistry and Fischer projections
Top images from around the web for Differentiate between D and L sugars based on their stereochemistry and Fischer projections
2.3E: Organic Molecules and Functional Groups - Biology LibreTexts View original
Is this image relevant?
organic chemistry - D/L Configuration - Chemistry Stack Exchange View original
Is this image relevant?
Carbohydrates · Biology View original
Is this image relevant?
2.3E: Organic Molecules and Functional Groups - Biology LibreTexts View original
Is this image relevant?
organic chemistry - D/L Configuration - Chemistry Stack Exchange View original
Is this image relevant?
1 of 3
Top images from around the web for Differentiate between D and L sugars based on their stereochemistry and Fischer projections
2.3E: Organic Molecules and Functional Groups - Biology LibreTexts View original
Is this image relevant?
organic chemistry - D/L Configuration - Chemistry Stack Exchange View original
Is this image relevant?
Carbohydrates · Biology View original
Is this image relevant?
2.3E: Organic Molecules and Functional Groups - Biology LibreTexts View original
Is this image relevant?
organic chemistry - D/L Configuration - Chemistry Stack Exchange View original
Is this image relevant?
1 of 3
- D and L sugars are stereoisomers differing in configuration at the chirality center farthest from the carbonyl group
- D sugars have the hydroxyl group on the right side of the at this chirality center ()
- L sugars have the hydroxyl group on the left side of the Fischer projection at this chirality center ()
- Fischer projections represent the three-dimensional structure of a molecule in a two-dimensional format
- Horizontal lines represent bonds pointing towards the viewer
- Vertical lines represent bonds pointing away from the viewer
- Carbonyl group (aldehyde or ketone) always placed at the top of the Fischer projection
- Longest carbon chain oriented vertically, with the carbonyl group at the top
D,L system vs R,S configuration
- Both D,L system and R,S configuration system describe stereochemistry of monosaccharides
- R,S system assigns absolute configuration based on Cahn-Ingold-Prelog (CIP) priority rules
- R (rectus) configuration has lowest priority group pointing away from viewer when highest priority group oriented away ()
- S (sinister) configuration has lowest priority group pointing towards viewer when highest priority group oriented away ()
- D,L system based on configuration of highest-numbered (farthest from carbonyl group) compared to D-glyceraldehyde
- D sugars have same configuration as D-glyceraldehyde at highest-numbered stereocenter (D-glucose)
- L sugars have opposite configuration as D-glyceraldehyde at highest-numbered stereocenter (L-glucose)
- In most cases, D sugars have R configuration and L sugars have S configuration at highest-numbered stereocenter
- Exceptions occur when sugar has even number of carbon atoms ( has S configuration)
Stereochemistry in natural sugars
- Most naturally occurring sugars are D sugars, having same configuration as D-glyceraldehyde at highest-numbered stereocenter
- Examples: D-glucose, , ,
- D-glyceraldehyde is simplest sugar with single chirality center and serves as reference for determining configuration of other sugars
- D-glyceraldehyde has hydroxyl group on right side of Fischer projection at chirality center
- L sugars (, ) less common in nature but still play important biological roles
- Stereochemistry of naturally occurring sugars essential for recognition by enzymes and proper functioning in biological systems
Optical activity and related concepts
- Stereocenter: A carbon atom bonded to four different groups, creating chirality
- : Mirror image molecules that are non-superimposable, differing in configuration at all stereocenters
- : Stereoisomers that differ in configuration at only one stereocenter
- : The ability of chiral molecules to rotate plane-polarized light
- : The change in optical rotation observed when a sugar converts between its α and β anomeric forms in solution
Carbohydrate Nomenclature
Identify the components of monosaccharide names and their meanings
- Monosaccharide names consist of prefix, root, and suffix
- Prefix indicates number of carbon atoms in monosaccharide
- Tri- (3 carbons), Tetr- (4 carbons), Pent- (5 carbons), Hex- (6 carbons), Hept- (7 carbons)
- Root describes type of carbonyl group present
- -ose: (aldehyde group)
- -ulose: (ketone group)
- Suffix indicates stereochemistry of monosaccharide
- -D: Configuration at highest-numbered stereocenter matches D-glyceraldehyde
- -L: Configuration at highest-numbered stereocenter opposite to D-glyceraldehyde
Identify common monosaccharides based on their structures and names
- Glucose (D-glucose): , most abundant monosaccharide in nature
- Key component of polysaccharides (starch, cellulose)
- Main energy source for cells
- Fructose (D-fructose): , commonly found in fruits and honey
- Sweetest naturally occurring sugar
- Ribose (D-ribose): , component of RNA and ATP
- Deoxyribose (D-deoxyribose): , component of DNA
- Lacks hydroxyl group at 2' position compared to ribose
- Galactose (): Aldohexose, component of lactose (milk sugar)
- Differs from glucose in configuration at C-4
Key Terms to Review (28)
Aldohexose: An aldohexose is a type of monosaccharide, the most basic unit of carbohydrates, that contains six carbon atoms and an aldehyde group at one end. Aldohexoses are important in the classification of carbohydrates and the understanding of the essential monosaccharides required for human health.
Aldopentose: An aldopentose is a monosaccharide containing five carbon atoms and an aldehyde group at one end. Aldopentoses are important in the context of understanding the classification of sugars and the essential monosaccharides required for human health.
Aldose: An aldose is a monosaccharide, or simple sugar, that contains a carbonyl group (C=O) at the first carbon atom and hydroxyl groups (OH) at the remaining carbons. Aldoses are a type of carbohydrate that serve as the building blocks for more complex sugars and play a crucial role in energy production and storage within the body.
D Sugars: D Sugars are a category of sugars that are part of the biomolecules known as carbohydrates, characterized by the orientation of the hydroxyl (-OH) group on the penultimate (second-to-last) carbon atom being on the right side in Fischer projection. They play crucial roles in energy storage, recognition processes, and structural components within organisms.
D-deoxyribose: D-deoxyribose is a monosaccharide that serves as the backbone of deoxyribonucleic acid (DNA) molecules. It is a sugar with five carbon atoms and lacks an oxygen atom at the 2' position, making it a deoxysugar.
D-erythrose: D-erythrose is an aldose, a monosaccharide with an aldehyde group at the end of the carbon chain. It is one of the four stereoisomers of the simple sugar erythrulose, and is classified as a D-sugar based on the configuration of the chiral carbon atoms.
D-fructose: D-fructose, also known as fruit sugar, is a monosaccharide that belongs to the class of carbohydrates known as sugars. It is a naturally occurring sugar found in many fruits, honey, and some vegetables, and is an important energy source for the body.
D-galactose: D-galactose is a monosaccharide, or simple sugar, that is an important component of many complex carbohydrates. It is a C-4 epimer of D-glucose, meaning it differs in the configuration of the hydroxyl group at the fourth carbon. D-galactose is a key term in understanding the topics of D,L Sugars and the Configurations of Aldoses.
D-glucose: D-glucose is a monosaccharide, the most abundant sugar found in nature. It is an aldose, meaning it has an aldehyde group at one end, and is the stereoisomer with the D-configuration, indicating the position of the hydroxyl group on the chiral carbon farthest from the aldehyde group.
D-glyceraldehyde: D-glyceraldehyde is a simple monosaccharide, specifically an aldose, that serves as an important model compound for understanding the configurations of sugars. It is the simplest possible aldose, containing three carbon atoms and a single aldehyde group.
D-ribose: D-ribose is a monosaccharide, a type of simple sugar, that is an essential component of ribonucleic acid (RNA). It is a key player in the topics of enantiomers, D-L sugars, and the configurations of aldoses.
Deoxyaldopentose: A deoxyaldopentose is a monosaccharide with five carbon atoms and lacking an oxygen atom on the second carbon, making it a deoxy sugar. These sugars are important components of nucleic acids like DNA and RNA.
Enantiomers: Enantiomers are a pair of stereoisomers that are non-superimposable mirror images of each other. They have the same molecular formula and connectivity, but differ in the spatial arrangement of their atoms, resulting in a unique handedness or chirality.
Epimers: Epimers are a type of stereoisomers that differ in the configuration of only one stereocenter, or chiral carbon, within a molecule. This subtle difference in the spatial arrangement of atoms can have significant implications in the context of carbohydrate chemistry and stereochemistry.
Fischer Projection: A Fischer projection is a way of representing the three-dimensional structure of a molecule, particularly organic compounds with tetrahedral carbon centers, on a two-dimensional plane. It is used to depict the relative orientation of substituents around a carbon atom and is crucial for understanding concepts such as enantiomers, diastereomers, and the configuration of sugars.
Ketohexose: A ketohexose is a monosaccharide, or simple sugar, that contains a ketone group (C=O) and six carbon atoms. Ketohexoses are an important class of carbohydrates that are involved in various metabolic processes within the body.
Ketose: Ketose, also known as a ketose sugar, is a type of monosaccharide where the carbonyl group (C=O) is located at the second carbon atom from the end of the carbon chain. This structural feature distinguishes ketoses from aldoses, where the carbonyl group is at the first carbon atom.
L Sugar: L Sugars are a type of sugar molecule that are part of the mirror-image forms found in nature, distinguished by their spatial arrangement around asymmetric carbon atoms. In organic chemistry, they represent the left-handed configuration in a pair of stereoisomers, which is opposite to the more common D sugars found in organisms.
L sugars: L sugars are a type of sugar molecule that are mirror images of D sugars, distinguished by the spatial arrangement of atoms around their chiral center farthest from the carbonyl group. They are named after the Latin "laevus," meaning left, indicating the direction in which they rotate plane-polarized light.
L-arabinose: L-arabinose is a monosaccharide, a type of simple sugar, that is classified as a pentose sugar. It is the C5 sugar that is the structural component of many plant polysaccharides and is an important intermediate in various metabolic pathways.
L-fucose: L-fucose is a monosaccharide that belongs to the group of D,L sugars. It is a deoxy sugar, meaning it lacks an oxygen atom at the C-6 position compared to other hexoses like glucose or galactose. L-fucose is an important component of many glycoproteins and glycolipids, and it plays crucial roles in various biological processes.
L-glucose: L-glucose is the enantiomer of the more common D-glucose, with the hydroxyl groups arranged in the opposite configuration around the chiral carbon atoms. As a result, L-glucose exhibits the opposite optical activity compared to D-glucose, making it an important concept in the study of optical activity, the classification of sugars, and the configurations of aldoses.
L-glyceraldehyde: L-glyceraldehyde is a simple monosaccharide, or sugar, that serves as an important intermediate in various metabolic pathways. It is the aldose form of glycerol, with a single aldehyde group and three carbon atoms. L-glyceraldehyde is a key component in understanding the concepts of D,L sugars and the configurations of aldoses.
Mutarotation: Mutarotation is the spontaneous interconversion between the '$\alpha$-' and '$\beta$-'anomeric forms of a monosaccharide in aqueous solution. This process occurs as the monosaccharide forms a cyclic structure and the orientation of the hydroxyl group on the anomeric carbon changes.
Optical Activity: Optical activity is the ability of certain molecules to rotate the plane of polarized light as it passes through a solution containing those molecules. This phenomenon is directly related to the concept of chirality, where molecules can exist in two non-superimposable mirror-image forms, known as enantiomers.
R-glyceraldehyde: R-glyceraldehyde is a simple sugar molecule that serves as a key intermediate in the context of D,L sugars. It is the simplest aldose, meaning it contains an aldehyde functional group, and is the fundamental building block for understanding the classification and stereochemistry of sugars.
S-Glyceraldehyde: S-glyceraldehyde is a simple sugar (monosaccharide) that is the stereoisomer of the D-glyceraldehyde molecule. It is an important intermediate in carbohydrate metabolism and serves as a key building block for larger sugar molecules.
Stereocenter: A stereocenter is a carbon atom in a molecule that is bonded to four different substituents, resulting in a chiral center that can exist in two non-superimposable mirror-image forms called enantiomers. Stereocenters are central to understanding the handedness and configuration of molecules, as well as their interactions in biological systems.