Oligosaccharide nomenclature
Encyclopedia
Oligosaccharides and polysaccharides are an important class of polymeric carbohydrates found in virtually all living entities. Their structural features make their nomenclature challenging and their roles in living systems make their nomenclature important.
residues joined through glycosidic linkage
, which can be hydrolyzed by acid to give the constituent monosaccharide units. While a strict definition of an oligosaccharide
is not established, it is generally agreed that a carbohydrate consisting of two to ten monosaccharide residues with a defined structure is an oligosaccharide.
Some oligosaccharides, for example maltose
, sucrose
, and lactose
, were trivially named before their chemical constitution was determined, and these names are still used today.
Trivial names, however, are not useful for most other oligosaccharides and, as such, systematic rules for the nomenclature of carbohydrates
have been developed. To fully understand oligosaccharide and polysaccharide
nomenclature, one must understand how monosaccharides are named.
An oligosaccharide has both a reducing and a non-reducing end. The reducing end of an oligosaccharide is the monosaccharide residue with hemiacetal
functionality, thereby capable of reducing the Tollens’ reagent, while the non-reducing end is the monosaccharide residue in acetal
form, thus incapable of reducing the Tollens’ reagent. The reducing and non-reducing ends of an oligosaccharide are conventionally drawn with the reducing-end monosaccharide residue furthest to the right and the non-reducing (or terminal) end furthest to the left.
Naming of oligosaccharides proceeds from left to right (from the reducing end to the terminal) as glycosyl [glycosyl]n glycoses or glycosyl [glycosyl]n glycosides, depending on whether or not the reducing end is a free hemiacetal group. In parentheses, between the names of the monosaccharide residues, the number of the anomeric carbon atom, an arrow symbol, and the number of the carbon atom bearing the connecting oxygen of the next monosaccharide unit are listed. Appropriate symbols are used to indicate the stereochemistry of the glycosidic bonds (α or β), the configuration of the monosaccharide residue (D orL), and the substitutions at oxygen atoms (O). Maltose
and a derivative of sucrose
illustrate these concepts:
Maltose: α-D-Glucopyranosyl-(1→4)-β-D-glucopyranose
Methyl 2,3,4-tri-O-benzyl-6-deoxy-6-fluoro-α-D-galactopyranosyl-(1→4)-2,3,6-tri-O-acetyl-β-D-glucopyranoside
In the case of branched oligosaccharides, meaning that the structure contains at least one monosaccharide residue linked to more than two other monosaccharide residues, terms designating the branches should be listed in square brackets, with the longest linear chain (the parent chain) written without square brackets. The following example will help illustrate this concept:
Allyl α-L-fucopyranosyl-(1→3)-[α-D-galactopyranosyl-(1→4)]-α-D-glucopyranosyl-(1→3)-α-D-galactopyranoside
These systematic names are quite useful in that they provide information about the structure of the oligosaccharide. They do require a lot of space, however, so abbreviated forms are used when possible. In these abbreviated forms, the names of the monosaccharide units are shortened to their corresponding three-letter abbreviations, followed by p for pyranose or f for furanose ring structures, with the abbreviated aglyconic alcohol placed at the end of the name. Using this system, the previous example would have the abbreviated name α-L-Fucp-(1→3)-[α-D-Galp-(1→4)]-α-D-Glcp-(1→3)-α-D-GalpOAll.
, a main component of the cell wall in plants, and starch, a name derived from the Anglo-Saxon stercan, meaning to stiffen.
To name a polysaccharide composed of a single type of monosaccharide, that is a homopolysaccharide, the ending “-ose” of the monosaccharide is replaced with “-an”. For example, a glucose
polymer is named glucan
, a mannose
polymer is named mannan
, and a galactose
polymer is named galactan. When the glycosidic linkages
and configurations of the monosaccharides are known, they may be included as a prefix to the name, with the notation for glycosidic linkages preceding the symbols designating the configuration. The following example will help illustrate this concept:
(1→4)-β-D-Glucan
A heteropolysaccharide is a polymer containing more than one kind of monosaccharide residue. The parent chain contains only one type of monosaccharide and should be listed last with the ending “-an”, and the other types of monosaccharides listed in alphabetical order as “glyco-” prefixes. When there is no parent chain, all different monosaccharide residues are to be listed alphabetically as “glyco-” prefixes and the name should end with “-glycan”. The following example will help illustrate this concept:
((1→2)-α-D-galacto)-(1→4)-β-D-Glucan
Oligosaccharides
Oligosaccharides are carbohydrates that are composed of several monosaccharideMonosaccharide
Monosaccharides are the most basic units of biologically important carbohydrates. They are the simplest form of sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose , fructose , galactose, xylose...
residues joined through glycosidic linkage
Glycosidic bond
In chemistry, a glycosidic bond is a type of covalent bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate....
, which can be hydrolyzed by acid to give the constituent monosaccharide units. While a strict definition of an oligosaccharide
Oligosaccharide
An oligosaccharide is a saccharide polymer containing a small number of component sugars, also known as simple sugars...
is not established, it is generally agreed that a carbohydrate consisting of two to ten monosaccharide residues with a defined structure is an oligosaccharide.
Some oligosaccharides, for example maltose
Maltose
Maltose , or malt sugar, is a disaccharide formed from two units of glucose joined with an αbond, formed from a condensation reaction. The isomer "isomaltose" has two glucose molecules linked through an α bond. Maltose is the second member of an important biochemical series of glucose chains....
, sucrose
Sucrose
Sucrose is the organic compound commonly known as table sugar and sometimes called saccharose. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in human nutrition. The molecule is a disaccharide composed of glucose and fructose with the molecular formula...
, and lactose
Lactose
Lactose is a disaccharide sugar that is found most notably in milk and is formed from galactose and glucose. Lactose makes up around 2~8% of milk , although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from or , the Latin word for milk,...
, were trivially named before their chemical constitution was determined, and these names are still used today.
Trivial names, however, are not useful for most other oligosaccharides and, as such, systematic rules for the nomenclature of carbohydrates
Monosaccharide nomenclature
Monosaccharide nomenclature is a set of conventions used in chemistry to name the compounds known as monosaccharides or "simple sugars" — the basic structural units of carbohydrates, which cannot be hydrolysed into simpler units....
have been developed. To fully understand oligosaccharide and polysaccharide
Polysaccharide
Polysaccharides are long carbohydrate molecules, of repeated monomer units joined together by glycosidic bonds. They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure,...
nomenclature, one must understand how monosaccharides are named.
An oligosaccharide has both a reducing and a non-reducing end. The reducing end of an oligosaccharide is the monosaccharide residue with hemiacetal
Hemiacetal
Hemiacetals and hemiketals are compounds that are derived from aldehydes and ketones respectively. The Greek word hèmi means half...
functionality, thereby capable of reducing the Tollens’ reagent, while the non-reducing end is the monosaccharide residue in acetal
Acetal
An acetal is a molecule with two single-bonded oxygen atoms attached to the same carbon atom.Traditional usages distinguish ketals from acetals...
form, thus incapable of reducing the Tollens’ reagent. The reducing and non-reducing ends of an oligosaccharide are conventionally drawn with the reducing-end monosaccharide residue furthest to the right and the non-reducing (or terminal) end furthest to the left.
Naming of oligosaccharides proceeds from left to right (from the reducing end to the terminal) as glycosyl [glycosyl]n glycoses or glycosyl [glycosyl]n glycosides, depending on whether or not the reducing end is a free hemiacetal group. In parentheses, between the names of the monosaccharide residues, the number of the anomeric carbon atom, an arrow symbol, and the number of the carbon atom bearing the connecting oxygen of the next monosaccharide unit are listed. Appropriate symbols are used to indicate the stereochemistry of the glycosidic bonds (α or β), the configuration of the monosaccharide residue (D orL), and the substitutions at oxygen atoms (O). Maltose
Maltose
Maltose , or malt sugar, is a disaccharide formed from two units of glucose joined with an αbond, formed from a condensation reaction. The isomer "isomaltose" has two glucose molecules linked through an α bond. Maltose is the second member of an important biochemical series of glucose chains....
and a derivative of sucrose
Sucrose
Sucrose is the organic compound commonly known as table sugar and sometimes called saccharose. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in human nutrition. The molecule is a disaccharide composed of glucose and fructose with the molecular formula...
illustrate these concepts:
In the case of branched oligosaccharides, meaning that the structure contains at least one monosaccharide residue linked to more than two other monosaccharide residues, terms designating the branches should be listed in square brackets, with the longest linear chain (the parent chain) written without square brackets. The following example will help illustrate this concept:
These systematic names are quite useful in that they provide information about the structure of the oligosaccharide. They do require a lot of space, however, so abbreviated forms are used when possible. In these abbreviated forms, the names of the monosaccharide units are shortened to their corresponding three-letter abbreviations, followed by p for pyranose or f for furanose ring structures, with the abbreviated aglyconic alcohol placed at the end of the name. Using this system, the previous example would have the abbreviated name α-L-Fucp-(1→3)-[α-D-Galp-(1→4)]-α-D-Glcp-(1→3)-α-D-GalpOAll.
Polysaccharides
Polysaccharides are considered to be polymers of monosaccharides containing ten or more monosaccharide residues. Polysaccharides have been given trivial names that reflect their origin. Two common examples are celluloseCellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
, a main component of the cell wall in plants, and starch, a name derived from the Anglo-Saxon stercan, meaning to stiffen.
To name a polysaccharide composed of a single type of monosaccharide, that is a homopolysaccharide, the ending “-ose” of the monosaccharide is replaced with “-an”. For example, a glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
polymer is named glucan
Glucan
A glucan molecule is a polysaccharide of D-glucose monomers linked by glycosidic bonds.Many beta-glucans are medically important.-Types:The following are glucans:-Alpha:...
, a mannose
Mannose
Mannose is a sugar monomer of the aldohexose series of carbohydrates. Mannose is a C-2 epimer of glucose. It is not part of human metabolism, but is a component of microbial cell walls, and is therefore a target of the immune system and also of antibiotics....
polymer is named mannan
Mannan
Mannan is a plant polysaccharide that is a polymer of the sugar mannose.Detection of mannan leads to lysis in the mannan-binding lectin pathway.It is generally found in yeast, bacteria and plants. It shows α linkage. It is a form of storage polysaccharide.-See Also:Mannan Oligosaccharides...
, and a galactose
Galactose
Galactose , sometimes abbreviated Gal, is a type of sugar that is less sweet than glucose. It is a C-4 epimer of glucose....
polymer is named galactan. When the glycosidic linkages
Glycosidic bond
In chemistry, a glycosidic bond is a type of covalent bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate....
and configurations of the monosaccharides are known, they may be included as a prefix to the name, with the notation for glycosidic linkages preceding the symbols designating the configuration. The following example will help illustrate this concept:
A heteropolysaccharide is a polymer containing more than one kind of monosaccharide residue. The parent chain contains only one type of monosaccharide and should be listed last with the ending “-an”, and the other types of monosaccharides listed in alphabetical order as “glyco-” prefixes. When there is no parent chain, all different monosaccharide residues are to be listed alphabetically as “glyco-” prefixes and the name should end with “-glycan”. The following example will help illustrate this concept:
See also
- OligosaccharideOligosaccharideAn oligosaccharide is a saccharide polymer containing a small number of component sugars, also known as simple sugars...
- Carbohydrate ConformationCarbohydrate conformationCarbohydrate conformation is the characteristic 3-dimensional shape of a carbohydrate. Conformations of monosaccharide and oligosaccharide heavily influence their reactivity and recognition by other molecules, which are essential to mammals and other organisms....
- MonosaccharideMonosaccharideMonosaccharides are the most basic units of biologically important carbohydrates. They are the simplest form of sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose , fructose , galactose, xylose...
- Monosaccharide nomenclatureMonosaccharide nomenclatureMonosaccharide nomenclature is a set of conventions used in chemistry to name the compounds known as monosaccharides or "simple sugars" — the basic structural units of carbohydrates, which cannot be hydrolysed into simpler units....