Carbohydrate chemistry
Carbohydrate chemistry is a subdiscipline of chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

 primarily concerned with the synthesis, structure, and function of carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...

 structures. Due to the general structure of carbohydrates, their synthesis is often preoccupied with the selective formation of glycosidic linkages and the selective reaction of hydroxyl groups. As a result, this chemistry relies heavily on the use of protecting groups.


Individual saccharide residues are termed monosaccharides.

Glycosidic bond formation

  • Chemical glycosylation
    Chemical glycosylation
    A chemical glycosylation reaction involves the coupling of a sugar to a glycosyl acceptor forming a glycoside. If the acceptor is another sugar, the product is an oligosaccharide. The reaction involves coupling a glycosyl donor to a glycosyl acceptor via activation utilizing a suitable activator...

  • Fischer glycosidation
    Fischer glycosidation
    Fischer glycosidation refers to the formation of a glycoside by the reaction of an aldose or ketose with an alcohol in the presence of an acid catalyst...

  • Glycosyl halide
  • Koenigs-Knorr reaction
    Koenigs-Knorr reaction
    The Koenigs–Knorr reaction in organic chemistry is the substitution reaction of a glycosyl halide with an alcohol to give a glycoside. It is one of the oldest and simplest glycosylation reactions...


An oligosaccharide (from the Greek oligos, a few, and sacchar, sugar) is a saccharide polymer containing a small number (typically two to ten[1]) of component sugars, also known as simple sugars (monosaccharides). Oligosaccharides can have many functions; for example, they are commonly found on the plasma membrane of animal cells where they can play a role in cell–cell recognition.
In general, they are found either O- or N-linked to compatible amino acid side-chains in proteins or to lipid moieties (see glycans).
Contents [hide]
1 Examples
2 Therapeutic effects
3 Sources
4 See also
5 References

Fructo-oligosaccharides (FOS), which are found in many vegetables, consist of short chains of fructose molecules. (Inulin has a much higher degree of polymerization than FOS and is a polysaccharide.) Galactooligosaccharides (GOS), which also occur naturally, consist of short chains of galactose molecules. These compounds can be only partially digested by humans.
Oligosaccharides are often found as a component of glycoproteins or glycolipids and as such are often used as chemical markers, often for cell recognition. An example is ABO blood type specificity. A and B blood types have two different oligosaccharide glycolipids embedded in the cell membranes of the red blood cells, AB-type blood has both, while O blood type has neither.
Mannan Oligosaccharides (MOS) are widely used animal feed to improve gastrointestinal health, energy levels and performance. They are normally obtained from the yeast cell walls of Saccharomyces cerevisiae. Research at the University of Illinois has demonstrated that Mannan Oligosaccharides differ from other Oligosaccharides in that they are not fermentable and their primary mode of actions include agglutination of type-1 fimbrae pathogens and immunomodulation [2]
[edit]Therapeutic effects

When oligosaccharides are consumed, the undigested portion serves as food for the intestinal microflora. Depending on the type of oligosaccharide, different bacterial groups are stimulated or suppressed.[3][4]
Clinical studies have shown that administering FOS, GOS, or inulin can increase the number of these friendly bacteria in the colon while simultaneously reducing the population of harmful bacteria.[5]

FOS and inulin are found naturally in Jerusalem artichoke, burdock, chicory, leeks, onions, and asparagus. FOS products derived from chicory root contain significant quantities of inulin, a fiber widely distributed in fruits, vegetables and plants. Inulin is a significant part of the daily diet of most of the world’s population. FOS can also be synthesized by enzymes of the fungus Aspergillus niger acting on sucrose. GOS is naturally found in soybeans and can be synthesized from lactose (milk sugar). FOS, GOS, and inulin are available as nutritional supplements in capsules, tablets, and as a powder.
Not all natural oligosaccharides occur as components of glycoproteins or glycolipids. Some, such as the raffinose series, occur as storage or transport carbohydrates in plants. Others, such as maltodextrins or cellodextrins, result from the microbial breakdown of larger polysaccharides such as starch or cellulose.

Reactions of carbohydrates

Carbohydrates are reactants in many organic reaction
Organic reaction
Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions and redox reactions. In organic synthesis,...

s. For example:
  • Cyanohydrin reaction
    Cyanohydrin reaction
    A Cyanohydrin reaction is an organic chemical reaction by an aldehyde or ketone with a cyanide anion or a nitrile to form a cyanohydrin. This nucleophilic addition is a reversible reaction but with aliphatic carbonyl compounds equilibrium is in favor of the reaction products. The cyanide source...

  • Lobry-de Bruyn-van Ekenstein transformation
    Lobry-de Bruyn-van Ekenstein transformation
    In carbohydrate chemistry, the Lobry–de Bruyn–van Ekenstein transformation also known as the Lobry–de Bruyn–van-Alberda–van-Ekenstein transformation is the base or acid catalyzed transformation of an aldose into the ketose isomer or vice versa, with a tautomeric enediol as reaction intermediate....

  • Amadori rearrangement
    Amadori rearrangement
    The amadori rearrangement is an organic reaction describing the acid or base catalyzed isomerization or rearrangement reaction of the N-glycoside of an aldose or the glycosylamine to the corresponding 1-amino-1-deoxy-ketose...

  • Nef reaction
    Nef reaction
    The Nef reaction is an organic reaction describing the acid hydrolysis of a salt of a primary or secondary nitroalkane to an aldehyde or a ketone and nitrous oxide ....

  • Wohl degradation
    Wohl degradation
    The Wohl degradation in carbohydrate chemistry is a chain contraction method for aldoses. The classic example is the conversion of glucose to arabinose as shown below. The reaction is named after the chemist Alfred Wohl....

  • Tipson-Cohen reaction
    Tipson-Cohen reaction
    The Tipson-Cohen reaction was first discovered in Washington D.C. at the National Bureau of Standards by Stuart Tipson and Alex Cohen. The Tipson-Cohen reaction occurs when two neighboring secondary sulfonyloxy groups in a sugar molecule are treated with zinc dust and sodium iodide in a refluxing...

  • Ferrier rearrangement
    Ferrier rearrangement
    The Ferrier rearrangement is an organic reaction that involves a nucleophilic substitution reaction combined with an allylic shift in a glycal . It was discovered by the carbohydrate chemist Robert J...

  • Ferrier II reaction

Functions of Carbohydrates

Carbohydrates have six major functions within the body:
  1. Providing energy and regulation of blood glucose
  2. Sparing the use of proteins for energy
  3. Breakdown of fatty acids and preventing ketosis
  4. Biological recognition processes
  5. Flavor and Sweeteners
  6. Dietary fiber

Providing energy and regulating blood glucose

Glucose is the only sugar used by the body to provide energy for its tissues. Therefore, all digestible polysaccharides, disaccharides, and monosaccharides must eventually be converted into glucose or a metabolite of glucose by various liver enzymes. Because of its significant importance to proper cellular function, blood glucose levels must be kept relatively constant.

Among the enormous metabolic activities the liver performs, it also includes regulating the level of blood glucose. During periods of food consumption, pancreatic beta cells sense the rise in blood glucose and begin to secrete the hormone insulin. Insulin binds to many cells in the body having appropriate receptors for the peptide hormone and causes a general uptake in cellular glucose. In the liver, insulin causes the uptake of glucose as well as the synthesis of glycogen, a glucose storage polymer. In this way, the liver is able to remove excessive levels of blood glucose through the action of insulin.

In contrast, the hormone glucagons is secreted into the bloodstream by pancreatic alpha cells upon sensing falling levels of blood glucose. Upon binding to targeted cells such as skeletal muscle and brain cells, glucagon acts to decrease the amount of glucose in the bloodstream. This hormone inhibits the uptake of glucose by muscle and other cells and promotes the breakdown of glycogen in the liver in order to release glucose into the blood. Glucagon also promotes gluconeogenesis, a process involving the synthesis of glucose from amino acid precursors. Through the effects of both glucagon and insulin, blood glucose can usually be regulated in concentrations between 70 and 115 mg/100 ml of blood.

Other hormones of importance in glucose regulation are epinephrine and cortisol. Both hormones are secreted from the adrenal glands, however, epinephrine mimics the effects of glucagon while cortisol mobilizes glucose during periods of emotional stress or exercise.

Despite the liver's unique ability to maintain homeostatic levels of blood glucose, it only stores enough for a twenty-four hour period of fasting. After twenty four hours, the tissues in the body that preferentially rely on glucose, particularly the brain and skeletal muscle, must seek an alternative energy source. During fasting periods, when the insulin to glucagons ratio is low, adipose tissue begins to release fatty acids into the bloodstream. Fatty acids are long hydrocarbon chains consisting of single carboxylic acid group and are not very soluble in water. Skeletal muscle begins to use fatty acids for energy during resting conditions; however, the brain cannot afford the same luxury. Fatty acids are too long and bulky to cross the blood-brain barrier. Therefore, proteins from various body tissues are broken down into amino acids and used by the liver to produce glucose for the brain and muscle. This process is known as gluconeogenesis or "the production of new glucose." If fasting is prolonged for more than a day, the body enters a state called ketosis. Ketosis comes from the root word ketones and indicates a carbon atom with two side groups bonded to an oxygen atom. Ketones are produced when there is no longer enough oxaloacetate in the mitochondria of cells to condense with acetyl CoA formed from fatty acids. Oxaloacetate is a four-carbon compound that begins the first reaction of the Krebs Cycle, a cycle containing a series of reactions that produces high-energy species to eventually be used to produce energy for the cell. Since oxaloacetate is formed from pyruvate (a metabolite of glucose), a certain level of carbohydrate is required in order to burn fats. Otherwise, fatty acids cannot be completely broken down and ketones will be produced.

Sparing Protein and Preventing Ketosis

So why are carbohydrates important if the body can use other carbon compounds such as fatty acids and ketones as energy? First of all, maintaining a regular intake of carbohydrates will prevent protein from being used as an energy source. Gluconeogenesis will slow down and amino acids will be freed for the biosyntheses of enzymes, antibodies, receptors and other important proteins. Furthermore, an adequate amount of carbohydrates will prevent the degradation of skeletal muscle and other tissues such as the heart, liver, and kidneys. Most importantly, ketosis will be prevented. Although the brain will adapt to using ketones as a fuel, it preferentially uses carbohydrates and requires a minimum level of glucose circulating in the blood in order to function properly. Before the adaptation process occurs, lower blood glucose levels may cause headaches in some individuals. To prevent these ketotic symptoms, it is recommended that the average person consume at least 50 to 100g of carbohydrates per day.

Although the processes of protein degradation and ketosis can create problems of their own during prolonged fasting, they are adaptive mechanisms during glucose shortages. In summary, the first priority of metabolism during a prolonged fast is to provide enough glucose for the brain and other organs that dependent upon it for energy in order to spare proteins for other cellular functions. The next priority of the body is to shift the use of fuel from glucose to fatty acids and ketone bodies. From then on, ketones become more and more important as a source of fuel while fatty acids and glucose become less important.

Flavor and Sweeteners

A less important function of carbohydrates is to provide sweetness to foods. Receptors located at the tip of the tongue bind to tiny bits of carbohydrates and send what humans perceive as a "sweet" signal to the brain. However, different sugars vary in sweetness. For example, fructose is almost twice as sweet as sucrose and sucrose is approximately 30% sweeter than glucose.

Sweeteners can be classified as either nutritive or alternative. Nutritive sweeteners have all been mentioned before and include sucrose, glucose, fructose, high fructose corn syrup, and lactose. These types of sweeteners not only impart flavor to the food, but can also be metabolized for energy. In contrast, alternative sweeteners provide no food energy and include saccharin, cyclamate, aspartame, and acesulfame. Controversy over saccharin and cyclamate as artificial sweeteners still exists but aspartame and acesulfame are used extensively in many foods in the United States. Aspartame and acesulfame are both hundreds of times sweeter than sucrose but only acesulfame is able to be used in baked goods since it is much more stable than aspartame when heated.

Dietary Fiber

Dietary fibers such as cellulose, hemicellulose, pectin, gum and mucilage are important carbohydrates for several reasons. Soluble dietary fibers like pectin, gum and mucilage pass undigested through the small intestine and are degraded into fatty acids and gases by the large intestine. The fatty acids produced in this way can either be used as a fuel for the large intestine or be absorbed into the bloodstream. Therefore, dietary fiber is essential for proper intestinal health.

In general, the consumption of soluble and insoluble fiber makes the elimination of waste much easier. Since dietary fiber is both indigestible and an attractant of water, stools become large and soft. As a result, feces can be expelled with less pressure. However, not enough fiber consumption will change the constitution of the stool and increase the amount of force required during defecation. Excessive pressure during the elimination of waste can force places in the large intestine wall out from between bands of smooth muscle to produce small pouches called diverticula. Hemorrhoids may also result from unnecessary strain during defecation.

The disease of having many diverticula in the large intestine is known as diverticulosis. Although diverticula is often asymptomatic, food particles become trapped in their folds and bacteria begin to metabolize the particles into acids and gases. Eventually, the diverticula may become inflamed, a condition known as diverticulitis. To combat the disease, antibiotics are administered to the patient to destroy the bacteria while the intake of fiber in the diet is decreased until the inflammation has subsided. Once the inflammation has been reduced, a high fiber diet is begun to prevent a relapse.

Besides the prevention of intestinal disease, diets high in fiber have other health benefits. High fiber intake reduces the risk of developing obesity by increasing the bulk of a meal without yielding much energy. An expanded stomach leads to satisfaction despite the fact that the caloric intake has decreased.

Beyond dieters, diabetics can also benefit from consuming a regular amount of dietary fiber. Once in the intestine, it slows the absorption of glucose to prevent a sudden increase in blood glucose levels. A relatively high intake of fiber will also decrease the absorption of cholesterol, a compound that is thought to contribute to atherosclerosis or scarring of the arteries. Serum cholesterol may be further reduced by a reduction in the release of insulin after meals. Since insulin is known to promote cholesterol synthesis in the liver, a reduction in the absorption of glucose after meals through the consumption of fiber can help to control serum cholesterol levels. Furthermore, dietary fiber intake may help prevent colon cancer by diluting potential carcinogens through increased water retention, binding carcinogens to the fiber itself and speeding the passage of food through the intestinal tract so that cancer-causing agents have less time to act.

Biological Recognition Processes

Carbohydrates not only serve nutritional functions, but are also thought to play important roles in cellular recognition processes. For example, many immunoglobulins (antibodies) and peptide hormones contain glycoprotein sequences. These sequences are composed of amino acids linked to carbohydrates. During the course of many hours or days, the carbohydrate polymer linked to the rest of the protein may be cleaved by circulating enzymes or be degraded spontaneously. The liver can recognize differences in length and may internalize the protein in order to begin its own degradation. In this way, carbohydrates may mark the passage of time for proteins.

Carbohydrate Structure

  • Carbohydrate
    A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...

  • Carbohydrate Conformation
    Carbohydrate conformation
    Carbohydrate 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....

  • Monosaccharide
    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...

  • Disaccharide
    A disaccharide or biose is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only. Like monosaccharides, disaccharides form an aqueous solution when dissolved in water...

  • Oligosaccharide
    An oligosaccharide is a saccharide polymer containing a small number of component sugars, also known as simple sugars...

  • 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,...

  • Anomeric effect
    Anomeric effect
    In organic chemistry, the anomeric effect or Edward-Lemieux effect is a stereoelectronic effect that describes the tendency of heteroatomic substituents adjacent to a heteroatom within a cyclohexane ring to prefer the axial orientation instead of the less hindered equatorial orientation that would...

  • Glycosidic bond
    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....

Carbohydrate function & Biology

  • Glycosylation
    Glycosylation is the reaction in which a carbohydrate, i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule . In biology glycosylation refers to the enzymatic process that attaches glycans to proteins, lipids, or other organic molecules...

  • Glycobiology
    Defined in the broadest sense, glycobiology is the study of the structure, biosynthesis, and biology of saccharides that are widely distributed in nature...

  • Glycomics
    Glycomics is the comprehensive study of glycomes , including genetic, physiologic, pathologic, and other aspects. Glycomics "is the systematic study of all glycan structures of a given cell type or organism" and is a subset of glycobiology...

  • Organic synthesis
    Organic synthesis
    Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

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