Monosaccharides, also called simple sugars, are the simplest forms of sugar and the most basic units (monomers) from which all carbohydrates are built.
A glycosidic bond or glycosidic linkage is a type of ether bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.
In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. These can be activated by enzyme hydrolysis, which causes the sugar part to be broken off, making the chemical available for use. Many such plant glycosides are used as medications. Several species of Heliconius butterfly are capable of incorporating these plant compounds as a form of chemical defense against predators. In animals and humans, poisons are often bound to sugar molecules as part of their elimination from the body.
In stereochemistry, an epimer is one of a pair of diastereomers. The two epimers have opposite configuration at only one stereogenic center out of at least two. All other stereogenic centers in the molecules are the same in each. Epimerization is the interconversion of one epimer to the other epimer.
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.
Glycal is a name for cyclic enol ether derivatives of sugars having a double bond between carbon atoms 1 and 2 of the ring. The term "glycal" should not be used for an unsaturated sugar that has a double bond in any position other than between carbon atoms 1 and 2.
An Endoglycosidase is an enzyme that releases oligosaccharides from glycoproteins or glycolipids. It may also cleave polysaccharide chains between residues that are not the terminal residue, although releasing oligosaccharides from conjugated protein and lipid molecules is more common.
The terms glycans and polysaccharides are defined by IUPAC as synonyms meaning "compounds consisting of a large number of monosaccharides linked glycosidically". However, in practice the term glycan may also be used to refer to the carbohydrate portion of a glycoconjugate, such as a glycoprotein, glycolipid, or a proteoglycan, even if the carbohydrate is only an oligosaccharide. Glycans usually consist solely of O-glycosidic linkages of monosaccharides. For example, cellulose is a glycan composed of β-1,4-linked D-glucose, and chitin is a glycan composed of β-1,4-linked N-acetyl-D-glucosamine. Glycans can be homo- or heteropolymers of monosaccharide residues, and can be linear or branched.
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 be expected from steric considerations. This effect was originally observed in pyranose rings by J. T. Edward in 1955 when studying carbohydrate chemistry.
The term glycosynthase refers to a class of proteins that have been engineered to catalyze the formation of a glycosidic bond. Glycosynthase are derived from glycosidase enzymes, which catalyze the hydrolysis of glycosidic bonds. They were traditionally formed from retaining glycosidase by mutating the active site nucleophilic amino acid to a small non-nucleophilic amino acid. More modern approaches use directed evolution to screen for amino acid substitutions that enhance glycosynthase activity.
Tunicamycin is a mixture of homologous nucleoside antibiotics that inhibits the UDP-HexNAc: polyprenol-P HexNAc-1-P family of enzymes. In eukaryotes, this includes the enzyme GlcNAc phosphotransferase (GPT), which catalyzes the transfer of N-acetylglucosamine-1-phosphate from UDP-N-acetylglucosamine to dolichol phosphate in the first step of glycoprotein synthesis. Tunicamycin blocks N-linked glycosylation (N-glycans) and treatment of cultured human cells with tunicamycin causes cell cycle arrest in G1 phase. It is used as an experimental tool in biology, e.g. to induce unfolded protein response. Tunicamycin is produced by several bacteria, including Streptomyces clavuligerus and Streptomyces lysosuperificus.
In enzymology, an UDP-N-acetylglucosamine 4-epimerase is an enzyme that catalyzes the chemical reaction
Dispersin B is a 40 kDa glycoside hydrolase produced by the periodontal pathogen, Aggregatibacter actinomycetemcomitans. The bacteria secrete Dispersin B to release adherent cells from a mature biofilm colony by disrupting biofilm formation. The enzyme catalyzes the hydrolysis of linear polymers of N-acetyl-D-glucosamines found in the biofilm matrices. Poly-acetyl glucosamines are integral to the structural integrity of the biofilms of various Gram-positive bacteria and Gram-negative bacteria and are referred to as PIA (PNAG,PS/A) in Staphylococcus species and PGA in Escherichia coli. By degrading the biofilm matrix, Dispersin B allows for the release of bacterial cells that can adhere to new surfaces close by and extend the biofilm or start new colonies. Currently there is interest in Dispersin B as a commercial anti-biofilm agent that could be combined with antibiotics for the treatment of bacterial infections.
A chemical glycosylation reaction involves the coupling of a glycosyl donor, to a glycosyl acceptor forming a glycoside. If both the donor and acceptor are sugars, then the product is an oligosaccharide. The reaction requires activation with a suitable activating reagent. The reactions often result in a mixture of products due to the creation of a new stereogenic centre at the anomeric position of the glycosyl donor. The formation of a glycosidic linkage allows for the synthesis of complex polysaccharides which may play important roles in biological processes and pathogenesis and therefore having synthetic analogs of these molecules allows for further studies with respect to their biological importance.
Intramolecular aglycon delivery is a synthetic strategy for the construction of glycans. This approach is generally used for the formation of difficult glycosidic linkages.
The Tipson–Cohen reaction is a name reaction first discovered by Stuart Tipson and Alex Cohen at the National Bureau of Standards in Washington D.C. The Tipson–Cohen reaction occurs when two neighboring secondary sulfonyloxy groups in a sugar molecule are treated with zinc dust (Zn) and sodium iodide (NaI) in a refluxing solvent such as N,N-dimethylformamide (DMF) to give an unsaturated carbohydrate.
The Crich β-mannosylation in organic chemistry is a synthetic strategy which is used in carbohydrate synthesis to generate a 1,2-cis-glycosidic bond. This type of linkate is generally very difficult to make, and specific methods like the Crich β-mannosylation are used to overcome these issues.
A glycosyl donor is a carbohydrate mono- or oligosaccharide that will react with a suitable glycosyl acceptor to form a new glycosidic bond. By convention, the donor is the member of this pair that contains the resulting anomeric carbon of the new glycosidic bond. The resulting reaction is referred to as a glycosylation or chemical glycosylation.
Carbohydrate synthesis is a sub-field of organic chemistry concerned specifically with the generation of natural and unnatural carbohydrate structures. This can include the synthesis of monosaccharide residues or structures containing more than one monosaccharide, known as oligosaccharides.
Trichloroacetonitrile is an organic compound with the formula CCl3CN. It is a colourless liquid, although commercial samples often are brownish. It is used commercially as a precursor to the fungicide etridiazole. It is prepared by dehydration of trichloroacetamide. As a bifunctional compound, trichloroacetonitrile can react at both the trichloromethyl and the nitrile group. The electron-withdrawing effect of the trichloromethyl group activates the nitrile group for nucleophilic additions. The high reactivity makes trichloroacetonitrile a versatile reagent, but also causes its susceptibility towards hydrolysis.
