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Chemical Glycosylation
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. Terminology The glycosylation reaction involves the coupling of a glycosyl donor and a glycosyl acceptor via initiation using an activator under suitable reaction conditions. * A glycosyl donor is a sugar with a suitable leaving group at the anomeric position. This group, u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glycosyl Donor
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.T. K. Lindhorst "Essentials of Carbohydrate Chemistry and Biochemistry" 2007 Wiley-VCH Verlag, Weinheim The resulting reaction is referred to as a glycosylation or chemical glycosylation. In a glycosyl donor, a leaving group is required at the anomeric position. The simplest leaving group is the OH group that is naturally present in monosaccharides, but it requires activation by acid catalysis in order to function as leaving group (in the Fischer glycosylation). More effective leaving groups are in general used in the glycosyl donors employed in chemical synthesis of glycosides. Typical leaving groups are halides, thioalkyl groups, or imidates, but acetate, phosphate, and O-pentenyl groups are also employed. Natural glycosyl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 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 ''anomeric effect'' was introduced in 1958. The name comes from the term used to designate the lowest-numbered ring carbon of a pyranose, the ''anomeric'' carbon. Isomers that differ only in the configuration at the anomeric carbon are called '' anomers''. The anomers of D-glucopyranose are diastereomers, with the ''beta'' anomer having an OH group pointing up equatorially, and the ''alpha'' anomer having that OH group pointing down axially. The anomeric effect can also be generalized to any cyclohexyl or linear syst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thioglycosides
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 formal terms, a glycoside is any molecule in which a sugar group is bonded through its anomeric carbon to another group via a glycosidic bond. Glycosides can be linked by an O- (an ''O-glycoside''), N- (a ''glycosylamine''), S-(a ''thioglycoside''), or C- (a '' C-glycoside'') glycosidic bond. According to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anomerization
In carbohydrate chemistry, a pair of anomers () is a pair of near-identical stereoisomers that differ at only the anomeric carbon, the carbon that bears the aldehyde or ketone functional group in the sugar's open-chain form. However, in order for anomers to exist, the sugar must be in its cyclic form, since in open-chain form, the anomeric carbon is planar and thus achiral. More formally stated, then, an anomer is an epimer at the hemiacetal/hemiketal carbon in a cyclic saccharide. Anomerization is the process of conversion of one anomer to the other. As is typical for stereoisomeric compounds, different anomers have different physical properties, melting points and specific rotations. Nomenclature Two anomers are designated alpha (α) or beta (β), according to the configurational relationship between the ''anomeric centre'' and the ''anomeric reference atom'', hence they are relative stereodescriptors. The anomeric centre in hemiacetals is the anomeric carbon C-1; in hemi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stereochemistry
Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereoisomers, which by definition have the same molecular formula and sequence of bonded atoms (constitution), but differ in structural formula (the three-dimensional orientations of their atoms in space). For this reason, it is also known as 3D chemistry—the prefix "stereo-" means "three-dimensionality". Stereochemistry spans the entire spectrum of organic, inorganic, biological, physical and especially supramolecular chemistry. Stereochemistry includes methods for determining and describing these relationships; the effect on the physical or biological properties these relationships impart upon the molecules in question, and the manner in which these relationships influence the reactivity of the molecules in question ( dynamic stereochemis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Berichte Der Deutschen Chemischen Gesellschaft
''Chemische Berichte'' (usually abbreviated as ''Ber.'' or ''Chem. Ber.'') was a German-language scientific journal of all disciplines of chemistry founded in 1868. It was one of the oldest scientific journals in chemistry, until it merged with ''Recueil des Travaux Chimiques des Pays-Bas'' to form ''Chemische Berichte/Recueil'' in 1997. ''Chemische Berichte/Recueil'' was then merged with other European journals in 1998 to form ''European Journal of Inorganic Chemistry''. History Founded in 1868 as ''Berichte der Deutschen Chemischen Gesellschaft'' (, CODEN BDCGAS), it operated under this title until 1928 (Vol. 61). The journal was then split into: * ''Berichte der Deutschen Chemischen Gesellschaft, A: Vereins-Nachrichten'' (, CODEN BDCAAS), and * ''Berichte der Deutschen Chemischen Gesellschaft, B: Abhandlungen'' (, CODEN BDCBAD). Vol. 78 and 79 (1945–1946) were omitted and not published due to World War II. The journal was renamed ''Chemische Berichte'' (, CODEN CHBEAM) in 19 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polar Effect
The polar effect or electronic effect in chemistry is the effect exerted by a substituent on modifying electrostatic forces operating on a nearby reaction center. The main contributors to the polar effect are the inductive effect, mesomeric effect and the through-space electronic field effect. An electron-withdrawing group (EWG) draws electrons away from a reaction center. When this center is an electron rich carbanion or an alkoxide anion, the presence of the electron-withdrawing substituent has a stabilizing effect. Examples of electron withdrawing groups are * halogens (F, Cl); * nitriles CN; * carbonyls RCOR'; * nitro groups NO2. An electron-releasing group (ERG) or electron-donating group (EDG) releases electrons into a reaction center and as such stabilizes electron deficient carbocations. Examples of electron releasing groups are * alkyl groups; * alcohol groups; * amino groups. The total substituent effect is the combination of the polar effect and the combined ste ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
