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Carbohydrate Synthesis
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. Background Generally speaking, carbohydrates can be classified into two groups, simple sugars, and complex carbohydrates. Simple sugars, also called monosaccharides, are carbohydrates that can not be converted into smaller sugars by hydrolysis. When two or more monosaccharide units are connected via a glycoside linkage, complex carbohydrates are formed. Complex carbohydrates, according to the different number of monosaccharide units, can be classed into three groups, disaccharides, oligosaccharides, and polysaccharides. A disaccharide is formed from two monosaccharides. Oligosaccharides can be formed by a small number of monosaccharides linked together. Higher oligosaccharides are called pol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry''. Oxford University Press. pp. 1–15. . Study of structure determines their structural formula. Study of properties includes physical and chemical properties, and evaluation of chemical reactivity to understand their behavior. The study of organic reactions includes the chemical synthesis of natural products, drugs, and polymers, and study of individual organic molecules in the laboratory and via theoretical ( in silico) study. The range of chemicals studied in organic chemistry includes hydrocarbons (compounds containing only carbon and hydrogen) as well as compounds based on carbon, but also containing other elements, especially oxygen, nitrogen, sulfur, phosphorus (included in ... [...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] |
Intramolecular Aglycon Delivery
Intramolecular aglycon delivery is a synthetic strategy for the construction of glycans. This approach is generally used for the formation of difficult glycosidic linkages. Introduction Glycosylation reactions are very important reactions in carbohydrate chemistry, leading to the synthesis of oligosaccharides, preferably in a stereoselective manner. The stereoselectivity of these reactions has been shown to be affected by both the nature and the configuration of the protecting group at C-2 on the glycosyl donor ring. While 1,2-''trans''-glycosides (e.g. α-mannosides and β-glucosides) can be synthesised easily in the presence of a participating group (such as OAc, or NHAc) at the C-2 position in the glycosyl donor ring, 1,2-''cis''-glycosides are more difficult to prepare. 1,2-''cis''-glycosides with the α configuration (e.g. glucosides or galactosides) can often be prepared using a non-participating protecting group (such as Bn, or All) on the C-2 hydroxy group. However, 1,2-''ci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halide
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluoride, chloride, bromide, iodide, astatide, or theoretically tennesside compound. The alkali metals combine directly with halogens under appropriate conditions forming halides of the general formula, MX (X = F, Cl, Br or I). Many salts are halides; the ''hal-'' syllable in ''halide'' and ''halite'' reflects this correlation. All Group 1 metals form halides that are white solids at room temperature. A halide ion is a halogen atom bearing a negative charge. The halide anions are fluoride (), chloride (), bromide (), iodide () and astatide (). Such ions are present in all ionic halide salts. Halide minerals contain halides. All these halides are colourless, high melting crystalline solids having high negative enthalpies of formation. Test ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orthoester
In organic chemistry, an ortho ester is a functional group containing three alkoxy groups attached to one carbon atom, i.e. with the general formula . Orthoesters may be considered as products of exhaustive alkylation of unstable orthocarboxylic acids and it is from these that the name 'ortho ester' is derived. An example is ethyl orthoacetate, , more correctly known as 1,1,1-triethoxyethane. Synthesis Ortho esters can be prepared by the Pinner reaction, in which nitriles react with alcohols in the presence of one equivalent of hydrogen chloride. The reaction proceeds by formation of imido ester hydrochloride: :RCN + R′OH + HCl → C(OR′)=NH2sup>+Cl− Upon standing in the presence of excess alcohol, this intermediate converts to the ortho ester: : C(OR′)=NH2sup>+Cl− + 2R′OH → RC(OR′)3 + NH4Cl The reaction requires anhydrous conditions. Although a less common method, ortho esters were first produced by reaction of 1,1,1-trichloroalkanes with sodium alkoxide ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glycosidic Linkage
A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate. A glycosidic bond is formed between the hemiacetal or hemiketal group of a saccharide (or a molecule derived from a saccharide) and the hydroxyl group of some compound such as an alcohol. A substance containing a glycosidic bond is a glycoside. The term 'glycoside' is now extended to also cover compounds with bonds formed between hemiacetal (or hemiketal) groups of sugars and several chemical groups other than hydroxyls, such as -SR (thioglycosides), -SeR (selenoglycosides), -NR1R2 (N-glycosides), or even -CR1R2R3 (C-glycosides). Particularly in naturally occurring glycosides, the compound ROH from which the carbohydrate residue has been removed is often termed the aglycone, and the carbohydrate residue itself is sometimes referred to as the 'glycone'. S-, N-, C-, and O-glycosidic bonds Glycosid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anti-periplanar
In organic chemistry, anti-periplanar, or antiperiplanar, describes the bond angle in a molecule. In this Conformational isomerism, conformer, the dihedral angle of the bond and the bond is greater than +150° or less than −150° (Figures 1 and c:File:Synantipericlinal.svg, 2). Anti-periplanar is often used in textbooks to mean strictly anti-coplanar, with an dihedral angle of 180° (Figure 3). In a Newman projection, the molecule will be in a staggered arrangement with the anti-periplanar functional groups pointing up and down, 180° away from each other (see Figure 4). Figure 5 shows 2-chloro-2,3-dimethylbutane in a sawhorse projection with chlorine and a hydrogen anti-periplanar to each other. Syn-periplanar or synperiplanar is similar to anti-periplanar. In the syn-periplanar conformer, the A and D are on the same side of the plane of the bond, with the dihedral angle of and between +30° and −30° (see Figure 2). Molecular orbitals An important factor in the an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hyperconjugation
In organic chemistry, hyperconjugation (σ-conjugation or no-bond resonance) refers to the delocalization of electrons with the participation of bonds of primarily σ-character. Usually, hyperconjugation involves the interaction of the electrons in a sigma (σ) orbital (e.g. C–H or C–C) with an adjacent unpopulated non-bonding p or antibonding σ* or π* orbitals to give a pair of extended molecular orbitals. However, sometimes, low-lying antibonding σ* orbitals may also interact with filled orbitals of lone pair character (n) in what is termed ''negative hyperconjugation''. Increased electron delocalization associated with hyperconjugation increases the stability of the system. In particular, the new orbital with bonding character is stabilized, resulting in an overall stabilization of the molecule. Only electrons in bonds that are in the β position can have this sort of direct stabilizing effect — donating from a sigma bond on an atom to an orbital in another ato ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stereoselectivity
In chemistry, stereoselectivity is the property of a chemical reaction in which a single reactant forms an unequal mixture of stereoisomers during a non- stereospecific creation of a new stereocenter or during a non-stereospecific transformation of a pre-existing one. The selectivity arises from differences in steric and electronic effects in the mechanistic pathways leading to the different products. Stereoselectivity can vary in degree but it can never be total since the activation energy difference between the two pathways is finite. Both products are at least possible and merely differ in amount. However, in favorable cases, the minor stereoisomer may not be detectable by the analytic methods used. An enantioselective reaction is one in which one enantiomer is formed in preference to the other, in a reaction that creates an optically active product from an achiral starting material, using either a chiral catalyst, an enzyme or a chiral reagent. The degree of selectivity is meas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scheme2(Lu)
A scheme is a systematic plan for the implementation of a certain idea. Scheme or schemer may refer to: Arts and entertainment * ''The Scheme'' (TV series), a BBC Scotland documentary series * The Scheme (band), an English pop band * ''The Scheme'', an action role-playing video game for the PC-8801, made by Quest Corporation * Schemer (comics), Richard Fisk, a Marvel Comics villain turned antihero * Horace Schemer, a fictional character in the TV series ''Shining Time Station'' * Schemee, a fictional child character and Schemer's nephew in the TV Series ''Shining Time Station'' * ''Schemers'' (film), a Scottish film Other uses * Classification scheme, eg a thesaurus, a taxonomy, a data model, or an ontology * Scheme (programming language), a minimalist dialect of Lisp * Scheme (mathematics), a concept in algebraic geometry * Scheme (linguistics), a figure of speech that changes a sentence's structure * Scam, an attempt to swindle or cheat people through deception **Get-rich-quic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
