In chemistry, a racemic mixture or racemate is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as racemates.
In chemistry, an enantiomer, also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities which are mirror images of each other and non-superposable.
Lapsang souchong or Zhengshan xiaozhong is a black tea consisting of Camellia sinensis leaves that is smoke-dried over a pinewood fire. This smoking is accomplished either as a cold smoke of the raw leaves as they are processed or as a hot smoke of previously processed leaves. The intensity of the smoke aroma can be varied by locating the leaves closer or farther from the source of heat and smoke or by adjusting the duration of the process. The flavour and aroma of smoked lapsang souchong is described as containing empyreumatic notes, including wood smoke, pine resin, smoked paprika, and dried longan; it may be mixed with milk but is not bitter and usually not sweetened with sugar. The tea originates from the Wuyi Mountains region of Fujian and is considered a Wuyi tea. It is also produced in Taiwan. It has been labelled as smoked tea, smoky souchong, tarry lapsang souchong and lapsang souchong crocodile. While the tea leaf grading system adopted the term souchong to refer to a particular leaf position, lapsang souchong may be made with any leaf of the Camellia sinensis plant, though it is not unusual for the lower leaves, which are larger and less flavourful, to be used as the smoking compensates for the lower flavour profile and the higher leaves are more valuable for use in unflavoured or unblended teas. In addition to its consumption as a tea, lapsang souchong is also used in stock for soups, stews and sauces or otherwise as a spice or seasoning. Beginning in the early 21st century, an unsmoked variety of lapsang souchong was developed in the village of Tong Mu Guan in the Wuyi mountains. The unsmoked variety has become increasingly popular, particularly in the Chinese domestic market.
In chemistry, a molecule or ion is called chiral if it cannot be superposed on its mirror image by any combination of rotations, translations, and some conformational changes. This geometric property is called chirality. The terms are derived from Ancient Greek χείρ (cheir) 'hand'; which is the canonical example of an object with this property.
Enantioselective synthesis, also called asymmetric synthesis, is a form of chemical synthesis. It is defined by IUPAC as "a chemical reaction in which one or more new elements of chirality are formed in a substrate molecule and which produces the stereoisomeric products in unequal amounts."
The Robinson annulation is a chemical reaction used in organic chemistry for ring formation. It was discovered by Robert Robinson in 1935 as a method to create a six membered ring by forming three new carbon–carbon bonds. The method uses a ketone and a methyl vinyl ketone to form an α,β-unsaturated ketone in a cyclohexane ring by a Michael addition followed by an aldol condensation. This procedure is one of the key methods to form fused ring systems.
In stereochemistry, enantiomeric excess (ee) is a measurement of purity used for chiral substances. It reflects the degree to which a sample contains one enantiomer in greater amounts than the other. A racemic mixture has an ee of 0%, while a single completely pure enantiomer has an ee of 100%. A sample with 70% of one enantiomer and 30% of the other has an ee of 40%.
Tröger's base is a white solid tetracyclic organic compound. Its chemical formula is (CH
3C
6H
3NCH
2)
2CH
2. Tröger's base and its analogs are soluble in various organic solvents and strong acidic aqueous solutions due to their protonation. It is named after Julius Tröger, who first synthesized it in 1887.
Atropisomers are stereoisomers arising because of hindered rotation about a single bond, where energy differences due to steric strain or other contributors create a barrier to rotation that is high enough to allow for isolation of individual rotamers. They occur naturally and are of occasional importance in pharmaceutical design. When the substituents are achiral, these conformers are enantiomers (atropoenantiomers), showing axial chirality; otherwise they are diastereomers (atropodiastereomers).
Geranyl pyrophosphate (GPP), also known as geranyl diphosphate (GDP), is the pyrophosphate ester of the terpenoid geraniol. Its salts are colorless. It is a precursor to many thousands of natural products.
Farnesyl pyrophosphate (FPP), also known as farnesyl diphosphate (FDP), is the precursor to all sesquiterpenes, which comprises thousand of compounds. These include all sesquiterpenes as well as sterols and carotenoids. It is also used in the synthesis of CoQ, as well as dehydrodolichol diphosphate.
The article concerns the total synthesis of galanthamine, a drug used for the treatment of mild to moderate Alzheimer's disease.
Sesquiterpenes are a class of terpenes that consist of three isoprene units and often have the molecular formula C15H24. Like monoterpenes, sesquiterpenes may be cyclic or contain rings, including many combinations. Biochemical modifications such as oxidation or rearrangement produce the related sesquiterpenoids. It is estimated (2006) that 3000 sesquiterpenes have been identified.
Terpineol is any of four isomeric monoterpenoids. Terpenoids are terpene that are modified by the addition of a functional group, in this case, an alcohol. Terpineols have been isolated from a variety of sources such as cardamom, cajuput oil, pine oil, and petitgrain oil. Four isomers exist: α-terpineol, β-terpineol, γ-terpineol, and terpinen-4-ol. β-Terpineol and γ-terpineol differ only by the location of the double bond. Terpineol is usually a mixture of these isomers with α-terpineol as the major constituent.
The Hajos–Parrish–Eder–Sauer–Wiechert and Barbas-List reactions in organic chemistry are a family of proline-catalysed asymmetric aldol reactions.
Chiral Lewis acids (CLAs) are a type of Lewis acid catalyst. These acids affect the chirality of the substrate as they react with it. In such reactions, synthesis favors the formation of a specific enantiomer or diastereomer. The method is an enantioselective asymmetric synthesis reaction. Since they affect chirality, they produce optically active products from optically inactive or mixed starting materials. This type of preferential formation of one enantiomer or diastereomer over the other is formally known as asymmetric induction. In this kind of Lewis acid, the electron-accepting atom is typically a metal, such as indium, zinc, lithium, aluminium, titanium, or boron. The chiral-altering ligands employed for synthesizing these acids often have multiple Lewis basic sites that allow the formation of a ring structure involving the metal atom.
Merrilactone A is one of the four sesquiterpenes that were newly discovered from the fruit of Illicium merrillianum in 2000. Members of the genus Illicium include Chinese star anise, widely used as a spice for flavouring food and beverages, and also poisonous plants such as Japanese star anise. Chemical studies of Illicium have developed rapidly over the last 20 years, and merrilactone A has been shown to have neurotrophic activity in fetal rat cortical neuron cultures. This has led researchers to believe that Merrilactone A may hold therapeutic potential in the treatment of neuro-degenerative diseases such as Alzheimer's disease and Parkinson's disease.
Indacrinone is a loop diuretic. It can be used in patients of gout with hypertension as an antihypertensive because it decreases reabsorption of uric acid, while other diuretics increase it.
Bromochlorofluoromethane or fluorochlorobromomethane, is a chemical compound and trihalomethane derivative with the chemical formula CHBrClF. As one of the simplest possible stable chiral compounds, it is useful for fundamental research into this area of chemistry. However, its relative instability to hydrolysis, and lack of suitable functional groups, made separation of the enantiomers of bromochlorofluoromethane especially challenging, and this was not accomplished until almost a century after it was first synthesised, in March 2005, though it has now been done by a variety of methods. More recent research using bromochlorofluoromethane has focused on its potential use for experimental measurement of parity violation, a major unsolved problem in quantum physics. For example, the S enantiomer is predicted to be lower in energy by about 2.356×10−16 eV (56.97 mHz), and the frequency of the C−F vibrational mode should be about 2.4 mHz lower for the R-enantiomer.
Ugi’s amine is an organometallic compound with the formula (C5H5)Fe(C5H4CH N 2. It is named for the chemist who first reported its synthesis in 1970, Ivar Ugi. It is a ferrocene derivative. Ugi’s amine is a precursor to ligands, most notably, the Josiphos ligands, which have been used in asymmetric catalysis
