In stereochemistryStereoisomerismThe diastereomers in which only one chiral center has a different configuration and the rest have the same configuration are called epimers.
In organic matter, the difference between epimers is usually located on a single asymmetric carbon atom. Generally, this carbon will be marked, such asD-glucoseC2 isomer ofD-mannose。If not indicated, it is usually assumed to be C2, for example, D-mannose is the epimer of D-glucose.
Epimer refers to a pair of molecules with two or more tetrahedral chiral centers and only one asymmetric atom with different configurationsDiastereomer。The related isomerism phenomenon is called epimerism.If the chiral atoms with different configurations are at the end of the chain, these two isomers are also called“Terminal epimer”。In other cases, you can use“CnThe "epimer" indicates that n is the position number of the asymmetric atom, and C can also be the atom of other tetrahedral configurations.[1]
give an example
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α - D-glucopyranose and β - D-glucopyranose
β - D-glucopyranose and β - D-mannopyranose
The isomers of glucose are mannose (C2), alose (C3) and galactose (C4).[2]
Epimerism
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Having two chiral carbon atomsL-isoleucine, only on the α - carbon atom, the configuration changes, and some of them are converted intoDiastereomerD-Don'tisoleucineProcess.
It contains multiple chiral carbon atoms, one of which has the opposite configuration and the other has the same configuration, so the two isomers are mutually symmetricEpimer。The composition and structural formula of the two epimers are the same. They are not structural isomers, butStereoisomerismConfiguration isomers in.Only one chiral carbon atom between the molecules of epimers has the opposite configuration, so they are not enantiomeric, but are non enantiomers.Two optically active isomers containing only one chiral carbon atom, such as D-glyceraldehyde and L-glyceraldehyde, are not called epiisomers each other, although the chiral carbon atoms have opposite configurations. They are enantiomers each other.Under certain conditions, the change process from one kind of epimer to another is calledEpimerization。When epimerization occurs, the optical rotation will change, and even the optical rotation direction may change.The transition between two optically active isomers containing only one chiral carbon atom is not called epimerization, but racemization, or racemization.[3]
Pharmacokinetics of glycyrrhizic acid epimer in rats
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Glycyrrhizic acid is the main active ingredient in licorice, which has definite therapeutic effects, including anti-inflammatory, antiviral and antioxidant activities. It is a kind of treatment in clinicchronic hepatitisEffective drugs.Recently, it was reported that glycyrrhizic acid can inhibit the replication of SA RS associated virus.Therefore, the research and development of glycyrrhizic acid are increasingly valued at home and abroad.Glycyrrhizic acid has two epimers, α - glycyrrhizic acid and β - glycyrrhizic acid. In addition to their physical and chemical properties, there are also considerable differences in pharmacological effects, adverse reactions and clinical efficacy.Glycyrrhizic acid is metabolized by glucuronidase produced by liver and intestinal bacteria in vivo asGlycyrrhetinic acid(glycyrrhetic acid), especially intestinal metabolism, so after oral administration, only the concentration of glycyrrhetic acid can be detected in the blood.
By comparing the pharmacokinetic data of glycyrrhetinic acid epimers, it was shown that the main pharmacokinetic parameters A UC0-36 and Cmax of glycyrrhetinic acid in rats after intragastric administration of two epimers of glycyrrhetinic acid were significantly different. The AUC0-36 of α - glycyrrhizic acid group was transformed into glycyrrhetinic acid, and Cmax was greater than that of β - glycyrrhizic acid group,Because α - glycyrrhizic acid is more lipophilic than β - glycyrrhizic acid, it can be converted into glycyrrhetinic acid faster in vivo, which indicates that the pharmacokinetic characteristics of the two epimers of glycyrrhizic acid are different, which is related to the differences in pharmacological effects, adverse reactions and clinical efficacy, consistent with the literature and clinical reports, and can provide a basis for clinical rational drug use.[3]
Knowledge expansion
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In 1808, Marus discoveredpolarized light。Later, French physicist Biot, French crystallographer Wu Yu, chemists and others have discovered that many inorganic crystals and some organic substances havePlane polarized lightThe ability of the vibration plane to rotate.But they failed to explore thisOptical rotationThe reason for the difference.
Louis Pasteur (1822-1895) was Biot's assistant in 1848,Paris Normal UniversityOf young teachers have just graduated from Besanson Royal College (with a doctorate in science).In order to enable him to have some experience in crystallography research, his tutor asked him to make a research report on tartaric acid andRacemic tartaric acidThe crystal form of the working mirror was investigated again.In his work, Buss affirmed Prouostag's observation, and noted that the crystal of externally consumed ammonium sodium tartrate is composed of two crystals with different planar properties. Their crystal form relationship is like the relationship between left and right hands. When these two kinds of equal weight crystals are mixed together, their mixed solution does not showoptical rotation。
Because of thisOptical rotationPasteur infers that this is not a crystal property but a molecular property.He proposed that the molecules constituting the crystal are mirror images of each other, just like the two crystals themselves.He proposed that there areIsomerThat is, the difference in structure only lies in mutual mirror image, and the difference in nature only lies in rotationpolarized lightIn different directions.So Prouostage was the first to findRacemic tartaric acidOfoptical activity Because it is a mixture of "left-handed" and "right-handed" tartaric acid, he found thatEnantiomerismPhenomenon.
In 1874, Van Hoff proposedcarbon atomOftetrahedronHe proposed that if there are four different carbon atomsGroupThese four groups can have two different arrangements around the carbon atom, and two different tetrahedral space configurations.They are mirror images of each other, just like the relationship between people's left and right hands. They are similar in shape but cannot overlap.[1]
