Epimers Diastereomers that differ center

Epimers Diastereomers that differ in configuration at only one of their chirality centers. 

Some molecules have more than one chirality center. Enantiomers have opposite configuration at all chirality centers, whereas diastereomers have the same configuration in at least one center but opposite configurations at the others. Epimers are diastereomers that differ in configuration at only one chirality center. A compound with n chirality centers can have a maximum of 2n stereoisomers. 

Two diastereomers that differ in the configuration around one stereogenic center only are called epimers. 

Several stereochemical labels have been developed for diastereomers. Epimers are diastereomers that differ in configuration at only one of several chiral centers. The chiral center at which the difference in configuration occurs is said to be the epimeric center. Structures 69 and 70 are epimeric at C4. Anomers are epimers in the carbohydrate series that differ only at the... 

This experiment, first done by Emil Fischer, estabhshed that D-glucose and D-mannose have the same configurations about C3, C4, and C5. Diastereomeric aldoses that differ in configuration at only one carbon (such as D-glucose and D-mannose) are called epimers. In general, any pair of diastereomers that differ in configuration at only a single tetrahedral chirality center can be called epimers. 

Enzyme-substrate complex (Section 24.9) The species formed when a substrate (reactant) binds at the active site of an enzyme. Epimers, epimerization (Sections 18.3A and 22.8) Diastereomers that differ in configuration at only a single tetrahedral chirality center. Epimerization is the interconversion of epimers. 

Diastereomers that differ in configuration at only one asymmetric center are called epimers. For example, o-ribose and D-arabinose are C-2 epimers because they differ in configuration only at C-2 D-idose and D-talose are C-3 epimers. An epimer is a particular kind of diastereomer. (Recall that diastereomers are stereoisomers that are not enantiomers Section 4.11.)... 

When a molecule contains more than one chiral center, there are pairs of molecules not related by mirror symmetry. These molecules are called diastereomers. They differ in the relative chiralities at pairs of chiral centers (see Figure 14.3) and their chemical and physical properties are not identical. In this they differ from enantiomers, which have identical chemical and physical properties except those connected with their interaction with chiral detectors — plane-polarized light or enzymes, for example. Members of a pair of diastereoisomers that differ only in the configuration at one carbon atom are called epimers. 

The prefix 5a- or 5 - indicates the stereochemistry (trans or cis) of A-B ring fusion 5a-androstane and 5 -androstane, respectively. Coprostanol (5b-cholestan-3b-ol) and cholestanol (5a-cholestan-3b-ol), for example, are epimers that differ from each other at the C5 stereogenic center (Figure 1.8). Compounds with more than one stereogenic center (diastereomers) are discussed in more detail in section 1.3.3. 

According to the lUPAC definition, any diastereo-mer that has the opposite configuration at only one or two tetrahedral stereogenic centers is called an epimer, and the process of epimer formation by changing one of the asymmetric centers in the molecule is known as epimerization. The positions in two diastereomers that have different configurations are called epimeric. For example, for 2-(methylamino)-l-phenylpropan-l-ol (ephedrine), the IR,2R- and 1/ ,25-stereoisomers have the same configuration at Cl, but they are epimeric at the C2 atom (Figure 1.20). 

In the special case where two diastereomers differ at only one chirality center but are the same at all others, we say that the compounds are epimers. Cholestanol and coprostanol, for instance, are both found in human feces and... 

Diastereomers may be either chiral or achiral. For example, the cisjtrans 1,2-dibromoethylenes represent an achiral diastereomer pair, whereas threose/erythrose are chiral diastereomers. Epimers are a subclass of diastereomers in that they are molecules with several asymmetric centers with one being different and all the other centers being exactly the same. 

---