Stereoisomerism naming enantiomers

Aldotetroses are four-carbon sugars with two chirality centers and an aldehyde carbonyl group. Thus, there are 22 = 4 possible stereoisomeric aldotetroses, or two d,l pairs of enantiomers named erythrose and threose. 

Ibuprofen is a popular analgesic and anti-inflammatory drug. There are two stereoisomeric forms of ibuprofen. This drug can exist as (S)- and (/ )-stereoisomers (enantiomers). Only the (5)-form is active. The (/ )-form is completely inactive, although it is slowly converted in the body to the active (5)-form. The drug marketed under the trade names, commercially known as Advil , Anadin , Arthrofen , Brufen , Nurofen , Nuprin , Motrin etc., is a racemic mixture of (/ )- and (5)-ibuprofen. 

Two structures that constitute a stereoisomeric pair are referred to as enantiomers. The two enantiomers for alanine are illustrated in figure 3.8. These two isomers are called L-alanine and D-alanine, according to the way in which the substituents are arranged about the asymmetric carbon atom. The naming by D and l (for dextrorotatory and levorotatory see chapter 6) refers to a convention established by Emil Fischer many years ago. According to this convention all amino acids found in proteins are of the l form. Some D-amino acids are found in bacterial cell walls and certain antibiotics. 

The molecular helices and propellers discussed above contain no center of chirality, and the P and M nomenclature is thus the only way of describing their absolute configuration. This nomenclature, however, is also applicable to some series of chiral compounds which display several centers of chirality. As will be discussed in Section 6, the presence in a molecule of two or more centers of chirality usually implies the existence of several stereoisomers, but steric reasons may reduce down to two the possible number of stereoisomeric forms. Thus, 2,3-epoxycyclohexanone contains two asymmetric carbon atoms, but for steric reasons only two stereoisomers, namely the (2S 3S)-(—)- and the (2/ 3/J)-( + )-enantiomer, exist the former is depicted in diagram XL [49]. 

Stereoisomers have bonds attached in the same order but with different spatial arrangements. Stereoisomerism is also known as spatial isomerism, and there are two types of stereoisomers cis-trans isomers and enantiomers. Detailed naming rules for stereoisomers are an advanced topic. 

Diastereoisomers are all stereoisomeric compounds which are not enantiomers. In other words, the terminology distereoisomer essentially includes compounds containing both ring systems and double-bonds simultaneously. In apparent contrast to enantiomers diastereoisomers invariably display different physical and chemical characteristics, namely ... 

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