L, prefix

Relative to each other both hydroxyl groups are on the same side m Fischer pro jections of the erythrose enantiomers The remaining two stereoisomers have hydroxyl groups on opposite sides m their Fischer projections They are diastereomers of d and L erythrose and are called d and l threose The d and l prefixes again specify the con figuration of the highest numbered chirality center d Threose and l threose are enan tiomers of each other... 

As shown for the aldotetroses an aldose belongs to the d or the l series accord mg to the configuration of the chirality center farthest removed from the aldehyde func tion Individual names such as erythrose and threose specify the particular arrangement of chirality centers within the molecule relative to each other Optical activities cannot be determined directly from the d and l prefixes As if furns ouf bofh d eryfhrose and D fhreose are levorofafory buf d glyceraldehyde is dexfrorofafory... 

To the names of aldaric acids that are symmetrical, which therefore have no D- or L- prefix, the prefix meso- may be added for the sake of clarity. Examples mero-erythraric acid, meso-ribaric acid, meso-xylaric acid, meso-allaric acid, meso-galactaric acid. 

The D or L prefix must however be used when a meso-aldaric acid has become asymmetric as a result of substitution. 

The use of d- and L-prefixes is a nomenclature for orientation of atomic structure of sugar and amino acid molecules. It is a structural definition and is not related to the optical properties. 

The two anomers are designated a or p by comparison of the chiralities at the anomeric centre and at the highest numbered chiral centre. If these are the same (RS convention), the anomer is termed P, or a if they are different. Note that the d and l prefixes are assigned on the basis of the chirality (as depicted in Fischer projections) at the highest numbered chiral centre and its relationship to D-(i )-(+)-glyceraldehyde or l-(5)-(—)-glyceraldehyde (see Section 3.4.10). 

Sometimes the subscript s or g is added to a d or l prefix to indicate whether the chirality of a compound is being related to that of serine, the traditional configurational standard for amino acids, or to that of gly-ceraldehyde. In the latter case the sugar convention (Chapter 4) is followed. In this convention the configurations of the chiral centers furthest from Cl are compared. Ordinary threonine is ls- or d -threonine. The configuration of dextrorotatory (+)-tartaric acid can be described as 2R, 3R, or as ds, or as l. ... 

Assignment at the L-series (L-prefix) is omitted in most cases whereas D-amino acids are marked. 

According to the traditional system of carbohydrate nomenclature, the configuration of any monosaccharide having up to six carbon atoms is completely defined by a prefix D or L followed by a syllable glue- , mann- etc. This latter specifies both the number of carbon atoms in the sugar and the relative stereochemistry of all chiral centres, while the D or L prefix designates the enantiomeric series to which the compound belongs. 

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