Configurational prefixes

Chart I. Trivial names (with recommended three-letter abbreviations in parentheses) and structures (in the aldehydic, acyclic form) of the aldoses with three to six carbon atoms. Only the D-forms are shown the L-forms are the mirror images. The chains of chiral atoms delineated in bold face correspond to the configurational prefixes given in italics below the names... 

The name selected is that which comes first in the alphabet (configurational prefixes included). Trivial names are preferred for parent monosaccharides and for those derivatives where all stereocentres are stereochemically unmodified. 

The configurational prefixes are printed in lower-case italic (indicated in typescript by underlining), and are preceded by either d- or L-, as appropriate. For examples see 2-Carb-4.2 and 2-Carb-6.2... 

If the sign of the optical rotation under specified conditions is to be indicated, this is done by adding (+)- or (-)- before the configurational prefix. Racemic forms are indicated by ( )-. 

The anomeric symbol a or p, followed by a hyphen, is placed immediately before the configurational symbol D or L of the trivial name or of the configurational prefix denoting the group of chiral carbon atoms that includes the anomeric reference atom. 

The trivial names form the basis of the configurational prefixes (see 2-Carb-4.3). 

Systematic names are formed from a stem name and a configurational prefix or prefixes. The stem names for the aldoses with three to ten carbon atoms are triose,... 

The configuration of the CHOH groups of the sugar is designated by the appropriate configurational prefix(es) from Chart I. When used in systematic names, these prefixes are always to be in lower case letters (with no initial capital), and italicized in print. Each prefix is qualified by d or L (Chart I shows only the D structures). 

If sequences of chiral centres are separated by non-chiral centres, the non-chiral centres are ignored, and the remaining set of chiral centres is assigned the appropriate configurational prefix (for four centres or less) or prefixes (for more than four centres). 

Note 2. Since all aldoses up to the hexoses have trivial names that are preferred, the systematic names apply only to the higher aldoses. However, the configurational prefixes are also used to name ketoses (see below) and other monosaccharides. 

Systematic names for individual dialdoses are formed from the systematic stem name for the corresponding aldose (see 2-Carb-8.2), but with the ending odialdose instead of ose , and the appropriate configurational prefix (Chart I). A choice between the two possible aldose parent names is made on the basis of 2-Carb-2.2.2. 

The systematic names are formed from the stem name and the appropriate configurational prefix. 

For 2-ketoses, configurational prefixes are given in the same way as for aldoses (see 2-Carb-8.2 and 2-Carb-8.3). 

The systematic name of a diketose is formed by replacing the terminal -se of the stem name by -diulose . The locants of the (potential) carbonyl groups must be the lowest possible and appear before the ending. The stem name is preceded by the appropriate configurational prefix. If there is a choice of names, a decision is made on the basis of 2-Carb-2.2.2. In cyclic forms, locants may be needed for the positions of ring closure that of the (potential) carbonyl group is cited first. 

If the carbonyl group(s) divides the sequence of chiral centres, the configurational prefixes are assigned in the normal manner (see 2-Carb-8.4) for all chiral centres the non-chiral centres are ignored. 

The systematic name consists of the prefix deoxy- , preceded by the locant and followed by the stem name with such configurational prefixes as necessary to describe the configuration(s) at the asymmetric centres present in the deoxy compound. Configurational prefixes are cited in order commencing at the end farthest from C-l. Deoxy is regarded as a detachable prefix, i.e. it is placed in alphabetical order with any substituent prefixes. 

If the CH2 group divides the chiral centres into two sets, it is ignored for the purpose of assigning a configurational prefix the prefix(es) assigned should cover the entire sequence of chiral centres (see 2-Carb-8.4). 

Note. Cyclization of the second example between C-1 and a CH2OH group would necessitate a three-centre configurational prefix for the ring form. 

If there is a carbonyl group in the branch (or a terminal COOH or its equivalent), its position (assigned lowest number when stereochemistry is being considered) is used to define the configurational prefix (see examples 1 and 3 in Chart V). Use of the R,S system is generally preferred, as less open to misinterpretation. 

The prefix D or L must be given when a derivative of a meso form has become asymmetric by substitution. It is also necessary to define the configurational prefixes as D or L in the case where there are more than four contiguous asymmetric carbon atoms. 

Thus, description of a simple change of fatty acid at the primary position required frequent changes of configuration prefixes. Also, the R/S system, like the older D/L one, did not account for the stereospecificity of the acylglycerol derivatives toward lipases (phospholipase A2 in particular). Finally, nonrandom distribution of fatty acids in natural or synthetic enantiomeric acylglycerols could not be systematically correlated by reference to either the R/S or D/L configuration. 

When more than four chiral carbon atoms are present, an aldose is given two configurational prefixes, one for the four lowest-numbered chiral centers and one for the rest of the molecule. The configuration of the /zz g/zesr-numbered group is stated first. 

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