Continued from Preamble, 2-Carb-0 & 2-Carb-1
2-Carb-2.1. Choice of parent structure
In cases where more than one monosaccharide structure is embedded in a larger molecule, a parent structure is chosen on the basis of the following criteria, applied in the order given until a decision is reached:
2.1.1. The parent that includes the functional group most preferred by general principles of organic nomenclature [13,14]. If there is a choice, it is made on the basis of the greatest number of occurrences of the most preferred functional group. Thus aldaric acid > uronic acid/ketoaldonic acid/aldonic acid > dialdose > ketoaldose/aldose > diketose > ketose.
2.1.2. The parent with the greatest number of carbon atoms in the chain, e.g. a heptose rather than a hexose.
2.1.3. The parent with the name that comes first in an alphabetical listing based on:
126.96.36.199. the trivial name or the configurational prefix(es) of the systematic name, e.g. allose rather than glucose, a gluco rather than a gulo derivative;
188.8.131.52. the configurational symbol D rather than L ;
184.108.40.206. the anomeric symbol α rather than β.
2.1.4. The parent with the most substituents cited as prefixes (bridging substitution, e.g. 2,3-O-methylene, is regarded as multiple substitution for this purpose).
2.1.5. The parent with the lowest locants (see , p. 17) for substituent prefixes.
2.1.6. The parent with the lowest locant for the first-cited substituent.
The implications of these recommendations for branched-chain structures are exemplified in 2-Carb-18.
Note 1. To maintain homomorphic relationships between classes of sugars, the (potential) aldehyde group of a uronic acid is regarded as the principal function for numbering and naming (see 2-Carb-2.2.1 and 2-Carb-22).
Note 2. To maintain integrity of carbohydrate names, it is sometimes helpful to overstep the strict order of principal group preference specified in general organic nomenclature [13,14]. For example, a carboxymethyl-substituted sugar can be named as such, rather than as an acetic acid derivative (see 2-Carb-31.2).
2-Carb-2.2. Numbering and naming the parent structure
The basis for the name is the structure of the parent monosaccharide in the acyclic form. Charts I and IV (2-Carb-10) give trivial names for parent aldoses and ketoses with up to six carbon atoms. 2-Carb-8.2 and 2-Carb-10.3 describe systematic naming procedures.
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 carbon atoms of a monosaccharide are numbered consecutively in such a way that:
220.127.116.11. A (potential) aldehyde group receives the locant 1 (even if a senior function is present, as in uronic acids; see 2-Carb-2.1, note 1);
18.104.22.168. The most senior of other functional groups expressed in the suffix receives the lowest possible locant, i.e. carboxylic acid (derivatives) > (potential) ketonic carbonyl groups.
2-Carb-2.2.2. Choice of parent name
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.
2-Carb-2.2.3. Choice between alternative names for substituted derivatives
When the parent structure is symmetrical, preference between alternative names for derivatives should be given according to the following criteria, taken in order:
22.214.171.124. The name including the configurational symbol D rather than L.
126.96.36.199. The name that gives the lowest set of locants (see , p. 17) to the substituents present.
188.8.131.52. The name that, when the substituents have been placed in alphabetical order, possesses the lowest locant for the first-cited substituent.
13. IUPAC Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F and H, 1979 Edition, Pergamon Press, Oxford, U.K. Sections E and F are reprinted in ref. 2, pp. 1-18 and 19-26, respectively.
14. Guide to IUPAC Nomenclature of Organic Compounds, Recommendations 1993, Blackwell Scientific Publications, Oxford (1993).
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