Nomenclature of Carbohydrates (Recommendations 1996)

Preamble, 2-Carb-0 and 2-Carb-1



These Recommendations expand and replace the Tentative Rules for Carbohydrate Nomenclature [1] issued in 1969 jointly by the IUPAC Commission on the Nomenclature of Organic Chemistry and the IUB-IUPAC Commission on Biochemical Nomenclature (CBN) and reprinted in [2]. They also replace other published JCBN Recommendations [3-7] that deal with specialized areas of carbohydrate terminology; however, these documents can be consulted for further examples. Of relevance to the field, though not incorporated into the present document, are the following recommendations:

Nomenclature of cyclitols, 1973 [8]

Numbering of atoms in myo-inositol, 1988 [9]

Symbols for specifying the conformation of polysaccharide chains, 1981 [10]

Nomenclature of glycoproteins, glycopeptides and peptidoglycans, 1985 [11]

Nomenclature of glycolipids, in preparation [12]

The present Recommendations deal with the acyclic and cyclic forms of monosaccharides and their simple derivatives, as well as with the nomenclature of oligosaccharides and polysaccharides. They are additional to the Definitive Rules for the Nomenclature of Organic Chemistry [13,14] and are intended to govern those aspects of the nomenclature of carbohydrates not covered by those rules.

2-Carb-0. Historical development of carbohydrate nomenclature.[15]

2-Carb-0.1. Early approaches

In the early nineteenth century, individual sugars were often named after their source, e.g. grape sugar (Traubenzucker) for glucose, cane sugar (Rohrzucker) for saccharose (the name sucrose was coined much later). The name glucose was coined in 1838; Kekulé in 1866 proposed the name 'dextrose' because glucose is dextrorotatory, and the laevorotatory 'fruit sugar' (Fruchtzucker, fructose) was for some time named 'laevulose' (American spelling 'levulose'). Very early, consensus was reached that sugars should be named with the ending '-ose', and by combination with the French word 'cellule' for cell the term cellulose was coined, long before the structure was known. The term 'carbohydrate' (French 'hydrate de carbone') was applied originally to monosaccharides, in recognition of the fact that their empirical composition can be expressed as Cn(H2O)n. However the term is now used generically in a wider sense (see 2-Carb-1.1).

2-Carb-0.2. The contribution of Emil Fischer

Emil Fischer [16] began his fundamental studies on carbohydrates in 1880. Within ten years, he could assign the relative configurations of most known sugars and had also synthesized many sugars. This led to the necessity to name the various compounds. Fischer and others laid the foundations of a terminology still in use, based on the terms triose, tetrose, pentose, and hexose. He endorsed Armstrong's proposal to classify sugars into aldoses and ketoses, and proposed the name fructose for laevulose, because he found that the sign of optical rotation was not a suitable criterion for grouping sugars into families.

The concept of stereochemistry, developed since 1874 by van't Hoff and Le Bel, had a great impact on carbohydrate chemistry because it could easily explain isomerism. Emil Fischer introduced the classical projection formulae for sugars, with a standard orientation (carbon chain vertical, carbonyl group at the top); since he used models with flexible bonds between the atoms, he could easily 'stretch' his sugar models into a position suitable for projection. He assigned to the dextrorotatory glucose (via the derived glucaric acid) the projection with the OH group at C-5 pointing to the right, well knowing that there was a 50% chance that this was wrong. Much later (Bijvoet, 1951), it was proved correct in the absolute sense.

Rosanoff in 1906 selected the enantiomeric glyceraldehydes as the point of reference; any sugar derivable by chain lengthening from what is now known as D-glyceraldehyde belongs to the D series, a convention still in use.

2-Carb-0.3. Cyclic forms

Towards the end of the nineteenth century it was realized that the free sugars (not only the glycosides) existed as cyclic hemiacetals or hemiketals. Mutarotation, discovered in 1846 by Dubrunfaut, was now interpreted as being due to a change in the configuration of the glycosidic (anomeric) carbon atom. Emil Fischer assumed the cyclic form to be a five-membered ring, which Tollens designated by the symbol <1,4>, while the six-membered ring received the symbol <1,5>.

In the 1920s, Haworth and his school proposed the terms 'furanose' and 'pyranose' for the two forms. Haworth also introduced the 'Haworth depiction' for writing structural formulae, a convention that was soon widely followed.

2-Carb-0.4. Nomenclature commissions

Up to the 1940s, nomenclature proposals were made by individuals; in some cases they were followed by the scientific community and in some cases not. Official bodies like the International Union of Chemistry, though developing and expanding the Geneva nomenclature for organic compounds, made little progress with carbohydrate nomenclature. The IUPAC Commission on Nomenclature of Biological Chemistry put forward a classification scheme for carbohydrates, but the new terms proposed have not survived. However in 1939 the American Chemical Society (ACS) formed a committee to look into this matter, since rapid progress in the field had led to various misnomers arising from the lack of guidelines. Within this committee, the foundations of modern systematic nomenclature for carbohydrates and derivatives were laid: numbering of the sugar chain, the use of D and L and α and β, and the designation of stereochemistry by italicized prefixes (multiple prefixes for longer chains). Some preliminary communications appeared, and the final report, prepared by M.L. Wolfrom, was approved by the ACS Council and published in 1948 [17].

Not all problems were solved, however, and different usages were encountered on the two sides of the Atlantic. A joint British-American committee was therefore set up, and in 1952 it published 'Rules for Carbohydrate Nomenclature' [18]. This work was continued, and a revised version was endorsed in 1963 by the American Chemical Society and by the Chemical Society in Britain and published [19]. The publication of this report led the IUPAC Commission on Nomenclature of Organic Chemistry to consider the preparation of a set of IUPAC Rules for Carbohydrate Nomenclature. This was done jointly with the IUPAC-IUB Commission on Biochemical Nomenclature, and resulted in the 'Tentative Rules for Carbohydrate Nomenclature, Part I, 1969', published in 1971/72 in several journals [1]. It is a revision of this 1971 document that is presented here. In the present document, recommendations are designated 2-Carb-n, to distinguish them from the Carb-n recommendations in the previous publication.

2-Carb-1. Definitions and conventions

2-Carb-1.1. Carbohydrates

The generic term 'carbohydrate' includes monosaccharides, oligosaccharides and polysaccharides as well as substances derived from monosaccharides by reduction of the carbonyl group (alditols), by oxidation of one or more terminal groups to carboxylic acids, or by replacement of one or more hydroxy group(s) by a hydrogen atom, an amino group, a thiol group or similar heteroatomic groups. It also includes derivatives of these compounds. The term 'sugar' is frequently applied to monosaccharides and lower oligosaccharides. It is noteworthy that about 3% of the compounds listed by Chemical Abstracts Service (i.e. more than 360 000) are named by the methods of carbohydrate nomenclature.

Note. Cyclitols are generally not regarded as carbohydrates. Their nomenclature is dealt with in other recommendations [8,9].

2-Carb-1.2. Monosaccharides

Parent monosaccharides are polyhydroxy aldehydes H-[CHOH]n-CHO or polyhydroxy ketones H-[CHOH]n-CO-[CHOH]m-H with three or more carbon atoms.

The generic term 'monosaccharide' (as opposed to oligosaccharide or polysaccharide) denotes a single unit, without glycosidic connection to other such units. It includes aldoses, dialdoses, aldoketoses, ketoses and diketoses, as well as deoxy sugars and amino sugars, and their derivatives, provided that the parent compound has a (potential) carbonyl group.

1.2.1. Aldoses and ketoses

Monosaccharides with an aldehydic carbonyl or potential aldehydic carbonyl group are called aldoses; those with a ketonic carbonyl or potential ketonic carbonyl group, ketoses.

Note. The term 'potential aldehydic carbonyl group' refers to the hemiacetal group arising from ring closure. Likewise, the term 'potential ketonic carbonyl group' refers to the hemiketal structure (see 2-Carb-5).

1.2.2. Cyclic forms

Cyclic hemiacetals or hemiketals of sugars with a five-membered (tetrahydrofuran) ring are called furanoses, those with a six-membered (tetrahydropyran) ring pyranoses. For sugars with other ring sizes see 2-Carb-5.

2-Carb-1.3. Dialdoses

Monosaccharides containing two (potential) aldehydic carbonyl groups are called dialdoses (see 2-Carb-9).

2-Carb-1.4. Diketoses

Monosaccharides containing two (potential) ketonic carbonyl groups are termed diketoses (see 2-Carb-11).

2-Carb-1.5. Ketoaldoses (aldoketoses, aldosuloses)

Monosaccharides containing a (potential) aldehydic group and a (potential) ketonic group are called ketoaldoses (see 2-Carb-12); this term is preferred to the alternatives on the basis of 2-Carb-2.1.1 (aldose preferred to ketose).

2-Carb-1.6. Deoxy sugars

Monosaccharides in which an alcoholic hydroxy group has been replaced by a hydrogen atom are called deoxy sugars (see 2-Carb-13).

2-Carb-1.7 Amino sugars

Monosaccharides in which an alcoholic hydroxy group has been replaced by an amino group are called amino sugars (see 2-Carb-14). When the hemiacetal hydroxy group is replaced, the compounds are called glycosylamines.

2-Carb-1.8. Alditols

The polyhydric alcohols arising formally from the replacement of a carbonyl group in a monosaccharide with a CHOH group are termed alditols (see 2-Carb-19).

2-Carb-1.9. Aldonic acids

Monocarboxylic acids formally derived from aldoses by replacement of the aldehydic group by a carboxy group are termed aldonic acids (see 2-Carb-20).

2-Carb-1.10. Ketoaldonic acids

Oxo carboxylic acids formally derived from aldonic acids by replacement of a secondary CHOH group by a carbonyl group are called ketoaldonic acids (see 2-Carb-21).

2-Carb-1.11. Uronic acids

Monocarboxylic acids formally derived from aldoses by replacement of the CH2OH group with a carboxy group are termed uronic acids (see 2-Carb-22).

2-Carb-1.12. Aldaric acids

The dicarboxylic acids formed from aldoses by replacement of both terminal groups (CHO and CH2OH) by carboxy groups are called aldaric acids (see 2-Carb-23).

2-Carb-1.13. Glycosides

Glycosides are mixed acetals formally arising by elimination of water between the hemiacetal or hemiketal hydroxy group of a sugar and a hydroxy group of a second compound. The bond between the two components is called a glycosidic bond.

For an extension of this definition, see 2-Carb-33.

2-Carb-1.14. Oligosaccharides

Oligosaccharides are compounds in which monosaccharide units are joined by glycosidic linkages. According to the number of units, they are called disaccharides, trisaccharides, tetrasaccharides, pentasaccharides etc. The borderline with polysaccharides cannot be drawn strictly; however the term 'oligosaccharide' is commonly used to refer to a defined structure as opposed to a polymer of unspecified length or a homologous mixture. When the linkages are of other types, the compounds are regarded as oligosaccharide analogues. (See 2-Carb-37.)

Note. This definition is broader than that given in [6], to reflect current usage.

2-Carb-1.15. Polysaccharides

'Polysaccharide' (glycan) is the name given to a macromolecule consisting of a large number of monosaccharide (glycose) residues joined to each other by glycosidic linkages. The term poly(glycose) is not a full synonym for polysaccharide (glycan) (cf. [20]), because it includes macromolecules composed of glycose residues joined to each other by non-glycosidic linkages.

For polysaccharides containing a substantial proportion of amino sugar residues, the term polysaccharide is adequate, although the term glycosaminoglycan may be used where particular emphasis is desired.

Polysaccharides composed of only one kind of monosaccharide are described as homopolysaccharides (homoglycans). Similarly, if two or more different kinds of monomeric unit are present, the class name heteropolysaccharide (heteroglycan) may be used. (See 2-Carb-39.)

The term 'glycan' has also been used for the saccharide component of a glycoprotein, even though the chain length may not be large.

The term polysaccharide has also been widely used for macromolecules containing glycose or alditol residues in which both glycosidic and phosphate diester linkages are present.

2-Carb-1.16. Conventions for examples

1.16.1. Names of examples are given with an initial capital letter (e.g. 'L-glycero-β-D-gluco-Heptopyranose') to clarify the usage in headings and to show which letter controls the ordering in an alphabetical index.

1.16.2. The following abbreviations are commonly used for substituent groups in structural formulae: Ac (acetyl), Bn or PhCH2 (benzyl), Bz or PhCO (benzoyl), Et (ethyl), Me (methyl), Me3Si (not TMS) (trimethylsilyl), ButMe2Si (not TBDMS) (tert-butyldimethylsilyl), Ph (phenyl), Tf (triflyl = trifluoromethanesulfonyl), Ts (tosyl = toluene-p-sulfonyl), Tr (trityl).


1. IUPAC Commission on the Nomenclature of Organic Chemistry (CNOC) and IUPAC-IUB Commission on Biochemical Nomenclature (CBN), Tentative rules for carbohydrate nomenclature, Part I, 1969, Biochem J., 125, 673-695 (1971); Biochemistry, 10, 3983-4004 (1971); Biochim. Biophys. Acta, 244, 223-302 (1971); Eur. J. Biochem., 21, 455-477 (1971) and 25, 4 (1972); J. Biol. Chem., 247, 613-635 (1972); ref.2, pp.127-148.

2. International Union of Biochemistry and Molecular Biology, 'Biochemical Nomenclature and Related Documents', Portland Press, London (1992).

3. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Conformational nomenclature for five- and six-membered ring forms of monosaccharides and their derivatives (Recommendations 1980), Eur.J.Biochem., 111, 295-298 (1980); Arch. Biochem. Biophys., 207, 469-472 (1981); Pure Appl. Chem., 53, 1901-1905 (1981); ref. 2, pp. 158-161.

4. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Nomenclature of branched-chain monosaccharides (Recommendations 1980), Eur. J. Biochem., 119, 5-8 (1981); corrections: Eur. J. Biochem., 125, 1 (1982); Pure Appl. Chem., 54, 211-215 (1982); ref.2, pp. 165-168.

5. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Nomenclature of unsaturated monosaccharides (Recommendations 1980), Eur. J. Biochem., 119, 1-3 (1981); corrections: Eur. J. Biochem., 125, 1 (1982); Pure Appl. Chem., 54, 207-210 (1982); ref.2, pp. 162-164.

6. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Abbreviated terminology of oligosaccharide chains (Recommendations 1980), J. Biol. Chem., 257, 3347-3351 (1982); Eur. J. Biochem., 126, 433-437 (1982); Pure Appl. Chem., 54, 1517-1522 (1982); Arch. Biochem. Biophys., 220, 325-329 (1983); ref. 2, pp. 169-173.

7. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Polysaccharide nomenclature (Recommendations 1980), Eur. J. Biochem., 126, 439-441 (1982); Pure Appl. Chem., 54, 1523-1526 (1982); J. Biol. Chem., 257, 3352-3354 (1982); Arch. Biochem. Biophys., 220, 330-332 (1983); ref. 2, pp. 174-176.

8. IUPAC-IUB Commission on Biochemical Nomenclature (CBN), Nomenclature of cyclitols (Recommendations 1973), Biochem. J., 153, 23-31 (1976); Eur. J. Biochem., 57, 1-7 (1975); Pure Appl. Chem., 37, 283-297 (1974); ref. 2, pp.149-155.

9. Nomenclature Committee of IUB (NC-IUB), Numbering of atoms in myo-inositol (Recommendations 1988), Biochem. J., 258, 1-2 (1989); Eur. J. Biochem., 180, 485-486 (1989); ref.2, pp. 156-157.

10. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Symbols for specifying the conformation of polysaccharide chains (Recommendations 1981), Eur. J. Biochem, 131, 5-7, (1983); Pure Appl. Chem., 55, 1269-1272 (1983); ref. 2, pp. 177-179.

11. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Nomenclature of glycoproteins, glycopeptides and peptidoglycans, Eur. J. Biochem., 159, 1-6 (1986); Glycoconjugate J., 3, 123-124 (1986); J. Biol. Chem., 262, 13-18 (1987); Pure Appl. Chem., 60, 1389-1394 (1988); Royal Society of Chemistry Specialist Periodical Report, 'Amino Acids and Peptides', vol. 21, p. 329 (1990); ref. 2, pp. 84-89.

12. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Nomenclature of glycolipids, in preparation. [Now published in Adv. Carbohydr. Chem. Biochem. 1999, 55, in press; Carbohydr. Res., 1998, 312, 167-175; Eur. J. Biochem., 1998, 257, 293-298; Glycoconjugate J., 1999, 16, 1-6; J. Mol. Biol., 1999, 286, 963-970; Pure Appl. Chem., 1997, 69, 2475-2487.]

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).

15. This text is largely based on an essay entitled 'Development of Carbohydrate Nomenclature' by D. Horton, included in 'The Terminology of Biotechnology: A Multidisciplinary Problem' (ed. K.L. Loening, Springer-Verlag, Berlin and Heidelberg, 1990).

16. E. Fischer, Ber., 23, 2114 (1890).

17. Rules of carbohydrate nomenclature (1948), Chem. Eng. News, 26, 1623 (1948).

18. Rules of carbohydrate nomenclature (1952), J. Chem. Soc., 5108 (1952); Chem. Eng. News, 31, 1776 (1953). error details

19. Rules of carbohydrate nomenclature (1963), J. Org. Chem., 28, 281 (1963).

20. IUPAC Commission on Macromolecular Nomenclature, Nomenclature of regular single-strand organic polymers (Recommendations 1975), Pure Appl. Chem., 48, 373-385 (1976); 'Compendium of Macromolecular Nomenclature', Blackwell Scientific Publications, Oxford, p.91 (1991).

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