2-Carb-34

Continued from 2-Carb-33

Contents

• 2-Carb-34. Replacement of ring oxygen by other elements
  • 34.1. Replacement by nitrogen or phosphorus
  • 34.2. Replacement by carbon
• References for this section

2-Carb-34.1. Replacement by nitrogen or phosphorus

Names should be based on those of the amino sugars (see 2-Carb-14) (or the analogous phosphanyl sugars) with the amino or phosphanyl group at the non-anomeric position. Ring-size designators (furano, pyrano etc.) are the same as for the oxygen analogues.

Examples:

5-Amino-5-deoxy-D-glucopyranose; trivial name nojirimycin

1-Amino-1,5-anhydro-1-deoxy-D-mannitol or 1,5-dideoxy-1,5-imino-D-mannitol;
trivial name deoxymannojirimycin

Note the extension of the use of 'anhydro' in the above example to include the elimination of water between -NH₂ and -OH (cf. 2-Carb-26).

5-Deoxy-5-ethylamino-α-D-glucopyranose

5-Deoxy-5-phosphanyl-D-xylopyranose

Note. Use of the terms 'aza sugar', 'phospha sugar' etc. should be restricted to structures where carbon, not oxygen, is replaced by a heteroatom. Thus the structure below is a true aza sugar. The term 'imino sugar' may be used as a class name for cyclic sugar derivatives in which the ring oxygen atom has been replaced by nitrogen.

Methyl 3-deoxy-3-aza-α-D-ribo-hexopyranoside

2-Carb-34.2. Replacement by carbon

The (non-detachable) prefix 'carba-' signifies replacement of a heteroatom by carbon in general natural product nomenclature [26], and may be applied to replacement of the hemiacetal ring oxygen in carbohydrates if there is a desire to stress homomorphic relationships. If the original heteroatom is unnumbered, the new carbon atom is assigned the locant of the non-anomeric adjacent skeletal atom, with suffix 'a'.

Note. The draft natural product rules [26] recommend that the new carbon atom takes the locant of the lower-numbered proximal atom. However, carbohydrate chemists regard the ring oxygen as formally originating from the non-anomeric (usually higher-numbered) position.

Additional stereochemistry (if any) at the new carbon centre is specified by use of the R/S system ([13], Section E).

Structures of this type can also be named as cyclitols [8].

Examples:

5a-Carba-β-D-glucopyranose

1-(2-Deoxy-4a-carba-β-D-erythro-pentofuranosyl)thymine
or 4'a-carbathymidine

5a-Carba-β-D-fructofuranosyl 5a-carba-α-D-glucopyranoside

1-[(4aS)-2-Deoxy-4a-fluoro-4a-carba-β-D-erythro-pentofuranosyl]thymine
or (4'aS)-4'a-fluoro-4'a-carbathymidine

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.

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.

26. IUPAC Nomenclature of Organic Chemistry, Section F, revised version in preparation.

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