Continued from 2-Carb-25 and 2-Carb-26
The cyclic product of condensation of two monosaccharide molecules with the elimination of two molecules of water (commonly called an intermolecular anhydride), is named by placing the word 'dianhydride' after the names of the two parent monosaccharides. When the two parent monosaccharides are different, the one preferred according to the order of preference given in 2-Carb-2.1 is cited first. The position of each anhydride link is indicated by a pair of locants showing the positions of the two hydroxy groups involved; the locants relating to one monosaccharide (in a mixed dianhydride, the second monosaccharide named) are primed. Both pairs of locants immediately precede the word 'dianhydride'.
α-D-Fructopyranose α-D-sorbopyranose 1,2':1',2-dianhydride
(α-D-Galactopyranuronic acid) β-L-rhamnopyranose 1,2':1',2-dianhydride
2-Carb-28. Cyclic acetals
Cyclic acetals formed by the reaction of saccharides or saccharide derivatives with aldehydes or ketones are named in accordance with 2-Carb-24.1, bivalent substituent names (formed by general organic nomenclature principles) being used as prefixes. In indicating more than one cyclic acetal grouping of the same kind, the appropriate pairs of locants are separated typographically when the exact placement of the acetal groups is known.
3,4,6-Tri-O-acetyl-α-D-glucopyranose (R)-1,2-(methyl orthoacetate)
Note 1. The last two examples contain cyclic ortho ester structures. These compounds are conveniently named as cyclic acetals.
Note 2. In the last four examples, new asymmetric centres have been introduced at the carbonyl carbon atom of the aldehyde or ketone that has reacted with the saccharide. When known, the stereochemistry at such a new centre is indicated by use of the appropriate R or S symbol (, Section E) placed in parentheses, immediately before the locants of the relevant prefix.
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.
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