Continued from 2-Carb-34
Internal bridging of carbohydrate structures by bivalent substituent groups creates additional rings, which can be named either by use of a substituent prefix representing the bridging group, or by fusion nomenclature. The following recommendations for the use of these two approaches are not thoroughly developed; they simply represent an attempt to rationalize and codify current literature practice in the use of systems not in general well suited to carbohydrate applications. Bridging substituent prefix nomenclature (2-Carb-35.1) is based on the system well established for simple cyclic acetals (2-Carb-28), and fusion nomenclature (2-Carb-35.2) on current literature usage and requirements for general natural product nomenclature .
2-Carb-35.1. Use of bivalent substituent prefixes
Where the new bridge is attached to oxygen (or a replacement heteroatom, e.g. nitrogen in an amino sugar) already indicated in the name of the unbridged carbohydrate, the bivalent substituent prefix denotes substitution at two heteroatoms as outlined in 2-Carb-24.1 and 2-Carb-25 [method (b)]. Heteroatoms not directly bonded to the carbohydrate chain are regarded as part of the bridge.
Where the new bridge is attached through C-C bonds to the carbohydrate chain, the bridge prefix denotes a double C-substitution. Procedures are as outlined in 2-Carb-16.
Note 1. The alternative fusion name (see 2-Carb-35.2) is 2,2,2',2'-tetramethyl-4,4',5,5'-tetrahydro-(2,3,4,5-tetradeoxy-β-D-fructopyranoso)[2,3-d:4,5-d']bis[1,3]dioxole; this is clearly less desirable on grounds of complexity.
Note 2. The use of prefixes ending in '-ylidene' for gem-bivalent substituent groups is traditional in the carbohydrate field, although no longer recommended in general organic nomenclature .
Note. The alternative fusion name (see 2-Carb-35.2) is hexahydro(methyl 2,3-dideoxy-β-D-glucopyranosido)[2,3]benzene
Note. The alternative fusion name (see 2-Carb-35.2) is (methyl 2,3-dideoxy-β-D-erythro-hexopyranosido)[2,3]benzene
Note. The isomeric chromene would be named as a 2-O,1-C-substituted system.
The prefix 'cyclo-' may be used for a single-bond bridge .
2-Carb-35.2. Ring fusion methods
Fusion methods are employed as in general natural product nomenclature , except that the original carbohydrate ring is cited first, in parentheses (with terminal '-e', if present, replaced by '-o'). For designating stereochemistry, bonds in the new ring are considered as equivalent to OH, unless OH (or its equivalent) is still present at the ring junction. Substituents on the carbohydrate portion are included within the parentheses enclosing the fusion prefix. Substituents on the new ring (including 'hydro-' prefixes) precede the carbohydrate term(s). If there is a choice, the new ring is numbered in the direction used to define the fusion locants.
Note. General natural product fusion nomenclature  would require the carbohydrate portion to be cited last (e.g. oxazologlucopyranose), whereas it is cited first here and in the literature.
Note 1. The alternative name using a substituent prefix (see 2-Carb-35.1) is 2-amino-1-O,2-N-(benzylylidene)-2-deoxy-α-D-glucopyranose.
Note 2. Literature fusion names for this type of compound use 'glucopyrano[2,1-d]oxazoline' terminology. However, names for partially hydrogenated heterocycles ending in 'oline' were abandoned by IUPAC in 1983 , in favour of 'dihydro......ole'. Use of 'pyranoso' rather than 'pyrano' is recommended to avoid confusion with the normal fusion prefix from 'pyran' and to simplify rules for naming derivatives (e.g. glycosides).
Note. The alternative name using a substituent prefix (see 2-Carb-35.1) is 3,4,6-tri-O-acetyl-2-amino-2-deoxy-1-O,2-N-[(methylamino)methylylidene]-α-D-glucopyranose.
Note. The alternative name using a substituent prefix (see 2-Carb-35.1) is 2-amino-1,2-N-carbonyl-1,2-dideoxy-1-N-phenyl-α-D-glucopyranosylamine
Note 1. The alternative name using a substituent prefix (see 2-Carb-35.1) is 4-O-acetyl-3-amino-2,3,6-trideoxy-1-O,3-N-(ethan-1-yl-1-yliene)-3-C-methyl-α-L-ribo-hexopyranose
Note 2. This example would not normally be regarded as a fused system for nomenclature purposes, since it is not ortho- or ortho- and peri-fused .
2-Carb-35.3. Spiro systems
Spiro systems can be named by normal procedures . For clarity, any anhydro or deoxy prefixes or chalcogen replacement prefixes (e.g. thio) referring to the spiro junction should appear next to the carbohydrate stem. The carbohydrate component is cited first. Configuration at the spiro junction is assigned by the R,S system.
The following spiro disaccharide example is best named by use of a gem-bivalent substituent prefix:
Stereochemistry at C-1 of the glucose residue could be indicated as R or S, e.g. [(1R)-2,3-O-L-glucopyranosylidene].....
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).
26. IUPAC Nomenclature of Organic Chemistry, Section F, revised version in preparation. [Now published in Pure Appl. Chem., 1999, 71, 587-643.]
27. IUPAC Commission on Nomenclature of Organic Chemistry, Revision of the extended Hantzsch-Widman system of nomenclature for heteromonocycles, Pure Appl. Chem., 55, 409-416 (1983).
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