L-threo-Hexo-2,5-diulose
meso-xylo-Hepto-2,6-diulose
Continued from 2-Carb-10
Contents
The systematic name of a diketose is formed by replacing the terminal '-se' of the stem name by '-diulose'. The locants of the (potential) carbonyl groups must be the lowest possible and appear before the ending. The stem name is preceded by the appropriate configurational prefix. If there is a choice of names, a decision is made on the basis of 2-Carb-2.2.2. In cyclic forms, locants may be needed for the positions of ring closure; that of the (potential) carbonyl group is cited first.
Examples:
meso-xylo-Hepto-2,6-diulose
2-Carb-11.2. Multiple sets of chiral centres
If the carbonyl group(s) divides the sequence of chiral centres, the configurational prefixes are assigned in the normal manner (see 2-Carb-8.4) for all chiral centres; the non-chiral centres are ignored.
Examples:
α-D-threo-Hexo-2,4-diulo-2,5-furanose
L-altro-Octo-4,5-diulose
not L-talo-octo-4,5-diulose
L-glycero-D-manno-Nono-2,7-diulose
D-glycero-D-ido-Nono-3,6-diulose
2-Carb-12. Ketoaldoses (aldoketoses, aldosuloses)
Names of ketoaldoses are formed in the same way as those of diketoses, but with use of the termination '-ulose' in place of the terminal '-e' of the corresponding aldose name (2-Carb-8.2). The carbon atom of the (potential) aldehydic carbonyl group is numbered 1, and this locant is not cited in the name. The locant of the (potential) ketonic carbonyl group is given (as an infix before '-ulose') unless it is 2; it may then be omitted (in this text, this locant is always retained for the sake of clarity). In cyclic forms, locants may be needed for the positions of ring closure; that of the (potential) carbonyl group is cited first. The position of the ring-size designator (e.g. pyrano) depends upon which carbonyl group is involved in ring formation (see examples).
Examples:
Methyl β-D-xylo-hexopyranosid-4-ulose
Methyl α-L-xylo-hexos-2-ulo-2,5-furanoside 
In a biochemical context, the naming of aldoketoses as 'dehydro' aldoses is widespread. Thus D-xylo-hexopyranos-4-ulose would be termed 4-dehydro-D-glucose. This usage of 'dehydro' can give rise to names which are stereochemically redundant, and should not be employed for naming derivatives.
Note. In Enzyme Nomenclature [23] dehydro names are used in the context of enzymic reactions. The substrate is regarded as the parent compound, but the name of the product is chosen according to the priority given in 2-Carb-2.2.
Examples:
D-Glucose + O2 = 2-dehydro-D-glucose +H2O2
(EC 1.1.3.10)
Sucrose + acceptor = β-D-fructofuranosyl 3-dehydro-α-D-allopyranoside + reduced acceptor (EC 1.1.99.13)
L-Sorbose + NADP+ = 5-dehydro-D-fructose + NADPH
(reaction of sorbose dehydrogenase, EC 1.1.1.123)
23. IUB Nomenclature Committee, 'Enzyme Nomenclature', Academic Press, Orlando, Florida (1992).
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