D-Hexuloses

I. I. Cubero and M. T. P. Lopez-Espinosa, Branched-chain sugars. 12. Synthesis of 3,4-anhydro-l-deoxy-3-C-methyl-D-hexulose derivatives, Carbohydr. Res., 154 (1986) 71-80. 

Irvine and Scott found that the mono-O-methyl-D-fructose obtained by methylation of a -di-0-isopropylidene-D-fructose and subsequent hydrolytic removal of the acetone groups gave the same mono-O-methyl-D-hexulose phenylosazone as that obtained by methylation of l,2 5,6-di-0-isopropylidene-a-D-glucofuranose, hydrolytic cleavage of the acetone residues, and formation of the phenylosazone. Further evidence for the structures of these two diacetals was obtained when Karrer and Hurwitz showed that each was unaffected... 

Similar to DHAP aldolases, the 3-hexulose 6-phosphate aldolase found in Methylomonas Ml 5 is highly specific for the aldol donor component D-ribulose 5-phosphate, but accepts a wide variety of aldehydes as replacement for formaldehyde as the acceptor. With propanal,... 

R)-2-Hydroxy-3-thiopropanal (Table 5), which could not be isolated from the reaction mixture, can be directly converted into 6-thio-D-wnimo-2-hexulose (7%) and 6-thio-L-xylo-2-hexulose (93 %) via rabbit muscle aldolase catalyzed condensation with dihydroxyacetonephos-phate28. 

The taste properties of various other ketoses, including 2-pentuloses, 2-hexuloses, and 2-octuloses, have also been studied (see Table XV) to determine the significance of the 2-hydroxyl-2-hydroxymethyl arrangement of 2-ketopyranoses. Some of these, for example, a-D-tagatose (25), -d-g/uco-2-heptulose (26), a-D-mnMno-2-heptulose (27), a-D-fa/o-2-heptulose (28), a-D-a/tro-2-heptulose (29), and D-g/ycero-a-D-g/ co-2-octulose (30),... 

Treatment of 3-deoxy-l,2 5,6-di-0-isopropylidene-a-D-erythro-hex-3-enofuranose with iodine and thallous fluoride in anhydrous ether afforded227 3-deoxy-l-fluoro-3-iodo-l,2 5,6-di-0-isopropyli-dene-D-xy/o-4-hexulose in 80% yield, together with small proportions of (tentatively identified) 3-deoxy-4-fluoro-3-iodo-l,2 5,6-di-0-iso-propylidene-a-D-allofuranose and two unidentified products. A mechanism proposed for the furanose ring-opening involves the formation of a 3,4-iodonium ion, and attack by fluoride at C-l. 

Recorded as o-allulose but preferred name is D-psicose or D-ri6o-2-hexulose. 

Crystallographic data have not yet been reported for one of the four hexuloses, namely, D- or L-psicose, not yet crystallized. Preliminary results are available for /3-D-fructopyranose.18a As expected, the sugar has the 1C (d) conformation. The hemiacetal group on C-2 is not bound to a hydrogen atom, whereas 0-6 is linked to two hydrogen atoms. 

The 2,5-anhydrides of 2-ketoses constitute a special case, in which the hemiacetalic carbon atom is involved in the anhydride bridge. Such anhydrides more closely resemble the 1,6-anhydroaldoses (glycosans) than the 2,5-anhydroaldoses. An example of a 2,5-anhydride of a 2-hexulose is obtained by the action of base on a D-fructosyl fluoride derivative treatment of l-0-methyl-/3-D-fructopyranosyl fluoride at 90° with concentrated, aqueous sodium hydroxide leads,80 in poor yield, to 2,5-anhydro-l-0-methyl-/3-D-fructopyranose. 

On deamination, 2-amino-l,5-anhydro-2-deoxy-l>mannitol gave l,5-anhydro-2-deoxy-D-eryf/iro-3-hexulose as the major product.54 The substitution product 1,5-anhydro-D-glucitol was formed to a small extent, and inversion again predominated, as with other axial amines (60, 72, and methyl 4-amino-4-deoxy-a-D-galactopyranoside) this is in accord with the predominant inversion of configuration reported for deamination, in water-rich media, of simple cyclohexyla-mines,154 and aminodecahydronaphthalenes39 in which the amino group is axial. As discussed previously (see p. 15), the extent of inversion can vary considerably with the nature of the solvent, and steric factors appear to be important in deaminations of per-O-acetyl amines (see pp. 37 and 49). 

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