D-Psicose

Draw Haworth structures for the two possible isomers of D-altrose (Figure 7.2) and D-psicose (Figure 7.3). 

Some examples will illustrate the applicability of this generalization in so far as it concerns alkaline scission. 5,6-Anhydro-l,2-isopropylidene-D-glucofuranose with alcoholic sodium hydroxide gives a mixture of isopropylidene-D-glucose and isopropylidene-L-idose. The latter results from inversion on C5, the former presumably by inversion on the non-asymmetric C6.7 3,4-Anhydro-l,2-isopropylidene-D-psicose (or allu-lose17) (XX) when treated with sodium hydroxide yields a mixture of products among which 1,2-isopropylidene-D-fructose (XIX) was detected (in the representations inversions are denoted by circles above the arrows and the carbons inverted are noted below the arrows). With sodium methoxide, however, l,2-isopropylidene-4-methyl-D-sorbose (XXI) is the chief product and results from inversion on C4.1S... 

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

Maltose (4-O-a-D- glucopyran- osyl-D-gluco- pyranose) 37 48 D-arabinose (2) maltulose (4-O-o-d- glucopyran- osyl-D- fructose) D-fructose (3) D-mannose (4) 4-O-ck-D- glucopyran- osyl-D- psicose D-glucose (1) imidazoles 3... 

The substrate spectrum of SuSyl from yeast is well documented for a variety of acceptors [24, 29, 30]. In the series of ketoses we concluded that SuSyl favors the 3S,4R configuration because L-sorbose 4 and D-xylulose 5 are accepted and D-tagatose 6, D-psicose 7, and D-sorbose 8 are not substrates (Fig. 2.2.6.1 and... 

Preliminary investigations on the substrate spectrum of the SllA mutant of SuSyl expressed in yeast reveal L-glucose 29 and L-rhamnose 30 as new substrates, as well as D-xylulose 5 with a relative activity of 112%. Most interestingly, both mutants accept D-psicose and L-fucose as new acceptor substrates. 

Hence, the proportion of the a-furanose form increases15 in the series 1-deoxy-D-psicose—D-psicose — D-aifro-3-heptulose, as the side chain changes from CH3 to CH2OH to CHOH-CH2OH, from 21 to 39 to 54%. 

The composition of a solution of 3-O-methyl-D-psicose15 at 27° is 31 7 56 6, whereas that of D-psicose is 22 24 39 15. In this case, the methoxyl group in the / -pyranose form (17) is axial, and 1,3-parallel interaction with one of its equatorial neighbors cannot be avoided. There is a similar interaction in the / -furanose form, too, but not in the a anomers. 

The composition of 6-0-methyl-D-ii/ to-2-hexulose (6-O-methyl-D-tagatose) in aqueous solution at 35° is 21% of a-furanose, 69% of/ -fura-nose, and 10% of the keto form.15 The ratio of a- to / -furanose for 6-0-methyl-D-psicose was found to be — 2.4 1 that of a- to / pyranose for 5-O-methyl-D-psicose, —1.25 1 the proportion of the keto form was not determined.13... 

Four sugars quite frequently occur as furanose residues in Nature. These sugars are D-fructose, n-arabinose, D-ribose, and 2-deoxy-n-erytAro-pentose D-Galactose, L-fucose, and D-psicose have also been found naturally in the furanose form. 

NMR spectral information about D-psicose (D-allulose) is particularly interesting because little is known of the solution characteristics of this keto-hexose. Having not as yet been obtained in any crystalline modifica-... 

Hexokinase will also phosphorylate D-fructose(IX) and fructose analogs. This shows that the enzyme also will accept furanose rings at the active site. The same hydroxyls appear to be important for binding and activity since d-tagatose(X) and D-psicose(XI), the C-4 and C-3 epimers of fructose, are not substrates for hexokinase (37). 

The presence of D-psicose (D-n o-hexulose, D-allulose) in distillery slop (from the fermentation of cane molasses) is claimed,96 but sharp experimental support is lacking. 

Ohle and Just112 have carried out the following sequence 1,2-isopro-pylidene-D-fructopyranose 3-p-toluenesulfonate —> l,2-isopvopylidene-3,4-anhydro-D-psicose —> l,2-isopropylidene-4-methyl-D-sorbose (VII), ([a]D -81.6°). Since the introduction of a methyl group does not alter greatly the specific rotation, it is to be expected that the parent 1,2-iso-... 

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