Psicose 6-

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

Another o-2-ketohexose, psicose, yields a mixture of allitoi and altritoi when reduced with NaBH4. What is the structure of psicose ... 

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... 

L-Allose phenylosazone, prepared from L-psicose, was decomposed by benzaldehyde to L-allosone, which was converted into L-alloascorbic acid.187... 

L-Fructose from L-fructose, L-mannose, L-psicose CaY Water [224]... 

Ketoses fructose, psicose, erythro-2-pentulose and sorbose, tagatose ... 

Com symp simple sugars, psicose, maltulose, oligosaccharides... 

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. 

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. 

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