Psicose solution

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... 

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-... 

The refining of solutions containing D-fructose requires careful control in order to prevent such side reactions as the epimerization of D-fructose (D-arafoino-hexulose) to D-psicose (D-rifeo-hexulose). Such processes, in which the use of weakly basic ion-exchange resins is important, have been described by Khaleeluddin and coworkers.48... 

Epimerization of reducing sugars occurs in neutral solution using DCC. For example, fructose on heating with DCC in anhydrous methanol gives mixtures of glucose, manose and psicose. ... 

It will be recalled that Lobry de Bruyn and Alberda van Ekenstein claimed that pseudofructose (n-psicose) was one of the products formed as a result of a transformation of D-fructose and n-glucose in mildly alkaline solution. The doubt that one can have about its presence in the glutose mixture rests on their observation that D-psicose is fermentable. Synthetic D-psicose prepared by Steiger and Reichstein is... 

The tautomeric equilibria of aldopentoses, aldohexoses and hexuloses in DMSO have been examined by C-n.m.r. spectroscopy the mutarotation kinetics of aqueous D-glucose have been investigated by i.r. methods, and Raman spectroscopic data on the tautomeric transformations of glucose in aqueous solution over a wide pH range confirmed that the ring-chain tautomerism depends on pH." The ring shapes of the two fiiranose and two pyranose forms of psicose in aqueous solution, riiown by n.m.r. spectroscopy to be present in almost equal proportions, have been analyzed by MM3."... 

The epoxide ring also may be opened hydrolytically, through the action of either alkali or acid in aqueous solution. The configurational course of the hydrolytic scission is the same as that depicted above with sodium methoxide. Thus, 3,4-anhydro-l,2-0-isopropylidene-D-psicose is hydrolyzed by aqueous sodium hydroxide to a mixture of products containing... 

Analysis of the deuterium isotopic shifts in the C-NMR spectrum has been particularly useful for sugar and oligosaccharide structural studies and spectral assignments (18, 151). Application of the differential isotope shift technique was used to study the tautomers of psicose, (33a-33d), in solution (Fig. 2.37a) (384). Signal assignments were made by comparison of calculated and observed cumulative isotope shifts. This method distinguished the C-1 and C-6 resonances. 

C]-D-erythrose, unidirectional rate constants for interconversions of the species present were obtained. Assignments of the signals of D-psicose in solution, in which both furanose and pyranose species are present have been made by using differential isotope-shift measurements. 

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