Allose solution

P-D-Allose internal standard solution, 1 mg mM - dissolve 200 mg P-D-Allose (Sigma Cat. No. A-6390) in 50% (v/v) saturated benzoic acid solution and make up to 200 ml. Store in the dark. (This is sufficient for at least 36 tests - it is expensive, so make just a sufficient amount.)... 

Take 0.25 ml of the mixed sugars standard solution, add 0.25 ml allose internal standard solution and 0.5 ml 2 M sulphuric acid, mix and substitute instead of the hydrolysate solution in the above procedure for preparation of alditol acetates. The concentration of sugars should give a linear relationship with peak area over the normal ranges. The GLC determination conditions will depend on the instrument, but the following are suggested ... 

The 2,3,4,5-tetra-0-acetyI-a(deht/do-pentoses are hydrated to the extent of — 90% in 7 3 oxolane -deuterium oxide.80 On the other hand, the 2,3,4,5-tetra-O-methylaldohexoses are hydrated74 to a lesser extent in aqueous solution at 37 °. When the carbon chain is in the planar, zigzag form, hydration is favored, and the ratio of aldehydrol to free aldehyde is — 2 1 (mannose and galactose) but when the chain is in a sickle form, hydration is impeded by 1,3-parallel interactions, and the ratio is —1 2 (glucose and allose). 

There is also an axial methoxyl group flanked by two equatorial hydroxyl groups in both of the pyranose forms of 3-O-methyl-D-allose. The pyranose forms are thereby destabilized, and, in solution, the proportions of the furanose forms are more than doubled,88 to give the composition 14 65 7.5 13.5 at 31 °. 

Fusion of an oxirane ring to a pyranose ring also deforms it, and thereby lowers its stability. The composition of 2,3-anhydro-D-mannose in aqueous solution,165 as determined by g.l.c. of the trimethylsilyl derivatives, is 23 7 65 5. This is remarkably similar to the composition of a solution of 2,3-O-isopropylidene-L-rhamnose. For 2,3-anhydro-D-allose, the ratios are166 41 12 5 42 (or 41 5 12 42). In this case, although the proportion of furanose forms is substantial, there is no clear preponderance of the //-furanose form, presumably because OH-1 and OH-2 are trans but OH-1 is quasi-equatorial by contrast, in the (preponderant)... 

Figure 2. The anomeric region of the 100 MHz NMR spectrum of D-allose in D20 (lower curve), and in 0.8 M NaCl, 0.8 M CaCl2, and 1.0 M LaCls solution in D20 (successive curves) at equilibrium...

The NMR spectra of D-allose show that the signal of the anomeric proton of the a-furanose form also increases and moves downfield on the addition of metal ions. The spectrum of the /2-furanose form, like that of the /2-pyranose form, is not affected (Figure 2). It appears that a cis-cis sequence of three hydroxyl groups on a five-membered ring also constitutes an arrangement suitable for the formation of complexes with metal ions. Since the proportion of furanoses in the equilibrium solution of D-allose is small, the changes in their proportion cannot be accurately measured. Hence the equilibrium of 5-O-methyl-D-ribose was studied ... 

Eschenmoser and co-workers [35] studied the aldomerization of glycoaldehyde phosphate which led to mixtures containing mostly racemates of the two diastereomeric tetrose 2,4-di-phosphate and eight hexose 2,4,6-triphosphates (O Scheme 2, route A). At 20 °C in the absence of air, a 0.08-molar solution of glycolaldehyde phosphate 2 in 2-M NaOH gave 80% yield of a 1 10 mixture of tetrose 3 and hexose 4 derivatives with DL-allose 2,4,6-triphosphate comprising up to 50% of the mixture of sugar phosphate [36]. 

Eschenmoser et al. have also postulated that the Btlrgi-Dunitz trajectory must be taken into account in discussions of the kinetic preference for formation of allose 2,4,6-triphosphate in the hexose series and of ribose 2,4-diphosphate in the pentose series, by aldomerization of glycolaldehyde phosphate in aqueous NaOH solution [37]. In this analysis, however, an additional interaction between the donor and acceptor substituents (b <-> f in Figure 6.40) is supposed to increase when the approach is non-perpendicular. 

SOLUTION TO 25a The only OH group in an axial position in (a) is the one at C-3. Therefore, this sugar is the C-3 epimer of D-glucose, which is D-allose. The substituent at the anomeric carbon is in the 8-position. Thus, the sugar s name is propyl j8-D-alloside or propyl j8-D-allopyranoside. Because the sugar is an acetal, it is a nonreducing sugar. 

Boiling a solution of sugar phenylosotriazoles in methanolic sulfuric acid causes the elimination of water and formation of a 3,6-anhydro ring, with a partial Walden inversion at C-3. Thus, n-am mo-hexose ( n-glucose ) phenylosotriazole (2) yields a mixture of D-ara6zno-hexose ( n-glucose ) and n-n to-hexose ( n-allose ) 3,6-anhydrophenylosotria-zoles (12) and (13), respectively. - Similarly, L-xi/lo-hexose phenylosotriazole afforded 3,6-anhydro-D-Z /a o-hexose phenylosotriazole. ... 

The assignments of H signals then allows the quantitative determination of all forms of monosaccharides in aqueous solution as reproduced in Fig. 4.2.13. The most important hexoses, namely glucose, mannose, and galactose, all occur as pyranoses only. The axial 3-OH group of allose, however, interacts repulsively with the a-OH group on C-1 and thereby overcomes the anomeric effect. The combination of both repulsive effects then also leads to 12% fura-nose. The latter effect is even more pronounced in altrose and ribose (Stod-dart,1971) (Fig. 4.2.13). 

Purify 2-deoxy-D-allose by two reciystallisations from absolute EtOH. The p-nitrophenylhydrazone has m 61-62°, [a]i 5 -55° (MeOH). An equilibrium solution at 31° in D2O contains 15% a-pyranose, 58% p-pyranose, 12% a-furanose and 15% P-furanose forms as estimated by HNMR spectroscopy, [see Angyal Adv Carbohydrate Chem Biochem 42 15 1984 for ratio of anomers in solution, Zoibach Ollapally J Org Chem 129 1790 1964] [Beilstein 1IV4283.]... 

For the same conformational reasons, the P anomers of d aldoses dominate in aqueous solution when the Cf atom has the D configuration (ribose, xylose, allose, glucose, gulose, galactose). The a anomers, however, predominate when the atom has the l configuration (arabinose, lyxose, altrose, mannose, idose, talose). 

Two kits are available from Englyst Carbohydrate to help ensure that accurate analytical results are obtained. The kit for the colorimetric procedure contains color reagent and a second kit contains a solution of allose as internal standard for the GC procedure. Both kits contain the required enzymes, sugar solutions, and reference materials and are rigorously tested in-house. 

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