Arabinose specific rotation

At that time certain 2-desoxyhexoses had been fairly extensively studied, but the only known 2-desoxypentose was 2-desoxy-L-arabinose the specific rotation of which had not been reported. Levene therefore synthesized 2-desoxy-D-xylose and 2-desoxy-L-arabinose. ... 

Synthetic 2-desoxy-L-ribose (-L-arabinose), prepared by the action of dilute sulfuric acid on L-arabinal (L-ribal), had the same numerical values of initial and equilibrium specific rotation (but opposite sign) as had the sugar of thymus nucleic acid. Hence the sugar was identified as 2-desoxy-D-ribose. On treatment with dilute sul-... 

The yields vary considerably, even for the same species. It should, however, be remembered that larch heartwood apparently contains much more arabinogalactan than does the sapwood, that the lower portion of the trunk is reported to yield more material than the upper, and that the content of arabinogalactan in the tree may well vary with the time of year. The ratio between galactose and arabinose residues also varies considerably, although there is no general difference as between the different species. It is evident that the wood is usually richer in arabinogalactan A than in B. Where no separation of these two components was undertaken, a molar ratio of galactose to arabinose of 5 to 6 1 is most common. The specific rotation is low and positive, with no evident difference between the two fractions. 

A summary of the yields obtained and the chemical properties of the arabinogalactans of this type so far investigated is presented in Table X. Even before purification, the yields, throughout, are very low. The ratio of D-galactose to L-arabinose varies widely, with no noticeable trend with respect to species, and the same is true of the specific rotations. 

Fig. 4. Effect of pH on the specific rotations [a] of sugar-molybdate complexes. A L-rhamnose(8), B D-xylose(6), C D-galac-tose(7), D D-glucose(5), E D-arabinose(4) (similar to ref. 16).

The specific rotation of a-xylose is +79° and, after mutarotation, it falls to +19°. Draw the pyranose form that predominates at equilibrium. Similarly, the specific rotation of a-arabinose is +175° and it falls to +104° after mutarotation. Draw the pyranose form that predominates at equilibrium. 

The compound pictured below is a sugar called (-)-arabinose. Its specific rotation is -105. (a) Draw the enantiomer of (-)-arabinose. (h) Does (-)-arabinose have any other enantiomers (c) Draw a diastereomer of (-)-arabinose. (d) Does (-)-arabinose have any other diastereomers (e) If possible, predict the specific rotation of the structure that you drew for (a), (f) If possible, predict the specific rotation of the structure that you drew for (c). (g) Does (-)-arabinose have any optically inactive diastereomers If it does, draw one. 

Hydroxyproline glycosylated with 1 4 arabinose residues has also been released by alkaline degradation of the chitobiose-specific lectin from potato (Allen et al., 1978). Using a combination of optical rotation measurements, Cl- and EI-MS (Ashford et al., 1982), it was established that the hydroxyproline of potato lectin is glycosylated with identical sequences (9) of arabinose residues as found in tobacco and runner bean cell wall glycoprotein. 

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