L-Psicose

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]... 

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. 

L-Psicose (XIII), a colorless sirup, [a]21D — 3.3° in water, has been... 

Upon application of these principles to the biochemical oxidation of allitol (XII), it becomes apparent that L-psicose (XIII) would be the product expected with A. suboxydans and indeed this enantiomorph is the one that was obtained using A. xylinum. 

The aldol reactions of 25 with appropriate aldehydes in the presence of L-proline have been also used by Enders and co-workers [141,142,143] for the preparation of aminosugars D-ery-f/tro-pentos-4-ulose, 5-amino-5-deoxy-L-psicose (37a), and 5-amino-5-deoxy-L-tagatose (37b) derivatives. 

Emil Fischer first described the condensation of D-fructose with acetone in 1895, and most of the early work on cyclic acetals of ketoses was performed with D-fructose. In 1934, Reichstein and Griissner published their classic synthesis of L-ascorbic acid (vitamin C), in which L-sorbose was converted into 2,3 4,6-di-0-isopropylidene-a-L-sorbofuranose or other di-alkylidene acetals. The emphasis of research activity then shifted to L-sorbose, and to the elucidation of an optimal procedure for preparing such diacetals. At about the same time, Levene and Tipson used isopropylidene acetals as derivatives for the purification of L-cri/thro-pentulose (as the di-isopropylidene acetal) and D-thrco-pentulose (as the monoisopropyli-dene acetal). Soon thereafter, Reichstein and coworkers used diisopropylidene acetals of D- and L-psicose, and D-tagatose, to purify the respective sugars. 

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