Psicose preparation

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... 

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

Reliable information relating to a ketose of formula I came first from the research of Ohle and Just.8 They prepared the first crystalline derivatives of D-psicose, namely l,2-isopropylidene-3,4-anhydro-D-psicose (V), and some of its esters by means of a Walden inversion in the detosyla-tion of 3-tosyl-l,2-isopropylidene- a -D-fructose (IV).12 Attempts to... 

The synthesis of D-psicose as a colorless sirup ([< ]% + 3.1° in water) by Steiger and Reichstein13 may be regarded as the first authentic preparation of this ketohexose. The Kiliani-Fischer cyanohydrin synthesis furnished D-allonic lactone (VII) from D-ribose. This lactone, on reduction with sodium amalgam, gave D-allose (VIII) which was transformed into D-psicose (I) by refluxing with pyridine. Pyridine had been introduced into the Lobry de Bruyn-Van Ekenstein reaction by Fischer, Danilov and their coworkers.13 ... 

In a series of reactions similar to those used in the preparation of D-psicose, Wolfrom, Olin and Evans30 synthesized D-sorbose (II) from D-xylonyl chloride tetraacetate (XIX) via the l-desoxy-l-diazo-fcefo-D-sorbose tetraacetate (XX) and fcefo-D-sorbose pentaacetate (XXI). 

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. 

Photooxidation of ( , )-1,4-disubstituted butadienes produces the corresponding 3,6-dihydro-1,2-dioxines 465 that are dihydroxylated into diols 466. Upon reduction (Zn/AcOH, or H2/Pd-C, or H2/Pt-C Mg/l2 (cat.), or thioureas) racemic alditols 467 are obtained. Isomerization of the dioxines catalyzed by iVA -bis(salicylidene)ethylenedianiinocobalt (II) gives the corresponding racemic uloses 468 (O Scheme 109). The method has been used to prepare ( )-psicose, ( )-l-deoxypsicose ( )-6-deoxypsicose [551]. 

Preparation. Isomerization of D-allose in anhydrous pyridine gives syrupy d-psicose, which may be isolated as the crystalline l,2 3,4-diisopropylidene acetal.150 D-Psicose is not fermentable by yeast. A review of the chemistry of D-psicose has appeared.151... 

Psicofuranine is the name given to an antitumor, antibacterial antibiotic substance produced by a streptomycete species. The structure was shown by Schroeder and Hoeksema to be that of 6-amino-9-D-psicofuranosylpurine (30). Identification of the sugar as D-n6o-hexulose (D-psicose) was afforded by its recognition as being a ketohexose by means of the Jordan-Pryde test and from preparation of the phenyl-... 

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. 

Rare sngars such as o-allose, o-psicose, o-tagatose, and o-talose have been incorporated into health foods and drinks [5], where they are used as bulking, browning, and low-calorie sweetening agents in food preparation [6-8]. These rare sugars have a taste similar to suctosc. 

In the transketolase-catalysed condensation (see Vol. 27, Chapter 2, Refs. 6,16) of hydroxypyruvate with a mixture of all four 4-deoxytetrose isomers, only the 2R- isomers reacted and only products with S-stereochemistry at the new chiral centre (C-3), le., 6-deoxy-D-fhictose and 6-deoxy-L-sorbose, were formed." A preparation of D- and L-foictose by enzyimc tddol condeos on is referred to below (Ref. 23), and the enzymic conversion of D- and L- r> thro-peittulose, D4i ose and D-psicose to the corre randk 3,4-rhreo-compounds is covered hi Part 4 tsi dds Chtqner (Rrf. 65). 

In this section, a highly efficient synthetic system for the preparation of 2-C-hydroxymethylaldopentoses is discussed. The reactions of four different keto-hexoses (o-psicose, D-fructose, L-sorbose and D-tagatose) were studied imder various conditions in order to elucidate the relationship between the two key processes, the coordination of the sugar to the nickel complex, and the rearrangement of the carbon skeleton of the substrate ketose. The system was then compared with that of the epimerization of the aldose/nickel(II)/ethylenediamine complex. 

Very interesting applications of the preparative potential of microbial ketol isomerases were reported by Fessner and co-workers, who gained access to preparative amounts of L-rhamnose isomerase (EC 5.3.1.14) as well as L-fucose isomerase (EC 5.3.1.3) from E. colihy cloning and over-expression [95]. In this way they were able to convert (Scheme 34) a variety of d- and L-pentoses and -hex-oses into the corresponding 2-ketoses, such as L-mannose (111) (to L-fructose, 113), D-gulose (114) (to D-sorbose, 8) and D-allose (22) (to o-psicose, 10), to mention just a few. 

Interesting extensions of isomerase chemistry are coupled enzyme systems. These could be advantageous for the removal of the desired isomer from the sometimes unfavourable equihbriiun to increase yields, as pointed out by Fess-ner and co-workers. Other apphcations could make rare sugars conveniently accessible from easily available starting materials, for example, in the preparation of D-psicose from o-fructose [6] by the combination of o-xylose isomerase with D-tagatose 3-epimerase. Clearly, the wide range of other available enzymes, for example, oxidoreductases, would allow for even more exciting opportunities to access unusual carbohydrates. 

Branch at C-2. - Full details (see Vol. 27, p. 10, ref. 49 and Vol. 26, p. 11, ref. 56) of the preparation of branched C-2-(hydroxymethyl)pentoses from four different ketohexoses (o-psicose, D-fructose, L-sorbose and D-tagatose) by an interesting isomerization reaction catalysed by Ni(II)-JV,iV -dialkyl cyclohexanediamine have been reported. ... 

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