Sorbose preparation

A similar series of reactions applied to L-sorbose (once a rare sugar but now easily obtained from sorbitol by bacterial oxidation16) gives rise to 2-keto-L-gulonic acid.4 The method is not confined to keto-hexoses and has been employed in the preparation from L-erythropentulose (XXXI) of the 2-keto-L-ribonic acid (XXXV) which undergoes immediate transformation to the corresponding L-erythroascorbic acid (XXXVI).16... 

The ketone catalyst is readily prepared from D-fructose by ketalization and oxidation. The other enantiomer of this ketone, prepared from L-sorbose,... 

In the continuation of this work, a broad range of OZTs was prepared from selectively protected derivatives of D-fructose and L-sorbose (Scheme 26).47... 

The direct syntheses of D-glucosyl-L-sorboside from sucrose and L-sorbose and of sucrose from D-glucosyl-D-xyloketoside and D-fructose can be obtained in phosphate-free enzyme preparations.40 The reactions are ... 

Finally, when L-sorbose (81) was treated with hydrogen cyanide, a branched-chain, sugar lactone was formed which was characterized by converting it into a diacetal.127 An X-ray structure determination of this material revealed it to be 2,21 5,6-di-0-isopropylidene-[2-C-(hy-droxymethyl)-L-gulono-l,4-lactone] (82). However, all subsequent efforts to prepare 82 resulted in the formation of 2,3 5,6-di-0-isopropyli-dene-2-C-(hydroxymethyl)-L-gulono-l,4-lactone (83). 

L-Iditol (sorbi6rite), the last of the four naturally occurring hexitols, occurs in service berries along with sorbitol. After removing sorbitol from the juice by fermentation to L-sorbose with the sorbose bacterium, Acetobacter xylinum, the n-iditol is crystallized as a benzylidene derivative. It has been prepared by the action of sodium amalgam on... 

L-idose or L-sorbose. More recently it has been prepared by the more convenient hydrogenation of these sugars. " ... 

Not able to reproduce a previously reported approach [30] to (5) from D-galactose, Tyler and co-workers designed an efficient sequence starting from L-sorbose [46], via a partially protected 6-azido-6-deoxy-L-tagatose derivative, and obtained an overall yield of 20%. Ogawa and co-workers [47] prepared D-galactonojirimycin as well as 1-deoxygalactonojirimycin from L-quebrachitol (11), a natural product found in the serum of the rubber tree. 

Dialkyl dithioacetal derivatives of ketoses, such as D-fiuctose and L-sorbose, me inaccessible directly from the parent sugars, the ketose undergoing extensive decomposition under the conditions employed for mercaptaladon of aldoses. Such derivatives can, however, be prepared by indirect methods. Acetylation of D-fiuctose [40] and L-soibose with acetic adiydride and zinc chloride [41] leads to good yields of acyclic pentaacetates in which foe ketose carbonyl is not involved in a cyclic acetal. Subsequent treatment of these acetylated derivatives with thiols affords foe acetylated dialkyl dithioacetals in satisfactory yields, and conventional deacetylation affords foe unprotected dialkyl dithioacetals [40,41]... 

Other ketones and aldehydes have been used for preparing protected derivatives of L-sorbose that are structurally analogous to 26. These include cyclohexanone,113-115 formaldehyde,81,118 acetone,81, 118,117 benzaldehyde,81,118 and 1-methylcyclohexanone.115 The resulting acetals have been converted into L-ascorbic acid. 

An alternative procedure for the protection of L-sorbose (25), followed by oxidation at C-l and cyclization of the product to L-ascorbic acid, was developed by Hinkley and Hoinowski.257 L-Sorbose (25) was converted into methyl a-L-sorbopyranoside (37) by treatment with methanol and hydrogen chloride.258 Glycoside 37 was then oxidized with air in the presence of a suspension of platinum oxide in aqueous sodium hydrogencarbonate solution at 60°, to afford methyl ot-L-xylo-2-hexulopyranosidonic acid (38), which, when heated in hydrochloric acid, was converted into L-ascorbic acid (1), presumably by way of L-xy/o-2-hexulosonic acid (see Scheme 5). Acid 38 has also been prepared by oxidation of 37 with nitrogen tetraoxide.259,280 Yields were not reported for this reaction sequence, and it appears to offer no potential... 

Compound 43 has been prepared from a mixture of L-gulose and L-sorbose, or from L-gulose.293-296 The mixture of L-gulose and L-sorbose... 

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