Tagatose preparation

A D,L-tagatose preparation (m. p. 119-121°) has been obtained83 by recrystallizing together equal quantities of d- and L-tagatose. 

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. 

Recently Gatzi and Reichstein28 have prepared D-sorbose by refluxing D-gulose with pyridine and by the action of very dilute potassium hydroxide on D-galactose. The product of the latter reaction was contaminated with a little D-tagatose. 

This preparation was repeated later68 and the crystalline product classified as a-D-tagatose because this crystalline sugar of the D-series mutarotated in the levo direction, namely from +2.7° to —4° (see page 112). 

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. 

Deoxy-D-well studied as the o-erythro isomer. It has been prepared in two ways from the decomposition of l,l -(carboxymethylamino)bis(l-deoxy-D-tagatose), ( di-D-tagatosegly-cine ), and from iV-butyl-D-galactosylamine. " These two methods and the isolation procedures are similar to the corresponding ones described for the erythro isomer. The 3-deoxy-n-i/ireo-hexosulose (42) was obtained as a colorless, amorphous powder, [ ]d + 10° — + 12.7° (in water), and was characterized as osazones. The (2,5-dichlorophenyl)osazone and the (2,4-dinitrophenyl)osazone are crystalline, the latter yielding a triacetate. " ... 

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. 

Petersen-Skytte, U., D-Tagatose as a flavor creator in various food systems plus examples of preparing these food systems. Res. Disclosure, 491, P232, 2005. 

Preparative chromatography. A soln. of D-tagatose in aq. NHg-n-propanol adsorbed on silica gel-H (E. Merck, Darmstadt), left 12 hrs. on the column, and... 

Preparation, D-Tagatose has been prepared by the isomerization of D-galactose 102) with aqueous alkali or pyridine and by the oxidation of D-talitol with Acetobacter suboxydans 108),... 

In the really enzymemimetic process, the aldol reaction of (S)-2 with aldehydes, one obtains as depicted in scheme 3 polyhydroxylated ketones of the anti-(3S,4S) -configuration, hitherto difficult to prepare by either chemical or enzymatic methods (D-tagatose-1,6-diphosphate aldolase) [9]. Whereas excellent diastereomeric excess could be obtained after flash-chromatography (de > 95%), the maximum enantiomeric excess of so far up to 82% has yet to be optimized [16]. 

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