A-D-Tagatose

The taste properties of various other ketoses, including 2-pentuloses, 2-hexuloses, and 2-octuloses, have also been studied (see Table XV) to determine the significance of the 2-hydroxyl-2-hydroxymethyl arrangement of 2-ketopyranoses. Some of these, for example, a-D-tagatose (25), -d-g/uco-2-heptulose (26), a-D-mnMno-2-heptulose (27), a-D-fa/o-2-heptulose (28), a-D-a/tro-2-heptulose (29), and D-g/ycero-a-D-g/ co-2-octulose (30),... 

Figure 2. Hydroxyl PMR signals for a-D-tagatopyranose (upper left) and a-D-mannoheptulopyranose (lower left) in methyl sulfoxide-d6. 13C NMR spectra of a,fi-D-tagatose (3) and a-D-lyxose in water and of a,/ -D-tagatose in methyl sulfoxide-(ppm relative to downfield 13CS2)-...

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). 

A one-pot procedure has been proposed for the conversion of dihydroxyacetone and PEP into D-tagatose-1,6-diphosphate 6 (Scheme 13.12). The reaction mixture contains glycerolkinase, pyruvate kinase, triose phosphate isomerase, and a D-tagatose 1,6-diphosphate aldolase [27]. 

Tagatose ( ) a-D-Glucose minus a-D-Xylose (-) -o-Glucose minus/3-D-Xylose(-... 

The substrate spectrum of SuSyl from yeast is well documented for a variety of acceptors [24, 29, 30]. In the series of ketoses we concluded that SuSyl favors the 3S,4R configuration because L-sorbose 4 and D-xylulose 5 are accepted and D-tagatose 6, D-psicose 7, and D-sorbose 8 are not substrates (Fig. 2.2.6.1 and... 

Schleifer, K.H. Hartinger, A. Gotz, F. Occurence of D-tagatose-6-phosphate pathway of D-galactose metabolism among Staphylococci. FEMS Microbiol. Lett., 3, 9-11 (1978)... 

The composition of 6-0-methyl-D-ii/ to-2-hexulose (6-O-methyl-D-tagatose) in aqueous solution at 35° is 21% of a-furanose, 69% of/ -fura-nose, and 10% of the keto form.15 The ratio of a- to / -furanose for 6-0-methyl-D-psicose was found to be — 2.4 1 that of a- to / pyranose for 5-O-methyl-D-psicose, —1.25 1 the proportion of the keto form was not determined.13... 

While the lyases that transfer a pyruvate unit form only a single stereogenic center, the group of dihydroxyacetone-phosphate-(DHAP, 41)-dependent aldolases create two new asymmetric centers, one each at the termini of the new C-C bond. A particular advantage for synthetic endeavors is the fact that Nature has evolved a full set of four stereochemically-complementary aldolases [189] (Scheme 6) for the retro-aldol cleavage of diastereoisomeric ketose 1-phosphates— D-fructose 1,6-bisphosphate (42 FruA), D-tagatose 1,6-bisphosphate (43 TagA), L-fuculose 1-phosphate (44 FucA), and L-rhamnulose 1-phosphate (45) aldolase (RhuA). In the direction of synthesis this formally allows the... 

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