Galactopyranosides , preparation

An X-ray crystallographic analysis has been performed44 on methyl 4,6-dichloro-4,6-dideoxy-a-D-galactopyranoside prepared by way of reaction of methyl a-D-glucopyranoside with sulfuryl chloride the molecule has the Cl (d) conformation, and the bond distances and valency angles are similar to those in simple sugars. 

Like in gangliosides, lactones might be found in some bacterial capsular polysaccharides containing 1-carboxyethylsubstituents. But their identification remains problematic due to the conditions of isolation and preparation of analytic samples. To facilitate their detection by NMR, and in order to determine if the formation or hydrolysis of lactones occurred during analytical procedures, synthetic model substances, 2,3- and/or 3,4-lactones based on gluco-12, manno-13, and galactopyranosides 14 were prepared and characterized by NMR spectroscopy (Fig. 2).20 The relative lactonisation rates in acetic acid-fi 4 and hydrolysis rates in buffered D20 were evaluated. 

Anhydro-D-dulcitol (XXXV) has been prepared by a method which demonstrates its structure. Hockett and coworkers11 prepared it from methyl 3,6-anhydro-a-D-galactopyranoside but both the anhydride itself and its tetraacetate were liquid. Carr63 obtained another anhydro derivative of dulcitol by heating it with phosphoric acid. This also was a liquid but gave rise to a crystalline dibenzoate and a dicarbanilate and was a dianhydro derivative, but no constitutional studies have yet been carried out on this substance. 

Novel macrobicyclic compounds have been prepared (151) from the tetraol obtained on de-O-benzylidenation of the bisgalactosido-18-crown-6 derivative aa-DD-117 in Figure 18. Selective tritylation of the two hydroxymethyl groups of the tetraol, followed by a base-promoted reaction with pentaethylene glycol ditosylate afforded aa-DD-155 with a polyether chain bridging the 4 and 4 positions of the D-galactopyranosidic rings across presumably the /3 face of the molecule. 

The benzyl protected methyl / -D-galactoside cyclic sulfate 56 can be prepared similarly from methyl 2,3-di-O-benzoyl-/ -D-galactopyranoside 248b (Equation 25) <1992S1035>. 

Several 0-aminoacyl sugars were prepared to study a relationship between taste and chemical structure. Methyl a-D-glucopyranoside, methyl a-D-galactopyranoside and methyl a-D-mannopyranoside were selected as sugar skeletons. As basic amino acids, esters of lysine, ornithine, a,Y-diaminobutyric acid, and a,p-diaminopropionic acid were introduced into 2-0-, 3-0-, and 4-0- positions of sugars leaving only 6-hydroxyl group free. The results of sensory analysis are list in Table VI. O-... 

Following the work of Mclnnes,289,290 methanolysis in the presence of potassium carbonate was used to prepare methyl 6-O-acetyl- and methyl 6-0-octadecanoyl-/3-D-glucopyranoside,291 o-nitrophenyl /3-D-galactopyranoside 6-phosphate,292 methyl 5-thio-a-D-glucopyranoside 6-phosphate,293 and 6,6 -di-0-hexadecanoyl-a,a-trehalose,294 from the appropriate, per-0-(trialkylsilyl)ated precursors. 

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