Galactofuranoside

The 1,3-dipolar cycloaddition. The interesting approach to aza-disaccharides in which the aza-part is linked to normal sugar was proposed by Martin.7 The sugar nitrone 1 reacted with 5-O-allyl-galactofuranoside to afford adduct 2 (Fig. 1). 

Crystalline 1,4-anhydro-D-sorbitol is of much more recent origin than 1,4-anhydro-D-mannitol, inasmuch as its preparation was first recorded in 1946.10 It was obtained by the restricted dehydration of D-sorbitol and has been given the trivial name arlitan. Two groups of workers simultaneously effected proof of its constitution. Hockett and coworkers11 treated the anhydride with lead tetraacetate and since its rate of oxidation coincided with that of ethyl D-galactofuranoside and since one molecular proportion of formaldehyde was formed, the authors concluded that the ring must involve Cl and C4 of a hexitol chain. Assuming that no other carbon atoms are involved, sorbitan is either 1,4-anhydro-D-sorbitol or 1,4-anhydro-D-dulcitol (Walden inversion at C4 of the sorbitol molecule). They therefore synthesized 3,6-anhydro-D-dulcitol (enantio-morphous with 1,4-anhydro-L-dulcitol) but found it to be different from arlitan. 

The separation of glycosides on a cellulose column was first applied to a mixture of pyranosides28 subsequently, separations were achieved for the methyl D-fructofuranosides and D-galactofuranosides.28 This technique was soon applied to many other mixtures it permits not only the isolation of crystalline products, but also a more quantitative evaluation of the formation of glycofuranosides.80-34... 

Wolfrom and coworkers88-71 were able to prepare various 1-thio-a-D-galactofuranosides, generally isolated as the acetates, after purification by column chromatography. Thus, the Pacsu and Wilson method gave sirupy ethyl 1-thio-a-D-galactofuranoside, and a crystalline acetate. This product was also obtained by treatment of the dithioacetal with dilute hydrochloric acid and then mercuric oxide. Ethyl 2-acetamido-2-deoxy-l-thio-a-D-galactofuranoside was prepared in 32% yield, and the /3-d anomer in 3% yield. 

Several oligosaccharides containing o-fructofuranose residues have been prepared,121 as well as an a-D-glucopyranosyl D-galactofuranoside.124... 

The data in Table VIII are presented in the order of the conformational stability observed for methyl glycosidation (see Table I on p. 99 and Table II on p. 105). In each of the three cases where data for both anomers are available, the trans-1,2 anomer is the more stable, and a lower rate-constant is observed. This is the same pattern as that observed in Table II. However the order of conformational stability given earlier is not observed here. The arabinofuranosides show the maximum stability, and the D-galactofuranosides and L-fucofuranosides, having similar conformations, show a similar stability, However, the furanosides of D-lyxose, n-mannose, and i>rhamnose show an unexpectedly high stability which is almost as great as those of the furanosides of the first-mentioned sugars. These data lead to the conclusion that the conformational stability for transition complexes... 

An entropy value for the acidic hydrolysis of ethyl 0-D-galactofuranoside was reported by Overend and coworkers.136 The negative value (—7.1 e.u.) was interpreted as being diagnostic of an A-2 mechanism, in contrast to the positive values (+13.7 e.u., mean value) and A-l mechanism found for a large number of pyranosides. The proposed intermediate is shown in formula (34). It was considered that the planar, furanoid ring is capable of... 

In contrast, ethyl /J-D-galactofuranoside (43) is oxidized at a lower but steadier rate141 more than two moles of oxidant are consumed per mole, and one mole of formaldehyde is formed. The 5,6-glycol is attacked first, to give (44), and then the tram-2,3-glycol is attacked, to afford the trialdehyde (45). Compound (44) cannot give a hemiacetal. The consumption... 

A series of similar changes was observed on treatment of 2-desoxy-D-galactose with ethanolic hydrogen chloride and it was possible to prepare ethyl 2-desoxy-a/8-D-galactofuranoside and ethyl 2-desoxy-aj8-D-galacto-pyranoside. Essentially similar results were observed with desoxy-pentoses, and the methyl glyco-furanosides and -pyranosides of 2-desoxy-L-ribose were prepared.141... 

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