Methyl /3-arabinofuranoside

The calculated optical rotations of methyl p-D-arabinofuranoside, methyl P-D-fhictofuranoside and sucrose as a function of ring conformations and, in the case of sucrose, of linkage conformation, has been described. " Anomeric C-(substituted)phenyl D-glucopyranosides can be distinguished on the basis of their Cotton effects at 260-280 nm. ... 

Only one site for periodic acid cleavage in methyl a-D-arabinofuranoside... 

Methanolysis of dimethylxylan in the presence of hydrogen chloride leads to the isolation of methyl 2,3-dimethyl-D-xylopyranoside in 90% yield,70 methyl 2,3,5-trimethyl-L-arabinofuranoside in 6% yield, and... 

From their kinetic results Bishop and collaborators >8) calculated the velocity constants of the furanoside anomerisations of their seven aldoses (Table 1), and rationalised them in terms of ring conformations and group interactions. Thus, for example, in the extreme cases methyl a-D-arabinofuranoside (4), having the fewest non-bonded steric interactions, is the most stable pentofuranoside, while methyl p-o-lyxofurano-side (5), having the least stable ring, reacts most rapidly. 

However, there still remain a number of characteristic features (not yet mentioned) which differentiate the mass spectra of furanoid from those of pyranoid compounds. For example, the mass spectrum of methyl tri-O-methyl-a,/S-L-arabinofuranoside (see Fig. 2) contains no D and no Bt ions, their formation being structurally impossible. The peak at m/e 88 is of low intensity, as the formation of both of the m/e 88 fragments (Hf and H ) proceeds concomitantly with the formation of unfavored carbenes ... 

In the case of the methyl D-fructofuranosides, there is a relationship to the D-arabinofuranosides, with a different type of C-l, C-2 interaction. Here, the hydrogen atom on C-l has been replaced by a hydroxymethyl group, and the difference in the C-2 interactions with the C-3 hydroxyl group should be small for the anomers the effect of the aglycon group (OMe) and the hydroxymethyl group will probably be similar. 

For the D-fructofuranosides, there is apparently little difference between interactions of either the aglycon methyl group or the hydroxymethyl group (on C-2) with the C-3 hydroxyl group the anomers are formed in approximately equal yields. The high yields obtained indicate the conformational stability of the D-fructofuranoside structure, which is very similar to that of the D-arabinofuranosides. 

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... 

It was shown that methyl 2,3-anhydro-/l-D-ribofuranoside (180) forms an equilibrium mixture with methyl 3,5- anhy dr o -/T i)- x y 1 oI uranoside (181), whereas the corresponding a anomer 182 gives in sodium methoxide solution the major product of epoxide-ring opening, namely methyl 2-0-methyl-a-D-arabinofuranoside (183).523,524... 

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