Pyranose derivatives manno

A comparison of the three binary copolymerizations of 1,6-anhydro-/S-D-gluco-, -galacto-, and -manno-pyranose derivatives gives some insight into the mechanism of copolymerization, if it is assumed on this evidence that the per-p-xylyl and perbenzyl derivatives can be used interchangeably.107... 

Scheme 1) whereas the reaction with the D-man/io-hexodialdo-l,5-pyranose derivative 3 produced, in low yield, the cyanohydrin 4 having an L-glycero-D-manno configuration and the stereoisomeric epimer at C-5, rather than at C-6 [14J. With an atm toward the synthesis of d- and L-glycero-D-manno-heptoses, the reaction of 3 with other reagents (2-inethyl-furan, alkyl magnesium chlorides) was also explored, without any substantial improvement of either stereoselectivity or yield. 

Takahashi, T. et al. A New Synthetic Approach to Pseudo-Sugars by Asymmetric Diels-Alder Reaction. Synthesis of Optically Pure Pseudo-f3-D-mannopyranose, I-Amino-I-deoxypseudo-a-D-manno-pyranose and Pseudo-a-L-mannopyranose Derivatives. 3.1 1990 [182]... 

The resonance frequency of the axial chlorine is always lower than that of the equatorial chlorine (David 1979). Figure 2.6 suggests another point of view the dispersion of equatorial resonances, close to 0.5 Hz, has an order of magnitude, called the crystal effect by the specialists, of intermolecular origin. When first analysed, they should not be considered significant. On the other hand, the variation range of the axial resonances, 1.7 MHz, is quite superior to the crystal effects. This dispersion expresses the before-mentioned fact that the anomeric effect of chlorine (as with any other substituent) in a pyranose is not independent of the configuration of the rest of the molecule. Thus, the resonance of the axial D-manno chloride is by far the lowest and it is well known that the anomeric effect is intensified in a-D-manno derivatives. 

Many derivatives of the dianhydro compounds have been prepared analogously. Thus, such substituted 1,6 2,3-dianhydro-/3-D-manno-pyranose (117) derivatives as the 4-O-alkyl,52,155,442,479,499,504-506,632,635 4-azido-4-deoxy,537,740,741 4-deoxy-4-fluoro,448,629 4-S-benzyl-4-thio,443 and 4-deoxy742 (compare Ref. 329) were prepared from the corresponding 2-sulfonates, and similar derivatives of l,6 3,4-dianhydro-/3-D-galactopyranose380,384,507,520,537,629,878,741 (compare Ref. 329) (119) and 1,6 3,4-dianhydro-R-D-allopyranose155,384 (32) were also prepared. 

O-AIkylidene and -arylidene derivatives of D-gluco-, D-allo-, D-manno-, and D-talo-pyranose are difficult to prepare directly. Lem-ieux and Detert59 prepared these from the 1,2-O-ethoxyethylidene orthoester, and were able to recover quantitative yields of 1,2-O-iso-propylidene, 1,2-O-cyclohexylidene, 1,2-O-cyclopentylidene, and diastereoisomeric 1,2-O-benzylidene acetals of D-glucopyranose. In their procedure, the orthoester is allowed to react, with scrupulous exclusion of moisture, with a ketone or aldehyde in the presence of an acid catalyst. 

The PFj-catalysed copolymerization of l,6-anhydro-2,3,4-tri-0-(4-methyl-benzyl)-P-D-glucopyranose and l,6-anhydro-2,3,4-tri-0-benzyl-p-D-manno-pyranose gave stereoregular polymers, as predicted by classical theory. Conformational analysis was invoked to explain differences in the reactivities of the monomers and the derived cations towards polymerization and copolymerization. 

The maleimide derivative (26), obtained by treating dextran with N-chloro-methylmaleimide, has been used as an oriented, impermeant probe in studies of the sulphydryl-containing polypeptides of human erythrocyte membranes. Base-catalysed condensation of periodate-oxidized dextran with nitromethane gave a nitrodextran that yielded an aminodextran on reduction. The nitrodextratf was shown to contain residues of 3-deoxy-3-nitro-D-manno-, -gluco-, -galacto-, and -talo-pyranose in the molar proportions 6 5 1 2. 

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