Monosaccharides modeling results

Equatorially positioned methyl-branched derivatives may be obtained by reductive cleavage of spiro epoxides [94], Thus the Peterson olefination of 188gives the exocyclic 3 -methylene function in 189. By means of a Sharpless epoxidation the allylic 4"-hydroxy group should determine the chirality of the resulting epoxide. However, the Sharpless method does not show any reaction neither in a monosaccharide model system nor in this trisaccharide precursor [95]. Amazingly, the classical epoxidation with m-chloroperbenzoic acid is employed to give exclusively the desired (3"R) epoxide 190 in excellent yield. These results may be associated with a sufficient chiral induction of the stereochemical information at C-l", C-4", and C-5". A subsequent reduction furnishes the original E-D-C trisaccharide sequence 191 of mithramycin [95, 96]. 

Table I, which lists a number of mono-, oligo-, and polysaccharides and derivatives whose motional descriptions are available based on qualitative arguments, summarizes the experimental conditions and types of measurements used to obtain those descriptions. Table II deals specifically with those carbohydrates for which a quantitative treatment and dynamic modeling have been undertaken. In naming the compounds listed in Tables I and II, IUPAC rules are used for monosaccharide and less complex oligosaccharide molecules. However, empirical names are used for unusual oligosaccharides involving a complex aglycon substituent and polysaccharides. The gross motional features of a number of the compounds in Table I have been discussed in references 6-8, and will be mentioned here only if necessary for further clarification or for comparison with quantitative results.

As demonstrated in previous publications, model reactions of L-proline and monosaccharides result in complex mixtures of proline specific compounds (J —4 ) During the Maillard reaction of L-proline and reducing sugars more than 120 proline specific compounds were identified by MS-, IR-, 1H- and 13c-NMR-spectroscopy (among them ... 

The model monosaccharides just listed were prepared from common precursor IV.l (Scheme 39), which was readily obtained by azidonitration of 3,4,6-tri-O-acetyl-D-galactal followed by deacetylation with sodium methoxide. Treatment of IV.l with acetone and toluene p-sulfonic acid monohydrate at room temperature led to predominant formation of the thermodynamically favored 3,4-O-isopropylidene (IV.2) in 61% yield while also producing 27% of the 4,6-O-isopropylidene derivative IV.3. The position of the isopropylidene IV.2 was verified by the use of NMR chemical shift analysis to confirm the position of the acetate group in the resultant acetylated adduct IV.4. Synthesis of the 4-O-sulfate derivative (IV.7) from IV.2 utilized a step that differentiated the 3-OH and 4-OH positions after benzylation and de-isopro-pylidination of IV.2, a selective methylation at the 3-OH of diol IV.5 was achieved via a tin procedure [91] to give methyl glycoside IV.6. Conversion of the azide into... 

Volatile components formed from the reaction of monosaccharides or disaccharides with P-alanine were investigated in a dry condition as a model system of cookie processing. Maltol is a common compound formed in the Maillard reaction, but it was very difficult to detect it in previous experiments using actual cookie materials. In this work, we investigated the principal compounds and maltol formation from the reaction of monosaccharides or disaccharides with P-alanine at 150 °C for 10 min. Neither the reaction of monosaccharides nor the disaccharides with P-alanine resulted in the formation of maltol. 2,3-Dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one (DDMP) was detected as a principal product from the reaction of monosaccharides with P-alanine. 5-Hydroxymethyl-2-furfural was also confirmed as being a major product in both reactions. 

The apparent molal volumes and molal compressibilities of several monosaccharides, disaccharides and methyl pyranosides in dilute aqueous solution have been studied at 5, 15, and 25°C. The results were discussed in the light of solute-solvent interactions and a model for the hydration of galactose and lactose was proposed.The molal volumes of small carbohydrate molecules have been measured in an attempt at elucidating the relationship between molecular properties and sweetness. Molal volumes reflect fine differences in structure fe.q., axial or equatorial disposition of particular hydroxy groups) which are in turn related to differences in taste. In order to interpret differences in sweetness the viscosimetric constants and the heats of dilution of three monosaccharides, three disaccharides and the very sweet chlorinated sugar (21) have been determined, and their i.r. and Raman spectra have been recorded. The osmotic... 

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