Disaccharides melibiose

The naturally occurring trisaccharide rajfinose (melitriose) is hydrolyzed as easily as sucrose, by nearly all yeasts, into fructose and the disaccharide melibiose (Scheibler and Mittelmeier, 1889). The fructose part appears to be combined in the same manner as in sucrose (Fischer, 1898). 

The disaccharide melibiose is present in some plant juices. 

Deduce the structure of the disaccharide melibiose from the following data ... 

The ability of the custom-built dual gate/ion mobility quadrupole ion trap mass spectrometer equipped with electrospray ionization (ESI-DG-IM-QIT-MS) to perform mobility-filtered ion selection prior to mass analysis has been evaluated with peptides in the positive ion mode and carbohydrates in the negative ion mode. The separation of a disaccharide melibiose [a-D-Gal-(l-6)-D-Glc] and a trisaccharide rafflnose [a-D-Gal-(l-6)-a-D-Glc-(l-2)-P-D-Fru] as chlorine adducts in the negative... 

Similarly, per-O-trimethylsilylated mono- and P-linked disaccharides (lactose and cellobiose, not melibiose) could be converted into the corresponding a-glycosyl iodides, which upon SN2 displacement with CbT using TBACN mainly afforded P-cyano derivatives in good overall yields [191]. The cyanoglycosides were transformed into aminomethyl glycosides via reduction under mild conditions (Scheme 2.52). 

Disaccharides cellobiose and cellobiulose, (gentiobiose, isomaltose, kojibiose, laminarabiose, leucrose, melibiose, nigerose, palatinose, sophorose, trehalose, turanose, and xylobiose), lactose and lactulose, maltose and maltulose ... 

When sugars are treated with aqueous ammonia for a short time at low temperature in the absence of a catalyst, the reaction is arrested before heterocyclic compounds can be formed in appreciable proportion, and the products are mainly epimerization products of the sugars, probably formed by way of their 2,3-enediols. These epimerization products are summarized in Table I which shows the reactions of D-glucose, D-fructose, lactose, maltose, and melibiose with aqueous ammonia for a short time at low temperature. A dark-colored, high polymer is also formed in some instances (the browning reaction). In the ammoniacal solution, the monosaccharides are epimerized the disaccharides are epimerized and, in addition, may be hydrolyzed to monosaccharides that can also be epimerized hence, the variety of products obtained may be considerable. 

Isolactose is a disaccharide arising when a mixture of glucose and galactose is treated with Kefir extract (1902). It is different from lactose and melibiose, and forms a crystalline phenylosazone. 

Melibiose [0-a-D-galactopyranosyl-(l—>6)-D-glucopyranose] is a constituent of the trisaccharide raffinose (see Section II,2,f), and is liberated on hydrolysis of the latter by invertase. A detailed, structural elucidation of this disaccharide was described by French.115 Melibiose is found in the exudates115 and nectaries204 of several plants, and is also found in the tissues of various plants.75,110,123 205-209 In Aconitum... 

Wine contains traces of these disaccharides saccharose 25, maltose 26, and melibiose 27 ... 

In ammoniacal solutions of copper salts, the oxidation products are likely to contain nitrogen thus, hexoses give oxalic acid, imidazoles, hydrogen cyanide, and urea. Kinetic studies have been reported for the reaction of Cu(II) in the presence of ammonia with maltose, lactose, melibiose, and cellobiose.190 For the oxidation by tetraamminecopper(II) in ammoniacal and buffered media the rate of reaction is first order in disaccharide concentration, order one-half in ammonia concentration, but it is independent of Cu(II) concentration. The reaction rate is decreased by the addition of ammonium chloride, because of the common ion effect. These kinetics suggested mechanisms involving an intermediate enediolate ion, with the rate of reaction being equal to the rate of enolization.191 A similar mechanism has been proposed for the oxidation of D-fructose by a copper-pyridine complex in an excess of pyridine.192... 

In the bacterium E. coli, glucose is taken up by group translocation, lactose is taken up by secondary active transport (using H + ), and maltose is taken up by means of a binding-protein system. Outline how it would be possible to determine whether melibiose (a disaccharide of glucose and galactose) is taken up by . coli and. if it is, whether one of the mechanisms described earlier applies. 

The hydrogen bonding in melibiose monohydrate includes a homodromic cycle. Cyclic hydrogen-bonding schemes are not common in mono- and disaccharides, but in the crystal structure of the epimeric a,yS-melibiose monohydrate, 6-0-a-D-galactopyranosyl-cr,/ -D-glucopyranose-H20 [MELIBM01] (Fig. 13.49),... 

Melibiose (6-0-(3-D-Gal-D-G1c) (disaccharide) Widespread in plant exudates from Raffinose hydrolysis Sweet [[Pg.404]

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