Fragmentation sugar

In an attempt to avoid the need for derivatisation Rinehart and Cook -6 applied the technique of Field Desorption Mass Spectrometry to neomycin and successfully observed an intense response for the molecular ion at m/e 615(M + H) together with very small peaks at m/e 455, 307 and 206 representing the loss of sugar fragments. 

The similarity in the pyrimidine carbon resonances in cytidine and deoxycytidine is indicative of the independence of these shifts from the sugar fragments. The differences observed between the chemical shifts of uracil and thymine, or uridine and thymidine, indicate that they must result from the presence of the 5-methyl group in the latter. The downfield shifts ( — 7.5 ppm) of the 05 peaks of uracil or uridine upon 5-methyl substitution are typical for a carbon directly substituted by a... 

H). C,8H34N206S. the first lincosaminide antibiotic to which a structure was assigned, is defined chemically as methyl 6,8-dideoxy-6-(l-methyl-fro/M-4-propyl-L-pyrrolidin-2-ylcarbonylamino)-l-thio-D-erythro-L>-gal-actu-octopyranoside. Both lincomycin and the semisynthetic clindamycin (I, R = H, R = Cl), CisH ClNjOsS, are widely used in clinical practice. The trivial name of the sugar fragment of this antibiotic, methyl a-thiolincosaminide, has lent itself to the other members of this family, whether produced as secondary metabolites of soil microorganisms or derived semisynthetically by chemical modification. 

The antibiotic lincomycin (Figure 8.32) from Streptomyces lincolnensis bears a superficial similarity to the aminoglycosides, but has a rather more complex origin. The sugar fragment is termed methyl a-thiolincosaminide, contains a thiomethyl group, and is known to be derived... 

A New Mechanism of the Maillard Reaction Involving Sugar Fragmentation and Free Radical Formation... 

Thus we propose the existence of a new pathway to browning in the Maillard reaction, involving sugar fragmentation and free radical formation prior to the Amadori rearrangement. 

Relation of Sugar Fragmentation to Formation of Free Radicals and the Main Intermediates (4)... 

Further degradation leading to sugar fragmentation and to discoloration... 

Pyrazines are formed from many amino acid-sugar systems by the condensation of a-diketones arising from sugar fragmentation with amino acids via Strecker degradation and ammonia or amino acids. 

Reaction C Sugar dehydration Reaction D Sugar fragmentation... 

Table 2.2 Sugar fragmentation products in decreasing order of reactivity...

J-Hydroxyamino acids under pyrolysis conditions (250 °C) can give rise to a-hydroxyaldehydes and a-aminoalcohols, which can enrich the pool of sugar fragmentation products.59... 

Scheme 2.6 Formation of quinones from sugar fragmentation products...

That reactive a-oxoaldehydes derived from sugar fragmentation and glycolysis are probably intermediates in the crosslinking processes is supported by the work of Oimomi et al.,5S0 who took the next step by showing that, whereas incubation with 3-deoxyglucosone increased the fluorescent Maillard products from BSA about 10-fold, preincubation of the 3-DG with AG brought the fluorescence down by a factor of almost 5. 

T. Hayashi and M. Namiki, Formation of two-carbon sugar fragment at an early stage of the browning reaction of sugar with amine, Agric. Biol. Chem., 1980, 44, 2575-2580. 

M. Namiki and T. Hayashi, A new mechanism of the Maillard reaction involving sugar fragmentation and free radical formation, in B, 1983, 21-46. 

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