Anhydro degradation mechanism

To accommodate these facts, the earliest mechanisms proposed for degradation of D-fructose assumed that it was present in the furanose form, and that the ring remained intact. It was assumed that the initial reaction was the elimination of water, to form the 1,2-enolic form of 2,5-anhydro-D-mannose, and that further dehydration resulted in 2-furaldehyde. The necessity for D-glucose to isomerize to D-fructose was assumed to account for the much lower reaction-rate of D-glucose. This mechanism does not account for the observation that 2,5-anhydro-D-mannose is less reactive than D-fructose, nor is there any evidence that 2,5-anhydro-D-mannose is present in reacting D-fructose solutions. Nevertheless, similar mechanisms have since been proposed.13-16 Because of the ease of mutarotation of D-fructose... 

Since phenyl a-D-galactopyranoside did react, although slowly, it is apparent that this substance was converted to some intermediate common to it and the jS-D-galactopyranoside, or else it was degraded by a mechanism unique to itself. The conversion of phenyl /3-D-mannopyranoside to l,6-anhydro-/3-D-mannopyranose9 was effected with relative ease, whereas phenyl a-D-mannopyranoside reacted at about the same rate but the intermediate product, which was apparently not stabilized by 1,6-anhydride formation, underwent extensive destruction in the alkali.8... 

Tetracyclines Tetracyclines are broad spectrum antibiotics obtained from Streptomyces strains or prepared semisynthetically. Use of tetracyclines has resulted in three types of renal effects. First, the use of outdated tetracyclines results in direct proximal tubular toxicity characterized by the increased excretion of amino acids, glucose, and phosphate (Fan-coni syndrome). The mechanism of this response is unclear, but appears to be due to the formation of the degradation product anhydro-4-epi-tetracycline. Second, administration of some tetracyclines, particularly demeclocycline, can result in a dose-dependent, reversible nephrogenic diabetes insipidus, which appears to result from an inhibition of ADH effects on water reabsorption. Lastly, in patients with preexisting compromised renal function, tetracyclines can induce increased sodium excretion and azotemia. The mechanism of the naturesis may be due to an effect of tetracyclines on luminal membrane sodium conductance, while the azotemia appears to result from the antianabolic effects of the tetracyclines. 

It has been suggested that 6 is not itself a primary product of the pyrolysis, and that the principal mechanism of its formation must involve a volatile precursor that has not yet been identified.213 Such a pyrolysis intermediate may be 1,2-anhydro-o-D-glucopyranose196,207,230 (4) (the suggestion is opposed in Ref. 211, in relation to the smooth thermal degradation of 2-O-methyIcellulose to yield l,6-anhydro-2-0-methyl-j8-D-glucopyranose284 compare Ref. 279), or, more likely, 1,4-anhydro-a-D-glucopyranose232,235,261 (21) (compare Ref. 280). However, compound 21 appears to be rather stable attempts at its conversion into levoglucosan have not yet been made.281... 

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