On the Basis of Degradation

Synthetic studies of validamycins were initially devoted to establishing the structure of validamycin A. The structure in which a ) -D-glucopyranosyl group is attached to 0-3 of the validamine residue was initially proposed on the basis of degradative studies. However, the original structure was re-... 

It is important not to assume that a lack of change or a very slow change will continue forever. One should not ignore the possibility that an induction period exists, particularly when durability is being assessed on the basis of degradation after a single time period (single-point data). 

The maximal quantity of sucrose released corresponded to about 75% of that theoretically expected from a D-glucosyl-sucrose. The disproportionately large amount of reducing sugars present in the mixture after the fifth day of incubation can be accounted for on the basis of degradation of some of the newly formed sucrose. In separate tests, the... 

The structures of dibenzazonines have been determined on the basis of degradation studies and/or spectroscopic properties. Structural determinations are further confirmed by comparison with synthetic samples. 

Erybidine (1) crystallizes as colorless needles and has the characteristic UV absorption at 284 nm. Its 1H-NMR spectrum shows the presence of an /V-methyl (2.82) and three methoxyl groups [3.92 (3H) and 3.87 (6H)]. Treatment with diazomethane gives a tetramethoxy derivative identified as O-methylerybidine (9) on the basis of degradation studies and comparison with a synthetic sample, thus establishing the monophenolic nature of the alkaloid. The hydroxyl group of... 

Chaksine (91) was isolated in 1935 by Siddiqui and Ahmad (143) from the seeds of Cassia absus L. (Caesalpiniaceae), a plant used in folk medicine. On the basis of degradation reaction products, Wiesner et al. proposed structure 91 (144), but Singh et al. arrived at a different structure (92) that would satisfy the experimental data (145). Final proof of structure 91 was obtained... 

The problem of the structure of the y-pyrone nucleus arose when it was discovered that the conventional formulas established on the basis of degradation and synthesis were unable to account for all the properties of y-pyrones. 2,6-Dimethyl-y-pyrone, for instance, does not form a phenylhydrazone its double bonds are not reduced by zinc and glacial acetic acid. 

The liposidomycins are a family of novel lipid-containing nucleoside antibiotics that were found in the culture filtrate and mycelia of Streptomyces griseoporeus These antibiotics, which have unique biological activity and structures, inhibit the formation of the lipid intermediate in bacterial peptidoglycan synthesis three times more than does tunicamycin and have extremely high specificity. The structures of liposidomycins B (1) and C were proposed on the basis of degradation and spectroscopic studies. They are identical except for slight variations in the lipid portion. 

On the basis of degradative studies, narcissidine was assigned the structure XXXIX. The partial absolute stereochemistry described in XXXIX is derived from the isolation of pluviine from the sodium and amyl alcohol reduction of narcissidine (66). The absolute and relative OH OCH3... 

Another prospect for the use of cell cultures is to establish a standard screening procedure for comparison of the rates of metabolism of different xenobiotics in plants (59-61). The metabolism rates could be rankedi and compared with other types of test results to establish a broad basis for the prediction of behavior of the xenobiotic in the ecosystem. Presentlyi there is no standard procedure for ranking xenobiotics on the basis of degradation in plant systems. 

On the basis of degradation mechanisms of hydrocarbon membranes, blocking of the aromatic ring by suitable substitution, such as fluorine atoms, can limit the HO addition reactions (Mitov et al. 2006a). The SOj groups cannot only promote proton conductivity, but can also reduces the activity of the aromatic ring toward HO addition. 

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