Oxidative degradation pathway

We cannot deny the possibility of a metabolic route for PEGs other than the oxidative degradation pathway via carboxylated PEG, although further evidence on the point seems to be required. The metabolic route for PEGs supported by plural researchers is the oxidative route as shown in Figure 3. 

As mentioned previously, oxidative degradation pathways can be complex, and it is useful to consider the chemistry of oxidative degradation. The oxidative degradation of pharmaceuticals has been discussed in the literature,23-27 and we assert that there are three major pathways, (1) autoxidation or radical-mediated oxidation, (2) peroxide-mediated, and (3) photochemically induced (see Table 5). Traditionally, dilute aqueous peroxide solutions have been used for oxidative stress testing of pharmaceuticals. Landmark papers by Boccardi23 24 in 1992 and 1994 identified autoxidation as the major oxidative degradation pathway for pharmaceuticals. Boccardi showed that the use of radical initiators such as... 

Terbutaline sulfate degrades through an oxidative degradation pathway resulting in a number of impurities. One of these, 3,5-dihydroxy-a)- er -butylaminoacetophenone has its own specifications and test procedure. 

Figure 6.6 Alternative oxidative degradation pathways in the presence of excess H202. (Adapted from Valderrama et al. [17]).

Figure 3.3 Oxidative degradation pathways of the guanine moiety of DNA upon OH addition at C8.

Chemiluminescence has also been proposed as a novel tool in paper conservation studies [654,655]. CL phenomena can be used for assessing the thermal and oxidative degradation pathways of paper-based historical documents. In contrast with the usual accelerated degradation experiments in climatic chambers, measurement of isothermal CL is quick. The influence of all paper components (alkalinity, metal content, cellulose peroxides and carbonyl groups, moisture) and exposure to light will be investigated in the framework of the PAPYLUM project (ending October 2004). 

Oxidation of methionine (Met) to methionine sulfoxide (MetO Figure 5) is the major oxidative degradation pathway in proteins, howevei MetO was found in only 11 of 73 proteins in a survey of protein degradation and is much less prevalent than degradation at Asx. 

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