Skatolyl hydroperoxide

The mechanism of metabolic degradation of indol-3-ylacetic acid (39) is a matter of debate. A possible route demonstrated in vitro includes oxidative decarboxylation to skatolyl hydroperoxide (40), catalyzed by horseradish peroxidase isoenzyme C (HRP-C), followed by rearrangement to 3-(hydroxymethyl)oxindole (41), as shown in equation 12 . 

The FOX assay applied to a skatole oxidation product isolated by HPLC gave a positive result, supporting the contention that it is skatolyl hydroperoxide (40) . Mixtures of 183 and the eight diastereoisomeric hydroperoxides 184 and 185 derived from thymidine (42), as shown in equation 64, can be separated and detected by RP-HPLC with UVD at 229 nm. Each isomer is determined by applying the FOX assay using a capillary reactor heated at 60 °C to provide sufficient time for total oxidation of the Fe(ll) ions, followed by UVD at 596 mn . A commercial kit based on the FOX assay for hydroperoxide determination in plasma, serum and tissue homogenizates appears in Table 2. 

Oxidation of IAA (2.49) results in cation 2.50, which undergoes decarboxylation and results in the skatolyl radical (2.51). This compound reacts with molecular oxygen to form peroxyl radical 2.52. With IAA or another cellular reductor, the hydroperoxide 2.53 is formed. It is this compound that activates the peroxidase, and thus allows the oxidation of other substrates, such as coniferyl alcohol. Among the degradation products of 2.53, 3-methylene 2-oxindole (2.54) is the most abundant. 

---