Indole, oxidation

In our previous indole oxidation experiments, H202 has been added continuously with a flow rate of 10 pmol min 1 to a buffered indole solution in a batch reactor. In this case a constant maximum conversion at pH values between 3.0 and 8.0 was observed, whereas the indole conversion of the tandem system is limited by the H202 formation rate. At pH... 

Scheme 17.26 Generation of a novel spirocyclic structure by indole oxidation.

In a recent investigation to develop novel cytochrome P450 biocatalysts, DNA shuffling was used to produce chimeric cytochrome P450s mutants with enhanced biocatalytic activities, which were then co-expressed with NADPH-cytochrome reductase in E. coli to form an efficient system, in this case demonstrated to be effective for indole oxidation [69]. 

The indole oxidation has been shown to proceed via the hydroperoxide intermediate 9 (126), but whether this is formed via coordination catalysis, for example, as suggested in Reaction 41 for a phenol substrate (10— 12,13,14) (124), or via Haber-Weiss initiation, poses the same problem encountered in the organometallic type systems. A reactivity trend observed for Reaction 40 using tetraphenyl-porphyrin complexes (Co(II) Cu(II) Ni(II)) is reasonable in that the Co(II) system is known to give 1 1 02-adducts (at least, at low temperatures) but the reactivity trend also was observed for the catalyzed decomposition rate of 9. It is interesting to note that in Reac-... 

Selective indole oxidation is not an easy task and usually requires several steps with conventional synthetic organic methods. Here again, CPO allows the synthesis of oxindoles with high yields and selectivity [68, 69]. The key of the selectivity is the direct oxygen transfer from compound I to the substrates, yielding the oxindole derivative with substituted indoles, the yield is nearly quantitative (Fig. 6.6). 

H-3,l-Benzoxaziu 2,4-Dioxo-5-fluor-1,2-dihydro- E4, 219 (2,3-Dioxo — 2,3-H2 — indol Oxid.)... 

The slow continuous addition of hydrogen peroxide. results in better CFO pefforr aocef ,T which can be even further improved by sensor-controlled addition of HsOs 3I, increasing the CTO total turnover number for indole oxidation more than 20-fold to ca- 800 000. 

Oxidation of Primary Alcohols. Primary alcohols can be oxidized in the presence of a variety of functional groups, including tetrahydropyranyl ethers (eq 1), epoxides (eq 2), acetals (eq 3), silyl ethers, peroxides, lactones, alkenes, alkynes, esters, amides, sulfones, and indoles. Oxidation of substrates with labile a-centers proceeds without epimerization. ... 

Ley conditions to furnish aldehyde 316. During this conversion to the aldehyde, indole nitrogen protection was critical to avoid multiple side products resulting from competing indole oxidation. 

Metab. from the marine bacterium Vibrio parahaemolyticus isolated from the toxic mucus of the boxfish Ostracion cubicus. Also isol. as the product of indole oxidation by a strain of Claviceps purpurea. Exhibits antibacterial activity. Oil. 

Fig. 12 (a) Aspartic peracid catalytic cycle for epoxidation and indole oxidation [174, 175]. (b) Enantio- and site-selective oxidatitm of a ctnnplex bis-indole [176]. (c) Site-selective oxidation of an advanced intermediate in natural product total synthesis [177]... 

There are, however, certain types of natural reactions that occur in many situations, that are probably brought about by similar enzymes, and that may profit from an electrochemical study. Three of these that we have worked on for many years have been phenol oxidation, oxidative decarboxylation, and indole oxidation. The coupling of aromatic ethers electrochemically is unlikely to be a natural reaction, but the results have been so interesting and so analogous to phenol coupling, that this topic will be discussed briefly also. 

McClay K, Boss C, Keresztes I, Steffan RJ. 2005. Mutations of toluene-4-monooxygenase that alter regiospecificity of indole oxidation and lead to production of novel indigoid pigments. Appl Environ Microbiol 71 5476-5483. 

Keywords C-H functionalization Indole Oxidative cross-coupling Palladium... 

More recently Miller and Movassaghi apphed pteptide catalyst 28 in the chem-oselective oxidation of many indoles to the corresponding hydroxyl-indolenines, obtaining significant levels of enantioselectivity in this catalytic asymmetric indole oxidation [42]. 

Nitrosation.—Copper(ii) is claimed to retard the nitrosation of phenol by HNO2 and the subsequent oxidation of >-nitrosophenol to the nitro-compound by HNO3 through formation of complexes with HNO2 and the nitroso-phenol. The nitrosation of iV-methylindole (a reaction studied almost a century ago by Fischer) has been re-examined and the products have finally been characterized. With equimolar amounts of substrate and HNO2, a di-indole (48) (40%) and very little of the di-indole oxide (49) are formed, whereas with excess of HNO2 the... 

In the light of these considerations, the results of Jori et al. are questionable and should be considered with utmost caution. All available literature clearly shows that formylkynurenine is not the only product formed upon photooxidation of tryptophan, although seemingly it represents the major reaction pathway. Initial attack by oxygen at indole C-3 is implicated in all current interpretation of indole oxidations, and decomposition of the resulting hydroperoxide usually leads to opening of the indole ring (see also previous Section III. 1.1.). One reason for the lower yields of products obtained from free tryptophan than from a derivative is the occurrence of deamination in the case of the former. 

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