Indoles biological hydroxylation

The biological hydroxylation of the indole nucleus of tryptophan at the 5-position has been extensively studied (402). Arene oxides (33) seem to be involved as intermediates in the biological hydroxylation (51, 95, 209). 

From the historical point of view, interest in the chemical oxidation of tryptophan and related indole compounds was stimulated by attempts to elucidate the fate of tryptophan in animal metabolism. Biological hydroxylations and oxidative degradations of the indole nucleus represent main steps in the metabolic pathway of tryptophan (see Section II.4). 

It is an indole ethylamine formed in biological systems from the amino acid L-tryptophan by hydroxylation with tryptophan hydroxylase enzyme, followed by the decarboxylation by the nonspecific aromatic L-amino acid decarboxylase. 5-HT is then taken up into secretory granules and stored. 

Like histamine, serotonin is widely distributed in nature, being found in plant and animal tissues, venoms, and stings. It is synthesized in biologic systems from the amino acid l -tryptophan by hydroxylation of the indole ring followed by decarboxylation of the amino acid (Figure... 

A particular type of hydroxylation of aromatic compounds is the hydroxylation of indoles (XIII), which yield biologically active oxindoles (XIV) in nearly quantitative yields (Scheme VIII) [79],... 

Many of the biologically important -phenylalkyl-amines and also indolylalkylamines contain alcoholic and/or phenolic hydroxyls. For a separation by GC, these polar groups must be derivatized. This can be done by silylation. We use a one-step method [49], Both reagents, carbon disulfide and the silylating agent (usually trimethylsilylimidazole), are added to a solution of the amine in a polar solvent such as dimethylforma-mide or pyridine. A two-step procedure has also been described [56, 57]. The free bases are dissolved in ethyl acetate and treated with carbon disulfide, the solution is evaporated to dryness, and mustard oil is dissolved in pyridine and silylated at 100 °C. If the reaction time is sufficiently long, this procedure also silylates the indole nitrogen. Trifluoroacetylation has also been used to block the hydroxyls of the mustard oils [60]. 

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