Biologically important compounds indoles

It is important to have an idea how widespread the relaxation mechanisms discussed previously are present in chemistry and biology. In a recent review article2 many more compounds that emit an additional, anomalous TICT fluorescence have been presented, ranging from a variety of naphthalene and anthracene derivatives to biologically important compounds like indoles and purine derivatives. The question remains whether other systems which do not show the anomalous fluorescence band might nevertheless be understood on the same basis. It may be the case that either the two fluorescence bands are superimposed or that the product fluorescence has not yet been observed because of quenching processes or because of a red shift into the infrared region. 

The quenching of chemically excited triplet acetone by biologically important compounds such as indoles, tyrosine derivatives, quinones, riboflavin, and xanthene dyes has been studied. Quenching occurs by electron and Forster transfer processes. Triplet-state parameters have been presented for the... 

To make use of the Mannich reaction it is possible to methylate the N-atom of the new side chain and eliminate trimethylamine. The product, a 3-methyleneindoleninium salt, can then be trapped with suitable nucleophiles. In the example shown in Scheme 7.7b, cyanide ion is used, and reduction of the resultant nitrile yields the important amine trypta-mine. Indol-3-ylacetonitrile is also the source of indol-3-ylacetic acid and other biologically useful compounds (see Section 7.1.7). 

This oxazole synthesis has been used to prepare some important biologically active compounds such as 3-[2-R-l,3-oxazol-5-yl)indoles (370) (R = Me pimpri-nine R = Et pimprinethine R = Pr WS-30581A] and l-Boc-2-chloro-3-(2-methyl-l,3-oxazol-5-yl)indole, a structural fragment of the cytotoxic marine peptide diazonamide A (371). 

Phenylalanine, tyrosine, and tryptophan are converted to a variety of important compounds in plants. The rigid polymer lignin, derived from phenylalanine and tyrosine, is second only to cellulose in abundance in plant tissues. The structure of the lignin polymer is complex and not well understood. Tryptophan is also the precursor of the plant growth hormone indole-3-acetate, or auxin (Fig. 22-28a), which has been implicated in the regulation of a wide range of biological processes in plants. 

Indole is an important heterocyclic system because it is built into proteins in the form of the amino acid tryptophan (Chapter 49), because it is the basis of important drugs such as indomethacin, and because it provides the skeleton of the indole alkaloids—biologically active compounds from plants including strychnine and LSD (alkaloids are discussed in Chapter 51). 

In general, the side chain derivatives of azaindoles undergo reactions analogous to those with indoles. The azagramines and 3-carboxaldehydes are the most useful, leading to many other azalogs of indole derivatives of biological importance. Unfortunately, most of the reactions and compounds involve the more accessible 7-azaindoles, so few comparisons in reactivity differences can be made. 

In a gas chromatographic study on biologically important amines, Fales and Pisano1 investigated some indole bases, such as tryptamine and serotonine. When the indole bases were gas chromatographed on a 0.75 % SE-30 column on Gas Chrom P, extensive tailing was observed, probably due to adsorptive interactions between the compound and the support. However, when a thicker layer of SE-30 was used (4 %) the compounds showed well-formed peaks without tailing. 

Tryptophan is probably the indole derivative most widely distributed in nature. It is converted into many compounds of important biological significance. Compounds biogenetically related to tryptophan include... 

Two important synthetic indoles are indole-3-butyric acid and indole-3-propionic acid. These two synthetics have the same indole ring as the naturally-occurring lAA but differ in their side chains. When longer side chains are added, the compounds appear to lose biological activity. Certain plants, however, apparently possess enzymes that shorten the side chains and transform them into biologically active ones (10). 

Nature abounds with compounds having a heterocyclic aromatic ring fused to one or more other rings. Two such compounds especially important in the biological world are indole and purine ... 

Nevertheless, it is now possible to formally summarise present knowledge concerning the biogenesis of various monoterpenoid-derived indole alkaloids of biological importance as depicted in Figs. 2-4, which, if not fully accurate in sequence or in cetail, do serve to bring out the firmly established basis upon which these compounds must be included in any comprehensive discussion of biological activity in terpenoid derivatives. 

The indole nucleus is an important scaffold found in many biologically active compounds, and as a result, many methods have been developed for its construction [54], Most of these rely on the assembly of the pyrrole ring on a preformed benzene nucleus. In principle, the indole nucleus could also be assembled by constructing a benzene ring on a preformed pyrrole ring. However, of the methods reported to date, the second method is much rarer. Recently, RCM has been utilized for... 

As a result of the biological importance of a class of benzo-fused indole-containing compounds known as the carbazoles, many methods have been developed for their synthesis [56]. Therefore, it will come as no snrprise that alkene RCM has been nsed as a strategy for the assembly of the benzene ring moieties that form part of the carbazole nnclens. 

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