Abstract
Two or more indole molecules tailored to a single non-metal central atom, through any of their C2–7 positions are not only structurally engaging but also constitute a class of important pharmacophores. Although the body of such multi-indolyl non-metallide molecules are largely shared to the anticancer agent bis(indolyl)methane, other heteroatomic analogs also possess similar medicinal properties. This concise review will discuss various catalytic and uncatalytic synthetic strategies adopted for the synthesis of the non-ionic (non-metallic) versions of these important molecules till date.
Highlights
Indole can be considered as a “prodigy” in the family of nitrogen-based heterocycles, because of its diverse presence in bioactive molecules [1,2,3,4,5,6,7,8], coupled with the distinct nucleophilic chemistry revolving its aromatic benzo-fused pyrrole system as encountered throughout the bibliography [9,10,11,12,13,14,15]
It is obvious that a non-metal hydride will become exceptionally crucial when its hydrogen atoms are replaced by this special heterocycle, forming a multi-indolyl hetero non-metallide
Related molecules consisting of heteroatoms at the central tethering position have appeared in the spotlight of anticancer research recently
Summary
Indole can be considered as a “prodigy” in the family of nitrogen-based heterocycles, because of its diverse presence in bioactive molecules [1,2,3,4,5,6,7,8], coupled with the distinct nucleophilic chemistry revolving its aromatic benzo-fused pyrrole system as encountered throughout the bibliography [9,10,11,12,13,14,15]. To synthesize the unsymmetrical bis(indolyl)sulfide 88, Janosik reacted the indole disulfide with free indole and obtained the product in 81% yield, where the sulfur linkages were 2,3’- with respect to the two indole nuclei (Scheme 11a) [73,74,75,76]. Elemental sulfur has been utilized in preparing bis(indol-3yl)sulfides under transition-metal compound catalyzed spontaneous oxidation of the central chalcogen atom. Such reactions were carried out by Shibahara (2014) and Yang (2016) [82,83]. Xu recently found indole-2-carboxylic acid derivatives as IDO1/ TDO dual inhibitors In their effort to synthesize the following bis(indol-4-yl)amine derivatives via a Buchwald amination led to the 4-amino-substituted compounds or acids after basic hydrolysis (Scheme 21) [108]. Selenation occurs at C-3 instead of C-7 for the C-3 unsubstituted substrates
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