4-Aminocoumarin Derivatives as Multifaceted Building Blocks for the Development of Various Bioactive Fused Coumarin Heterocycles: A Brief Review

Aminocoumarins are found to be present in many natural products, pharmaceuticals, and organic materials. These derivatives demonstrate numerous biological activities including DNA gyrase, anti-proliferative and anti-breast cancer activities. Among the allaminocoumarin derivatives, 4-aminocoumarin derivatives have been reported to exhibit anticancer and anti-fungal properties. 4-Aminocoumarins and their derivatives are important precursors for the synthesis of coumarin fused N-heterocycles. Due to the presence of an amino group as well as enamine carbon, it is very reactive towards electrophiles and in most of the cases, it has a higher tendency to cyclize immediately by the various reaction path ways and provides the heterocyclic products. Unlike other aromatic amines, it did not give any Schiff base on reaction with aldehydes or ketones. Lamellarins, ningalin A, ningalin B, schumanniophytin, santiagonamine, goniothaline, and polyneomarline C are important natural coumarin fused N-heterocycles and show excellent biological activities, including antitumor, reversal of multidrug resistance, anti-HIV, wound healing, anti-malarial, anti-hepatitis, and anti-syphilis activities. The synthesized coumarin fused N-heterocycles have been reported to display Topoisomerases I inhibitory, DYRK1A inhibitory, and anti-cancer activities. Most of the syntheses of pyrrolo/imidazolo/indolo[3,2-c]coumarin, pyrido/quinolino[3,2-c]coumarins, pyrimidino[ c]coumarin and oxazino[c]coumarin have been synthesized easily from 4-aminocoumarin. This paper reviews the research data in the literature on the synthesis of bioactive coumarin fused heterocycles using 4-aminocoumarin derivatives over the period of 2-3 decades. It covers the synthetic applicability of 4-aminocoumarin for the development of coumarin fused 5-, 6-, and 8-membered ring derivatives via classical reaction protocols, microwavemediated reactions, organo-catalyzed reactions, transition metal-catalyzed reactions, and green reaction protocols.