Isolation, Derivatization and Bioactive Properties of Natural Lignin Based Hydroxycinnamic Acids: A Review

Lignin, one of the major components of lignocellulosic materials, is the largest natural source of aromatic building blocks on the planet having high service potential for producing valuable chemicals and fuels. It is surrounded by an extensive network of hemicellulose and cellulose in lignocelluloses such as agricultural residues, processing by-products, forestry residues, etc. Therefore, its extraction needs proper procedures, which have been researched worldwide in the past few decades. Lignin is a complex phenolic polymer with hydroxycinnamyl alcohols i.e. p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol as its monomers. Also, lignin based phenolic acids i.e. substituted hydroxycinnamic acids such as p-coumaric acid, ferulic acid, caffeic acid, syringic acid, are core structural moieties in various drug categories such as antimicrobial, anti-inflammatory, analgesic, anti- tyrosinase, antihistamine, antirheumatic and anti-thrombosis agents. Therefore, differently substituted hydroxycinnamic acids isolated from lignin have been explored recently with a view of dual advantage of valorization of unavoidable wastes; and exploiting drugs, which would probably have no harmful side effects because of their natural origin. In this review, recent research findings on the extraction of lignin followed by classification of natural phenolic acids, isolation of substituted hydroxycinnamic acids from lignin and their derivatization for various bioactive properties are discussed.