Valorizing Lignin to Bioactive Natural Compounds

Lignin, as the most abundant renewable aromatic polymer in nature, holds significant potential for the sustainable synthesis of high-value natural bioactive compounds (NBCs). However, current research exhibits a disjointed approach, in which upstream lignin depolymerization processes remain disconnected from downstream catalytic synthesis of these medicinally and nutritionally valuable chemicals. Consequently, most studies are limited to using lignin model derivatives as substrates. Furthermore, existing literature on synthesizing natural active components from lignin and its derivatives is fragmented and lacks comprehensive reviews. To address this gap, this review first outlines lignin depolymerization methods and their resulting primary aromatic monomers. Subsequently, following the classification framework of NBCs, it systematically evaluates recent advances in synthesizing high-value natural products (e.g., flavonoids, curcumin analogs, and tetrahydroisoquinolines) from lignin and its derived feedstocks using chemo-catalytic, biocatalytic, and chemo-bio cascade strategies. This integrated analysis aim is to bridge upstream depolymerization with downstream conversion processes, providing theoretical guidance and technical references for enhancing lignin valorization and enabling accelerated synthesis of NBCs from lignin.