(95e) Efficient Preparation of ?-O-4 Dilignols and Their Oxidative Coupling Studies

Lignin, as the second most abundant biopolymer, is one of the targets for plant biorefinery studies. Due to its complicated chemical structure, the complex chemical behavior of lignin is usually studied via model compounds, preferably with β-O-4 dilignols. Although several lignin β-O-4 dimers have been synthesized, those compounds are not truly representative of the lignin structure, because the β-aryl ether residues in lignins contain C3-side chains. In the present study, β-O-4 dilignols with two monolignols were synthesized with moderate to high yields. This synthetic method can be exploited for chemical investigations into lignin’s depolymerization and chemical modification. The β-O-4 dilignols that act as one of the lignin building blocks can be transformed into bio-based dibenzo[b,d]oxepine compounds in excellent yield by using stoichiometric amount of hypervalent iodine reagent as a green reagent. Overoxidation of β-O-4 dilignols lead to the formation of quinones derivatives. Preliminary studies of dibenzo[b,d]oxepine cytotoxicity on human cancer cell lines showed that dibenzo[b,d]oxepine with S type structure exhibited moderate cytotoxicity against MCF7 cell line. The use of lignin derived building blocks instead of the conventional petrochemicals to synthesis of biological active compounds represents a sustainable alternative to classical synthetic approaches.