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No clear picture has yet been elaborated concerning the mechanism of lignin growth, and thus this topic is the focus of the present paper. Namely, the enzymatic dehydrogenative polymerization (DHP formation) of coniferyl alcohol (CA, as a monolignol) and three dilignols and their reaction kinetics were investigated. The dilignols [guaiacylglycerol-β-coniferyl ether (IβO4), dehydrodiconiferyl alcohol (IIβ5), and pinoresinol (IIIββ)] and CA as a monolignol [(3-OCD3)-coniferyl alcohol (CAOCD3)] were synthesized and subjected to enzymatic DHP formation. The dilignol derived from CAOCD3 could be identified by its higher molecular weight in comparison with the starting dilignols (IβO4, IIβ5, and IIIββ). Based on the observed consumption rate of the CA and its dilignols, it was proposed that a radical transfer system exists between the dilignols, which is generated from the CA and the starting substrates.

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We isolated seven new iridoid glucosides (valerianairidoids I–VII; 1–3, 6, 7, 9, and 12) and six known compounds from the methanol extract of the dried rhizomes and roots of Valeriana fauriei. Chemical and spectroscopic data were used to elucidate the chemical structures of the seven new iridoid glucosides, and their absolute configurations were determined by comparing their electronic circular dichroism (ECD) spectra with those determined experimentally. Aglycones 1a, 6a, and 9a, which were obtained by enzymatic hydrolysis of the isolated iridoid glucosides, exhibited anti-proliferative activities against cancer stem cells (CSCs) established by a sphere-formation assay using human breast cancer (MDA-MB-231) and human astrocytoma (U-251MG) cells. Interestingly, these iridoids selectively showed anti-proliferative activities against CSCs from MDA-MB-231 cells. These results suggest that the iridoids obtained in this study may have potency as a breast cancer treatment and as preventive agent via exterminating CSCs.