Update on naturally occurring novel arylnaphthalenes from plants

Arylnaphthalene compounds, also called cyclolignolides, are lignans and have been extensively studied and documented, especially podophyllotoxin and its derivatives. Great progress has been made in phytochemical studies on arylnaphthalenes in the last 20 years (1999–2019), and arylnaphthalenes have been reported to have various biological activities. A total of 338 new arylnaphthalene compounds from over 60 families, including Acanthaceae, Phyllanthaceae, Lamiaceae, Lauraceae, Schisandraceae, Berberidaceae, and Boraginaceae, have been discovered. This paper will highlight their structural features, sources, and biological activities and briefly discuss their structure–activity relationships.