Argopsin, also known as 1-chloropannarin, is a secondary metabolite produced by many lichen species, such as Biatora cuprea[1] and Micarea lignaria.

[2] Argopsin (also known as 1'-chloropannarin) is a chlorinated depsidone compound first isolated from the lichen Argopsis friesiana by Siegfried Huneck and Elke Mackenzie in 1975.

Its UV spectrum matched that of pannarin, and infrared spectroscopy revealed characteristic aldehyde (1725 cm⁻¹) and hydroxyl (3500 cm⁻¹) bands.

The researchers synthesized argopsin by chlorinating pannarin in acetic acid, which produced a compound identical to the naturally occurring substance.

[3] In the lichen A. friesiana, argopsin occurs alongside atranorin, though its presence is described as "inconstant".