Quinaphthin, a binaphthyl quinonoid secondary metabolite produced by Helicoon richonis

Abstract

The aero-aquatic fungus Helicoon richonis(Boudier) Linder produces quinaphthin 4, an αβ′-binaphthyl quinone constituted by union of juglone at position 8 to 3-hydroxyjuglone at position 2. The compound exists as a 6-membered cyclic hemiketal {systematic name 3,6a,9-trihydroxydibenzo[b,kI]xanthene-4,8,13(6aH)-trione}. Methyl iodide in the presence of silver oxide converts quinaphthin into the trimethyl derivative of an isomer of the compound. The structures of both compounds have been determined by X-ray crystallographic analysis.