Chemical and chemotaxonomical studies on filices. LVIII. Chemical studies on the constituents of Monachosorum arakii Tagawa (Pteridaceae)

A novel pterosin-type dinorsesquiterpene, mukagolactone (I), was isolated from the fronds of Monachosorum arakii TAGAWA (Pteridaceae), along with three new dinorsesquiterpene dimers, monachosorins A (II), B (III) and C (IV). Their structures were elucidated on the basis of spectroscopic and chemical data. Compound II may have been formed by an aldol-type condensation of 6-(2-hydroxyethyl)-5, 7-dimethylindan-1-one and the corresponding 5-formyl compound. The reduction of II afforded III, and the acid isomerization of II gave IV.