Lichen substances—128 Mass spectroscopy of natural products—12. Comparative positive and negative ion mass spectroscopy of nitrogen-containing and ring C cleaved usnic acid derivatives

Abstract

The mass spectral fragmentation behaviour of some nitrogen-containing and ring C cleaved usnic acid derivatives has been studied. The principal fragmentation pathway is drastically changed in the nitrogen-containing compounds when compared to that observed with the ring C cleaved derivatives. The main fragment ions of the ring C derivatives are also present in the mass spectrum of usnic acid itself.

Analysis of Lichen Metabolites, a Variety of Approaches

“…The classical fragmentation patterns of depsidones include neutral loss of CO 2 on their central ring to yield a dibenzofurane moiety alongside different elimination processes depending on the nature of the substituents (Parrot et al 2013). Mass spectrum behavior of dibenzofuran and usnic acid derivatives was thoroughly discussed (Kutney et al 1974;Schmidt et al 1981). Hüneck and Schmidt (1980) described the fragmentation behavior of 16 usnic acid derivatives and established elimination mechanisms using deuterated analogues in both positive and negative modes.…”