Tetra-, penta-, and hexa-nor-lanostane triterpenes from the medicinal fungus Ganoderma australe

Chemical investigation on the medicinal fungus Ganoderma australe led to the identification of ten new nor-lanostane triterpenes, namely two hexa-nor ones, ganoaustratetraenones A (1) and B (2), five penta-nor ones, ganoaustraldehydes A-E (3-7), and three tetra-nor ones ganoaustrenoic acids A-C (8-10). The chemical structures along with the absolute configurations were determined by extensive spectroscopic analysis of 1D & 2D NMR and HRESIMS data. The postulated biosynthesis pathways of these compounds were proposed. Ganoaustraldehydes A (3) and B (4) showed moderate inhibition against nitric oxide production in RAW264.7 macrophage cells with the respective IC₅₀ values of 32.5, 34.2 µM (the IC₅₀ of positive control pyrrolidine dithiocarbamate was 20.0 µM).