Lanostane-Type Triterpenes from the Mushroom Astraeus pteridis with Antituberculosis Activity

Astraeus pteridis (Shear) Zeller, which mimics a truffle in its early developmental stage, is an earth-star fungus in the Astraeaceae, (Phylum Basidiomycota, Order Boletales). It is known only from western North America, occurring alone or in groups on the ground in forests of conifers, with which it forms symbiotic, mycorrhizal associations [1]. It is unpalatable because of its leathery texture and powdery spore mass. The related Astraeus hygrometricus (Pers.) Morgan has been used traditionally in Chinese folk medicine as a hemostatic agent [2]. Several triterpenoids have been isolated from A. hygrometricus, but no biological activities have been investigated [3]. Bioassay-guided fractionation of the EtOH extract of the Truffle-mimiking mushroom Astraeus pteridis led to the isolation and identification of three new (3–5) and two known (1, 2) lanostane triterpenes, and phenylalanine betaine. The structures of the isolates were elucidated based on 1D and 2D NMR spectroscopic data, HRESIMS results, and X-ray crystallographic analysis. The antituberculosis activity of the isolates was evaluated. Compounds 5 and 1 showed moderate antituberculosis activity with MIC values of 34.0 and 58.0 µg/mL, respectively.

Acknowledgements: We are grateful to the University of Illinois at Chicago for the antituberculosis and cytotoxicity assays and to A. Beyerle of the North American Truffling Society for the collection of specimens. References: [1] Molina A, Trappe, (1982), J Forest Sci, 28: 423–458. [2] Ying J, et al. (1987), Icones of medicinal fungi from China. Science Press, Beijing, China. [3] Takaishi Y, et al. (1987), Phytochemistry, 26: 2341–2344.