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Strophasterols A to D with an unprecedented steroid skeleton: from the mushroom Stropharia rugosoannulata.

The mushroom Stropharia rugosoannulata is called saketsubatake in Japanese, and wine-cap stropharia in English. It belongs to the family Strophariaceae, which is widespread in northern temperate zones throughout the world. It is edible and is cultivated for food. During screening for anti-Endoplasmic reticulum (ER)-stress and anti-Methicillin-resistant Staphylococcus aureus (MRSA) effects of the extracts of various mushrooms, we found activity in the extract of this mushroom. ER-stress induces apoptotic pathways with a signaling between ER and mitochondria. By triggering apoptosis on neural cells, the stress is a major cause of degenerative diseases such as Alzheimer disease. [1, 2] MRSA has developed resistance to most antibiotics and is one of the most prevalent pathogen in nosocomial infections. Therefore, anti-ER and anti-MRSA substances are urgently required. Recently we reported that several active steroids were isolated from this mushroom. [3] In further search for bioactive compounds from the mushroom, we discovered four novel steroids with a very unique and unprecedented carbon skeleton. Here, we describe the isolation, structure determination, and biological activity of the compounds from the mushroom.