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Regular Article Nat. Prod. Bioprospect. 2013, 3, 48–51 DOI 10.1007/s13659-013-0003-1 Five new 5,6-seco-tremulane sesquiterpenoids from the basidiomycete Conocybe siliginea Xiao-Yan YANG,a,b Tao FENG,a Jian-Hai DING,a,b Xia YIN,a,b Hua GUO,a,b Zheng-Hui LI,a and Ji-Kai LIUa,* aState Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China bUniversity of Chinese Academy of Sciences, Beijing 100049, China Received 6 January 2013; Accepted 13 March 2013 © The Author(s) 2013. This article is published with open access at Springerlink.com Abstract: Five new 5,6-seco-tremulane sesquiterpenoids (1–5), as well as three known analogues (6–8), were isolated from the basidiomycete Conocybe siliginea. The structures of new compounds were elucidated by extensive spectroscopic methods. The known compounds were identified by comparing their spectroscopic data with those reported in the literature. Keywords: Conocybe siliginea, 5,6-seco-tremulane sesquiterpenoidsIntroduction The genus Conocybe belongs to the order Agaricales and family Bolbitiaceae. Our previous study on the secondary metabolites of the Conocybe siliginea resulted in the isolation of a series of tremulane sesquiterpenoids.1–3 As a part of our efforts to find the structurally diverse and biologically active secondary metabolites from higher fungi,4–8 a further investigation on C. siliginea has led to the isolation of five new sesquiterpenoids, 11,12-epoxy-10α-hydroxy-5,6-seco-1,6(13)-tremuladien-5,12-olide (1), 11-acetoxy-5,6-seco-1,6(13)-tremuladien-5,12-olide (2), 11-aldehyde-5,6-seco-1,6(13)-tremuladien-5,12-olide (3), 11-acetoxy-10α-hydroxy-5,6-seco-1,6(13)-tremuladien-5,12-olide (4), and 12-acetoxy-5,6-seco-1,6(13)-tremuladien-5,11-olide (5). The new compounds were elucidated by means of spectroscopic methods, which represented 5,6-seco-tremulane sesquiterpe-noids. By comparison with spectroscopic data reported in the literature, three known compounds were identified as conocenolide A (6),2 conocenolide B (7),2 and 10β,11-dihydroxy-5,6-seco-1,6(13)-tremuladien-5,12-olide (8).1 So far, 5,6-seco-tremulane sesquiterpenoids have been found limited to basidiomycete C. siliginea1–3 and Irepex lacteus,9 and only dermatolactone showed cytotoxic activity and weak antimicrobial activity.9 This paper describes the isolation and structure elucidation of five new 5,6-seco-tremulane sesquiterpenoids. Results and Discussion Compound 1 was obtained as colorless oil. Its molecular formula C15H20O4 was established by the HREIMS at m/z 264.1363 [M]+ (calcd. for 264.1362), indicating six degrees of unsaturation. The IR spectrum indicated the presence of hydroxyl (3434 cm–1) and carbonyl groups (1779 cm–1). The 1H and 13C NMR data (Table 1) revealed the existence of two methyls, four methylenes (one oxygenated and one olefinic), five methines (two oxygenated and one olefinic), and four quaternary carbons (two olefinic and one carbonyl). Comparison of 1H and 13C NMR data of 1 (Table 1) with those of 10β,11-dihydroxy-5,6-seco-1,6(13)-tremuladien-5,12-olide (8)1 showed that they are similar in structure, except for the absence of an oxymethylene (δC 70.8, C-12) instead of the appearance of an acetal carbon (δH 6.10, δC 107.9 ) in 1, as *To whom correspondence should be addressed. E-mail: jkliu@mail.kib.ac.cn