An unusual highly functionalized lactarane sesquiterpene, named velleratretraol (1), was isolated from the ethanol extract of the fruiting body of the mushroom Lactarius vellereus. Its structure was determined through spectroscopic analysis and singlecrystal X-ray diffraction studies. The proposed assignment of the absolute configuration is based on computational results. It showed weak activity against HIV-1 cells with an effective concentration of 68.0 mg ml À1 and a selectivity index of 2.0. The Journal of Antibiotics (2009) 62, 129-132; doi:10.1038/ja.2008; published online 23 January 2009Keywords: lactarane sesquiterpene; Lactarius vellereus; velleratretraol; X-ray
INTRODUCTIONThe Russulaceae family is one of the largest in the subdivision Basidiomycotina in Whittaker's Kingdom of Fungi and comprises hundreds of species. 1 Sesquiterpenes play an important biological role in a majority of the Lactarius species. They are responsible for the pungent and bitter taste of the milky juice, the color change in the latex upon air exposure, 2 and they constitute a chemical defense system against intruders such as bacteria, fungi, animals and insects. 3 The fungal subdivision Basidiomycotina produces many toxic sesquiterpenes derived from the protoilludane skeleton. This skeleton is transformed and rearranged into a multitude of compounds. Fungal sesquiterpenes formed via the humulane-protoilludane biosynthetic pathway are characteristic for the subdivision Basidiomycotina. The largest group of sesquiterpenes, belonging to the classes of lactaranes, secolactaranes, marasmanes, isolactaranes, norlactaranes and caryophyllanes, are believed to be biosynthesized from humulane. 4 Fungi of the genus Lactarius have been shown to be a good source of bioactive secondary metabolites. [5][6][7] China is extraordinarily rich in higher fungi, with over 6000 species reported to belong to about 1200 genera. In our on-going research to explore the biologically active natural products of the higher fungi of China, [8][9][10][11][12] the chemical constituents of the fruiting bodies of Lactarius vellereus were investigated. This report describes the isolation and structure elucidation of an unusual highly functionalized lactarane sesquiterpene, named velleratretraol (1), and its anti-HIV activity. (d, 35.9) by analysis of the DEPT spectra. An analysis of the 1 H-NMR spectrum indicated the presence of three methyl groups at d¼1.03 (s), 1.12 (s) and 1.27 (s). The first two resonances were ascribed to geminal methyl groups, and the third one was ascribed to the methyl group on the carbon atom bearing the tetramethylene oxide carbocycle group. In particular, a doublet occurring at d¼3.73 (d, 11.8) was attributed to the C-4 bearing a secondary OH group, and two resonances at d¼5.55 (s) and 5.35 (s) were assigned at C-14 and C-15, respectively. Its formula indicated a sesquiterpene skeleton containing 4 degrees of unsaturation. The structure was suggested to be a tetracyclic sesquiterpene.
RESULTS AND DISCUSSIONThe key connectivity of the pr...