Two new cytochalasans, trichoderones A (1) and B (2), and three known analogues, aspochalasins D (3), J (4), and I (5), were isolated from the endophytic fungus Trichoderma gamsii. Their structures were determined by analysis of their spectroscopic data. The absolute configurations of 1 and 2 were established by quantum chemical electronic circular dichroism calculations. Compounds 3 and 4 displayed cytotoxic activity against the HeLa cell line. Trichoderone A (1) possesses an unprecedented 7/6/6/5/5 pentacyclic system, whereas trichoderone B (2) contains the rare 6/5/6/6/5 pentacyclic skeleton with a 12‐oxatricyclo [6.3.1.02,7] moiety.

Trichodermone (1), the first spiro-cytochalasan with an unprecedented tetracyclic nucleus (7/5/6/5), together with its possible biosynthetic precursor aspochalasin D (2), was isolated from the endophytic fungus Trichoderma gamsii. Compound 2 displayed moderate inhibitory activity against HeLa cells with an IC50 value of 5.72 μM.

Endophytes, as members of special niche of fungi inhabiting unique environments, namely, the normal plant tissues or organs, have acquired genetic and species diversities, which could transform into chemo-structural and bioactive diversities. 1 Thus, endophytes are considered an outstanding source of bioactive natural products, and many different secondary metabolites with diverse structural features have been isolated from endophytes. [1][2][3][4][5][6] During an ongoing search for new bioactive secondary metabolites from endophytic fungi, the extract of one endophytic fungus Trichoderma gamsii inhabiting the traditional Chinese medicinal plant Panax notoginseng (BurK.) F.H.Chen displayed cytotoxic activity against HeLa cells. Bioactivityguided separation of this extract, resulted in two new cytochalasans, trichalasin A (1) originated from valine, and trichalasin B (2) together with aspochalasins I (3) 7 and J (4) 7 derived from leucine ( Figure 1). In this note, we present the isolation, structural elucidation and bioactivity of these compounds.The culture of T. gamsii was isolated from traditional Chinese medicinal plant P. notoginseng (BurK.) F.H.Chen. The isolate was identified based on the sequence (Genbank Accession No. JF964996) obtained the by analysis of ITS region of the rDNA. The fungal strain was cultured on the slants of potato dextrose agar at 25 1C for 10 days. The agar plugs were used to inoculate 250-ml Erlenmeyer flasks, each containing 40 ml of media (0.4% glucose, 1% malt extract and 0.4% yeast extract), and the final pH of the media was adjusted to 6.5 before sterilization. Flask cultures were incubated at 25 1C on a rotary shaker at 170 r.p.m. for 5 days. Fermentation was carried out in Fernbach flasks (500 ml) each containing 80 g of rice. Spore inoculum was prepared by suspension in sterile, distilled H 2 O to give a final spore/cell suspension of 1Â10 6 per ml. Distilled H 2 O (100 ml) was added to each flask, and the contents were soaked overnight before autoclaving at 15 lb in À2 for 30 min. After cooling to room temperature, each flask was inoculated with 5 ml of the spore inoculum and incubated at 25 1C for 40 days.The fermented material was extracted with ethyl acetate (20 l), and the organic solvent was evaporated to dryness under vacuum to afford a crude extract (100 g), which was fractionated by silica gel column chromatography (10Â100 cm) using CH 2 Cl 2 -CH 3 OH gradient elution. The fraction (0.8 g) which eluted with 100:2 CH 2 Cl 2 -CH 3 OH was separated by column chromatography, and further purification by reversed-phase HPLC (Lumtech, Berlin, Germany; YMC-Pack ODS-A column; 10 mm; 250Â10 mm; 2 ml min À1 , 75% MeOH in H 2 O for 5 min, and followed by 75-90% for 60 min) afforded trichalasin A (1; 1.5 mg, t R 21.5 min) and aspochalasin J (4; 5 mg, t R 29.3 min). Other fraction (0.3 g) eluted with 100:2 CH 2 Cl 2 -CH 3 OH was separated by Sephadex LH-20 CC repeatedly to obtain trichalasin B (2; 2 mg). One fraction eluted with 100:8 CH 2 Cl 2 -CH 3 OH was separated by Sephadex ...