Synthesis, Structure, and Cytotoxicity Studies of Some Fungal Isochromanes Kouji Kuramochi,* ,† Kazunori Tsubaki, † Isoko Kuriyama, ‡ Yoshiyuki Mizushina, ‡,§ Hiromi Yoshida, ‡ Toshifumi Takeuchi, ⊥ Shinji Kamisuki, ⊥ Fumio Sugawara, ⊥ and Susumu Kobayashi ∥ † Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, Sakyo-ku, Kyoto 606-8522, Japan ‡ Laboratory of Food & Nutritional Sciences, Faculty of Nutrition, Kobe Gakuin University, Nishi-ku, Kobe, Hyogo 651-2180, Japan § Cooperative Research Center of Life Sciences, Kobe Gakuin University, Chuo-ku, Kobe, Hyogo 650-8586, Japan ⊥ Department of Applied Biological Science, University Tokyo of Sciences, 2641 Yamazaki, Noda, Chiba 278-8510, Japan ∥ Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan *S Supporting Information ABSTRACT: Ustusorane D and penicisochromans B−D are natural isochromans isolated from Aspergillus ustus 094102 and Penicillium sp. PSU-F40, respectively. Herein, we report the syntheses of (−)-ustusorane D and (+)-penicisochroman B and the structures of penicisochromans C and D. The relative configuration of natural ustusorane D and the absolute configuration of natural penicisochro- man B were determined. Two plausible structures for penicisochro- man C were evaluated through synthesis, but their 1 H and 13 C NMR data were not in agreement with those of the natural product. The structural revision and the determination of the absolute configuration of natural penicisochroman D were achieved. Structure−activity relationship studies of the synthetic compounds as well as a series of related isochromans indicated that the enone of the furanone moiety was essential for the cytotoxicity of these compounds toward HCT116 human colon cancer cells. Pseudodeflectusin, the related natural isochroman, suppressed cell growth and induced apoptosis in HCT116 cells. P seudodeflectusin (1) is an isochroman derivative that was first isolated from the culture broth of Aspergillus pseudodeflectus by our group in 2004 (Figure 1). 1 This compound exhibits cytotoxicity toward several human cancer cell lines, including those derived from the stomach (NUGC- 3), cervix (HeLa-S3), and peripheral blood (HL-60). The related natural products, ustusoranes C (2) and D (3), were isolated from Aspergillus ustus 094102 by Lu et al., 2 whereas penicisochromans B (4), C (5), and D (6) were isolated from the sea fan-derived fungus Penicillium sp. PSU-F40 by Trisuwan et al. 3 The 1 H and 13 C NMR spectra of 3 are different from those of 4, suggesting that these compounds could be a pair of diastereomers. The relative and absolute configurations of compounds 3−6 have not yet been determined. The total syntheses of pseudodeflectusin and ustusorane C were accomplished by our group 4,5 and successfully revealed the absolute configurations of these natural products. In the current paper, we report the syntheses of (−)-ustusorane D and (+)-penicisochroman B, as well as the proposed structures for penicisochromans C and D. The relative configuration of ustusorane D and absolute configuration of penicisochroman B have been also reported. The NMR data for natural penicisochroman C were similar to those of the two plausible structures of penicisochroman C synthesized in the current study. The proposed structure for natural penicisochroman D has been revised, and its absolute configuration was determined. Furthermore, the cytotoxicities of these synthetic Received: June 10, 2013 Figure 1. Chemical structures of pseudodeflectusin (1), ustusoranes C (2) and D (3), and penicisochromans B (4), C (5), and D (6). Article pubs.acs.org/jnp © XXXX American Chemical Society and American Society of Pharmacognosy A dx.doi.org/10.1021/np400460m | J. Nat. Prod. XXXX, XXX, XXX−XXX