**4. Conclusions**

In this study, four new decalin derivatives designated as altercrasins B–E (**2**–**5**) were isolated from a strain of *Alternaria* sp. OUPS-117D-1 originally derived from the sea urchin *A. crassispina*. Their chemical structures were confirmed by NMR spectral analysis, and their plausible stereochemistry was deduced by considering the NMR chemical shifts and spin–spin coupling constants, as well as the assignment of ECD Cotton effects. As a result of the assay for cytotoxicity, **4** and **5** bearing a diene moiety (C-6 to C-8) exhibited significant cytotoxic activity against these cancer cells, especially the HL-60 cell line. In especially, the activity of **4** was equal to that of 5-fluorouracil.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1660-3397/17/4/218/s1, Table S0: Spectral data including 2D NMR data for **1**, Table S1: Spectral data including 2D NMR data for **2**, Table S2: Spectral data including 2D NMR data for **3**, Table S3: Spectral data including 2D NMR data for **4**, Table S4: Spectral data including 2D NMR data for **5**, Figure S1: 1H and 13C NMR spectrum of **1** in acetone-*d*6, Figure S2: 1H-1H COSY of **1**, Figure S3: NOESY of **1**, Figure S4: HMQC of **1**, Figure S5: HMBC of **1**, Figure S6: FABMS of **1**, Figure S7: 1H and 13C NMR spectrum of **2** in acetone-*d*6, Figure S8: 1H-1H COSY of **2**, Figure S9: NOESY of **2**, Figure S10: HMQC of **2**, Figure S11: HMBC of **2**, Figure S12: FABMS of **2**, Figure S13: 1H and 13C NMR spectrum of **3** in acetone-*d*6, Figure S14: 1H-1H COSY of **3**, Figure S15: NOESY of **3**, Figure S16: HMQC of **3**, Figure S17: HMBC of **3**, Figure S18: FABMS of **3**, Figure S19: 1H and 13C NMR spectrum of **4** in acetone-*d*6, Figure S20: 1H-1H COSY of **4**, Figure S21: NOESY of **4**, Figure S22: HMQC of **4**, Figure S23: HMBC of **4**, Figure S24: FABMS of **4**, Figure S25: 1H and 13C NMR spectrum of **5** in acetone-*d*6, Figure S26: 1H-1H COSY of **5**, Figure S27: NOESY of **5**, Figure S28: HMQC of **5**, Figure S29: HMBC of **5**, Figure S30: FABMS of **5**.

**Author Contributions:** Conceived and designed the experiments: T.Y., T.N. (Tatsuo Nehira), and T.K.; Performed the experiments: T.Y., A.S., and T.N. (Takumi Nishii); Analyzed the data: T.Y.; and Wrote the paper: T.Y.

**Funding:** This research received no external funding.

**Acknowledgments:** We thank Endo (Kanazawa University) for supply of the cancer cells. We are grateful to M. Fujitake and K. Minoura of this university for MS and NMR measurements, respectively.

**Conflicts of Interest:** The authors declare no conflict of interest.
