| Summary: | Two new spiro-heterocyclic <i>γ</i>-lactam derivatives, cephalimysins M (<b>1</b>) and N (<b>2</b>), were isolated from the fermentation cultures of the marine-derived fungus <i>Aspergillus fumigatus</i> CUGBMF17018. Two known analogues, pseurotin A (<b>3</b>) and FD-838 (<b>4</b>), as well as four previously reported helvolic acid derivatives, 16-<i>O</i>-propionyl-16-<i>O</i>-deacetylhelvolic acid (<b>5</b>), 6-<i>O</i>-propionyl-6-<i>O</i>-deacetylhelvolic acid (<b>6</b>), helvolic acid (<b>7</b>), and 1,2-dihydrohelvolic acid (<b>8</b>) were also identified. One-dimensional (1D), two-dimensional (2D) NMR, HRMS, and circular dichroism spectral analysis characterized the structures of the isolated compounds.
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