| Summary: | Three new diketopiperazine alkaloids, including two oxepine-containing diketopiperazines, chrysopiperazines A and B (<b>1</b> and <b>2</b>), and one quinazoline-containing diketopiperazine, chrysopiperazine C (<b>5</b>), together with three known analogues (<b>3</b>, <b>4,</b> and <b>6</b>), were isolated from the gorgonian-derived <i>Penicillium chrysogenum</i> fungus. The relative and absolute configurations of C-3 and C-15 in <b>1</b> and <b>2,</b> C-3 and C-14 in <b>5</b> were established by NOE modified Marfey’s analysis and electronic circular dichroism (ECD) calculations. Particularly, the absolute configurations of C-19 in <b>1</b> and <b>3</b>, which was very challenging to be identified due to the flexible conformation in a short aliphatic chain, were successfully determined by the vibrational circular dichroism (VCD) method, supplying with a reliable and optional method to define the absolute configurations. Additionally, this is the first report on oxepine-containing diketopiperazines from the genus <i>Penicillium</i>.
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