Paenibacillin A, a new 2(1<i>H</i>)-pyrazinone ring-containing natural product from the endophytic bacterium <i>Paenibacillus</i> sp. Xy-2

<div><p>A new 2(1<i>H</i>)-pyrazinone ring-containing natural product, paenibacillin A (<b>1</b>), together with five known diketopiperazine derivatives <b>2</b>–<b>6</b> and two known isoflavones <b>7</b>–<b>8</b>, was isolated from the culture of an endophytic bacterium <i>Paenibacillus</i> sp. Xy-2. The structure of compound <b>1</b> was elucidated by extensive spectral methods, including UV, IR, HR-ESI-MS, 1D and 2D NMR and ECD experiments. Compound <b>1</b> exhibited moderate cytotoxicity against HL-60 cell line with IC<sub>50</sub> value of 50.48 μM.</p></div>