Three new 2,5-diketopiperazines from the fish intestinal <i>Streptomyces</i> sp. MNU FJ-36

<p>The gut actinobacteria of marine-inhabited fish is one of the most important reservoirs of novel natural products. Currently, the <i>Streptomyces</i> sp. MNU FJ-36 was isolated from the intestinal fabric of <i>Katsuwonus</i> sp. and determined by 16S rRNA analysis. From the cultures of the <i>S</i>. sp. MNU FJ-36, three new 2,5-diketopiperazines (2,5-DKPs) were discovered and identified as 3-(3-hydroxy-4-methoxybenzyl)-6-isobutyl-2,5-diketopiperazine (<b>1</b>), 3-(1,3-benzodioxol-5-ylmethyl)-6-isobutyl-2,5-diketopiperazine (<b>2</b>) and 3-(1,3-benzodioxol-5-ylmethyl)-6-isopropyl-2,5-diketopiperazine (<b>3</b>). Their structures were elucidated on the basis of spectroscopic data analysis. All the compounds were also evaluated for their inhibitory activity against P388, A-549 and HCT-116 cell lines with the MTT assay.</p>