Five new diketopiperazine derivatives, (3Z,6E)-1-N-methyl-3-benzy lidene-6-(2S-methyl-3-hydroxypropylidene)piperazine-2,5-dione (1), (3Z,6E)-1-N-methyl-3-benzylidene-6-(2R-methyl-3-hydroxypropylidene)piperazine-2,5-dione (2), (3Z,6Z)-3- (4-hydroxybenzylidene)-6-isobutylidenepiperazine-2,5-dione (3), (3Z,6Z)-3-((1
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Five new diketopiperazine derivatives, (3Z
)-3- (4-hydroxybenzylidene)-6-isobutylidenepiperazine-2,5-dione (3
), and (3Z
), were isolated from the marine-derived actinomycete Streptomyces
sp. FXJ7.328. The structures of 1
were determined by spectroscopic analysis, CD exciton chirality, the modified Mosher’s, Marfey’s and the C3
Marfey’s methods. Compound 3
showed modest antivirus activity against influenza A (H1N1) virus with an IC50
value of 41.5 ± 4.5 μM. In addition, compound 6
displayed potent anti-H1N1 activity with IC50
value of 28.9 ± 2.2 and 6.8 ± 1.5 μM, respectively. Due to the lack of corresponding data in the literature, the 13
C NMR data of (3Z
) were also reported here for the first time.