Cryptic piperazine derivatives activated by knocking out the global regulator LaeA in Aspergillus flavipes.

Genome sequencing on an intertidal zone-derived Aspergillus flavipes strain revealed its great potential to produce secondary metabolites. To activate the cryptic compounds of A. flavipes, the global regulator flLaeA was knocked out, leading to substantial up-regulation of the expression of two NRPS-like biosynthetic gene clusters in the ΔflLaeA mutant. With a scaled-up fermentation of the ΔflLaeA strain, five compounds, including two previously undescribed piperazine derivatives flavipamides A and B (1 and 2), along with three known compounds (3-5), were obtained by LC-MS guided isolation. The new compounds were elucidated by spectroscopic analysis and electronic circular dichroism (ECD) calculations, and the biosynthetic pathway was proposed on the bias of bioinformatic analysis and 13C isotope labeling evidence. This is the first report to access cryptic fungi secondary metabolites by inactivating global regulator LaeA and may provide a new approach to discovering new secondary metabolites by such genetic manipulation.

Identification of seven undescribed cucurbitacins in Cucumis sativus (cucumber) and their cytotoxic activity.

Cucurbitacin C-type cucurbitacins that are only identified in Cucumis sativus (cucumber) are, in part, responsible for the health benefits and bitter flavor. Nevertheless, detailed information about those functional ingredients in cucumber is scarce. In this study, ten cucurbitacin C analogues including seven undescribed ones have been isolated from the bitter leaves of cucumber, in which six compounds showed growth inhibition capabilities against tumor cell lines HepG2, A549, DU145 and HCT116. Intriguingly, cucurbitacin C6 and C7 exhibited a significant inhibition effect compared to the positive control taxol (IC50 = 1.86 ± 0.17 µM) on HepG2 cell line with IC50 values of 10.06 ± 0.34 µM and 4.16 ± 0.42 µM, respectively. The mechanism of cucurbitacin-induced apoptosis is likely down-regulating the expression of caspase-related proteins. This work enlarges the knowledge of the cucurbitacins in cucumber and highlights the importance of cucumber as a source of specialized metabolites in the food and medicinal industries.