Unstable Tetramic Acid Derivatives from the Deep-Sea-Derived Fungus Cladosporium sphaerospermum EIODSF 008

Abstract

Seven new unstable tetramic acid derivatives, cladosporiumins I-O (1–7), together with the known analogue cladodionen (8) were isolated from the extract of the deep-sea-derived fungus Cladosporium sphaerospermum EIODSF 008. Their structures were elucidated by spectroscopic analysis, quantum chemical calculations and ECD spectra. Compound 4 was a Mg complex of tetramic acid derivative. In acidic solvent, 4 could change to 1 and 6, and 7 could change to 5. In addition, 1, 5 and 8 existed as two exchangeable isomers, respectively. The structures of cladosporiumins E-H were reassigned as their Na complexes. The antibacterial and cytotoxic activities of 1–8 were also evaluated. However, because of their instability, all of the isolated compounds did not show significant antibacterial activity as the preliminary EtOAc extracts of the fungal strain.

Cladodionen Is a Potential Quorum Sensing Inhibitor Against Pseudomonas aeruginosa

“…The anti-QS activity of cladosporiumins has not been reported before. In addition, only five compounds, i.e., apiodionen, bripiodionen, vermelhotin, hypoxyvermelhotins and cladosporiumin I(1) [17,18], have the similar skeletons to cladodionen, comprising 2,4-pyrrolidinedione and a pyrene ring or a dihydropyran ring by a double bond. The anti-QS activity of the aforementioned compounds has not yet been investigated.…”

“…There was no difference in the growth dynamics of P. aeruginosa PAO1 between the control group and cladodionen-treated groups ranging from 100 µM to 400 µM. Figure S1,S2 and Table S1), the active compounds were identified as a pair of known isomers, cladodionen [17,18]. They were inseparable hybrid polyketide of two E/Z geometric isomers due to spontaneous and rapid isomerization between two forms ( Figure S3).…”

“…The results showed that it afforded a baseline separation of two chromatographic peaks (60% MeOH/H 2 O), but HPLC techniques failed to separate these two components. Based on the electrospray ionization mass spectrometry (ESIMS m/z 234.1 [M + H] + ) and nuclear magnetic resonance (NMR) spectroscopic analyses (Figures S1, S2 and Table S1), the active compounds were identified as a pair of known isomers, cladodionen [17,18]. They were inseparable hybrid polyketide of two E/Z geometric isomers due to spontaneous and rapid isomerization between two forms ( Figure S3).…”

“…Z148 with anti-QS activity from Jiaozhou Bay, China. The bioactive compound isolated from the secondary metabolites of this fungus was identified as cladodionen, a known natural product from Cladosporium and an inseparable hybrid polyketide of two E/Z geometric isomers [17][18][19]. The inhibitory effect of cladodionen on QS has not been reported; as such, the in vitro activity against QS systems of P. aeruginosa was evaluated in this study.…”

Anti-Xanthomonas activity of Antarctic fungi crude extracts

“…According to Tosi et al (2002) Cladosporium is the most frequently observed genus in association with antarctic mosses. Antimicrobial molecules were reported as produced by representatives of this genus (Zhang et al, 2001;Xiong et al, 2009;Liang et al, 2018), but studies related to the bioactivity of Cladosporium against Xanthomonas are still scarce. In a previous study published by our research group, a representative of Cladosporium showed potencial to inhibit the cell growth of X. citri, X. euvesicatoria and X. axonopodis pv.…”