Unstable Tetramic Acid Derivatives from the Deep-Sea-Derived Fungus <i>Cladosporium sphaerospermum</i> EIODSF 008

• Main Authors: Xiao Liang, Zhong-Hui Huang, Xuan Ma, Shu-Hua Qi
• Format: Article
• Language: English
• Published: MDPI AG 2018-11-01
• Series: Marine Drugs
• Subjects: deep-sea-derived fungus; <i>Cladosporium sphaerospermum</i>; tetramic acid; cladosporiumins I-O
• Online Access: https://www.mdpi.com/1660-3397/16/11/448

Seven new unstable tetramic acid derivatives, cladosporiumins I-O (<b>1</b>&#8315;<b>7</b>), together with the known analogue cladodionen (<b>8</b>) were isolated from the extract of the deep-sea-derived fungus <i>Cladosporium sphaerospermum</i> EIODSF 008. Their structures were elucidated by spectroscopic analysis, quantum chemical calculations and ECD spectra. Compound <b>4</b> was a Mg complex of tetramic acid derivative. In acidic solvent, <b>4</b> could change to <b>1</b> and <b>6</b>, and <b>7</b> could change to <b>5</b>. In addition, <b>1</b>, <b>5</b> and <b>8</b> existed as two exchangeable isomers, respectively. The structures of cladosporiumins E-H were reassigned as their Na complexes. The antibacterial and cytotoxic activities of <b>1</b>&#8315;<b>8</b> 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.