Unguisin G, a new kynurenine-containing cyclic heptapeptide from the sponge-associated fungus Aspergillus candidus NF2412

One new cyclic heptapeptide containing non-proteinogenic amino acid residues kynurenine and gamma-aminobutyric acid, named unguisin G, as well as three known congeners unguisins A, E and F, were isolated from a sponge-derived fungus Aspergillus candidus NF2412. The structures were elucidated by comprehensive spectroscopic analyses of HRESIMS and NMR data. The absolute configuration of amino acid residues of 1 was determined by advanced Marfey's method. All compounds were evaluated on antimicrobial activities against nine pathogens by the agar diffusion method. (C) 2020 Elsevier Ltd. All rights reserved.