New Antifungal Metabolites from the Mariana Trench Sediment-Associated Actinomycete sp. SY1965.

New streptothiazolidine A (), streptodiketopiperazines A () and B (), and ()-1-(3-ethylphenyl)-1,2-ethanediol (), together with eight known compounds (-), were isolated from the Mariana Trench sediment-associated actinomycete sp. SY1965. The racemic mixtures of (±)-streptodiketopiperazine ( and ) and (±)-1-(3-ethylphenyl)-1,2-ethanediol ( and ) were separated on a chiral high-performance liquid chromatography (HPLC) column. Structures of the new compounds were elucidated by their high-resolution electrospray ionization mass spectroscopy (HRESIMS) data and extensive nuclear magnetic resonance (NMR) spectroscopic analyses. Streptothiazolidine A is a novel salicylamide analogue with a unique thiazolidine-contained side chain and its absolute configuration was established by a combination of nuclear Overhauser effect spectroscopy (NOESY) experiment, electronic circular dichroism (ECD) and C NMR calculations. New streptothiazolidine A () and streptodiketopiperazines A () and B () showed antifungal activity against with MIC values of 47, 42, and 42 g/mL, respectively.