Compound isolation, purification, and identification

The WT P. citrinum and mutants were cultured on 2 L YES medium at 28 °C for 5 days. The cells were extracted with ethyl acetate three times and the extracts were evaporated to dryness. The crude extracts were then isolated by silica chromatography, the fractions containing target compounds were collected, and the solvent was removed by rotary evaporation. The target fractions were further purified by Sephadex LH-20 (40–70 μm; GE Healthcare Life Science, USA) chromatography. The obtained subfractions were purified by Prep-HPLC (Agilent 1260 with DAD-detector) equipped with a semi-preparative Ultimate XB-C18 column (10 × 250 mm, 5 µm, Welch, China). A linear gradient of 40–80% acetonitrile (v/v) over 30 min in H₂O (0.01% triethylamine, v/v) at a flow rate of 4 mL min⁻¹ was used for compounds purification. The resulting compounds were collected and dried for NMR analysis. NMR spectra were recorded on a Bruker NEO 600 MHz High-Performance Digital NMR (BrukerBiospin, Sweden), using CDCl₃ solvent (Cambridge Isotope Laboratories, USA). High-resolution mass spectrometry (HRMS) was performed on an Agilent 1290 Infinity/6230 TOF LCMS system, using electrospray ionization in positive mode.