Figure 3.

(A) rp-HPLC of the active fraction (Agilent HC-C18(2) 4.6 × 150 mm, 5 μm, eluent: solvent A—10 mM NH₄OAc, pH 5, solvent B—MeCN, gradient elution from 15 to 90 solvent B for 10 min, flow rate 1.5 mL/min, UV 275 nm, sample volume 2 uL, active component is highlighted with yellow. (B) The structure of Cst with the indication of NMR chemical shifts in DMSO-d6 at 35 °C. Green numbers stand for the ¹H chemical shifts, black—for the ¹³C, and blue—for ¹⁵N. Chemical shifts are provided in ppm, measured with respect to trimethylsylan as an external reference standard. ¹³C and ¹⁵N shifts were referenced indirectly, using the gyromagnetic ratios as implemented in Topspin software (Bruker Biospin Gmbh, Germany). (C) The positive mode HCD mass spectra of Cst and proposed fragmentation of the parent ion of the compound at m/z 412.17.