It tof

All the commercially available chemicals were used without further purification. NMR spectra were recorded on a JEOL ECS-400 (400 MHz, Japan). Chemical shifts are reported in ppm and refer to residual protons in the deuterated solvent as the internal standard. IR spectra were recorded on a Nicolet 380 FT-IR (Thermo Scientific, England). UV/VIS-spectra were recorded on a Specord 210 (Analytik Jena, Jena, Germany). Mass spectrometry was performed on an IT-TOF from Shimadzu, Japan with direct injection of the samples. For the original NMR, IR and mass spectrometry of compounds, please see the Supplementary Materials. Flash purification was performed with a Puriflash 4250-250 from Interchim, France.
Tryptanthrins 4, which are initially needed, were prepared with isatin 5 and isatoic anhydride according to Bergman et al. [37 (link)], which is extendable to all commercially available isatins. For tryptanthrin derivatives with substituents at positions 1–4 (R’ 2’-5’ in quingdainones), another method was used due to the unavailability of various isatoic acids. 2-Chloroisatins 6 were prepared according to Grimshaw et al. [38 (link)]. These 2-chloroisatins reacted with 2-aminobenzoic acids at 130 °C in DMF to form tryptanthrins without any further additives [39 (link)]. Unsubstituted quingdainone was obtained according to [12 (link)].

Analyses were performed with an Interface-Time of Flight (IT-TOF), Shimadzu using electronspray (ESI) ionization. The peaks were separated in the C-18 reversed-phase HPLC column (Waters, USA). The solvent system consisted of 10% to 100% acetonitrile (v/v) for 15 min, gradiently at a flow rate of 0.5 mL/min. The detection was accomplished using a Diode Array Detection system (DAD) Series SPD-M20A (Shimadzu). The PDA data was shown the signal at a wavelength of 254 and 350 nm.

Silica gel H was purchased from Sigma-Aldrich, whereas silica gel 60 (230˗400 mesh), dimetylsulfoxide (DMSO), methanol (MeOH), ethanol (EtOH), n-hexane and ethyl acetate (EtOAc) were purchased from Merck Co. (Germany). 3-(4,5-Dimethylthiazol-2yl)-2, 5-diphenyl tetrazolium bromide (MTT reagent) was provided by Invitrogen (Carlsbad, USA). RPMI-1640 medium (pH 7.4), penicillin/streptomycin and fetal bovine serum (FBS) were purchased from Nacalai Tesque (Japan) and Trypsin-EDTA 10X was supplied by Biowest (USA). The ultraviolet (UV) spectra and the Infrared (IR) spectra were recorded on a UV spectrophotometer (UV-1601 Shimadzu, Japan) and the FT-IR spectrometer Spectrum RXI (Perkin Elmer, USA), respectively. The nuclear magnetic resonance (NMR) spectra were recorded on a 600 MHz Bruker (Switzerland) spectrometer. Optical rotation was performed in Jusco (Tokyo, Japan). Mass spectra were recorded for electron spray ionization (ESI) mass spectrometry on IT-TOF from Shimadzu, Japan. High-performance liquid chromatography (HPLC) analysis was also conducted.

The LC-MS analysis of the peptides was performed on a Shimadzu LCMS-8050 equipped with a triple quadrupole mass spectrometer (using a UHPLC Nexera X2 system) and on an Agilent 6470 Triple Quadrupole LC/MS System equipped with a standard Jet Stream ESI source and Agilent Technologies 1290 Infinity II system. The LC-MS analysis on both instruments were carried out in SIM (selected ion monitoring) mode and with a Q1Q3 scan. The LC system was operated with a mobile phase consisting of solvent A: 0.1% formic acid in H₂O and solvent B: 0.1% formic acid in MeCN. The gradient conditions (B %) were from 5 to 80% B, within 15 min. The flow rate was 0.2 mL/min, and the injection volume 5 μL. The separation was performed on an Aeris Peptide XB-C18 column (50 mm × 2.1 mm) with a 3.6 μm bead diameter. The peptide samples were dissolved in 400 μl of a water: acetonitrile mixture (80: 20). Most analysis were carried out on a Shimadzu IT-TOF, which is a hybrid system consisting of an ion trap and a time-of-flight mass analyzer; it also includes an electrospray (ESI) ion source. In our experiments, we set the potential between the spray needle and the orifice to 4.5 kV. The LC separation on this instrument was performed in the same condition as described above.