Fig 1.
Reaction of amines with o-quinones via Michael-type addition or Schiff base reaction
Fig 2.
Chemical structure of 4-propylamino-5-methyl-o-quinone
Fig 3.
1H NMR spectra monitoring the reaction of 4MC in 10mM Na2CO3/D2O with time.
Dioxane was used as a reference. (a) Full overview of the 1H NMR spectra (b) 1H NMR spectra in the aromatic region.
Fig 4.
a) 1H NMR spectra monitoring the reaction of 4MC and NaIO4 in 10 mM Na2CO3/D2O with time. The molar ratio between 4MC and NaIO4 is 0.5. Dioxane was used as a reference. b) Relative integrated peak area of b1, b2, and b3 with respect to the total aromatic protons.
Fig 5.
1H NMR spectra monitoring the reaction of 4MC, PA and NaIO4 in 10 mM Na2CO3/D2O with time.
The molar ratio between 4MC, PA and NaIO4 is 1:3:0.5. Dioxane was used as a reference.
Fig 6.
UV-vis absorbance monitoring the reaction under different conditions: a) 4MC in 10 mM Na2CO3 aqueous solution; (b) 4MC and NaIO4 in 10 mM Na2CO3. The molar ratio between 4MC and NaIO4 is 0.5; (c) 4MC, PA and NaIO4 in 10 mM Na2CO3. The molar ratio between 4MC, PA and NaIO4 is 1:3:0.5.
Fig 7.
HPLC-UV chromatograms (monitored at 254 nm) of the reaction mixture of 4MC, PA, and NaIO4 with time.
The ratio of 4MC, PA and NaIO4 is 1:3:0.5.
Fig 8.
a) LC-MS chromatograms (monitored at 254 nm) of the reaction mixture of 4MC, PA, and NaIO4 over time. The ratio of 4MC, PA and NaIO4 is 1:3:0.5. b) Extracted ion chromatogram (positive ion mode) corresponding to PMB (m/z = 179.5–180.5) c) ESI-MS spectra [m/z 50–2000] summed over the 10.00–10.53 min retention time window; d) Extracted UV spectra corresponding to the 10.00–10.53 min retention time e) Proposed representative chemical structure of product.
Fig 9.
Chemical structure of 4-methyl-o-benzoquinone with numbers indicating the position of C atoms on the aromatic ring.
Fig 10.
An overview of the proposed structures of the products.
The number under each structure corresponds to the number in S1 Table.
Fig 11.
DLS measurement of the reaction system as a function of time: a) Intensity as a function of time, b) the diffusion coefficient as a function of time within 4 h, c) the diffusion coefficient as a function of time within 24 h.