UV light absorption parameters of the pathobiologically implicated bilirubin oxidation products, MVM, BOX A, and BOX B

The formation of the bilirubin oxidation products (BOXes), BOX A ([4-methyl-5-oxo-3-vinyl-(1,5-dihydropyrrol-2-ylidene)acetamide]) and BOX B (3-methyl-5-oxo-4-vinyl-(1,5-dihydropyrrol-2-ylidene)acetamide), as well as MVM (4-methyl-3-vinylmaleimide) were synthesized by oxidation of bilirubin with H2O2 without and with FeCl3, respectively. Compound identity was confirmed with NMR and mass spectrometry (MS; less than 1 ppm, tandem MS up to MS4). UV absorption profiles, including λmax, and extinction coefficient (ε; estimated using NMR) for BOX A, BOX B, and MVM in H2O, 15% CH3CN plus 10 mM CF3CO2H, CH3CN, CHCl3, CH2Cl2, and 0.9% NaCl were determined. At longer wavelengths, λmax's for 1) BOX A were little affected by the solvent, ranging from 295-297 nm; 2) BOX B, less polar solvent yielded λmax's of lower wavelength, with values ranging from 308-313 nm, and 3) MVM, less polar solvent yielded λmax's of higher wavelength, with values ranging from 318-327 nm. Estimated ε's for BOX A and BOX B were approximately 5- to 10-fold greater than for MVM.