DETERMINATION OF THE SEQUENTIAL ORDER OF ACIDITY IN A POLYHYDROXYLATED BENZOPHENONE SERIES - CONSEQUENCE ON THE OXIDATION REACTION IN RELATION TO HEPATOTOXICITY
R. Largeron et al., DETERMINATION OF THE SEQUENTIAL ORDER OF ACIDITY IN A POLYHYDROXYLATED BENZOPHENONE SERIES - CONSEQUENCE ON THE OXIDATION REACTION IN RELATION TO HEPATOTOXICITY, Perkin transactions. 2, (5), 1996, pp. 893-899
The pK(a) values of successive acid-base equilibria involved in the py
rogallol ring ionization of exifone, 2,3,4-trihydroxybenzophenone 1, a
nd related methoxy derivatives were determined by UV-VIS absorption sp
ectrometry and potentiometric titration. Due to strong intramolecular
hydrogen bonding, the sequential order of acidity of the three hydroxy
groups of 1 was found to be 4-OH > 3-OH > 2-OH. The polyhydroxylated
benzophenones were oxidized to 3,4-quinone only in a narrow range of a
cidity in which the monoanionic 4-olate species predominated in soluti
on. The attachment of an amino-alcohol residue resulted in the trappin
g of the transient 3,4-quinone and provided a convenient route to nove
l 1,4-benzoxazine derivatives. Cytotoxicity experiments in rat hepatoc
ytes indicated that some of these compounds were significantly less to
xic than the parent exifone.