Solid-State Thermolytic Epimerization and Polymerization of (+)-Catechin and (-)-Epicatechin Proceed through Quinone Methide Intermediates.
A mechanism involving a quinone methide intermediate is proposed for the thermally driven epimerization and polymerization reactions of solid-state catechin and epicatechin. Epimerization of catechin to epicatechin maximized after heating at 180 degrees C for 30 min (0.76:1, epicatechin/catechin ratio), whereas maximum epicatechin to catechin epimerization occurred after heating at 250 degrees C for 2 min at a ratio of 1.34:1 (catechin/epicatechin). These results imply that the conversion of epicatechin to catechin is the thermodynamically favored process. Conversion to nonepimerized products was optimal (99%) after 8 min at 220 degrees C for catechin and after 2 min at 265 degrees C for epicatechin (99.8%). Pyrocatechol was identified by HPLC as a degradation product in both catechin and epicatechin. Heating catechin at 220 degrees C for 8 min produced a 5-fold increase in chromatographic peak area at 450 nm, indicative of quinone methide formation that was thermally stable over time and degraded in the presence of sodium borohydride.
Oomah
B Dave
BD
oomahd@agr.gc.ca.
Quigley
Nicole
N
Latorre
Marie-Laure
ML
Rayne
Sierra
S
Mazza
Giuseppe
G