Elimination of the 7-Trifluoromethyl Group from 6,7-Bis(trifluoromethyl)-8-ribityllumazines. Stereoselective Catalysis by the Lumazine Synthase of Bacillus subtilis
Both diastereomers of 6,7-bis(trifluoromethyl)-7-hydroxy-8-ribityllumazine decompose in neutral or mild basic aqueous solution by elimination of the 7-CF3 group yielding 6-(trifluoromethyl)-7-oxo-8-ribityllumazine. It is suggested that the reaction starts with deprotonation of the 7-OH group, followed by release of the CF3 carbanion and formation of a carbonyl oxygen. The reaction was catalyzed diastereoselectively by the lumazine synthase/riboflavin synthase complex from Bacillus subtilis, which resulted from a decrease in the pK(2) of the 7-OH group by the enzyme.