Anti-riboflavin activity of 8-O-alkyl derivatives of riboflavin in some Gram-positive bacteria.

Two new 8-O-alkyl derivatives of riboflavin (RF), i.e., 8-methoxy- (MOF), and 8-ethoxy-8-demethyl-D-riboflavin (EOF), their tetraacetate, and the tetraacetate of 8-hydroxy-8-demethyl-D-riboflavin (HOF) were synthesized. The anti-RF activity of MOF, EOF and HOF was estimated from the ratio CR/CI, where CI is the concentration of test flavin added to the culture medium and CR is the minimum concentration of RF needed to restore the growth inhibition. Their activity was also compared with that of roseoflavin (RoF). The decreasing order of anti-RF activity was as follows: MOF greater than RoF greater than EOF in Sarcina lutea: RoF greater than MOF greater than EOF in Bacillus cereus and Staphylococcus aureus. HOF showed no activity in any of the bacteria tested. The redox potential of these compounds decreases as follows: RF greater than RoF greater than EOF greater than MOF greater than HOF, and the RF activity of MOF and EOF could be explained by the redox potential difference between these compounds and RF.