SummaryThree new 8N-alkyl analogues of roseoflavin (MM) , i.e., 8-ethylamino-(EH), 8-methylethylamino (ME) , 8-diethylamino-8-de methyl-D-riboflavin (EE), their tetraacetates , and 8-amino-8-demethyl-D riboflavin (HH) tetraacetate, were synthesized . A relation between the anti-riboflavin activity and the chemical structure of 8N-alkyl analogues (8N-methyl, ethyl) was studied by a restoration by riboflavin (RF) of inhibitory effect of the analogues on a growth of Gram positive bacteria, i.e., Sarcina lutea, Bacillus cereus, and Staphylococcus aureus. The inhibitory effect of most of the analogues was restored by RF . But in some cases, i.e., 8-methylamino-8-demethyl-D-riboflavin (MH) in Sar. lutea and MM in Staph. aureus, the effect was not completely restored . Apparently, the inhibition in early phase of growth was restored, but the maximum growth was still suppressed. The non-alkylated amino analogue (HH) showed only unrestorable suppression of maximum growth in Sar. lutea. Of restorable effect by RF of N-alkyl analogues, approximate decreasing orders of anti-RF activity were as follows. Dialkylated analogue> monoalkylated. HH showed insignificant anti-RF activity . In each group, methylated analogue>ethylated.In B. cereus monoalkylated analogues , and in Staph. aureus monoalkylated and EE showed no significant inhibitory effect. Redox potentials of the N-alkyl analogues were measured, and a definite relation between the chemical structure and the potential was found (RF =EE>ME>MM>HH>EH>MH). But the anti-RF activity of the analogues was not completely explained by the difference of the redox potential from RF.

SummaryTwo 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>RoF>EOF in Sarcina lutea; RoF>MOF>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>RoF>EOF>MOF>HOF, and the anti-RF activity of MOF and EOF could be explained by the redox potential difference between these compounds and RF.

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