Ribocil is a highly selective chemical modulator of bacterial riboflavin riboswitches, strongly inhibiting GFP expression with a 50% effective concentration (EC50: 0.3 μM).

Ribocil is a highly specific bioactive synthetic mimic of FMN, which competes with the natural ligand to inhibit FMN riboswitch-mediated expression of ribB and inhibits bacterial growth. Ribocil-B shows superior microbiological activity as compared to Ribocil-A (minimum inhibitory concentration (MIC) = 1 μg/ml versus MIC ≥ 64 μg/ml), inhibition of riboflavin synthesis (IC50 = 0.13 μM versus IC50 > 26 μM), and binding affinity to the E. coli FMN aptamer (Kd = 6.6 nM versus Kd ≥ 10,000 nM) [1]