Synthesis and Biological Evaluation of 7α,7α,7α,8α,8α,8α- Hexafluororiboflavin and 7α,7α,7α,8α,8α,8α-Hexafluoro-FMN
7α,7α,7α,8α,8α,8α-Hexafluororiboflavin (4) has been prepared and its oxidation-reduction potential determined polarographically to be + 0.02 V with respect to the standard hydrogen electrode. Compound 4 does not by itself promote the growth of Lactobacillus casei. However, in the presence of low riboflavin (1) concentrations, the hexafluoro analog 4 has some growth enhancing activity. The FMN analog 7α,7α,7α,8α,8α,8α-hexafluororiboflavin 5′-phosphate (10) was also synthesized and found to bind tightly to apoflavodoxin from Megasphaera elsdenii. The dissociation constant (3.2 × 10-9m) is about one order of magnitude larger than that of FMN (1.1 × 10-10м). However, apoflavodoxin reconstituted with hexafluororiboflavin 5′-phosphate (10) has no coenzyme activity. Hexafluoro-FMN (10) was also unable to act as a coenzyme for luciferase from Photobacterium fisheri. Hexafluororiboflavin 4 did not inhibit the light riboflavin synthase from Bacillus subtilis to a significant extent {Ki> 10-4 м).