Synthesis and Biological Evaluation of 7a,7a,7a,8a,8a,8a- Hexafluororiboflavin and 7a,7a,7a,8a,8a,8a-Hexafluoro-FM N

7a,7a,7a,8a,8a,8a-H exafluororiboflavin (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 o f Lactobacillus casei. However, in the presence o f low riboflavin (1) concentrations, the hexafluoro analog 4 has som e growth enhancing activity. The FM N analog 7a,7a,7a,8a,8a,8a-hexafluororiboflavin 5'-phosphate (10) was also synthesized and found to bind tightly to apoflavodoxin from Megasphaera elsdenii. The dissociation constant (3.2 x 109 m ) is about one order o f magnitude larger than that o f FM N (1 .1 x 10i o m ). However, apoflavodoxin reconstituted with hexafluororiboflavin 5 '-phosphate (10) has no coenzyme activity. Hexafluoro-FM N (10) was also unable to act as a coenzym e for luciferase from Photobacterium fisheri. Hexafluororiboflavin 4 did not inhibit the light riboflavin synthase from Bacillus subtilis to a significant extent (Ä ̂ > 10-4 m).