Flavin-mediated dual oxidation controls an enzymatic Favorskii-type rearrangement

Abstract

Flavoproteins catalyze a diversity of fundamental redox reactions and are one of the most studied enzyme families1,2. As monooxygenases, they are universally thought to control oxygenation by means of a peroxyflavin species that transfers a single atom of molecular oxygen to an organic substrate1,3,4. Here we report that the bacterial flavoenzyme EncM5,6 catalyzes the peroxyflavin-independent oxygenation-dehydrogenation dual oxidation of a highly reactive poly(β-carbonyl). The crystal structure of EncM with bound substrate mimics coupled with isotope labeling studies reveal previously unknown flavin redox biochemistry. We show that EncM maintains an unanticipated stable flavin oxygenating species, proposed to be a flavin-N5-oxide, to promote substrate oxidation and trigger a rare Favorskii-type rearrangement that is central to the biosynthesis of the antibiotic enterocin. This work provides new insight into the fine-tuning of the flavin cofactor in offsetting the innate reactivity of a polyketide substrate to direct its efficient electrocyclization.

Photoinduced processes in macrocyclic isoalloxazine–anthracene systems

“…The mixture was heated at 60 C for 15 0 and then at 100 C for another additional 15 0 . After being allowed to dry, the mixture was purified by column chromatography (CH 2 13 …”

“…The isoalloxazine moiety is an electroactive and photoactive unit that has the ability to accept one or two electrons and one or two protons to its central pyrazine unit and is responsible for the catalytic activity of flavoenzymes [6]. These particular chemical properties allow flavoenzymes to play an important role in many biological events such as cell apoptosis [7], oxygen activation [8], dehydrogenation of metabolites [9], light driven DNA repair [10], blue light photoreceptors (BLUF) [11,12] redox reactions [13] and halogenation of aromatic substrates [14]. The modulation of their reactivity is strongly dependent on the chemical environment and weak interactions such as hydrogen bonding [15][16][17][18], p-p stacking [16,19], steric effects [20] and charge transfer processes [21,22] play a key role in modulating such reactivity (Scheme 1).…”

“…8H) 13. C NMR (101 MHz, CDCl 3 ) d ppm 154.82, 132.34, 125.55, 125.17, 121.09, 120.57, 102.79, 68.07, 33.98, 32.90, 29.31, 28.20, 25.78.…”

“…Calc. C. 53.12H 4.46 Br 35.34 Found: C 53.4H 4.42 Br 35.41 1 H NMR (400 MHz, CDCl 3 ) d 8.76 (s, 2H, H-15, H-20), 7.64 (d, J = 8.5 Hz, 2H, H-14, H-19), 7.34 (t, J = 7.5 Hz, 2H, H-13, H-18), 6.73 (d, J = 7.5 Hz, 2H, H-12, H-17), 4.25 (t, J = 5.7, 8.3 Hz, 4H, H-d.d 0 , H-e,e 0 ), 3.60 (t, J = 6.5 Hz, 4H, H-CH 2 Br), 2.23 (m, 8H, CH 2 -CH 2 ) 13. C NMR (101 MHz, CDCl 3 ) d 154.63, 132.34, 125.47, 125.16, 121.29, 120.57, 102.85, 67.23, 33.75, 29.95, 28.05.…”

“…) 13. C NMR (101 MHz, CDCl 3 ) d ppm 164.54, 160.80, 154.91, 154.39, 148.11, 134.80, 133.42, 132.38, 125.68, 125.12, 124.79, 124.72, 121.19, 120.54, 119.53, 119.44, 103.49, 102.19, 69.…”