Flavin-oxygen derivatives involved in hydroxylation by p-hydroxybenzoate hydroxylase.

Asymmetric azidohydroxylation of styrene derivatives mediated by a biomimetic styrene monooxygenase enzymatic cascade

“…It should be noted that sodium azide may interfere with the steady-state kinetics of substrate epoxidation catalysed by the SMO. [55][56][57] Our one-pot cascade may be more efficient as a twostep approach, adding the sodium azide in the second step. To access the β-azido alcohol isomers, several halohydrin dehalogenases (HHDHs, EC 3.8.1.2, Enzymicals screening kit, see ESI) 58,59 were screened towards racemic styrene oxide rac-2a (Table 3), using sodium azide for the selective epoxide ring opening, 58 giving two possible products, 1-azido-2phenylethanol 3 or 2-azido-1-phenylethanol 4.…”

“…It should be noted that sodium azide may interfere with the steady-state kinetics of substrate epoxidation catalysed by the SMO. 55–57 Our one-pot cascade may be more efficient as a two-step approach, adding the sodium azide in the second step.…”

Flavoenzyme-Catalyzed Oxygenations and Oxidations of Phenolic Compounds

“…[37,43] Some benzoate derivatives bind to the enzyme and elicit its reduction but are not converted, and are therefore called effectors. The potential substrate 4-aminobenzoate binds to the enzyme in a similar way as 4-hydroxybenzoate, [24] but the reduction reaction in the presence of 4-aminobenzoate is very slow, [39] indicating a fine-tuning of the mechanism by which the substrate exerts its effector action. The rate of reduction does not correlate with the orientation of the flavin ring observed in the crystal structures, and all evidence presently available suggests that the effector specificity is linked to the ionic state of the substrate and the hydrogen bond network connecting the 4-hydroxy group with the protein surface.…”

“…[24,44] The fast release of NADP from the reduced ternary complex is well established. [28,39,40] Furthermore, it has been demonstrated that the rate of dissociation of the substrate from the reduced enzyme-substrate complex is 5000 times slower than from the binary complex with the flavin in its oxidized state. [39] In addition to the increased reduction rate induced by substrate binding, the slow rate of substrate dissociation from the reduced enzyme is a second mechanism by which the enzyme controls the optimal use of valuable reducing equivalents.…”

“…The oxidative half reaction includes the reaction steps that lead to the hydroxylation of the substrate. [39,41] Upon reaction of the reduced enzyme-substrate complex with molecular oxygen the flavin C(4a)-hydroperoxide intermediate is formed. Several authors have discussed the actual way in which this reaction occurs, since in principle the reaction between singlet reduced flavin and triplet molecular oxygen is spin forbidden.…”