Flavinium salts

In the latter case the structure of the intermediate was elucidated by NMR During the catalytic action of these enzymes several intermediates (consecutive break-down products of (27) absorbing between 370 and about 420 nm are formed Structure (26) was for a long time not accepted because the C(10a) position of flavin was believed to be chemically rather unreactive until it was found that o-complexes are formed between quaternary flavinium salts and methoxide As shown later by NMR the formation of C(lOa) o-adducts is restricted to flavinium salts alkylated at N(I) In addition, careful oxidation of methanolic or acetonitrile solution of... 

Planar chiral flavinium salts-prospective catalysts for enantioselective sulfoxidation reactions. Ear. J. Org. 

The hydrogen peroxide-mediated oxidation of p-tolyl methyl sulfide with chiral iminium salt 20 (Figure 19.9), reported in 1993, gives a 32% ee [81]. The use of chiral flavinium salt catalysts afforded a 65% ee for the same transformation [119]. 

A related observation provides more information and virtually confirms that these compounds do not provide good models for the enzymic reaction. To obtain model peroxides in this series it is necessary to use alkyl flavinium salts to prevent the elimination of H2O2 which occurs in all but enzyme-bound flavin peroxides. The 5-alkyl salts provide the exact counterpart of the 4 a-peroxide believed to occur on the enzyme. However the 10 a-peroxide gives the only unambiguously identified fluorescent product. In the case of 4 a-substitution the product is not fluorescent. 

Although addition of the peroxide (16) to the flavinium salt should afford the direct analogue of the natural peroxide, no significant light results from the addition. 

Addition of various peroxides in buffer to flavinium salts such as (15) are presumed [30] to have given an intermediate related to the key compound in the bacterial reaction. 

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