Flavine-type catalysts

Baeyer-Villiger oxidation of ketones, in the presence of flavin catalyst, resulted in an excellent yield of the ester. A new flavin-type catalyst, 5-ethyl-3-methyl-2,4, 3/,5,-di-O-methyleneriboflavinium perchlorate, have been synthesized and used in these reactions.221... 

Among the non-metaUic catalytic systems for Baeyer-Villiger reactions [174], those with flavine-type catalysts are particularly interesting. Use of catalytic amounts (5 mol%) of flavine analogue 42 in the presence of hydrogen peroxide gave lactone 41 with a yield of up to 90% from ketone 43 (Scheme 9.4) [332]. 

Metalloenzymes or metal ion-activated enzymes catalyze an enormous variety of organic reactions that are not restricted to any particular reaction class, but appear as catalysts for all types of reactions. Thus neither the presence of the metal ion nor the reaction type seems to be restrictive as far as metal-assisted enzyme catalysis is concerned. In some cases the metal ion appears to function as an electron acceptor or donor, but flavin cofactors have substituted as redox centers during evolution in some enzymes. 

Flavoenzymes constitute about 2% of all biological catalysts and are classified in several ways. One classification is based on EC number (enzyme nomenclature) and refers to the type of reaction catalyzed. More sophisticated classifications concern the inclusion of sequence, fold, and function. Historically, a distinction is made between simple and complex flavoenzymes (4). The latter proteins contain besides flavin other cofactors like heme, tetrahydrobiopterin, and metal ions. 

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