Miscellaneous Enzymatic Reactions

Although the enzymatic DKR methodology has been exhaustively applied to different secondary alcohols through enzymatic hydrolysis or transesterification, relatively few examples are known in the case of amines, probably because this type of DKR implies the formation of imino compounds as intermediates, which are less stable than carbonyl compounds.However, in the last few 

Q glucose-6-phosphate dehydrogenase glucose-6-phosphate NADPH, 25°C 

The stereoselectivity of the hydroxynitrile lyase (HNL) catalysed cyanohydrin formation of monosubstituted cyclic ketones is of general interest for the synthesis of biologically active compounds. In the course of a systematic investigation of the stereoselectivity of HNL-catalysed addition of HCN to a variety of monosubstituted cyclopentanones, Kobler and Effenberger observed a DKR for the addition of HCN to alkyl 2-oxocyclopentanecarboxylates 

Lutz and colleagues have reported a new process concept of DKR via preferential crystallization combined with enzymatic racemisation. This methodology was successfully applied to the DKR of asparagine by using an enzyme 

The Strecker reaction, occurring between an aldehyde, ammonia and a eyanide source, constitutes one of the most important multieomponent reactions developed, leading to a-aminonitriles which are versatile substrates for 

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Miscellaneous Eliminations. Other known enzymatic reactions involv-ing pyridoxal phosphate are more difficult to explain or to duplicate. 

Miscellaneous Reactions of Oxirans.—The first successful enzymatic cyclization of a non-natural squalene has been disclosed. (18Z)-Oxidosqualene (188), which does not possess the naturally occurring a -trans stereochemistry, was caused to cyclize, in the presence of 2,3-epoxysqualene sterol cyclase, to (205)-epinorlanosterol (189). The polyene oxide (190) underwent an uncommon tricyclization in CH2CI2 containing Bp3-OEt2 to form the cw-fused A/B-ring 18-nor-steroid (191) (25%) this compound was found to be identical with a material derived by treatment of a naturally occurring steroid with BF3. 

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