Bioprocesses in Heterocyclic Chemistry

The use of biological methods has a small, but significant niche in synthetic heterocyclic chemistry, being used both on a research scale and for fine-chemicals production. The processes may use isolated enzymes or whole microorganisms, the main reactions being oxidations of a heterocyclic nucleus or of side-chains, but other reaction types are also used, for example enzymatic catalysis has been used to ribosylate purines and related bases by reaction with a 7-aUcylated nucleoside.  

The oxidation of pyridines to pyridones ° and the selective oxidation of a side-chain in aUcyl-pyridines and other azines, have been well studied.  

The enantioselective ctT-dihydroxylation of benzothiophenes and benzofnrans in the heterocyclic ring, by Pseudomonas putida, is analogous to well-known conversions of simple benzenoid compounds, bnt in the heterocyclic context, hydroxyl groups introduced at an a-carbon easily epimerise. Indole gives indoxyl probably via dehydration of an intermediate 2,3-diol. In contrast, cw-dihydroxylation of quinolines, or of 2-phenylpyridines, takes place selectively in the benzene ring.  

The introdnction of an amino acid side-chain onto 4-, 5-, 6- and 7-azaindoles by an enzyme-catalysed alkylation with serine is an impressive demonstration of the power of biological methods.  

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