HALOGENATION OF AROMATIC-COMPOUNDS - THERMODYNAMIC, MECHANISTIC AND ECOLOGICAL ASPECTS

Biological halogenation of aromatic compounds implies the generation o f reducing equivalents in the form of e.g. NADH. Thermodynamic calcula tions show that coupling the halogenation step to a step in which the reducing equivalents are oxidized with a potent oxidant such as O-2 or N2O makes the halogenation reaction thermodynamically feasible withou t the input of additional energy in the form of e.g. NADH. In a curren t model on the halogenation of tryptophan to 7-chloro-L-tryptophan NAD H and O-2 are proposed as co-substrates in a reaction in which the aro matic compound is oxidized via an epoxide as intermediate. The thermod ynamic calculations thus indicate that such a route hinges on mechanis tic insights but has no thermodynamic necessity. Furthermore the calcu lations suggest that halogenation of tryptophan and other aromatic com pounds should be possible with N2O, and possibly even with nitrate rep lacing O-2 as the oxidant. (C) 1998 Federation of European Microbiolog ical Societies. Published by Elsevier Science B.V. All rights reserved .