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Issue 24, 2000
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Oxidative cyclisation of N,N-dialkylcatechol amines to heterocyclic betaines via o-quinones: synthetic, pulse radiolytic and enzyme studies

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Abstract

Oxidation of N,N-dialkyldopamines by either dianisyltellurium oxide or tyrosinase gives 2,3-dihydro-1H-indolium-5-olates which are formed by cyclisation of an intermediate o-quinone. The kinetics of formation and cyclisation of the N,N-dimethyl-o-quinone have been studied using pulse radiolysis. The indolium-5-olates do not activate met-tyrosinase and these results support a mechanism of tyrosinase oxidation of phenols to o-quinones in which the o-quinone is formed in a single step and not via an intermediate catechol. Similar chemical and enzymatic oxidation of a higher homologue gives an analogous 1,2,3,4-tetrahydroquinolinium-6-olate. Pulse radiolysis studies show that this product is formed via a spiro intermediate and not by direct cyclisation to form the six-membered quinolinium ring. The novel betaines described have been fully characterised and converted to their dimethoxy iodide salts. In a preliminary investigation of potential anti-cancer pro-drugs, amide derivatives of dopamine do not cyclise when oxidised to the o-quinone but cyclisation of an N-benzoylmethyl derivative to the corresponding betaine was observed. This betaine then appears to equilibrate with an N-ylide which, in contrast to the betaine, is a substrate for tyrosinase.

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Publication details

The article was received on 22 Aug 2000, accepted on 27 Sep 2000 and first published on 22 Nov 2000


Article type: Paper
DOI: 10.1039/B006860H
J. Chem. Soc., Perkin Trans. 1, 2000, 4306-4315

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    Oxidative cyclisation of N,N-dialkylcatechol amines to heterocyclic betaines via o-quinones: synthetic, pulse radiolytic and enzyme studies

    J. Clews, C. J. Cooksey, P. J. Garratt, E. J. Land, C. A. Ramsden and P. A. Riley, J. Chem. Soc., Perkin Trans. 1, 2000, 4306
    DOI: 10.1039/B006860H

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