The acid-catalysed racemisation mechanism of catecholamines

Article abstract of DOI:10.1016/S0040-4020(01)80964-9

The racemisation rates of (-)-adrenaline (1), ()-isoprenaline (2), (-)-2-(3,4-dimethoxyphenyl)-2-hydroxy-N-isopropylamine (3), (+)-2-(4-meethoxyphenyl)-2-hydroxy-N-isopropylethylamine (4), (+)-2-phenyl-2-hydroxy-N-isopropylehylamine (5), ()-phenylephrine(6), and (+)-1-phenylethanol(7) were compared. The racemisatton rates decreased in the following order: 7> 1 ≈ 2 > 3 ≈ 4 ? 5, 6. In general, the reactivity of the series of the phenylethanolamine compounds (1) - (6) was seen to increase sharply as the electron-releasing ability of the p-substituent of the aromatic nucleus increases. The results strengthen the notion that the acid-catalysed racemisation of catecholamines proceeds via a quinonoid-type intermediate.