Indole from aminochromes

The n.m.r. spectra of several 5,6-dihydroxyindoles (and their diacetyl derivatives) obtained by reduction of different non-halo-genated aminochromes were compared with those obtained from the appropriate 5,6-dihydroxy-(or 5,6-diacetoxy)-iodoindoles produced by reduction of the corresponding iodoaminochromes. The n.m.r. data clearly demonstrated the presence of a- and /3-protons in the indole nuclei (except in the case of the products derived from 2-methylnoradrenochrome and the corresponding iodoaminochrome,... 

Fig. 46. Mechanism of electrochemical oxidation of dopamine. Dopamine (I) is oxidized to dopamine-o-quinone (II). After cyclization the indole (III) undergoes further electro-oxidation to aminochrome (IV). Adapted from [161].

It was concluded from the kinetic data that, as the potential became more positive, the catecholamine was oxidised to the open-chain quinone, which cyclised to the leucoaminochrome. The leuco compound, which is more easily oxidised than the original catecholamine was then oxidised to the aminochrome by some of the remaining uncyclised quinone, which was itself reduced back to the original catecholamine. On reversal of the scan, with the potential becoming more negative, the aminochrome was reduced back to the leucoaminochrome. Some of the latter compound then lost water to form the 5,6-dihydroxyindole (44), which was detected by its oxidation to the indole-5,6-dione (45) when the scan was again reversed (increasing potential) [106]. 

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