Aminochrome semicarbazones

The aglycone of betaniu, the red-violet pigment of the beet (Beta vulgaris var. rubra), known as betanidin, has recently been shown to have the structure depicted in structural formula 113.170,282 Betanidin had previously been reported by Piattelli and Minale to contain a dopachrome unit in its structure and consequently would have been formulated as 114.109 The Italian workers obtained pyrrole-2,3,5-tricarboxylic acid and pyridine-2,4,6-tricarboxylic acid on permanganate oxidation of betanidin and they also prepared a semi-carbazone of the pigment, the absorption spectrum of which showed the pH dependency expected for an aminochrome semicarbazone.169... 

The UV spectra of aminochrome semicarbazones have been extensively investigated. The main absorption maxima fall at ca. 360 nm at acidic and neutral pH, and shift to 435-460 nm in alkaline solution. 

The mechanisms of these interesting oxidations require further study, and attempts should be made to isolate the intermediate aminochromes (or a simple derivative, such as the semicarbazone). However, it is difficult to escape the conclusion that aminochromes can be readily obtained by the oxidation of compounds such as metanephrine and normetanephrine. 

One of the most characteristic reactions of the aminochromes is the ready formation of mono-derivatives with typical ketone reagents, e.g. semicarbazide, phenylhydrazine, etc. A relatively large number of derivatives of this nature have been prepared because of then-reported hemostatic activity (cf. refs. 2 and 3). Compounds of this type that had been described in the literature prior to December 1959 are listed in a previous review (Heacock3). Some further examples of this class of compounds have been described recently. They are N-ethylnoradrenochrome semicarbazone (84) (orange-red needles, m.p.180 215°)65 7-iodoadrenochrome methyl ether semicarbazone... 

Addition products have been obtained from aminochrome derivatives such as the semicarbazone, with sodium bisulfite. Recently Correia Alves reported the preparation of a compound described as adrenochrome semicarbazone sodium sulfonate (m.p. >300°) by treating a solution of adrenochrome monosemicarbazone (90) in sodium carbonate solution with sulfur dioxide at 40° for several days192 this compound was apparently different from the substance (m.p. 227-228°) obtained in a somewhat similar manner by Iwao193-194 and may be comparable to the compound (83) (m.p. > 300°) previously described in a Belgian patent179 (see Section IV,F). Iwao established the structure of his compound as the sodium salt of epinochrome-3-sulfonic acid monosemicarbazone (93).193... 

The removal of the semicarbazide residue from aminochrome mono-semicarbazones by alkaline degradation has been reported.303 The resulting 6-hydroxyindole derivatives could be readily isolated as their methyl ethers.303... 

The semicarbazone (134) was too water-soluble to isolate readily, but it was possible to isolate other derivatives of the aminochrome-thiol addition products of this type one such compound was the p-nitrophenylhydrazone of the addition product between adrenochrome and )S-mercaptopropionic acid which was readily obtained in pure crystalline form. The structure of this compound (135) was established by consideration of the microanalytical data and spectroscopic (u.v. visible, i.r. and n.m.r) properties. A total of five derivatives of this type have been prepared and fully identified (see Table 63) [249]. 

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