Ehrlich color reaction

By using an aromatic aldehyde carrying an electron-releasing group the intermediate cation can be stabilized. This is the basis of the classical Ehrlich color reaction for pyrroles, indoles and furans which have a free reactive nuclear position (Scheme 19). As expected, pyrroles react preferentially in the exposition and indoles in the (3-position, but if these positions are filled, reaction can occur at other... 

Gottschalkii was able to characterize the split product formed by the action of influenza virus on ovomucin, and on the sialoprotein inhibitor from urine, by its ease of humin formation and its abihty to give the Morgan-Elson color reaction for N-acylated 2-amino-2-deoxyhexoses. Accordingly, he assigned the structure of a AT-substituted D-fructosamine to this product. Odin and Klenk, independently, both suggested that this split product is closely related to a nonulosaminic acid, and noted its ability to give a direct Ehrlich color reaction. Klenk and his coworkers were then able to establish unequivocally that the principal product ... 

The indoles 38 and 39 give a negative Ehrlich color reaction, indicating substitution at position 2 and 3 of the indole ring. The mass spectra of these compounds show a base peak at m/z 198, C,4H,6N, which originated via cleavage of the C-8-C-9 bond. On the basis of spectral data, 38 seemed to be identical to deoxybrevianamide E which had been obtained by Birch and Wright (72) upon treatment of brevianamide E (44) with Zn and AcOH. Later, 38 and 44 were... 

It can be concluded from the publications of Rohde [2] and Freund and Lebach [3, 4] that it was Ehrlich who first suggested the use of 4-(dimethylamino)-benzalde-hyde in the presence of hydrochloric acid for color reactions with methylketols that was found also to apply to indole derivatives [S]. Auterhoff [6] designated a reagent for urobilinogen, consisting of a solution of 2 g 4-(dimethylamino)-benzaldehyde in 20 percent hydrochloric acid, correctly as Ehrlich s solution. Hence, it is essentially correct to refer to all reagents which contmn these components as Ehrlich s reagent. 

Kotake and Sakata (K13) reported that the ingestion of 3 g tryptophan or 1 g kynurenine by a human being resulted in an increase of Ae Ehrlich diazo reaction (i.e., red color with alkaline diazobenzenesidfonic acid). The same authors observed that a patient with pulmonary tuberculosis, when given 2 g tryptophan, showed a strong increase of the urinary diazo reaction. Later it was found that 5 of 19 patients with pulmonary tuberculosis excreted kynurenine when given 0.5 g tryptophan, whereas no excretion was observed in normal controls to whom larger amounts (3 g) of the amino acid (06) were administered. 

Qualitatively, the presence of the nonulosaminic acids is best indicated by the brilliant-red coloration formed on addition of an acidic solution of p-dimethylaminobenzaldehyde (the so-called direct Ehrlich reaction ), and by the bright-purple coloration which develops upon boiling with Bial s reagent for several minutes at 100°. In addition, the nonulosaminic acids give a blue-violet coloration with Dische s diphenylamine reagent for deoxypentoses and a positive reaction in the tryptophan-perchloric acid test. Since no single one of these color reactions is absolutely specific for a nonulosaminic acid, it is advisable to carry out at least two of these for a qualitative analysis. For quantitative determinations, all four reactions have been employed, using either A/ -acetylneuraminic acid (m. p., 183-185° [a] —32.0°) or methoxyneuraminic acid [m. p., 200° (dec.) [a]o —55.0°] as colorimetric standards. 

A comparison between certain chemical characteristics of the siaUc, iV-acetylneuraminic, and methoxyneuraminic acids, especially their functional groups and the color reactions afforded with Ehrlich s and Bial s reagents, suggested a close relationship between these nonulosaminic acids and indicated that methoxyneuraminic acid might be the methyl glycoside of a completely deacylated sialic acid. This concept was substantiated with the conversion of A-acetylneuraminic acid into methoxyneuraminic... 

The first observation on the reactions of glycosylamines with 3-dicarbonyl compounds is due to Elson and Morgan, who found that D-glucosylamine and 2,4-pentanedione, when heated in slightly alkaline solution, give a positive Ehrlich pyrrole test. They considered that 3-acetyl-2-methyl-4-(D-ara6wo-tetrahydroxybutyl)pyrrole (20) was formed and was responsible for the color reaction. 

Reaction of the amine with p-dimethylaminobenzaldehyde (Ehrlich reagent) or p-diethylaminobenzaldehyde to produce a colored Schiff base [23—25]. The color formation is ascribed to a resonance hybrid between a protonated Schiff base and a quinoid system (Eq. (2)) ... 

The Ehrlich reagent, developed originally for the colorimetric assay of pyrrole derivatives, was shown by Ehrlich to give a color with certain glycoproteins, with and without prior alkali treatment (3). The reagent consists of dimethylaminobenzaldehyde in strong hydrochloric acid. This assay later became the basis for the Morgan-Elson reaction for the deter-... 

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