Viable and straightforward approach to the preparation of water soluble pyrazol-5-one derivatives through glycoconjugation

Abstract The synthesis of water soluble pyrazol-5-one azo-dyes has been achieved. 6′-Aminolactosetriacetonide 9 was selected as the key building block to glyconjugate the pyrazole ring at its 3 position via a carboxamide or via a benzeneamide moiety in position 1 of the heterocycle. Diethyl-3-oxopentandionate 2 led eventually to a bicyclic compound, hampering the glyconjugation coupling process. The values of the molar extinction coefficients ( ɛ ) confirmed the tendency of pyrazolone azo dyes to exist in their tautomeric hydrazo form (especially in polar solvents); whereas the presence of substituents on the phenylazo group influenced the visible absorption maxima negligibly.