Synthesis of Water-Soluble Large Naturalised Dyes Through Double Glycoconjugation

Recently we started to develop a new class of dyes based upon the glycoconjugation of disperse dyes with mono- or disaccharides. We used the term naturalised to describe these dyes because we used natural lactose in the glycoconjugation process, and also because they are similar to real natural dyes, the hydrosolubility of which is based upon the saccharidic moiety attached to the chromophore, as in carminic acid or carthamin. Synthetic dyes submitted to the process of naturalisation consist of small chromophoric molecules, prevalently azoic, whereas larger dye molecules with a higher mass did not show appreciable solubility in water when a single molecule of lactose was added through a bivalent spacer, which is in contrast to the smaller dyes. To overcome this difficulty, herein we present the first approach to the insertion of two lactose units by a double glycoconjugation process. The procedure here presented allows the successful insertion of a spacer, the malonic acid, which can be linked with two lactose units so that even large dyes become soluble. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)