Glycoazodyes (or GADs) are a family of "naturalised" synthetic dyes, so called because they are the conjugation of common commercial azo dyes with a sugar through a "linker". This principle is summarised in the scheme below. Generations, Structure, and Synthesis First-generation The first-generation of Glycoazodyes was first reported in 2007. These Glycoazodyes use a diester linker, specifically a succinyl bridge. An ester group bonds the sugar to an n-alkane spacer, and the spacer bonds to the dye through another ester group. Synthesis First-generation Glycoazodyes are synthesized using glucose, galactose or lactose as the sugar group. The point of esterification is controlled by selectively protecting alcohol groups on the sugar, or by choosing an azo dye with a different alcohol group position. Either the dye or the sugar group can be succinylated by reacting a free alcohol group with succinic anhydride. The resulting hemisuccinate then reacts with a free alcohol group on either the dye or the sugar. The condensation product is then deprotected. Second-generation The second-generation of Glycoazodyes was first reported in 2008. These Glycoazodyes use an etherel linker. An ether group bonds the sugar and the dye to an n-alkane spacer, and the spacer bonds to the dye through another ether group. Like first-generation Glycoazodyes, second-generation Glycoazodyes use glucose, galactose or lactose as the sugar group. Synthesis Like first-generation Glycoazodyes, second-generation Glycoazodyes are synthesized using a glucose, galactose, or lactose sugar group. The point of the ether bond is controlled by selectively protecting alcohol groups on the sugar, or by choosing an azo dye with a different alcohol group position. An unprotected alcohol group of either the sugar or the dye is reacted with an n-carbon, terminal dibromoalkane in a solution of potassium hydroxide and 18-crown-6 ether, using non-anhydrous tetrahydrofuran as the solvent. The potassium hydroxide is used to produce an alkoxide ion from the alcohol while the 18-crown-6 ether acts as a phase-transfer agent. The reaction proceeds through a classic SN-2 nucleophilic substitution. A terminal Bromo group is eliminated, and a bond is formed between the oxygen of the alcohol and the carbon of the alkane. An ether is produced between the n-carbon linker and the sugar or the dye. At this stage, the terminal Bromo group that remains may react under the same conditions with the free alcohol of a corresponding sugar or dye. The condensation product is then deprotected. Third-generation The third-generation of Glycoazodyes was first