 Glycone

The glycone is the carbohydrate-derived residue of a glycoside, distinguished from its nonsugar partner, the aglycone. IUPAC records this usage particularly for naturally occurring glycosides. A residue within the intact compound and a free sugar recovered after cleavage are related chemical objects, but they do not necessarily have the same formula or bonding pattern.^[ref]

Methyl α-D-glucopyranoside makes the distinction concrete. Its sugar-derived part has the stereochemistry of an α-D-glucopyranosyl glycosyl group. The attached methyl-containing partner gives the classical oxygen-linked glycoside; formal hydrolysis yields free glucose and methanol. Naming the glycone does not erase the distinction between an attached residue and the free hemiacetal.

An original formula partition follows the glycosyl-prefix convention. Remove the anomeric $\mathrm{OH}$ from ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$ to obtain a group of composition ${\mathrm{C}}_6{\mathrm{H}}_{11}{\mathrm{O}}_5$; combine it with $\mathrm{OC}{\mathrm{H}}_3$ to recover ${\mathrm{C}}_7{\mathrm{H}}_{14}{\mathrm{O}}_6$. In this partition the linking oxygen belongs to the methyl-containing piece. A glycosyloxy-prefix partition includes that oxygen on the sugar-derived side instead. The structural convention must be stated before assigning atoms to named fragments.^[ref]

Formal hydrolysis also adds water, so it is incorrect to identify the formula of the free sugar simply by cutting the intact molecule into two unmodified fragments. The example connects residue naming with atom conservation. It does not specify a cleavage protocol or establish any biological activity of the resulting aglycone.