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.<Nomenclature of Carbohydrates (Recommendations 1996) by Alan D. McNaught>[Section2-Carb-33.1, paragraph defining aglycone and glycone]{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 $\mathrm{C_6H_{12}O_6}$ to obtain a group of composition $\mathrm{C_6H_{11}O_5}$; combine it with $\mathrm{OCH_3}$ to recover $\mathrm{C_7H_{14}O_6}$. 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.<Nomenclature of Carbohydrates (Recommendations 1996) by Alan D. McNaught>[Section2-Carb-33.2(b–c): glycosyloxy includes the linking oxygen, whereas O-glycosyl does not]{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>.


 Glycone (source code)