Ethers and glycosides

Ethers (R-O-R) are frequently found as natural products in nature. The most common ether is that of methanol and the phenolic hydroxyl group. The methyl ether (methoxyl group) is very stable and therefore not reactive. Shown below is the formation of methoxybenzene (2.30) from phenol and methanol.

o h2o

o h2o

Glycosides - formed between a sugar molecule and an alcohol - are in some sense similar to ethers. Glycosides are formed between the sugar molecule in a ring conformation (pyranose or furanose form) and an alcohol. The example below shows D-glucose (2.31), in equilibrium with P-D-glucopyranose (2.32).

OH OH

Figure 2-3. Formation of phenolic glycosides.

Figure 2-3. Formation of phenolic glycosides.

In presence of acid, cation 2.33 reacts with phenol (2.5) to result in a mixture of the a- and P-glucoside (2.34 and 2.35, respectively). Chemically this reaction involves the formation of an acetal (2.34 and 2.35) from a semi-acetal (the pyranose 2.32; the furanose could also react). Unlike typical ether bonds, the glycoside bond is susceptible to acid hydrolysis.

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