In chemistry (particularly organic chemistry), methoxy refers to the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula O–CH3. The term is used in organic chemistry usually to describe an ether. As quantified by the Hammett equation, methoxy is an electron-donating group.
The simplest methoxy compounds are methanol and dimethyl ether. Other methoxy ethers include anisole and vanillin. Many metal alkoxides contain methoxy groups, e.g. tetramethyl orthosilicate and titanium methoxide. Such compounds are often classified as methoxides.
In nature, methoxy groups are found on nucleosides that have been subjected to 2'-O-methylation, for example in variations of the 5'-cap structure known as cap-1 and cap-2. They are also common substituents in O-methylated flavonoids, whose formation is catalyzed by O-methyltransferases that act on phenols, e.g., Catechol-O-methyl transferase (COMT). A large number of natural products in plants, e.g. lignins, are generated via catalysis by caffeoyl-CoA O-methyltransferase.
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