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 compounds are notable by their absence. They do not occur in amino acids, the heterocycles that comprise the genetic code, nor in lipids. They are however common substituents in O-methylated flavonoids. Their biosynthesis entails O-methyltransferases, which 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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