Editing Alkaloid (section)

==Biosynthesis==
Biological precursors of most alkaloids are [[amino acid]]s, such as [[ornithine]], [[lysine]], [[phenylalanine]], [[tyrosine]], [[tryptophan]], [[histidine]], [[aspartic acid]], and [[anthranilic acid]].<ref name="Plemenkov 253">[[#Plemenkov|Plemenkov]], p. 253</ref> [[Nicotinic acid]] can be synthesized from tryptophan or aspartic acid. Ways of alkaloid biosynthesis are too numerous and cannot be easily classified.<ref name="Begley"/> However, there are a few typical reactions involved in the biosynthesis of various classes of alkaloids, including synthesis of [[Schiff bases]] and [[Mannich reaction]].<ref name="Plemenkov 253"/>

===Synthesis of Schiff bases===
{{Main|Schiff base}}

Schiff bases can be obtained by reacting amines with ketones or aldehydes.<ref>[[#Plemenkov|Plemenkov]], p. 254</ref> These reactions are a common method of producing C=N bonds.<ref name="Dewick 19">[[#Dewick|Dewick]], p. 19</ref>

[[File:Schiff base formation.svg|class=skin-invert-image|center]]

In the biosynthesis of alkaloids, such reactions may take place within a molecule,<ref name="Plemenkov 253"/> such as in the synthesis of piperidine:<ref name="ref19"/>

[[File:Schiff base formation intramolecular.svg|class=skin-invert-image|center]]

===Mannich reaction===
{{Main|Mannich reaction}}

An integral component of the Mannich reaction, in addition to an amine and a [[carbonyl]] compound, is a [[carbanion]], which plays the role of the nucleophile in the [[nucleophilic addition]] to the ion formed by the reaction of the amine and the carbonyl.<ref name = "Dewick 19" />

[[File:Mannich.png|class=skin-invert-image|center]]

The Mannich reaction can proceed both intermolecularly and intramolecularly:<ref>[[#Plemenkov|Plemenkov]], p. 255</ref><ref>[[#Dewick|Dewick]], p. 305</ref>

[[File:Mannich reaction intramolecular.svg|class=skin-invert-image|center]]