Skimmianine is a
furoquinoline alkaloid found in ''
Skimmia japonica
''Skimmia japonica'', the Japanese skimmia, is a species of flowering plant in the family Rutaceae, native to Japan, China, and Southeast Asia. Growing to tall and wide, it is a rounded evergreen shrub with glossy, leathery leaves. It is wid ...
'', a flowering plant in family
Rutaceae
The Rutaceae is a family, commonly known as the rue[RUTACEAE](_blank)
in BoDD – Botanical Der ...
that is native to Japan and China. It is also a strong
acetylcholinesterase
Acetylcholinesterase (HGNC symbol ACHE; EC 3.1.1.7; systematic name acetylcholine acetylhydrolase), also known as AChE, AChase or acetylhydrolase, is the primary cholinesterase in the body. It is an enzyme that catalyzes the breakdown of acety ...
(AChE) inhibitor.
Biosynthesis
The biosynthesis of skimmianine starts from
anthranilic acid
Anthranilic acid is an aromatic acid with the formula C6H4(NH2)(CO2H) and has a sweetish taste. The molecule consists of a benzene ring, ''ortho''-substituted with a carboxylic acid and an amine. As a result of containing both acidic and basic f ...
, which is very abundant in the family Rutaceae. By combining anthranilic acid acetate, anthraniloyl-CoA is formed as a starting unit and able to extend side chain by adding malonyl-CoA by
Claisen condensation
The Claisen condensation is a carbon–carbon bond forming reaction that occurs between two esters or one ester and another carbonyl compound in the presence of a strong base, resulting in a β-keto ester or a β- diketone. It is named after Ra ...
. Next, lactam is formed through the cyclization and generate a heterocyclic system, leading the dienol tautomer adopt the 4-hydroxy quinolone tautomer, which is 4-hydroxy-2-quinolone.
With the formation of quinolone, alkylation is happening at C-3 position by introducing dimethylallyl diphosphate. Another key step is the cyclization on the dimethylallyl sidechain, forming a new heterocyclic five-member-ring. Platydesmine is then forming an intermediate through the oxidative cleavage reaction
by losing an isopropyl group to form dictamine. Finally, skimmianine is formed through the hydroxylation of dictamine.

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References
Quinoline alkaloids
Furans
Plant toxins