Tetrahydrocoptisine (also known as stylopine) is an alkaloid isolated from Corydalis species.
The (S)-isomer of tetrahydrocoptisine is produced when the enzyme (S)-stylopine synthase acts on (S)-cheilanthifoline to form a second methylenedioxy ring:
Tetrahydrocoptisine is converted to coptisine by an oxidation reaction catalysed by the enzyme tetrahydroberberine oxidase.
Alternatively, it can be converted into protopine in two steps. The first is a methylation reaction by the enzyme (S)-tetrahydroprotoberberine N-methyltransferase using the cofactor, S-adenosyl methionine (SAM). This transfers a methyl group, giving S-adenosyl-L-homocysteine (SAH).
Then the product, (S)-cis-N-methylstylopine, is oxidised by the enzyme methyltetrahydroprotoberberine 14-monooxygenase: