Isoquinoline alkaloids constitute the group of the most abundant alkaloids in the plant kingdom. Isoquinolines are derived biosynthetically from the amino acid tyrosine generating the fundamental intermediate 3,4-dihydroxyphenylethylamine (dopamine) and carbonyl units of different origin. The carbonyl donor unit is an α-ketoacid for isoquinoline and an aldehyde, i.e. 4-hydroxyphenylacetaldehyde in the case of benzylisoquinoline alkaloids. Some representatives of isoquinoline and benzylisoquinoline alkaloids such as berberine are widely distributed in the plant kingdom. Others are more restricted to certain plant families such as pellotine in the Cactaceae, cularine in the Fumariacea and morphine in the Papaveraceae. Morphine is still the most used painkiller in medicine. Other isoquinoline flavonoids such as codeine or papaverine are also considered useful medicinal drugs.
(S)-reticuline biosynthesis (2)
bisbenzylisoquinoline alkaloid biosynthesis,
sanguinarine and macarpine biosynthesis
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