Biosynthesis of the necic acid moiety of lycopsamine type pyrrolizidine alkaloids : investigations into an acetohydroxyacid synthase
In this thesis, the first step of the formation of the branched-chain C7-necic acids of lycopsamine type PAs was elucidated. In Symphytum officinale (S. officinale, Boraginaceae), Heliotropium indicum (H. indicum, Heliotropiaceae, Boraginales), and Eupatorium cannabinum (E. cannabinum, Eupatorieae, Asteraceae) a duplicate of an acetohydroxyacid synthase (AHAS) catalytic subunit (CSU), now named C7-hydroxyacid synthase (C7HAS), was identified to be the first specific enzyme in the biosynthesis of the necic acid moiety. The enzyme catalyzes the transfer of an activated acetaldehyde formed from pyruvate to 2-oxoisovalerate, forming the direct precursor of the C7-necic acids, C7-pronecic acid.
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