Proposal for the classification of sinomenine alkaloids

Area of Science:

• Natural Product Chemistry
• Biochemistry
• Pharmacology

Background:

• Sinoacutine, an isoquinoline alkaloid, shares structural similarities with morphine and is classified under morphinane.
• Current understanding posits salutaridine as the precursor to morphine alkaloids, derived from (R)-reticuline.

Purpose of the Study:

• To investigate the biosynthetic pathway of sinoacutine.
• To determine the enzymatic basis for sinoacutine synthesis.
• To re-evaluate the classification of sinoacutine within alkaloid families.

Main Methods:

• Cloning and expression of the sinoacutine synthetase (SinSyn) gene from Sinomenium acutum.
• In vitro enzyme-catalyzed experiments using expressed SinSyn protein.
• Analysis of chemical structures using optical activity, nuclear magnetic resonance, and mass spectrometry.

Main Results:

• The study identified different biosynthetic precursors for sinoacutine and salutaridine.
• Sinoacutine was successfully synthesized in vitro, catalyzed by SinSyn acting on (S)-reticuline.
• Structural and spectral analyses confirmed the identity and properties of sinoacutine and salutaridine.

Conclusions:

• The biosynthetic pathway for sinoacutine differs from that of salutaridine.
• Sinoacutine synthetase (SinSyn) catalyzes the formation of sinoacutine from (S)-reticuline.
• Sinoacutine should be reclassified as a sinomenine alkaloid, distinct from the morphinane group.