Racemic and enantioselective synthesis of tetrahydroprotoberberine (THPB)
alkaloids, a family of natural products showing a wide range of biological activity, have
been based either on extension or enhancement of conventional methods or on new, recently
developed tactics. Classical approaches to synthesize the THPB scaffold have utilized
Bischler-Napieralski cyclization/reduction or Pictet-Spengler reactions to generate a
benzyltetrahydroisoquinoline motif, followed by Mannich type condensation to obtain the
tetracyclic THPB core. In recent developments, contiguously tetra-substituted ring D
moieties and chiral auxiliaries to install the chiral center have been utilized to synthesize
THPBs. The present review summarizes various approaches adopted to synthesize THPBs
and their congeners, based on the sequence of formation of rings B and C.
Keywords: THPB, tetrahydroprotoberberine, stepholidine, tetrahydropalmatine, chiral auxiliary, isocorypalmine, stylopine, govadine.
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