Synthesis of novel 5-oxaprotoberberines as bioisosteres of protoberberines

5-Oxaprotoberberinones and 5-oxaprotoberberinium were synthesized as bioisosteres of protoberberines. 5-Oxaprotoberberinones were prepared by linking phenol with the isoquinolone ring of 3-phenolisoquinolones by methyleneoxy bridge, while the quaternary 5-oxaprotoberberinium salt was synthesized by reduction and oxidation of the lactam moiety of 5-oxaprotoberberinone.