Synthesis and Biological Evaluation of Pyridooxazine–Tetrahydroisoquinoline Derivatives as MDR Modulators

Pyridooxazine–tetrahydroisoquinoline derivatives were designed and synthesized for MDR modulating activity. Pyridooxazin-2-one scaffolds were constructed in a one-pot annulation of N-substituted-2-chloroacetamides with 2-bromo-3-hydroxy pyridine via Smiles rearrangement. The Pictet–Spengler cyclization to form tetrahydroisoquinoline ring afforded target compounds in 17–37% overall yields. Some of these compounds exhibited multidrug resistance (MDR) reversing activity.