Synthesis and structure-activity relationship studies in translocator protein ligands based on a pyrazolo[3,4-b]quinoline scaffold

As a further development of our large program focused on the medicinal chemistry of translocator protein [TSPO (18 kDa)] ligands, a new class of compounds related to alpidem has been designed using SSR180575, emapunil, and previously published pyrrolo[3,4-b]quinoline derivatives 9 as templates. The designed compounds were synthesized by alkylation of the easily accessible 4-methyl-2-phenyl-1H- pyrazolo[3,4-b]quinolin-3(2H)-one derivatives 1315 with the required bromoacetamides. Along with the expected 2-(4- methyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazolo[3,4-b]quinolin-1-yl)acetamide derivatives 10, 2-(4-methyl-3-oxo-2-phenyl- 2H-pyrazolo[3,4-b]quinolin-9(3H)-yl)acetamide isomers 11 were isolated and characterized. The high TSPO affinity shown by new pyrazolo[3,4-b]quinoline derivatives 10 and especially 11 leads the way to further expand the chemical diversity in TSPO ligands and provides new templates and structureaffinity relationship data potentially useful in the design of new anxiolytic and neuroprotective agents.