Mefloquine derivatives: Crystal structures and anti-tubercular activities of diphenyl[((R*,S*)-2,8-bis(trifluoromethyl)quinolin-4-yl)-piperidin-2-yl-methanolato-O,N]boron and (±)-erythro-mefloquinium tetraphenylborate solvates

Thermolysis of (R*,S*)-(2-{[2,8-bis(trifluoromethyl)quinolin-4-yl](hydroxy)∼methyl}piperidin-1-ium) tetraphenylborate, (±)-erythro-mefloquinium tetraphenylborate, 3, in solution or neat, provides the oxazaborolidine derivative, diphenyl[(R*,S*)-(2,8-bis(trifluoromethyl)quinolin-4-yl)]piperidin-2-yl-methanolato-O,N]boron, 2. Crystal structures of solvates of 2 and 3 are reported. As shown by the 1H NMR spectrum, 2 undergoes a conformation equilibrium in solution. Both 2 and 3 exhibit important anti-tubercular activities as indicated by the minimum inhibitory concentrations (MIC) of 50 and 12.5 μg/ml, respectively, in in vitro assays against M. tuberculosis H37Rv ATTC 27294.