Structure-activity relationships and optimization of the selective MDR modulator 2-(3,4-dimethoxyphenyl)-5-(9-fluorenylamino)-2-(methylethyl)pentanenitrile and its N-methyl derivative

Abstract—Several ring-substituted derivatives of previously studied MDR inhibitors 2-(3,4-dimethoxyphenyl)-5-(9-fluorenylamino)- 2-(methylethyl)pentanenitrile and 2-(3,4-dimethoxyphenyl)-5-[(9-fluorenyl)-N-methylamino]-2-(methylethyl)pentanenitrile have been synthesised and studied with the aim of optimising activity and selectivity. The results show that MDR inhibition is scarcelysensitive to modulation of the electronic properties of the fluorene ring. Even if dramatic improvement was not obtained, one of the compounds (2) showed improved potencyand selectivity with respect to the leads and appears to be a better candidate for drug development.