Antimalarials: Synthesis of 4-aminoquinolines that circumvent drug resistance in malaria parasites

The strategies described here have permitted the synthesis of a series of 4-aminoquinoline antimalarials. Substantive improvements over previous syntheses include nucleophilic substitution with neat amine rather than in phenol, regioselective reductive alkylation to convert the terminal primary amine (12a-20a) on the diaminoalkane side chain to a diethylamino group, and purification by column chromatography with basic alumina. The H-1 nmr spectra obtained after regioselective reductive alkylation with sodium borodeuteride (in comparison with sodium borohydride) demonstrated that this reductive alkylation proceeds via formation and subsequent reduction of the corresponding diamides in situ.