Synthesis and comparison of antiplasmodial activity of (+), (−) and racemic 7-chloro-4-(N-lupinyl)aminoquinoline

Recently the N-(−)-lupinyl-derivative of 7-chloro-4-aminoquinoline ((−)-AM-1; 7-chloro-4-{N-[(1S,9aR)(octahydro-2H-quinolizin-1-yl)methyl]amino}quinoline) showed potent in vitro and in vivo activity against both Chloroquine susceptible and resistant strains of Plasmodium falciparum. However, (−)-AM-1 is synthesized starting from (−)-lupinine, an expensive alkaloid isolated from Lupinus luteus whose worldwide production is not sufficient, at present, for large market purposes. To overcome this issue, the corresponding racemic compound, derived from synthetic (±)-lupinine was considered a cheaper alternative for the development of a novel antimalarial agent. Therefore, the racemic and the 7-chloro-4-(N-(+)-lupinyl)aminoquinoline ((±)-AM-1; (+)-AM-1) were synthesized and their in vitro antimalarial activity and cytotoxicity compared with those of (−)-AM-1. The (+)-lupinine required for the synthesis of (+)-AM-1 was obtained through a not previously described lipase catalyzed kinetic resolution of (±)-lupinine. In terms of antimalarial activity, (±)-AM1 and (+)-AM1 demonstrated very good activity in vitro against both CQ-R and CQ-S strains of P. falciparum (range IC50 16-35 nM), and low toxicity against human normal cell lines (therapeutic index >1000), comparable with that of (−)-AM1. These results confirm that the racemate (±)-AM1 could be considered as a potential antimalarial agent, ensuring a decrease of costs of synthesis compared to (−)-AM1.