Purity >95%. Proguanil is an antimalarial compound used in combination therapy against Plasmodium infections. Cycloguanil is an active metabolite of proguanil, produced by the cytochrome P450 2C19 isoform. It acts as an inhibitor of dihydrofolate reductase (DHFR) (Ki s = 0.3 and 1.5 nM for Plasmodium and human forms, respectively). By blocking DHFR activity, cycloguanil prevents the production of tetrahydrofolic acid, an essential coenzyme involved in DNA and RNA synthesis.