One-pot, multi-component synthesis and structure-activity relationships of peptoid-based histone deacetylase (HDAC) inhibitors targeting malaria parasites

Malaria drug discovery has shifted from a focus on targeting asexual blood stage parasites, to the development of drugs that can also target exo-erythrocytic forms and/or gametocytes in order to prevent malaria and/or parasite transmission. In this work, we aimed to develop parasite-selective histone deacetylase inhibitors (HDACi) with activity against the disease-causing asexual blood stages of Plasmodium malaria parasites as well as with causal prophylactic and/or transmission blocking properties. An optimized one-pot, multi-component protocol via a sequential Ugi four-component reaction and hydroxylaminolysis was used for the preparation of a panel of peptoid-based HDACi. Several compounds displayed potent activity against drug-sensitive and drug-resistant P. falciparum asexual blood stages, high parasite-selectivity and submicromolar activity against exo-erythrocytic forms of P. berghei. Our optimization study resulted in the discovery of the hit compound 1u which combines high activity against asexual blood stage parasites (Pf 3D7 IC₅₀: 4 nM; Pf Dd2 IC₅₀: 1 nM) and P. berghei exo-erythrocytic forms (Pb EEF IC₅₀: 25 nM) with promising parasite-specific activity (SI^{Pf 3D7/HepG2}: 2496, SI^{Pf Dd2/HepG2}: 9990, and SI^{Pb EEF/HepG2}: 400).