Lohawittayanan D.Khulmanee T.Thima K.Chabang N.Yenjai W.Kanjanasirirat P.Schlaeppi P.Tantivess V.Phumisithikul T.Ratcha-in D.Chotsriluecha S.Chuchaisuwannasri D.Phanchana M.Pinthong N.Patrapuvich R.Charoensutthivarakul S.Mahidol University2026-04-292026-04-292026-04-21ACS Omega Vol.11 No.15 (2026) , 22796-22806https://repository.li.mahidol.ac.th/handle/123456789/116401The emergence of Plasmodium falciparum resistance to artemisinin-based therapies necessitates the urgent discovery of new antimalarials with novel scaffolds and mechanisms. The quinazolinedione scaffold, exemplified by the TCAMS hit TCMDC-125133, was identified as a promising, noncytotoxic starting point. Herein, we report a systematic lead optimization campaign commencing from a simplified and synthetically tractable analogue, compound 9 (IC<inf>50</inf> = 586 nM), which was previously reported by our group. A focused library of 57 novel derivatives was designed and synthesized via a concise 5-step route to systematically explore the structure–activity relationships of the terminal phenyl side chain and the quinazolinedione core. Our investigation revealed two critical findings: (i) the 3,4-difluorophenyl side chain was optimal for potency, and (ii) substitution of the core with small, electron-withdrawing halogens was highly beneficial. This strategy led to the discovery of compound 53 which pairs a 6,7-difluoro core with a 3,4-difluorophenyl side chain demonstrating a potent IC<inf>50</inf> of 116 nM against P. falciparum 3D7. Crucially, this potent analogue and every compound in the series exhibited negligible cytotoxicity against human HepG2 cells (IC<inf>50</inf> > 20 μM) indicating a high selectivity. This work validates the 7-halogenated quinazolinedione scaffold as a promising and selective chemotype for further antimalarial drug development.Chemical EngineeringChemistryArticleSCOPUS10.1021/acsomega.5c120062-s2.0-10503641844724701343