Synthesis and Biological Evaluation of Imidazopyridine-Isatin Hybrids as Inhibitors of Leishmania major Growth

Mahmoud A El Hassab,1 Wagdy M Eldehna,2 Zainab M Elsayed,3 Mostafa M Elbadawi,2 Ahmed T Negmeldin,4,5 Marwa Balaha,2,6 Sherry N Nasralla,7 Rehan Monir,8 Tamer M Ibrahim,2 Manabu Abe,9 Haytham O Tawfik,10 Adnan A Bekhit,7,11 Loah R Hemeda12 1Department of Medicinal Chemistry, Faculty of Pharmacy, King Salman International University (KSIU), South Sinai, Egypt; 2Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Kafrelsheikh University, Kafrelsheikh, Egypt; 3Scientific Research and Innovation Support Unit, Faculty of Pharmacy, Kafrelsheikh University, Kafrelsheikh, Egypt; 4Department of Pharmaceutical Sciences, College of Pharmacy and Thumbay Research Institute for Precision Medicine, Gulf Medical University, Ajman, United Arab Emirates; 5Department of Pharmaceutical Organic Chemistry, Faculty of Pharmacy, Cairo University, Cairo, Egypt; 6Department of Pharmacy, “G. d’Annunzio” University of Chieti-Pescara, Chieti, Italy; 7Pharmacy Program, Allied Health Department, College of Health and Sport Sciences, University of Bahrain, Salmaniya, Bahrain; 8Clinical Biochemistry Department, College of Medicine, King Khalid University, Asir, Saudi Arabia; 9Department of Chemistry, Graduate School of Advanced Science and Engineering, Hiroshima University, Hiroshima, Japan; 10Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Tanta University, Tanta, Egypt; 11Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt; 12Department of Medicinal Chemistry, Faculty of Pharmacy, Beni-Suef University, Beni-Suef, EgyptCorrespondence: Wagdy M Eldehna, Email wagdy2000@gmail.com Ahmed T Negmeldin, Email dr.ahmedthabet@gmu.ac.aeIntroduction: More than 20 different species of Leishmania cause leishmaniasis, a multifaceted disease that ranges from mild cutaneous lesions to fatal visceral forms.Methods: Sixteen novel hybrids were designed by covalently linking an imidazo[1,2-a]pyridine core to an isatin scaffold via a hydrazide linker, and their in vitro anti-promastigote, anti-amastigote, cytotoxicity, and molecular docking profiles were evaluated, with folate-rescue assays used to assess the anti-folate mechanism.Results: Several compounds showed potent anti-leishmanial activity compared to miltefosine, with the lead compound 5b exhibiting strong anti-promastigote (IC50 = 0.84 ± 0.06 μM) and anti-amastigote (IC50 = 1.28 ± 0.18 μM) activities, significantly surpassing miltefosine. Folic and folinic acids reversed the activity of 5b, confirming an anti-folate mechanism similar to that of the Lm-PTR1 inhibitor trimethoprim. The most active compounds showed higher selectivity indices (SI = 12.74) than miltefosine (SI = 438.03), and docking against Lm-PTR1 provided a plausible explanation for their potency, while in silico predictions indicated favorable drug-likeness and pharmacokinetic properties.Conclusion: These findings highlight a promising new chemotype targeting the leishmanial folate pathway and expand the chemical diversity available for anti-leishmanial drug development. Keywords: neglected tropical diseases, leishmaniasis, molecular modeling, anti-folate mechanism, imidazo[1,2-a]pyridine, isatin