Although the COVID-19 pandemic is over but the clouds of next pandemic can't be ignored and therefore, search for new effective and more safe drug candidates against SARS-CoV-2 is the need of time. The presented study investigates the potential for designing new least toxic but more effective drug candidates with enhanced therapeutic properties against SARS-CoV-2. Pyrimethamine, which was once a cornerstone in malaria treatment, has lost its effectiveness due to the development of drug resistance. Despite this, significant interest remains in modifying and repurposing the drug within medicinal chemistry. The presented study has demonstrated the synthesis of three novel organic co-crystal salts derived from pyrimethamine and the coformers homophthalic acid, chlorosalicylic acid, and 4-methoxy cinnamic acid via reflux method to obtain co-crystal salt I (PYM: HOM), II (PYM: CSAL), and III (PYM: MCIN), in a 1:1 stoichiometric ratio. Single-crystal X-ray diffraction, vibrational spectroscopy, and DSC/TGA analysis were used for the structural characterization and confirmation. Moreover, quantum chemical calculations were carried out to evaluate the structural and electronic properties of the binary complex of the co-crystals and crystal supercells. The interaction energies of the binary complexes were also computed to assess the relative stability of the crystal salts while comparing them with TGA/DTG data. As the COVID-19 pandemic has infected millions of people with mortality exceeding >1 million. There is an urgent need to find therapeutic agents that can help with virus eradication to prevent severe disease and deaths. These co-crystal salts were evaluated for their potential to inhibit SARS-CoV-2 propagation. Co-crystal salt II was observed as the most significant inhibitor at all the treatment points such as prophylactic, entry, and therapeutic (post-entry). Furthermore, pyrimethamine and coformers were also found to be effective at different targets as well. The identification of co-crystal salt II, comprising pyrimethamine and the coformers, shows promising antiviral activity against SARS-CoV-2, potentially laying the groundwork for the development of new drug candidates.
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