Synthesis and characterization of new thiazole-based Co(II) and Cu(II) complexes; therapeutic function of thiazole towards COVID-19 in comparing to current antivirals in treatment protocol

Abstract
Two thiazole-based complexes were prepared from Co(II) and Cu(II) ions. The new ligand and its complexes were fully characterized by analytical and spectral techniques. The ligand behaved as a neutral tridentate in its keto-form towards the metals via O(8), O(10) and O(18) atoms. This was suggested based on the lower shift of υ(CHO), υ(CO)amide and υ(CO) vibrations. The electronic transitions in Co(II)-HL and Cu(II)-HL complexes displayed d-d- transitions which belong to 4T1g→4A2g(F) & 4T1g(F)→4T1g (P) and 2Eg →2T2g, in the two complexes, respectively. ESR spectrum of Cu(II)-HL complex displayed g-factor by the following order; g//(2.1740)>g⊥(2.0935)>2.0023, which agrees with octahedral geometry. The geometry optimization was executed by DFT/B3LYP method under valence double zeta polarized basis set (6–31G*), to confirm the structural forms and the mode of bonding. The orientation and the charges of O(8), O(10) and O(18) atoms, support the coordination of the ligand in its keto-form with the metal ions. Pharmacophore profiles were obtained regarding thiazole ligand and other recommended drugs (arbidol, avigan and idoxuridine) that used in treatment protocol of COVID-19 pandemic. Also, query was run in MolPort-library to obtain antiviral analogues, to broaden the search for an effective treatment. Three analogues were obtained for arbidol, avigan and idoxuridine drugs, which have the following numbers; MolPort-047-605-644, MolPort-004-768-508 and MolPort-028-750-709, respectively. Moreover, molecular docking was carried out to obtain all interaction details and rank the efficiency of thiazole compound versus the three antivirals in their interaction with the two COVID-19 proteins. The outcomes suggested the significant antiviral activity of idoxuridine and thiazole (enol-form), which not reach to eliminate the pandemic exactly. While, arbidol and avigan did not have an effective antiviral role, although they still used in COVID-19 treatment protocol.