Synthesis, crystal structure, DFT and molecular docking studies of N-acetyl-2,4-[diaryl-3-azabicyclo[3.3.1]nonan-9-yl]-9-spiro-4′-acetyl-2′-(acetylamino)-4′,9-dihydro-[1′,3′,4′]-thiadiazoles: A potential SARS-nCoV-2 Mpro (COVID-19) inhibitor

In this paper, we describe the synthesis and crystal structure analysis of N-acetyl-2,4-[diphenyl-3-azabicyclo[3.3.1]nonan-9-yl]-9-spiro-4′-acetyl-2′-(acetylamino)-4′,9-dihydro-[1′,3′,4′]-thiadiazole (3a) and N-acetyl- 2,4-[bis(p-methoxyphenyl)-3-azabicyclo[3.3.1]nonan-9-yl]-9-spiro-4′-acetyl-2′-(acetylamino)-4′,9-dihydro-[1′,3′,4′]-thiadiazole (3b). The title compounds 3a and 3b are characterized by 1D NMR and single crystal x-ray diffraction analysis. Non-covalent interactions in a molecule were identified by Hirshfeld surface (d(norm) contacts and 2D fingerprint plot) analysis. In addition, the existence of chalcogen bond (S•••O bond) in the molecular structures (3a and 3b) are described by NCI-RDG and QTAIM analysis. NBO analysis is employed to describe the orbital interactions and electron transfer between sulfur and oxygen atoms. Molecular docking is carried out for compounds 3a and 3b with COVID-19 viral protein SARS-nCoV-2 M(pro) (PDB ID: 6LU7).