3-Methoxy- and 3-Ethoxysalicylaldehydes: Structural, DFT, and Optical Studies, and in Silico Prediction of the Antiviral Activity

3-Methoxysalicylaldehyde (1) and 3-ethoxysalicylaldehyde (2) were studied and analyzed. A Hirshfeld surface analysis has allowed to establish that reciprocal H⋅⋅⋅X (X = H, C, O) contacts are the dominant ones in the crystal structures of both aldehydes. The DFT-based calculations revealed electronic features of the studied compounds. Accordingly, the values of the HOMO and LUMO allowed to compute the so-called global descriptors. ADMET properties of 1 and 2 were revealed by the means of the SwissADME and ProTox-II online instruments. Potential antiviral activities of the reported salicylaldehyde derivatives against a number of the SARS-CoV-2 proteins were predicted in silico. Both molecules are potentially active toward all the applied proteins with the most pronounced activity revealed for Nonstructural protein 3 (Nsp3_range 207–379-MES). Molecular dynamics modeling was additionally applied to study the stability of the resulting Nsp3_range 207–379-MES–1 and Nsp3_range 207–379-MES–2 complexes.