Expedient multicomponent synthesis of a small library of some novel highly substituted pyrido[2,3-d]pyrimidine derivatives mediated and promoted by deep eutectic solvent and in vitro and quantum mechanical study of their antibacterial and antifungal activities.

A facile and efficient catalyst- and oxidant-free multicomponent synthesis of a small library of highly substituted pyrido[2,3-d]pyrimidine derivatives is reported. The products were obtained within relatively short reaction times in good to excellent yields in the presence of deep eutectic solvents as media and promoters. Simple purification and reusability of the deep eutectic solvent were the other beneficial factors of the reported protocol. All of the synthesized derivatives were thoroughly screened for possible in vitro antibacterial and antifungal effects against twenty-two bacterial and three fungal pathogens. Some of the prepared pyrido[2,3-d]pyrimidine derivatives showed remarkable antibacterial and antifungal activities in comparison with some typical known antibacterial and antifungal agents. Finally, the derivatives possessing bioactivity effects were subjected to quantum chemical computational studies in order to reveal the probable structural and electronic effects governing the spotted bioactivities. It was found that the observed bioactivities could be best devoted to the HOMO-LUMO energy gap and para delocalization index of the corresponding derivatives.