The main topic of the research is the synthesis, characterization, and biological evaluation of selected aza-heterocycles. Synthesis of tetrahydropyrimidines and investigation of their influence on selected cancer cell lines, their mechanism of action, pharmacokinetic parameters, and toxicology are the most important part of the research. Also, interaction with selected compounds with biomacromolecules such as DNK, and BSA is part of the investigation. Besides, antimicrobial activity on different strains of fungi and bacteria has been examined. One of the goals during the optimization of reaction conditions is an application of the principles of green chemistry and the development of new sustainable methods that will avoid the usage of harmful solvents and/or catalysts in the first place. Currently, new tetrahydropyrimidne-based polymers have been synthesized and their characteristics and potential application have been investigated.