Eight density functionals, CAM-B3LYP, $$\hbox {LC-}\omega \hbox {PBE}$$ , M11, MN12SX, N12SX, $$\omega \hbox {B97}$$ , $$\omega \hbox {B97X}$$ , and $$\omega \hbox {B97XD}$$ , related to the Def2TZVP basis sets, were assessed together with the SMD solvation model for the calculation of the molecular properties and structure of the therapeutic peptide of marine origin Parasin I. All the chemical reactivity descriptors for the system are calculated via conceptual density functional theory (CDFT). The active sites suitable for nucleophilic, electrophilic, and radical attacks are selected by linking them with the Fukui function indices, nucleophilic and electrophilic Parr functions, and condensed dual descriptor $$\Delta {f(r)}$$ , respectively. The study reveals that the MN12SX and N12SX density functionals are the most appropriate ones for predicting the chemical reactivity of the molecule under study. Additionally, the pKa value for the peptide is predicted with great accuracy based on our previously published methodology. Moreover, the ability of the studied molecule in acting as an efficient inhibitor of the formation of advanced glycation endproducts (AGEs), which constitutes a useful knowledge for the development of drugs for fighting diabetes, Alzheimer and Parkinson diseases is also presented. Finally, the bioactivity scores for Parasin I are predicted through different methodologies.