## 1 Introduction
In addition, peptide-based drugs can represent a viable solution to alleviate the symptoms of various diseases. Due to their low intrinsic toxicity, peptides are particularly appealing. The use of highly effective and precise peptide drugs would considerably help neurological conditions such as neurodegeneration, pain, psychiatric disorders, stroke and brain tumors [21; 22; 23]. As a result of advancements in biotechnology, a wide range of peptide drugs are currently produced on a commercial basis. However, because of limited absorption from the gastrointestinal tract, the majority of these therapeutic peptides are still delivered by parenteral method [24]. In addition to the parenteral route, the peptide-based drugs can also intranasally be administered [25]. Thus, with a biocompatibility closer to gastrointestinal or blood-brain barrier (BBB) administration, these treatments can be more effective in evaluating their intranasal or cutaneous pharmacological properties. Nevertheless, there has been an increase in research of peptide-based drug applicability in various diseases. More than 40 cyclic peptide drugs derived from natural compounds have been authorized in clinical trials during the last few decades [26]. Recently, the molecular way in which neuroprotective NAP peptide (\({}^{1}\)NAPVSIPQ\({}^{8}\)) and its analog with acetylsalicylic acid can stabilize axonal microtubules has been proved [27; 28; 29]. It was also reported that the semi-elastic lipid nanoparticles significantly enhanced peptide oral availability and could be a viable future oral peptide delivery technology for peptide medicines [30]. Furthermore, several toxin-derived peptides have been developed into pharmaceuticals which are used to treat diabetes, hypertension, chronic pain and other disorders [31]. Moreover, a similar study presents a critical theoretical foundation as well as significant empirical data on the essential physicochemical aspects of anticancer peptide-based drug development [32]. Different in vitro studies performed by [PERSON] and his team suggested that during A\(\beta\) polymerization and fibril formation, A\(\beta_{(16-20)}\) residues act as a binding sequence. This pentapeptide, \({}^{16}\)KVLFF [20], may be used as ligands that bind to A\(\beta\) and prevent the formation of amyloid fibrils [33; 34]. Thus, it may break the \(\beta\)-sheet structure of amyloid fibrils by intercalation among the A\(\beta\) monomers. It was also observed that the sequence 15-20 of A\(\beta\) represents the crucial fragment which forms \(\beta\)-sheet structures [35]. Therefore, an important step to prevent the development of A\(\beta\) fibrils could be to break the interaction between two fragments of A\(\beta_{(15-20)}\). On the other hand, a common problem in peptide-based drugs relates to the BBB and gastrointestinal administration specificity. Hence, these drugs must meet the criteria regarding the lipophilicity and molecular weight according to pharmacological rules [36]. Therefore, in the present study we investigated over 70 new peptide-based drugs (peptide conjugates based on the A\(\beta_{(15-20)}\) sequence) in respect to the lipophilicity and biocompatibility of different methods of administration (e.g., intranasal). We utilized a particular set of peptide conjugates never studied before.