## 2 Results and Discussion
### Design
#### 2.1.2 Design of Peptides  
Repeated combinations of poly-N-substituted glycine (NSG) form peptidomimetic compounds known as peptoids [35]. They are a class of artificial, unnatural peptide mimics that have a modular structure that allows a wide variety of structural components to be easily incorporated. Peptoids have the functionality of their side chains linked to the nitrogen of the polyamide backbone instead of the \(\alpha\)-carbon, creating an achiral and flexible oligomeric backbone without hydrogen bond donors. This N-alkyl backbone repeat motif allows peptoids greater stability against proteolytic degradation than analogous peptides [36]. Additionally, NSGs may be more hydrophobic and possess higher cellular permeability [37; 38; 39]. Figure 1 shows the similarities between peptides and peptoids in the spacing of the side chains and carbonyl groups and the variations in the chirality of the two monomers [40].  
\begin{table}
\begin{tabular}{c c c c} \hline
**Pep** & **Sequence** & \
\begin{tabular}{c} **MST** \\ **K\({}_{\text{D}}\) (\(\mu\)M)** \\ \end{tabular} &
\begin{tabular}{c} **SPR** \\ **K\({}_{\text{D}}\) (\(\mu\)M)** \\ \end{tabular} \\ \hline
**1**\({}^{\text{a}}\) & SLDC & 10.4 \(\pm\) 0.23 & 7.12 \(\pm\) 0.26 \\
**2**\({}^{\text{a}}\) & SKHS & 7.26 \(\pm\) 0.06 & 4.53 \(\pm\) 0.08 \\ \hline
**3** & (N-Me)SLDC & 24.8 \(\pm\) 0.71 & 7.60 \(\pm\) 2.69 \\
**4** & S(N-Me)LDC & 0.0325 \(\pm\) 0.002 & 0.58 \(\pm\) 0.34 \\
**5** & SL(N-Me)DC & 8.8 \(\pm\) 0.23 & NPD \({}^{\text{b}}\) \\
**6** & SLD(N-Me)C & 0.142 \(\pm\) 0.03 & 3.80 \(\pm\) 1.06 \\
**7** & (N-Me)SKHS & 0.336 \(\pm\) 0.02 & 4.19 \(\pm\) 0.86 \\
**8** & S(N-Me)KHS & 7.93 \(\pm\) 0.73 & 8.33 \(\pm\) 1.73 \\
**9** & SK(N-Me)HS & 0.0528 \(\pm\) 0.005 & 1.26 \(\pm\) 0.36 \\
**10** & SKH(N-Me)S & 3.04 \(\pm\) 0.85 & NPD \({}^{\text{b}}\) \\
**11** & NSLDC \({}^{\text{c}}\) & 0.0672 \(\pm\) 0.002 & 6.55 \(\pm\) 1.52 \\
**12** & SNLDC \({}^{\text{c}}\) & 0.701 \(\pm\) 0.03 & 3.81 \(\pm\) 2.13 \\
**13** & SLNDC \({}^{\text{c}}\) & 1.34 \(\pm\) 0.02 & NPD \({}^{\text{b}}\) \\
**14** & SLDNHC \({}^{\text{c}}\) & 0.0459 \(\pm\) 0.01 & NPD \({}^{\text{b}}\) \\
**15** & \(N\)hSKHS \({}^{\text{c}}\) & 7.4 \(\pm\) 0.35 & 2.09 \(\pm\) 2.41 \\
**16** & SNKHS \({}^{\text{c}}\) & 0.0391 \(\pm\) 0.003 & 1.70 \(\pm\) 0.13 \\
**17** & SKNHS \({}^{\text{c}}\) & 3.07 \(\pm\) 0.79 & NPD \({}^{\text{b}}\) \\
**18** & SKHNhs \({}^{\text{c}}\) & 0.0491 \(\pm\) 0.001 & 0.43 \(\pm\) 0.21 \\ \hline \end{tabular}
\end{table}
Table 1: Sequence and binding affinities between HA and peptides **1**, **2**, **3–18** determined using MST and SPR. The binding affinities of peptides **1** and **2** are reported as references. \({}^{\text{a}}\) [PERSON] et al. (2017) [23]. All peptides are amidated and acetylated. \({}^{\text{b}}\) NPD: nonpertinent data. \({}^{\text{c}}\) Abbreviations of peptoid monomers: \(N\)NS: \(N\)-(2-hydroxyethyl)glycine, \(N\)L: \(N\)-(isobutyl)glycine, \(N\)D: \(N\)-(1-carboxymethyl)glycine, \(N\)NC: \(N\)-(2-toethyl)glycine, \(N\)K: \(N\)-(4-aminobutyl)glycine, \(N\)H: \(N\)-(1-imidazolomethyl)glycine.  
Hence, we synthesized the peptoid analogues of **1** and **2** (**11**-**18**), replacing in a systematic manner Ser, Leu, Asp, Cys, Lys, and His with their NGS.