# Investigation of Naphthyl-Polyamine Conjugates as Antimicrobials and Antibiotic Enhancers

Melissa M Cadelis, Liam R Edmeades, Dan Chen, Evangelene S Gill, Kyle Fraser, Florent Rouvier, Marie-Lise Bourguet-Kondracki, Jean Michel Brunel, Brent R Copp

<figure><img src="image_1.png" /></figure>

## To cite this version:

Melissa M Cadelis, Liam R Edmeades, Dan Chen, Evangelene S Gill, Kyle Fraser, et al., Investigation of Naphthyl-Polyamine Conjugates as Antimicrobials and Antibiotic Enhancers. Antibiotics, 2023, 12 (6), 10.3390/antibiotics12061014. [DOI: 10.0041/antibiotics.12061014](https://doi.org/10.0041/antibiotics.12061014)

HAL Id: hal-04244699

https://hal.science/hal-04244699v1

Submitted on 16 Oct 2023

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
<figure><img src="image_3.png" /></figure>

Article

# Investigation of Naphthyl-Polyamine Conjugates as Antimicrobials and Antibiotic Enhancers

Melissa M. Cadelis <fnref n="1" />,<fnref n="2" /> ID, Liam R. Edmeades <fnref n="1" />, Dan Chen <fnref n="1" />, Evangelene S. Gill <fnref n="1" />, Kyle Fraser <fnref n="1" />, Florent Rouvier <fnref n="3" />, Marie-Lise Bourguet-Kondracki <fnref n="4" />, Jean Michel Brunel <fnref n="3" /> ID and Brent R. Copp <fnref n="1" />,* ID

<figure><img src="image_4.png" /></figure>

check for
updates

**Citation:** Cadelis, M.M.; Edmeades, L.R.; Chen, D.; Gill, E.S.; Fraser, K.; Rouvier, F.; Bourguet-Kondracki, M.-L.; Brunel, J.M.; Copp, B.R.

Investigation of Naphthyl-Polyamine Conjugates as Antimicrobials and Antibiotic Enhancers. *Antibiotics* **2023**, *12*, 1014. https://doi.org/10.3390/antibiotics12061014

Academic Editor: Rok Frlan

Received: 16 May 2023

Revised: 1 June 2023

Accepted: 2 June 2023

Published: 5 June 2023

<figure><img src="image_5.png" /></figure>

**Copyright:** © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).

**Abstract:** As part of our search for new antimicrobials and antibiotic enhancers, a series of naphthyl- and biphenyl-substituted polyamine conjugates have been synthesized. The structurally-diverse library of compounds incorporated variation in the capping end groups and in the length of the polyamine (PA) core. Longer chain (PA-3-12-3) variants containing both 1-naphthyl and 2-naphthyl capping groups exhibited more pronounced intrinsic antimicrobial properties against methicillin-resistant *Staphylococcus aureus* (MRSA) (MIC ≤ 0.29 µM) and the fungus *Cryptococcus neoformans* (MIC ≤ 0.29 µM). Closer mechanistic study of one of these analogues, **20f**, identified it as a bactericide. In contrast to previously reported diarylacyl-substituted polyamines, several examples in the current set were able to enhance the antibiotic action of doxycycline and/or erythromycin towards the Gram-negative bacteria *Pseudomonas aeruginosa* and *Escherichia coli*. Two analogues (**19a** and **20c**) were of note, exhibiting greater than 32-fold enhancement in activity. This latter result suggests that α,ω-disubstituted polyamines bearing 1-naphthyl- and 2-naphthyl-capping groups are worthy of further investigation and optimization as non-toxic antibiotic enhancers.

**Keywords:** antimicrobial activities; polyamine conjugates; antibiotic enhancement

## 1. Introduction

Host-defense peptides (HDPs), produced by a wide variety of organisms in nature, including microorganisms, plants, invertebrates, and mammals, play essential roles as a first line of protection against viral, fungal, and bacterial infections [1–6]. A subset of HDPs are the antimicrobial peptides, small (50 amino acids or less) amphipathic peptides of diverse sequence homology and secondary structures [7]. From a structural perspective, antimicrobial peptides are characterized as containing hydrophobic residues on one side of the molecule and hydrophilic cationic residues on the other. These peptides are thought to act directly on bacterial cell membranes, with the cationic charges aiding electrostatic attraction to the negatively charged cell membrane, followed by hydrophobic residue insertion into the membrane leading to disruption, increased membrane permeability, and, ultimately, cell death [7]. Drug development issues associated with HDPs, including susceptibility to proteolysis, high production costs, and, in some case, low to moderate activity under physiological salt conditions, prevent their direct introduction as clinical agents [8]. In order to overcome these deficiencies, an extensive amount of research has been directed towards the synthesis and biological evaluation of synthetic mimics of antimicrobial peptides, so-called SMAMPs [9–15]. Numerous different structural classes of SMAMPs have been identified, including shorter peptides (e.g., LTX-109 (1)), sterols (e.g., squalamine (2)), and hydantoins (e.g., 3) (Figure 1) [15–17]. Although they cover

<footnote n="1">¹ School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand</footnote>

<footnote n="2">² School of Medical Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand</footnote>

<footnote n="3">³ Membranes et Cibles Thérapeutiques (MCT), SSA, INSERM, Aix-Marseille Université, 27 bd Jean Moulin, 13385 Marseille, France</footnote>

<footnote n="4">⁴ Laboratoire Molécules de Communication et Adaptation des Micro-organismes, UMR 7245 CNRS, Muséum National d'Histoire Naturelle, 57 rue Cuvier (C.P. 54), 75005 Paris, France</footnote>

<footnote>* Correspondence: b.copp@auckland.ac.nz</footnote>
diverse chemo-types, all three of these examples are thought to act via a general bacterial
membrane-targeting mechanism, with insertion leading to membrane disruption [16,18,19].
LTX-109 is one example of a number of different antimicrobial peptides that have entered
clinical trials for the treatment of microbial infections [20].

<figure><img src="image_6.png" /><figcaption>**Figure 1.** Structures of SMAMPs 1–4.</figcaption></figure>

The discovery of squalamine (2), a polyamine-containing aminosterol isolated from the dogfish shark *Squalus acanthias*, and observation of its broad-spectrum activity towards both Gram-positive and Gram-negative bacteria [21] prompted further investigation of the marine environment in the search for new classes of antimicrobials [22]. The marine sponge natural product ianthelliformisamine C (4) exhibits antimicrobial activity and can also enhance the activity of legacy antibiotics towards drug resistant Gram-negative bacteria [23–25]. Ianthelliformisamine C has all the structural attributes of an SMAMP, with the secondary amines of the polyamine fragment being protonated at physiological pH and the terminal cinnamate capping group being lipophilic, defining this as a scaffold worthy of attention [22,26].

We recently reported the synthesis and antimicrobial evaluation of a set of α,ω-diacylaryl substituted polyamine analogues, of which examples 5–7 (Figure 2) are representative [27].

Analogues bearing a single aryl group at each end of a polyamine (PA) chain, e.g., 5, were found to be almost uniformly inactive towards a panel of Gram-positive and Gram-negative bacteria and fungal strains, with only the longer polyamine chain variants (PA-3-10-3 and PA-3-12-3) exhibiting weak-to-potent activity towards methicillin-resistant *Staphylococcus aureus* (MRSA). Increasing the lipophilicity by inclusion of one or two additional phenyl rings in the capping acid created sets of analogues, e.g., 6 and 7, that demonstrated good to excellent growth inhibition properties towards *Staphylococcus aureus* (MIC 3.13 µM for both), MRSA (MIC ≤ 0.28 µM and MIC ≤ 0.24 µM, respectively), and *Escherichia coli* (MIC 2.2 µM and MIC 7.6 µM, respectively). When counter screen cytotoxicity and hemolytic activities were combined with calculated LogP values, it became apparent that optimal selectivity for antimicrobial activity was observed for diaryl-containing capping groups with whole molecule cLogP in the range 7–8.5. Any analogues with cLogP greater than 9–10 appear to breach a ‘second hydrophobicity threshold’ [28], leading to greater disruption of mammalian membranes and inherent toxicity. Mechanism of ac-
tion studies carried out on the diaryl-analogue 6 identified it as a strong disruptor of bacterial cell membranes and to be bactericidal [27], making it a good starting point for further optimization.

<figure><img src="image_7.png" /><figcaption>**Figure 2.** Structures of α,ω-diacylaryl substituted polyamine analogues 5–7 [27].</figcaption></figure>

Mindful of not exceeding the second hydrophobicity threshold, we chose to prepare new examples of α,ω-disubstituted polyamines that targeted the cLogP range of approximately 5–9 and incorporated aryl-carboxylic acids **8–12** (Figure 3), which contained variations in shape, size, lipophilicity and position of attachment to the polyamine core.

<figure><img src="image_8.png" /><figcaption>**Figure 3.** Structures of aromatic head groups **8–12** with cLogP values of the corresponding methyl ester in parentheses.</figcaption></figure>

Herein, we report the synthesis of a set of new α,ω-disubstituted polyamines that explore variation in the size and shape of the chain end-groups within a narrow band of lipophilicity as well as variation in polyamine length. All analogues were evaluated for antimicrobial activities against a set of Gram-positive and Gram-negative bacteria and two fungi strains, and for the ability to enhance the antibiotic action of doxycycline and erythromycin towards the Gram-negative bacteria *Pseudomonas aeruginosa* and *E. coli*, respectively.

## 2. Chemistry

Of the five carboxylic acids required for this study (**8–12**), two (**8** and **10**) were commercially available. Carboxylic acids **9**, **11**, and **12** were prepared by reaction of naphthalen-
1-amine (13), naphthalen-2-amine (14), and 4-aminobiphenyl (15) with succinic anhydride, in yields of 45–97% (Scheme 1, Supplementary Materials Figures S1–S3).

<figure><img src="image_9.png" /><figcaption>**Scheme 1.** Synthesis of carboxylic acid derivatives **9**, **11**, and **12**. **Reagents and conditions:** (i) Arylamine (13–15) (1.0 equiv.), succinic anhydride (1.0 equiv.), CH₂Cl₂, r.t., N₂, 9–24 h (yields: **9**, 97%; **11**, 76%; and **12**, 45%).</figcaption></figure>

Syntheses of the core Boc-protected polyamine scaffolds **16a–f** (Figure 4) have been previously described [29–32]. These six polyamines (PA3-4-3, PA3-6-3, PA3-7-3, PA3-8-3, PA3-10-3, PA3-12-3) contain variations in chain length, lipophilicity, and spatial separation of the dialkylammonium ion positive charges, all of which were considered to potentially have some influence on bioactivity.

<figure><img src="image_10.png" /><figcaption>**Figure 4.** Boc-protected polyamine scaffolds **16a–f**.</figcaption></figure>

Reaction of carboxylic acids **8–12** with Boc-protected polyamines **16a–f** utilized coupling reagents EDC·HCl or EDC·HCl/HOBt in anhydrous CH₂Cl₂, and then the products were deprotected using 2,2,2-trifluoroacetic acid (TFA) to create the target compounds as their di-TFA salts (Scheme 2, Figures S4–S32).

The structures of the synthesized α,ω-disubstituted polyamine library are shown in Figure 5.
<figure><img src="image_11.png" /></figure>

**Key:** a n = 4, b n = 6, c n = 7, d n = 8, e n = 10, f n = 12

**Scheme 2.** General method for the synthesis of target polyamine analogues **17–21**. **Reagents and conditions:** (i) Carboxylic acid RCO₂H (8, 10, 12) (2.2 equiv.), Boc-protected polyamine (16a-f) (1 equiv.), with EDC·HCl/HOBt (2.6 equiv.), DIPEA (6 equiv.), CH₂Cl₂, 0 °C, N₂, 20 h (yields 24–72%) or carboxylic acid RCO₂H (9, 11) (2.5 equiv.), Boc-protected polyamine (16a-f) (1 equiv.), with EDC·HCl (2.8 equiv.), DMAP (5 equiv.), CH₂Cl₂, 0 °C, N₂, 12 h (yields 40–95%); (ii) TFA (0.2 mL), CH₂Cl₂ (2 mL), r.t., 2 h (yields 30–97%).

<figure><img src="image_12.png" /></figure>

**Key:** a n = 4, b n = 6, c n = 7, d n = 8, e n = 10, f n = 12

<caption>**Figure 5.** The structures of α,ω-disubstituted polyamines **17–21**.</caption>
### 3. Results and Discussion

The antimicrobial activity of each compound was initially assessed against various bacterial strains, including *S. aureus* and MRSA, *P. aeruginosa*, *E. coli*, *Klebsiella pneumoniae*, and *Acinetobacter baumannii*, as well as fungal strains such as *Candida albicans* and *Cryptococcus neoformans* (Table 1). As a set, analogues containing a 1-naphthyl substituted end group (**17a–f**, **18a–f**) were predominantly inactive towards all microbes, with the exceptions being the longer polyamine chain variants **17e** (MRSA MIC 9.7 µM), **17f** (MRSA MIC 0.29 µM, *A. baumannii* MIC 0.29 µM, *C. neoformans* MIC 0.29 µM), and **18f** (*S. aureus* MIC 3.15 µM, MRSA MIC ≤ 0.25 µM, *C. neoformans* MIC ≤ 0.25 µM). In contrast, the 2-substituted naphthyl analogue sets **19a–f** and **20a–f** contained a greater number of active compounds, with five analogues (**19c**, **19e**, **19f**, **20c**, and **20f**) exhibiting activity towards primarily the Gram-positive bacteria *S. aureus* and/or MRSA and the fungus *C. neoformans*. Direct comparison of antimicrobial activities exhibited by corresponding 1-naphthyl vs. 2-naphthyl substituted analogues suggested, however, that there was little to no difference between the series of compounds as far as intrinsic antimicrobial activity was concerned. For example, analogues **17f** vs. **19f** were equipotent towards the same three microbial strains (MRSA MIC 0.29 µM, *A. baumannii* MIC 0.29 µM, *C. neoformans* MIC 0.29 µM), and **18f** vs. **20f** were essentially identical growth inhibitors towards *S. aureus* (MIC 3.125 µM), MRSA (MIC ≤ 0.25 µM), *E. coli* (MIC 6.3–12.5 µM), and *C. neoformans* (MIC ≤ 0.25 µM). The biphenyl substituted series of analogues **21a–e** were noticeably different in their spectrum of antimicrobial activities, with all analogues exhibiting activity towards just MRSA with MIC 0.25–2.1 µM.

<table><caption>**Table 1.** Antimicrobial activities (MIC, µM) and cLogP values of analogues **17–21**.</caption><thead><tr><th>Cmpd</th><th>cLogP<sup>a</sup></th><th>S. a<sup>b</sup></th><th>MRSA<sup>c</sup></th><th>P. a<sup>d</sup></th><th>E. c<sup>e</sup></th><th>K. p<sup>f</sup></th><th>A. b<sup>g</sup></th><th>C. a<sup>h</sup></th><th>C. n<sup>i</sup></th></tr></thead><tbody><tr><td>17a</td><td>5.1</td><td>677</td><td>&gt;43.3</td><td>677</td><td>677</td><td>&gt;43.3</td><td>&gt;43.3</td><td>&gt;43.3</td><td>&gt;43.3</td></tr><tr><td>17b</td><td>6.0</td><td>200</td><td>&gt;41.7</td><td>200</td><td>200</td><td>&gt;41.7</td><td>&gt;41.7</td><td>&gt;41.7</td><td>&gt;41.7</td></tr><tr><td>17c</td><td>6.5</td><td>256</td><td>&gt;41.0</td><td>&gt;256</td><td>256</td><td>&gt;41.0</td><td>&gt;41.0</td><td>&gt;41.0</td><td>&gt;41.0</td></tr><tr><td>17d</td><td>6.9</td><td>50</td><td>&gt;40.3</td><td>&gt;100</td><td>100</td><td>&gt;40.3</td><td>&gt;40.3</td><td>&gt;40.3</td><td>&gt;40.3</td></tr><tr><td>17e</td><td>7.8</td><td>244</td><td>9.72</td><td>608</td><td>608</td><td>&gt;38.9</td><td>&gt;38.9</td><td>&gt;38.9</td><td>38.9</td></tr><tr><td>17f</td><td>8.7</td><td>25</td><td>0.29</td><td>300</td><td>100</td><td>&gt;37.6</td><td>0.29</td><td>&gt;37.6</td><td>0.29</td></tr><tr><td>18a</td><td>4.8</td><td>568</td><td>&gt;36.3</td><td>568</td><td>568</td><td>&gt;36.3</td><td>&gt;36.3</td><td>&gt;36.3</td><td>&gt;36.3</td></tr><tr><td>18b</td><td>5.7</td><td>&gt;200</td><td>&gt;35.2</td><td>&gt;200</td><td>&gt;200</td><td>&gt;35.2</td><td>&gt;35.2</td><td>&gt;35.2</td><td>&gt;35.2</td></tr><tr><td>18c</td><td>6.2</td><td>&gt;200</td><td>&gt;34.7</td><td>200</td><td>200</td><td>&gt;34.7</td><td>&gt;34.7</td><td>&gt;34.7</td><td>&gt;34.7</td></tr><tr><td>18d</td><td>6.6</td><td>107</td><td>&gt;34.2</td><td>&gt;107</td><td>&gt;107</td><td>&gt;34.2</td><td>&gt;34.2</td><td>&gt;34.2</td><td>&gt;34.2</td></tr><tr><td>18e</td><td>7.5</td><td>104</td><td>33.2</td><td>518</td><td>518</td><td>&gt;33.2</td><td>&gt;33.2</td><td>&gt;33.2</td><td>33.2</td></tr><tr><td>18f</td><td>8.4</td><td>3.15</td><td>≤0.25</td><td>&gt;100</td><td>12.5</td><td>&gt;32</td><td>&gt;32</td><td>&gt;32</td><td>≤0.25</td></tr><tr><td>19a</td><td>5.1</td><td>34</td><td>43.3</td><td>677</td><td>271</td><td>&gt;43.3</td><td>&gt;43.3</td><td>&gt;43.3</td><td>21.7</td></tr><tr><td>19b</td><td>6.0</td><td>65.2</td><td>41.7</td><td>&gt;130</td><td>130</td><td>&gt;41.7</td><td>&gt;41.7</td><td>&gt;41.7</td><td>20.9</td></tr><tr><td>19c</td><td>6.5</td><td>16.0</td><td>≤0.32</td><td>32.0</td><td>16.0</td><td>&gt;41</td><td>&gt;41</td><td>&gt;41</td><td>≤0.32</td></tr><tr><td>19d</td><td>6.9</td><td>7.9</td><td>40.3</td><td>126</td><td>126</td><td>&gt;40.3</td><td>&gt;40.3</td><td>&gt;40.3</td><td>40.3</td></tr><tr><td>19e</td><td>7.8</td><td>30</td><td>1.22</td><td>608</td><td>122</td><td>38.9</td><td>38.9</td><td>38.9</td><td>4.86</td></tr><tr><td>19f</td><td>8.7</td><td>100</td><td>0.294</td><td>300</td><td>300</td><td>&gt;37.6</td><td>0.294</td><td>&gt;37.6</td><td>0.294</td></tr><tr><td>20a</td><td>4.8</td><td>57</td><td>18.16</td><td>568</td><td>227</td><td>&gt;36.3</td><td>&gt;36.3</td><td>&gt;36.3</td><td>&gt;36.3</td></tr><tr><td>20b</td><td>5.7</td><td>&gt;200</td><td>&gt;35.2</td><td>&gt;200</td><td>50</td><td>&gt;35.2</td><td>&gt;35.2</td><td>&gt;35.2</td><td>35.2</td></tr><tr><td>20c</td><td>6.2</td><td>25</td><td>2.2</td><td>&gt;200</td><td>25</td><td>&gt;34.7</td><td>&gt;34.7</td><td>&gt;34.7</td><td>≤0.27</td></tr><tr><td>20d</td><td>6.6</td><td>13.3</td><td>&gt;34.2</td><td>&gt;107</td><td>107</td><td>&gt;34.2</td><td>&gt;34.2</td><td>&gt;34.2</td><td>17.1</td></tr><tr><td>20e</td><td>7.5</td><td>12.95</td><td>16.6</td><td>518</td><td>104</td><td>&gt;33.2</td><td>&gt;33.2</td><td>&gt;33.2</td><td>16.6</td></tr><tr><td>20f</td><td>8.4</td><td>3.125</td><td>≤0.25</td><td>&gt;100</td><td>6.3</td><td>&gt;32</td><td>&gt;32</td><td>&gt;32</td><td>≤0.25</td></tr><tr><td>21a</td><td>5.7</td><td>300</td><td>0.268</td><td>300</td><td>300</td><td>&gt;34.3</td><td>&gt;34.3</td><td>&gt;34.3</td><td>&gt;34.3</td></tr><tr><td>21b</td><td>6.6</td><td>300</td><td>2.08</td><td>300</td><td>300</td><td>&gt;33.3</td><td>&gt;33.3</td><td>&gt;33.3</td><td>&gt;33.3</td></tr><tr><td>21c</td><td>7.1</td><td>200</td><td>0.256</td><td>300</td><td>300</td><td>&gt;32.8</td><td>&gt;32.8</td><td>&gt;32.8</td><td>&gt;32.8</td></tr><tr><td>21d</td><td>7.6</td><td>300</td><td>0.506</td><td>300</td><td>300</td><td>&gt;32.4</td><td>&gt;32.4</td><td>&gt;32.4</td><td>&gt;32.4</td></tr><tr><td>21e</td><td>8.5</td><td>300</td><td>0.246</td><td>300</td><td>300</td><td>&gt;31.5</td><td>&gt;31.5</td><td>31.5</td><td>15.73</td></tr></tbody></table>

<footnote><sup>a</sup> cLogP values calculated in DataWarrior v05.05.00 [33]; <sup>b</sup> *S. aureus* (ATCC 25,923 or ATCC 29213) with streptomycin (MIC 21.5 µM) and chloramphenicol (MIC 1.5–3 µM) were used as positive controls, and values are presented as the mean (n = 3); <sup>c</sup> MRSA (ATCC 43300) with vancomycin (MIC 0.7 µM) was used as a positive control, and values are presented as the mean (n = 2); <sup>d</sup> *P. aeruginosa* (PAO1 or ATCC 27853) with streptomycin (MIC 21.5 µM) and colistin (MIC 1 µM) were used as positive controls, and values are presented as the mean (n = 3); <sup>e</sup> *E. coli* (ATCC 25922) with colistin (MIC 2 µM) was used as a positive control, and values are presented as the mean (n = 2); <sup>f</sup> *K. pneumoniae* (ATCC 700603) with colistin (MIC 0.2 µM) was used as a positive control, and values are presented as the mean (n = 2); <sup>g</sup> *A. baumannii* (ATCC 19606) with colistin (MIC 0.2 µM) was used as a positive control, and values are presented as the mean (n = 2); <sup>h</sup> *C. albicans* (ATCC 90028) with fluconazole (MIC 0.4 µM) was used as a positive control, and values are presented as the mean (n = 2); <sup>i</sup> *C. neoformans* (ATCC 208821) with fluconazole (MIC 26 µM) was used as a positive control, and values are presented as the mean (n = 2).</footnote>
The majority of the compounds, **17–21**, were evaluated for cytotoxicity towards human kidney epithelial cell line (HEK293) and for hemolytic activity towards human red blood cells (Table 2). Of the set of compounds tested, only biphenyl **21e** was considered to be hemolytic (HC₁₀ 6.3 µM), and the observation of cytotoxicity was limited to the four analogues **17e** (IC₅₀ 23.7 µM), **19a** (IC₅₀ 26 µM), **19c** (IC₅₀ 20.5 µM), and **19e** (IC₅₀ 4.75 µM). The latter results, in particular, emphasize that cytotoxicity in the current series is not determined by lipophilicity alone, as other analogues with similar cLogP values (e.g., **17a–d**, **18a–e**, **20a–e**) were deemed non-toxic.

<table><caption>**Table 2.** Cytotoxic (IC₅₀, µM) and hemolytic (HC₁₀, µM) properties of analogues **17–21**.</caption><thead><tr><th>Compound</th><th>Cytotoxicity <sup>a</sup></th><th>Hemolysis <sup>b</sup></th><th>Compound</th><th>Cytotoxicity <sup>a</sup></th><th>Hemolysis <sup>b</sup></th></tr></thead><tbody><tr><td><b>17a</b></td><td>nt <sup>c</sup></td><td>nt <sup>c</sup></td><td>20a</td><td>&gt;36.3</td><td>&gt;36.3</td></tr><tr><td><b>17b</b></td><td>&gt;41.7</td><td>&gt;41.7</td><td>20b</td><td>&gt;35.2</td><td>&gt;35.2</td></tr><tr><td><b>17c</b></td><td>&gt;41.0</td><td>&gt;41.0</td><td>20c</td><td>&gt;34.7</td><td>&gt;34.7</td></tr><tr><td><b>17d</b></td><td>&gt;40.3</td><td>&gt;40.3</td><td>20d</td><td>&gt;34.2</td><td>&gt;34.2</td></tr><tr><td><b>17e</b></td><td>23.7</td><td>&gt;38.9</td><td>20e</td><td>&gt;33.2</td><td>&gt;33.2</td></tr><tr><td><b>17f</b></td><td>&gt;37.6</td><td>&gt;37.6</td><td>20f</td><td>&gt;32.2</td><td>&gt;32.2</td></tr><tr><td><b>18a</b></td><td>nt <sup>c</sup></td><td>nt <sup>c</sup></td><td>21a</td><td>&gt;34.3</td><td>31.4</td></tr><tr><td><b>18b</b></td><td>&gt;35.2</td><td>&gt;35.2</td><td>21b</td><td>&gt;33.3</td><td>&gt;33.3</td></tr><tr><td><b>18c</b></td><td>&gt;34.7</td><td>&gt;34.7</td><td>21c</td><td>&gt;32.8</td><td>&gt;32.8</td></tr><tr><td><b>18d</b></td><td>&gt;34.2</td><td>&gt;34.2</td><td>21d</td><td>&gt;32.4</td><td>&gt;32.4</td></tr><tr><td><b>18e</b></td><td>&gt;33.2</td><td>&gt;33.2</td><td>21e</td><td>&gt;31.5</td><td>6.32</td></tr><tr><td><b>18f</b></td><td>&gt;32.2</td><td>&gt;32.2</td><td></td><td></td><td></td></tr><tr><td><b>19a</b></td><td>26.4</td><td>&gt;43.3</td><td></td><td></td><td></td></tr><tr><td><b>19b</b></td><td>41.7</td><td>&gt;41.7</td><td></td><td></td><td></td></tr><tr><td><b>19c</b></td><td>20.5</td><td>&gt;41.0</td><td></td><td></td><td></td></tr><tr><td><b>19d</b></td><td>40.3</td><td>&gt;40.3</td><td></td><td></td><td></td></tr><tr><td><b>19e</b></td><td>4.75</td><td>&gt;38.9</td><td></td><td></td><td></td></tr><tr><td><b>19f</b></td><td>&gt;37.6</td><td>&gt;37.6</td><td></td><td></td><td></td></tr></tbody></table>

All values presented as the mean (n = 2); <sup>a</sup> Concentration (IC₅₀, µM) of compound at 50% cytotoxicity on HEK293 human embryonic kidney cells with tamoxifen as the positive control (IC₅₀ 24 µM); <sup>b</sup> Concentration (HC₁₀, µM) of compound at 10% hemolytic activity on human red blood cells with melittin as the positive control (HC₁₀ 0.95 µM); <sup>c</sup> Not tested.

To conduct a detailed analysis of the antibacterial activity and initial assessment of the mechanism of action, analogue **20f** was selected due to its strong antibacterial properties, and because it was devoid of any observed cytotoxic or hemolytic effects. To evaluate the kinetics of antibacterial activity, real-time growth inhibition curves were measured for two Gram-positive bacteria (*S. aureus* (ATCC 25923), MRSA (CF-Marseille) [34]) and the Gram-negative bacterium *E. coli* (ATCC 25922). The test compound completely inhibited the growth of the Gram-positive bacteria strains at 3.15 µM (3.13 µg/mL) or higher concentrations, with growth observed at the lowest test concentration of 1.57 µM (1.56 µg/mL) (Figure 6A,B). In the case of the Gram-negative bacterium *E. coli* (Figure 6C), bacterial growth inhibition was observed at test concentrations of 6.29 µM (6.25 µg/mL) or higher. MIC values of 3.15 µM (3.13 µg/mL), 3.15 µM (3.13 µg/mL), and 6.29 µM (6.25 µg/mL) were determined for analogue **20f** against *S. aureus* (ATCC 25923), MRSA (CF-Marseille), and *E. coli* (ATCC 25922), respectively. These values corresponded to the inhibitory concentrations observed at the 18-hour mark in the real-time growth inhibition curve plots. Additionally, the same values were observed for the minimum bactericidal concentration (MBC) of **20f** against all three organisms, indicating its bactericidal activity.

The ability of compounds **17–21** to enhance the antibiotic activity of doxycycline against *P. aeruginosa* (ATCC 27853) and of erythromycin against *E. coli* (ATCC 25922) were determined (Table 3). In the case of doxycycline, a low-dose fixed concentration of 2 µg/mL (4.5 µM) was used, being 20-fold lower than the intrinsic MIC (40 µg/mL (90 µM)) against *P. aeruginosa*. Each of the compounds were then evaluated at a range of concentrations, with the upper limit being dependent upon the intrinsic MIC towards
*P. aeruginosa* (Table 1). Two examples of 1-naphthyl-substituted analogues (17b and 18c) were identified as modest enhancers of the action of doxycycline, with MICs of 12.5 µM, representing 16-fold enhancements over their intrinsic MIC values. A further five examples of 2-naphthyl-substituted variants, 19a, 19c, 19d, 20a, 20c, and 20f, exhibited notable levels of enhancement, with MICs of 16.9, 4.0, 15.7, 28, 6.25, and 12.6 µM, respectively. When compared to their intrinsic growth inhibition activities towards *P. aeruginosa* (Table 1), these represented 40-fold, 8-fold, 8-fold, 20-fold, >32-fold, and >8-fold enhancements, respectively. The ability of the two structurally related 2-naphthyl-substituted PA-3-4-3 (spermine) analogues 19a and 20a to enhance the action of doxycycline towards *P. aeruginosa* was investigated more closely, revealing a dose-dependent response when the doxycycline concentration was varied from 2 to 8 µg/mL (Table 4).

<figure><img src="image_13.png" /><figcaption>**Figure 6.** Bacterial growth inhibition exhibited by 20f against (A) *S. aureus* (ATCC 25923); (B) MRSA (CF-Marseille); and (C) *E. coli* (ATCC 25922) with different concentrations. Positive control was bacteria only and negative control was media only.</figcaption></figure>

<table><caption>**Table 3.** Antibiotic enhancement activity (MIC µM) of analogues 17–21.</caption><thead><tr><th>Compound</th><th>Dox/P.a <sup>a</sup></th><th>Eryth/E.c <sup>b</sup></th><th>Compound</th><th>Dox/P.a <sup>a</sup></th><th>Eryth/E.c <sup>b</sup></th></tr></thead><tbody><tr><td>17a</td><td>271 (2.5)</td><td>67.7 (10)</td><td>20a</td><td>28 (20)</td><td>nt <sup>c</sup></td></tr><tr><td>17b</td><td>12.5 (16)</td><td>100 (2)</td><td>20b</td><td>25 (&gt;8)</td><td>50 (1)</td></tr><tr><td>17c</td><td>64 (&gt;2.7)</td><td>64 (4)</td><td>20c</td><td>6.25 (&gt;32)</td><td>12.5 (2)</td></tr><tr><td>17d</td><td>126 (1)</td><td>31.5 (3)</td><td>20d</td><td>53.4 (&gt;2)</td><td>26.7 (4)</td></tr><tr><td>17e</td><td>608 (1)</td><td>122 (5)</td><td>20e</td><td>104 (5)</td><td>13.0 (8)</td></tr><tr><td>17f</td><td>300 (1)</td><td>50 (2)</td><td>20f</td><td>12.6 (&gt;8)</td><td>3.15 (2)</td></tr><tr><td>18a</td><td>568 (1)</td><td>568 (1)</td><td>21a</td><td>300 (1)</td><td>300 (1)</td></tr><tr><td>18b</td><td>100 (&gt;2)</td><td>200 (1)</td><td>21b</td><td>300 (1)</td><td>300 (1)</td></tr><tr><td>18c</td><td>12.5 (16)</td><td>200 (1)</td><td>21c</td><td>300 (1)</td><td>300 (1)</td></tr><tr><td>18d</td><td>&gt;107 (1)</td><td>107 (1)</td><td>21d</td><td>300 (1)</td><td>300 (1)</td></tr><tr><td>18e</td><td>207 (2.5)</td><td>51.8 (10)</td><td>21e</td><td>300 (1)</td><td>300 (1)</td></tr><tr><td>18f</td><td>50.3 (&gt;2)</td><td>6.29 (2)</td><td></td><td></td><td></td></tr><tr><td>19a</td><td>16.9 (40)</td><td>4.2 (64)</td><td></td><td></td><td></td></tr><tr><td>19b</td><td>65.2 (&gt;2)</td><td>65.2 (2)</td><td></td><td></td><td></td></tr><tr><td>19c</td><td>4.00 (8)</td><td>4.0 (4)</td><td></td><td></td><td></td></tr><tr><td>19d</td><td>15.7 (8)</td><td>15.7 (8)</td><td></td><td></td><td></td></tr><tr><td>19e</td><td>608 (1)</td><td>60.8 (2)</td><td></td><td></td><td></td></tr><tr><td>19f</td><td>300 (1)</td><td>300 (1)</td><td></td><td></td><td></td></tr></tbody></table>

<footnote><sup>a</sup> Concentration (µM) required to restore doxycycline activity at 4.5 µM against *P. aeruginosa* (ATCC 27853). Fold change shown in parentheses is the ratio between the intrinsic MIC of the test compound and the combination MIC; <sup>b</sup> Concentration (µM) required to restore erythromycin activity at 10.9 µM against *E. coli* (ATCC 25922). Fold change shown in parentheses is the ratio between the intrinsic MIC of the test compound and the combination MIC; <sup>c</sup> Not tested.</footnote>
<table><caption>**Table 4.** Dose response enhancement (MIC, µM) of doxycycline towards *P. aeruginosa* (ATCC 27853) by compounds **19a** and **20a**.</caption><thead><tr><th rowspan="2">Doxycycline Concentration (µg/mL)</th><th colspan="2">Compound</th></tr><tr><th>19a <sup>a</sup></th><th>20a <sup>a</sup></th></tr></thead><tbody><tr><td>2</td><td>16.9</td><td>28.4</td></tr><tr><td>4</td><td>8.5</td><td>14.2</td></tr><tr><td>6</td><td>8.5</td><td>14.2</td></tr><tr><td>8</td><td>4.2</td><td>3.5</td></tr></tbody></table>

Evaluation of compounds **17–21** to enhance the antibiotic activity of erythromycin, using a fixed low dose of 8 µg/mL (10.9 µM) against *E. coli* (ATCC 25922) identified three analogues in particular, **19a** (MIC 4.2 µM, 64-fold enhancement), **19d** (MIC 15.7 µM, 8-fold), and **20e** (MIC 13 µM, 8-fold enhancement), with strong levels of enhancement (MIC ≤ 20 µM). In addition, they were 8–10-fold more active in combination than when tested alone (Table 3).

Taken together, these studies have identified a number of predominantly 2-naphthyl-substituted polyamines as strong enhancers of the antibiotic action of doxycycline and/or erythromycin towards the Gram-negative bacteria *P. aeruginosa*, and *E. coli*. It is interesting to compare these results with our previous investigation of α,ω-diacylarylpolyamines, e.g., **6**, which revealed them to be active antimicrobials but with weak antibiotic enhancement properties (e.g., doxycycline vs. *P. aeruginosa*, 4-fold increase to an MIC of 12.5 µM) [27]. The current results lead us to conclude that substituted naphthyl-polyamines may be worthy of further optimization as antibiotic enhancers. It is pertinent to note that Yasuda et al. have previously reported that naphthylacetylspermine (22) (Figure 7), a synthetic analogue of joro spider toxin, renders *E. coli* sensitive to hydrophobic antibiotics, including novobiocin and erythromycin, albeit weakly, at doses of 64–128 µg/mL [35].

<figure><img src="image_14.png" /><figcaption>**Figure 7.** Structure of antibiotic enhancer naphthylacetylspermine (22).</figcaption></figure>

**4. Materials and Methods**

**4.1. Chemistry General Methods**

Infrared spectra were run as dry films on an ATR crystal and acquired with a Perkin-Elmer 100 Fourier Transform infrared spectrometer equipped with a Universal ATR Sampling Accessory. Mass spectra were acquired on a Bruker micrOTOF Q II mass spectrometer. Melting points were obtained on an Electrothermal melting point apparatus and are uncorrected. The ¹H, ¹³C NMR, and 2D NMR spectra were recorded at 298 °K on a Bruker AVANCE AVIII 400 MHz spectrometer at 400.13 and 100.62 MHz, using standard pulse sequences. Proto-deutero solvent signals were used as internal references (DMSO-d₆: δH 2.50, δC 39.52; CD₃OD: δH 3.31, δC 49.00). For ¹H NMR, the data are quoted as position (δ), relative integral, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, br = broad), coupling constant (J, Hz), and assignment to the atom. Atom positional assignments were made using 2D-NMR data acquired using standard pulse sequences. The ¹³C NMR data are quoted as position (δ) and assignment to the atom. Flash column chromatography was carried out using Davisil silica gel (40–60 µm) or LiChroprep RP-8 (40–63 µm) solid support. Silica gel thin layer chromatography (TLC) was conducted on 0.2 mm thick plates of DC-plastikfolien Kieselgel 60 F₂₅₄ (Merck). Reversed-phase TLC was carried out on 0.2 mm thick plates of DC-Kieselgel 60 RP-18 F₂₅₄S (Merck). All

<footnote><sup>a</sup> Concentration of test compound (µM) required to restore doxycycline activity at the dose specified against *P. aeruginosa* (ATCC 27853).</footnote>
solvents used were of analytical grade or better and/or purified according to standard procedures. Chemical reagents used were purchased from standard chemical suppliers and used as purchased. All samples were determined to be >95% purity. Protected polyamines di-tert-butyl butane-1,4-diylbis((3-aminopropyl)carbamate) (16a), di-tert-butyl hexane-1,6-diylbis((3-aminopropyl)carbamate) (16b), di-tert-butyl heptane-1,7-diylbis((3-aminopropyl)carbamate) (16c), di-tert-butyl octane-1,8-diylbis((3-aminopropyl)carbamate) (16d), di-tert-butyl decane-1,10-diylbis((3-aminopropyl)carbamate) (16e), and di-tert-butyl dodecane-1,12-diylbis((3-aminopropyl)carbamate) (16f) were synthesized using literature procedures [29–32].

### 4.1.1. General Procedure A—Diamide Bond Formation

The appropriate Boc-protected polyamine **16a–f** (1 equiv.) was added to a solution of carboxylic acid (2.2 equiv.), EDC·HCl (2.6 equiv.), HOBt (2.6 equiv.) and DIPEA (4–6 equiv.), that was stirred in anhydrous CH₂Cl₂ (1.5 mL) at 0 °C for 30 min under N₂. The mixture was allowed to come to room temperature and was stirred for a further 20 h under N₂. The reaction mixture was poured into CH₂Cl₂ (20 mL) and washed with saturated NaHCO₃ (2 × 30 mL) followed by H₂O (2 × 30 mL), and it was then dried under reduced pressure and purified by silica gel flash column chromatography (0–20% MeOH/CH₂Cl₂) to create the desired products.

### 4.1.2. General Procedure B—Diamide Bond Formation

The appropriate Boc-protected polyamine **16a–f** (1 equiv.) was added to a solution of carboxylic acid (2.5 equiv.) and EDC·HCl (2.8 equiv.) with DMAP (5 equiv.) stirred in anhydrous CH₂Cl₂ (1.5 mL) at 0 °C for 10 min under N₂. The mixture was allowed to come to room temperature and stirred for a further 12 h under N₂. The reaction mixture was poured into CH₂Cl₂ (20 mL) and washed with saturated NaHCO₃ (2 × 30 mL) followed by H₂O (2 × 30 mL), and it was then dried under reduced pressure and purified by silica gel flash column chromatography (0–20% MeOH/CH₂Cl₂) to create the desired products.

### 4.1.3. General Procedure C—Boc Deprotection

A solution of tert-butyl-carbamate derivative in CH₂Cl₂ (2 mL) and TFA (0.2 mL) was stirred at room temperature under N₂ for 2 h, and it was followed by solvent removal under reduced pressure. The crude product was purified using C₈ reversed-phase flash column chromatography eluting with 0–100% MeOH/H₂O (0.05% TFA) to create the corresponding polyamine conjugate as the TFA salt.

## 4.2. Synthesis of Compounds

### 4.2.1. 4-(Naphthalen-1-ylamino)-4-oxobutanoic Acid (9)

Naphthalen-1-amine (200 mg, 1.40 mmol) and succinic anhydride (140 mg, 1.40 mmol) were stirred in anhydrous CH₂Cl₂ (10 mL) for 9 h under an N₂ atmosphere. The solvent was then removed under reduced pressure, and the crude product was purified by C₈ reversed-phase column chromatography (100% H₂O to 100% MeOH) to create **9** as a pale pink solid (330 mg, 97%). R<sub>f</sub> = 0.43 (SiO₂, CH₂Cl₂:10% MeOH); m.p. 165–167 °C; IR (ATR) ν<sub>max</sub> 3302, 2919, 1711, 1531, 1401, 1176, 915, 773 cm⁻¹; ¹H NMR (DMSO-d₆, 400 MHz) δ 12.16 (1H, br s, OH), 9.94 (1H, br s, NH-5), 8.12–8.10 (1H, m, H-7), 7.94–7.91 (1H, m, H-10), 7.75 (1H, d, *J* = 7.8 Hz, H-11), 7.66 (1H, d, *J* = 7.8 Hz, H-13), 7.55–7.51 (2H, m, H-8, H-9), 7.47 (1H, dd, *J* = 7.8, 7.8 Hz, H-12), 2.75 (2H, t, *J* = 6.8 Hz, H₂-2), 2.60 (2H, *t*, *J* = 6.8 Hz, H₂-3); ¹³C NMR (DMSO-d₆, 100 MHz) δ 173.9 (C-1), 170.8 (C-4), 133.7 (C-6, C-10a), 128.0 (C-10), 127.8 (C-6a), 125.9 (C-8/C-9), 125.7 (C-12), 125.5 (C-8/C-9), 125.1 (C-11), 122.9 (C-7), 121.6 (C-13), 30.7 (C-2), 29.1 (C-3); (+)-HRESIMS *m/z* 266.0783 [M+Na]⁺ (calcd for C₁₄H₁₃NNaO₃, 266.0788).

### 4.2.2. 4-(Naphthalen-2-ylamino)-4-oxobutanoic Acid (11)

Naphthalen-2-amine (200 mg, 1.40 mmol) and succinic anhydride (140 mg, 1.40 mmol) were stirred in anhydrous CH₂Cl₂ (10 mL) for 9 h under an N₂ atmosphere. The solvent
was then removed under reduced pressure, and the crude product was purified by C8 reversed-phase column chromatography (100% H2O to 100% MeOH) to create **11** as a pink solid (260 mg, 76%). R<sub>f</sub> = 0.19 (SiO<sub>2</sub>, CH<sub>2</sub>Cl<sub>2</sub>:10% MeOH); m.p. 170–172 °C; IR (ATR) v<sub>max</sub> 3059, 1706, 1653, 1558, 1397, 1257, 824, 742 cm<sup>-1</sup>; <sup>1</sup>H NMR (DMSO-d<sub>6</sub>, 400 MHz) δ 10.18 (1H, br s, NH-5), 8.30 (1H, s, H-7), 7.85–7.77 (3H, m, H-8, H-11, H-12), 7.57 (1H, dd, *J* = 8.9, 2.0 Hz, H-13), 7.47–7.43 (1H, m, H-9), 7.40–7.36 (1H, m, H-10), 2.62 (2H, t, *J* = 6.0 Hz, H<sub>2</sub>-2), 2.56 (2H, t, *J* = 6.0, H<sub>2</sub>-3); <sup>13</sup>C NMR (DMSO-d<sub>6</sub>, 100 MHz) δ 173.9 (C-1), 170.4 (C-4), 136.9 (C-6), 133.5 (C-7a), 129.6 (C-11a), 128.3 (C-12), 127.4 (C-11), 127.2 (C-8), 126.3 (C-9), 124.4 (C-10), 119.8 (C-13), 114.8 (C-7), 31.2 (C-2), 29.0 (C-3); (+)-HRESIMS [M+Na]<sup>+</sup> *m/z* 266.0784 (calcd for C<sub>14</sub>H<sub>13</sub>NNaO<sub>3</sub>, 266.0788).

### 4.2.3. 4-([1,1'-Biphenyl]-4-ylamino)-4-oxobutanoic Acid (12)

4-Aminobiphenyl (500 mg, 2.95 mmol) and succinic anhydride (295 mg, 2.95 mmol) were stirred in anhydrous CH<sub>2</sub>Cl<sub>2</sub> (11 mL) for 24 h under an N<sub>2</sub> atmosphere. The solvent was removed under reduced pressure, and the product purified by recrystallisation from EtOH to create **12** as light orange crystals (356 mg, 45%). R<sub>f</sub> = 0.17 (SiO<sub>2</sub>, CH<sub>2</sub>Cl<sub>2</sub>:10% MeOH); m.p. >230 °C; IR (ATR) v<sub>max</sub> 3273, 3031, 2934, 2635, 1689, 1651, 1529, 1403, 1186, 832, 750, 685 cm<sup>-1</sup>; <sup>1</sup>H NMR (DMSO-d<sub>6</sub>, 400 MHz) δ 12.13 (1H, br s, OH), 10.05 (1H, br s, NH-5), 7.70–7.65 (2H, m, H-7), 7.65–7.59 (4H, m, H-8, H-11), 7.46–7.41 (2H, m, H-12), 7.34–7.29 (1H, m, H-13), 2.61–2.57 (2H, m, H<sub>2</sub>-2/H<sub>2</sub>-3), 2.55–2.52 (2H, m, H<sub>2</sub>-2/H<sub>2</sub>-3); <sup>13</sup>C NMR (DMSO-d<sub>6</sub>, 100 MHz) δ 173.8 (C-1), 170.1 (C-4), 139.7 (C-10), 138.8 (C-6), 134.6 (C-9), 128.9 (C-12), 127.0 (C-13), 126.9 (C-8/C-11), 126.2 (C-8/C-11), 119.3 (C-7), 31.1 (C-2/C-3), 28.8 (C-2/C-3); (+)-HRESIMS *m/z* 292.0950 [M+Na]<sup>+</sup> (calcd for C<sub>16</sub>H<sub>15</sub>NNaO<sub>3</sub>, 292.0944).

### 4.2.4. N<sup>1</sup>,N<sup>4</sup>-Bis(3-(1-naphthamido)propyl)butane-1,4-diaminium 2,2,2-trifluoroacetate (17a)

Following general procedure A, the reaction of 1-naphthoic acid (8) (94 mg, 0.55 mmol), di-tert-butyl butane-1,4-diylbis((3-aminopropyl)carbamate) (16a) (100 mg, 0.25 mmol), EDC·HCl (124 mg, 0.65 mmol), HOBt (87 mg, 0.64 mmol), and DIPEA (0.26 mL, 1.49 mmol) in CH<sub>2</sub>Cl<sub>2</sub> (1.5 mL) created di-tert-butyl butane-1,4-diylbis((3-(1-naphthamido)propyl)carbamate) (42 mg, 24%) as a white solid. Following general procedure C, the reaction of a sub-sample of this material (22 mg, 0.031 mmol) in CH<sub>2</sub>Cl<sub>2</sub> (2 mL) with TFA (0.2 mL) created the di-TFA salt **17a** as a white solid after purification (12 mg, 52%). R<sub>f</sub> = 0.48 (RP-18, MeOH:10% HCl, 7:3); m.p. 238–239 °C; IR (ATR) v<sub>max</sub> 3307, 2839, 1646, 1451, 1203, 1116, 1015 cm<sup>-1</sup>; <sup>1</sup>H NMR (DMSO-d<sub>6</sub>, 400 MHz) δ 8.70–8.65 (4H, m, NH<sub>2</sub>-14), 8.21–8.18 (2H, m, H-3), 8.04–7.97 (4H, m, H-6, H-7), 7.62 (2H, dd, *J* = 7.0, 1.0 Hz, H-9), 7.59–7.53 (6H, m, H-4, H-5, H-8), 3.43–3.39 (4H, m, H<sub>2</sub>-11), 3.03–2.97 (8H, m, H<sub>2</sub>-13, H<sub>2</sub>-15), 1.96–1.89 (4H, m, H<sub>2</sub>-12), 1.69–1.64 (4H, m, H<sub>2</sub>-16); <sup>13</sup>C NMR (DMSO-d<sub>6</sub>, 100 MHz) δ 168.9 (C-1), 134.5 (C-6a), 133.1 (C-2), 129.9 (C-7), 129.7 (C-2a), 128.2 (C-6), 126.7 (C-4), 126.2 (C-5), 125.3 (C-3/C-8), 125.2 (C-3/C-8), 124.9 (C-9), 46.1 (C-15), 44.8 (C-13), 36.3 (C-11), 26.0 (C-12), 22.7 (C-16); (+)-HRESIMS *m/z* 511.3068 [M+H]<sup>+</sup> (calcd for C<sub>32</sub>H<sub>39</sub>N<sub>4</sub>O<sub>2</sub>, 511.3068).

### 4.2.5. N<sup>1</sup>,N<sup>6</sup>-Bis(3-(1-naphthamido)propyl)hexane-1,6-diaminium 2,2,2-trifluoroacetate (17b)

Following general procedure A, the reaction of 1-naphthoic acid (8) (44.0 mg, 0.256 mmol), di-tert-butyl hexane-1,6-diylbis((3-aminopropyl)carbamate) (16b) (50 mg, 0.12 mmol), EDC·HCl (57.9 mg, 0.302 mmol), HOBt (40.8 mg, 0.30 mmol), and DIPEA (0.12 mL, 0.69 mmol) in CH<sub>2</sub>Cl<sub>2</sub> (1.5 mL) created di-tert-butyl hexane-1,6-diylbis((3-(1-naphthamido)propyl)carbamate) as a colorless oil (27 mg, 30%). Following general procedure C, the reaction of a sub-sample of this material (18 mg, 0.024 mmol) in CH<sub>2</sub>Cl<sub>2</sub> (2 mL) with TFA (0.2 mL) created the di-TFA salt **17b** as a white solid (16 mg, 87%) with no further purification required. R<sub>f</sub> = 0.47 (RP-18, MeOH:10% HCl, 7:3); m.p. 225–227 °C; IR (ATR) v<sub>max</sub> 3293, 3057, 2944, 2856, 1675, 1542, 1313, 1201, 1132, 786, 721cm<sup>-1</sup>; <sup>1</sup>H NMR (CD<sub>3</sub>OD, 400 MHz) δ 8.24–8.20 (2H, m, H-3), 8.03 (2H, d, *J* = 8.2 Hz, H-7), 7.98–7.94 (2H, m, H-6), 7.68 (2H, dd, *J* = 7.1, 1.4 Hz, H-9), 7.62–7.53 (6H, m, H-4, H-5, H-8), 3.59 (4H, t, *J* = 6.6 Hz, H<sub>2</sub>-11), 3.15 (4H, t, *J* = 7.4 Hz, H<sub>2</sub>-13), 3.07 (4H, t, *J* = 7.5 Hz, H<sub>2</sub>-15), 2.11–2.03 (4H, m, H<sub>2</sub>-12), 1.81–1.72 (4H, m, H<sub>2</sub>-16), 1.53–1.48 (4H,
m, H₂-17); ¹³C NMR (CD₃OD, 100 MHz) δ 173.4 (C-1), 135.2 (C-2/C-6a), 135.0 (C-2/C-6a), 131.9 (C-7), 131.4 (C-2a), 129.6 (C-6), 128.1 (C-4), 127.6 (C-5), 126.6 (C-9), 126.1 (C-3), 126.0 (C-8), 48.9 (C-15), 46.6 (C-13), 37.5 (C-11), 27.8 (C-12), 27.1 (C-17), 27.0 (C-16); (+)-HRESIMS m/z 539.3385 [M+H]⁺ (calcd for C₃₄H₄₃N₄O₂, 539.3381).

### 4.2.6. $N^1,N^7$-Bis(3-(1-naphthamido)propyl)heptane-1,7-diaminium 2,2,2-trifluoroacetate (17c)

Following general procedure A, the reaction of 1-naphthoic acid (8) (43.0 mg, 0.250 mmol), di-tert-butyl heptane-1,7-diylbis((3-aminopropyl)carbamate) (16c) (50 mg, 0.11 mmol), EDC·HCl (56.1 mg, 0.293 mmol), HOBt (39.6 mg, 0.29 mmol), and DIPEA (0.118 mL, 0.677 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl heptane-1,7-diylbis((3-aminopropyl)carbamate) as a colorless oil (45 mg, 54%). Following general procedure C, the reaction of a sub-sample of this material (6 mg, 0.008 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt 17c as a colorless gum after purification (5 mg, 81%). $R_f = 0.63$ (RP-18, MeOH:10% HCl, 7:3); IR (ATR) $v_{max}$ 3752, 326, 2927, 2857, 2305, 1678, 1665, 1543, 1199, 1136, 806, 723 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.12–8.09 (2H, m, H-3), 7.90 (2H, d, *J* = 8.5 Hz, H-7), 7.85–7.82 (2H, m, H-6), 7.55 (2H, dd, *J* = 7.2, 1.4 Hz, H-9), 7.49–7.40 (6H, m, H-4, H-5, H-8), 3.47 (4H, t, *J* = 6.6 Hz, H₂-11), 3.03 (4H, t, *J* = 7.4 Hz, H₂-13), 2.94 (4H, t, *J* = 7.7 Hz, H₂-15), 1.98–1.90 (4H, m, H₂-12), 1.67–1.59 (4H, m, H₂-16), 1.38–1.33 (6H, m, H₂-17, H₂-18); ¹³C NMR (CD₃OD, 100 MHz) δ 173.5 (C-1), 135.2 (C-2/C-6a), 134.9 (C-2/C-6a), 131.9 (C-7), 131.4 (C-2a), 129.6 (C-6), 128.1 (C-4), 127.5 (C-5), 126.6 (C-9), 126.1 (C-3), 125.9 (C-8), 49.0 (C-15), 46.5 (C-13), 37.5 (C-11), 29.6 (C-18), 27.8 (C-12), 27.3 (C-16/C-17); (+)-HRESIMS m/z 553.3534 [M+H]⁺ (calcd for C₃₅H₄₅N₄O₂, 553.3537).

### 4.2.7. $N^1,N^8$-Bis(3-(1-naphthamido)propyl)octane-1,8-diaminium 2,2,2-trifluoroacetate (17d)

Following general procedure A, the reaction of 1-naphthoic acid (8) (41.3 mg, 0.240 mmol), di-tert-butyl octane-1,8-diylbis((3-aminopropyl)carbamate) (16d) (50 mg, 0.11 mmol), EDC·HCl (54.3 mg, 0.283 mmol), HOBt (38.3 mg, 0.28 mmol), and DIPEA (0.114 mL, 0.653 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl octane-1,8-diylbis((3-aminopropyl)carbamate) as a colorless oil (37 mg, 44%). Following general procedure C, the reaction of a sub-sample of this material (13 mg, 0.017 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt 17d as a colorless gum after purification (4 mg, 30%). $R_f = 0.63$ (RP-18, MeOH:10% HCl, 7:3); IR (ATR) $v_{max}$ 3743, 3274, 3057, 2935, 2861, 1675, 1542, 1468, 1200, 1132, 784, 721 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.26–8.21 (2H, m, H-3), 8.03 (2H, d, *J* = 8.6 Hz, H-7), 7.98–7.94 (2H, m, H-6), 7.68 (2H, dd, *J* = 6.9, 1.2 Hz, H-9), 7.62–7.52 (6H, m, H-4, H-5, H-8), 3.60 (4H, t, *J* = 6.7 Hz, H₂-11), 3.17 (4H, t, *J* = 7.5 Hz, H₂-13), 3.06 (4H, t, *J* = 7.8 Hz, H₂-15), 2.12–2.03 (4H, m, H₂-12), 1.78–1.70 (4H, m, H₂-16), 1.50–1.39 (8H, m, H₂-17, H₂-18); ¹³C NMR (CD₃OD, 100 MHz) δ 173.5 (C-1), 135.2 (C-6a), 135.0 (C-2), 132.0 (C-7), 131.4 (C-2a), 129.6 (C-6), 128.1 (C-4), 127.6 (C-5), 126.6 (C-9), 126.1 (C-3), 126.0 (C-8), 49.0 (C-15), 46.6 (C-13), 37.5 (C-11), 30.0 (C-18), 27.8 (C-12), 27.4 (C-16/C-17), 27.3 (C-16/C-17); (+)-HRESIMS m/z 567.3680 [M+H]⁺ (calcd for C₃₆H₄₇N₄O₂, 567.3694).

### 4.2.8. $N^1,N^{10}$-Bis(3-(1-naphthamido)propyl)decane-1,10-diaminium 2,2,2-trifluoroacetate (17e)

Following general procedure A, the reaction of 1-naphthoic acid (8) (78 mg, 0.45 mmol), di-tert-butyl decane-1,10-diylbis((3-aminopropyl)carbamate) (16e) (100 mg, 0.21 mmol), EDC·HCl (103 mg, 0.54 mmol), HOBt (72 mg, 0.53 mmol), and DIPEA (0.22 mL, 1.26 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl decane-1,10-diylbis((3-(1-naphthamido)propyl)carbamate) (120 mg, 72%) as a colorless oil. Following general procedure C, the reaction of a sub-sample of this material (99 mg, 0.13 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt 17e (93 mg, 87%) as a yellow oil with no further purification required. $R_f = 0.27$ (RP-18, MeOH:10% HCl, 7:3); IR (ATR) $v_{max}$ 3306, 2944, 2832, 1685, 1448, 1113, 1022 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.23–8.20 (2H, m, H-3), 8.00 (2H, d, *J* = 8.3 Hz, H-7), 7.99–7.91 (2H, m, H-6), 7.65 (2H, dd, *J* = 7.0, 0.7 Hz, H-9), 7.58–7.50 (6H, m, H-4, H-5, H-8), 3.58 (4H, t,
$J = 6.6$ Hz, $H_2-11$), 3.14 (4H, t, $J = 7.4$ Hz, $H_2-13$), 3.03 (4H, t, $J = 7.8$ Hz, $H_2-15$), 2.09–2.02 (4H, m, $H_2-12$), 1.75–1.67 (4H, m, $H_2-16$), 1.42–1.33 (12H, m, $H_2-17$, $H_2-18$, $H_2-19$); $^{13}$C NMR (CD$_3$OD, 100 MHz) $\delta$ 173.5 (C-1), 135.2 (C-2/C-6a), 135.0 (C-2/C-6a), 131.9 (C-7), 131.4 (C-2a), 129.6 (C-6), 128.1 (C-4), 127.6 (C-5), 126.6 (C-9), 126.1 (C-3), 126.0 (C-8), 49.1 (C-15), 46.6 (C-13), 37.6 (C-11), 30.4 (C-18/C-19), 30.2 (C-18/C-19), 27.8 (C-12), 27.5 (C-17), 27.4 (C-16); (+)-HRESIMS *m/z* 595.3998 [M+H]$^+$ (calcd for $C_{38}H_{51}N_4O_2$, 595.4007).

### 4.2.9. $N^1, N^{12}$-Bis(3-(1-naphthamido)propyl)dodecane-1,12-diaminium 2,2,2-trifluoroacetate (17f)

Following general procedure A, the reaction of 1-naphthoic acid (8) (52 mg, 0.30 mmol), di-tert-butyl dodecane-1,12-diylbis((3-aminopropyl)carbamate) (16f) (71 mg, 0.14 mmol), EDC·HCl (69 mg, 0.36 mmol), HOBt (47 mg, 0.35 mmol), and DIPEA (0.14 mL, 0.80 mmol) in CH$_2$Cl$_2$ (1.5 mL) created di-tert-butyl dodecane-1,12-diylbis((3-(1-naphthamido)propyl)carbamate) (43 mg, 37%) as a white wax. Following general procedure C, the reaction of a sub-sample of this material (19 mg, 0.023 mmol) in CH$_2$Cl$_2$ (2 mL) with TFA (0.2 mL) created the di-TFA salt **17f** (18 mg, 92%) as a white wax with no further purification required. $R_f = 0.15$ (RP-18, MeOH:10% HCl, 7:3); IR (ATR) $v_{max}$ 3326, 2944, 2834, 1654, 1450, 1246, 1116, 1022 cm$^{-1}$; $^1$H NMR (CD$_3$OD, 400 MHz) $\delta$ 8.23–8.20 (2H, m, H-3), 8.00 (2H, d, $J = 8.2$ Hz, H-7), 7.95–7.92 (2H, m, H-6), 7.66 (2H, dd, $J = 7.0, 1.0$ Hz, H-9), 7.59–7.50 (6H, m, H-4, H-5, H-8), 3.58 (4H, t, $J = 6.6$ Hz, $H_2-11$), 3.15 (4H, t, $J = 7.4$ Hz, $H_2-13$), 3.04 (4H, t, $J = 7.8$ Hz, $H_2-15$), 2.09–2.02 (4H, m, $H_2-12$), 1.75–1.68 (4H, m, $H_2-16$), 1.43–1.30 (16H, m, $H_2-17$, $H_2-18$, $H_2-19$, $H_2-20$); $^{13}$C NMR (CD$_3$OD, 100 MHz) $\delta$ 173.4 (C-1), 135.2 (C-2/C-6a), 135.0 (C-2/C-6a), 131.9 (C-7), 131.4 (C-2a), 129.6 (C-6), 128.1 (C-4), 127.5 (C-5), 126.6 (C-9), 126.1 (C-3), 125.9 (C-8), 49.1 (C-15), 46.6 (C-13), 37.6 (C-11), 30.6 (C-18/C-19/C-20), 30.5 (C-18/C-19/C-20), 30.2 (C-18/C-19/C-20), 27.8 (C-12), 27.5 (C-17), 27.4 (C-16); (+)-HRESIMS *m/z* 623.4321 [M+H]$^+$ (calcd for $C_{40}H_{55}N_4O_2$, 623.4320).

### 4.2.10. $N^1, N^4$-Bis(3-(4-(naphthalen-1-ylamino)-4-oxobutanamido)propyl)butane-1,4-diaminium 2,2,2-trifluoroacetate (18a)

Following general procedure B, the reaction of carboxylic acid 9 (76 mg, 0.31 mmol), di-tert-butyl butane-1,4-diylbis((3-aminopropyl)carbamate) (16a) (50 mg, 0.12 mmol), EDC·HCl (67 mg, 0.35 mmol), and DMAP (76 mg, 0.62 mmol) in CH$_2$Cl$_2$ (1.5 mL) created di-tert-butyl butane-1,4-diylbis((3-(4-(naphthalen-1-ylamino)-4-oxobutanamido)propyl)carbamate) as a colorless oil (54 mg, 53%). Following general procedure C, the reaction of a sub-sample of this material (26 mg, 0.030 mmol) in CH$_2$Cl$_2$ (2 mL) with TFA (0.2 mL) created the di-TFA salt **18a** as a colorless oil after purification (22 mg, 83%). $R_f = 0.47$ (RP-18, MeOH:10% HCl, 7:3); IR (ATR) $v_{max}$ 3278, 1676, 1202, 1160, 799, 766 cm$^{-1}$; $^1$H NMR (CD$_3$OD, 400 MHz) $\delta$ 8.04 (2H, dd, $J = 9.0, 2.0$ Hz, H-10), 7.89 (2H, dd, $J = 7.0, 2.0$ Hz, H-7), 7.76 (2H, d, $J = 8.5, 7.95–7.57$) (2H, m, H-11), 7.56–7.50 (4H, m, H-8, H-9), 7.46 (2H, t, $J = 7.8$ Hz, H-12), 3.32–3.28 (4H, m, $H_2-15$), 2.92–2.89 (4H, m, $H_2-2$), 2.83 (4H, t, $J = 7.0$ Hz, $H_2-17$), 2.65–2.62 (4H, m, $H_2-3$), 2.57–2.54 (4H, m, $H_2-19$), 1.82–1.75 (4H, m, $H_2-16$), 1.36–1.32 (4H, m, $H_2-20$); $^{13}$C NMR (CD$_3$OD, 100 MHz) $\delta$ 176.3 (C-1), 174.3 (C-4), 135.7 (C-6), 134.3 (C-10a), 130.2 (C-6a), 129.4 (C-7), 127.6 (C-13), 127.4 (C-8/C-9), 127.3 (C-8/C-9), 126.6 (C-12), 124.0 (C-11), 123.6 (C-10), 47.8 (C-19), 46.0 (C-17), 36.6 (C-15), 32.0 (C-2), 31.6 (C-3), 27.7 (C-16), 23.9 (C-20); (+)-HRESIMS *m/z* 653.3807 [M+H]$^+$ (calcd for $C_{38}H_{49}N_6O_4$, 653.3810).

### 4.2.11. $N^1, N^6$-Bis(3-(4-(naphthalen-1-ylamino)-4-oxobutanamido)propyl)hexane-1,6-diaminium 2,2,2-trifluoroacetate (18b)

Following general procedure B, the reaction of carboxylic acid 9 (71 mg, 0.29 mmol), di-tert-butyl hexane-1,6-diylbis((3-aminopropyl)carbamate) (16b) (50 mg, 0.12 mmol), EDC·HCl (62 mg, 0.32 mmol), and DMAP (71 mg, 0.58 mmol) in CH$_2$Cl$_2$ (1.5 mL) created di-tert-butyl hexane-1,6-diylbis((3-(4-(naphthalen-1-ylamino)-4-oxobutanamido)propyl)carbamate) as a colorless oil (97 mg, 92%). Following general procedure C, the reaction of a sub-sample of this material (44 mg, 0.050 mmol) in CH$_2$Cl$_2$ (2 mL) with TFA (0.2 mL) created the di-TFA
salt **18b** as an orange oil after purification (39 mg, 86%). $R_f = 0.47$ (RP-18, MeOH:10% HCl, 7:3); IR (ATR) $v_{max}$ 3279, 3050, 1671, 1542, 1201, 1132, 800, 777 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.01 (2H, dd, *J* = 9.0, 2.5 Hz, H-10), 7.85 (2H, dd, *J* = 7.5, 3.5 Hz, H-7), 7.71 (2H, d, *J* = 8.5, Hz, H-13), 7.57 (2H, dd, *J* = 7.5, 1.0 Hz, H-11), 7.51–7.47 (4H, m, H-8, H-9), 7.42 (2H, t, *J* = 7.8 Hz, H-12), 3.31–3.26 (4H, m, H₂-15), 2.88 (8H, t, *J* = 6.5 Hz, H₂-2, H₂-17), 2.61–2.53 (8H, m, H₂-3, H₂-19), 1.82–1.75 (4H, m, H₂-16), 1.33–1.26 (4H, m, H₂-20), 0.91–0.87 (4H, m, H₂-21); ¹³C NMR (CD₃OD, 100 MHz) δ 176.3 (C-1), 174.2 (C-4), 135.7 (C-6), 134.4 (C-10a), 130.0 (C-6a), 129.4 (C-7), 127.5 (C-13), 127.33 (C-8/C-9), 127.27 (C-8/C-9), 126.5 (C-12), 123.7 (C-11), 123.6 (C-10), 48.7 (C-19), 46.0 (C-17), 36.5 (C-15), 32.0 (C-2), 31.5 (C-3), 27.8 (C-16), 26.8 (C-20/C-21), 26.7 (C-20/C-21); (+)-HRESIMS [M+H]⁺ *m/z* 681.4104 (calcd for C₄₀H₅₃N₆O₄, 681.4123).

### 4.2.12. $N^1,N^7$-Bis(3-(4-(naphthalen-1-ylamino)-4-oxobutanamido)propyl)heptane-1,7-diaminium 2,2,2-trifluoroacetate (**18c**)

Following general procedure B, the reaction of carboxylic acid **9** (68 mg, 0.29 mmol), di-*tert*-butyl heptane-1,7-diylbis((3-aminopropyl)carbamate) (**16c**) (50 mg, 0.11 mmol), EDC·HCl (60 mg, 0.31 mmol), and DMAP (69 mg, 0.57 mmol) in CH₂Cl₂ (1.5 mL) created di-*tert*-butyl heptane-1,7-diylbis((3-(4-(naphthalen-1-ylamino)-4-oxobutanamido)propyl)carbamate) as a colorless oil (94 mg, 95%). Following general procedure C, the reaction of a sub-sample of this material (82 mg, 0.092 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **18c** as a colorless oil after purification (59 mg, 69%). $R_f = 0.42$ (RP-18, MeOH:10% HCl, 7:3); IR (ATR) $v_{max}$ 3279, 3053, 1671, 1537, 1201, 1131, 800, 777 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.05 (2H, dd, *J* = 9.5, 1.5 Hz, H-10), 7.87 (2H, dd, *J* = 7.5, 2.5 Hz, H-7), 7.74 (2H, d, 8.0 Hz, H-13), 7.61 (2H, dd, *J* = 7.5, 1.0 Hz, H-11), 7.55–7.48 (4H, m, H-8, H-9), 7.45 (2H, t, *J* = 8.0 Hz, H-12), 3.33–3.30 (4H, m, H₂-15), 2.91 (8H, t, *J* = 6.5 Hz, H₂-2, H₂-17), 2.65–2.61 (8H, m, H₂-3, H₂-19), 1.85–1.79 (4H, m, H₂-16), 1.42–1.35 (4H, m, H₂-20), 1.01–0.98 (6H, m, H₂-21, H₂-22); ¹³C NMR (CD₃OD, 100 MHz) δ 176.2 (C-1), 174.1 (C-4), 135.7 (C-6), 134.3 (C-10a), 130.0 (C-6a), 129.4 (C-7), 127.5 (C-13), 127.3 (C-8/C-9), 127.2 (C-8/C-9), 126.5 (C-12), 123.7 (C-11), 123.6 (C-10), 48.8 (C-19), 46.0 (C-17), 36.6 (C-15), 32.0 (C-2), 31.6 (C-3), 29.4 (C-22), 27.7 (C-16), 27.0 (C-20/C-21), 26.9 (C-20/C-21); (+)-HRESIMS [M+H]⁺ *m/z* 695.4265 (calcd for C₄₁H₅₅N₆O₄, 695.4279).

### 4.2.13. $N^1,N^8$-Bis(3-(4-(naphthalen-1-ylamino)-4-oxobutanamido)propyl)octane-1,8-diaminium 2,2,2-trifluoroacetate (**18d**)

Following general procedure B, the reaction of carboxylic acid **9** (67 mg, 0.28 mmol), di-*tert*-butyl octane-1,8-diylbis((3-aminopropyl)carbamate) (**16d**) (50 mg, 0.11 mmol), EDC·HCl (59 mg, 0.31 mmol), and DMAP (67 mg, 0.55 mmol) in CH₂Cl₂ (1.5 mL) created di-*tert*-butyl octane-1,8-diylbis((3-(4-(naphthalen-1-ylamino)-4-oxobutanamido)propyl)carbamate) as a colorless oil (69 mg, 69%). Following general procedure C, the reaction of this material (69 mg, 0.076 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **18d** as a colorless oil after purification (37 mg, 54%). $R_f = 0.40$ (RP-18, MeOH:10% HCl, 7:3); IR (ATR) $v_{max}$ 3052, 1655, 1542, 1201, 1132, 799, 777 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.05 (2H, dd, *J* = 8.0, 1.5 Hz, H-10), 7.88 (2H, dd, *J* = 7.5, 2.0 Hz, H-7), 7.75 (2H, d, *J* = 8.0 Hz, H-13), 7.62 (2H, dd, *J* = 7.5, 1.0 Hz, H-11), 7.56–7.49 (4H, m, H-8, H-9), 7.46 (2H, t, *J* = 8.0 Hz, H-12), 3.34–3.31 (4H, m, H₂-15), 2.95–2.91 (8H, m, H₂-2, H₂-17), 2.67–2.62 (8H, m, H₂-3, H₂-19), 1.86–1.80 (4H, m, H₂-16), 1.45–1.39 (4H, m, H₂-20), 1.07–1.01 (8H, m, H₂-21, H₂-22); ¹³C NMR (CD₃OD, 100 MHz) δ 176.2 (C-1), 174.1 (C-4), 135.7 (C-6), 134.3 (C-10a), 130.0 (C-6a), 129.4 (C-7), 127.4 (C-13), 127.3 (C-8/C-9), 127.2 (C-8/C-9), 126.5 (C-12), 123.6 (C-11), 123.5 (C-10), 48.9 (C-19), 46.0 (C-17), 36.6 (C-15), 32.0 (C-2), 31.6 (C-3), 29.8 (C-22), 27.8 (C-16), 27.2 (C-20/C-21), 27.1 (C-20/C-21); (+)-HRESIMS [M+2H]²⁺ *m/z* 355.2250 (calcd for C₄₂H₅₈N₆O₄, 355.2254).
4.2.14. $N^1$, $N^{10}$-Bis(3-(4-(naphthalen-1-ylamino)-4-oxobutanamido)propyl)decane-1,10-diaminium 2,2,2-trifluoroacetate (18e)

Following general procedure B, the reaction of carboxylic acid 9 (63 mg, 0.26 mmol), di-tert-butyl decane-1,10-diylbis((3-aminopropyl)carbamate) (16e) (50 mg, 0.10 mmol), EDC·HCl (55 mg, 0.29 mmol), and DMAP (63 mg, 0.52 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl decane-1,10-diylbis((3-(4-(naphthalen-1-ylamino)-4-oxobutanamido)propyl)carbamate) as a colorless oil (67 mg, 72%). Following general procedure C, the reaction of a sub-sample of this material (27 mg, 0.029 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **18e** as a colorless oil after purification (26 mg, 93%). $R_f = 0.23$ (RP-18, MeOH: 10% HCl, 7:3); IR (ATR) $v_{max}$ 2937, 1673, 1538, 1202, 1133, 800, 776, 721 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) $\delta$ 8.05 (2H, dd, *J* = 8.0, 1.5 Hz, H-10), 7.88 (2H, dd, *J* = 7.4, 2.4 Hz, H-7), 7.76 (2H, d, *J* = 8.5, Hz, H-13), 7.62 (2H, d, *J* = 7.5 Hz, H-11), 7.56–7.50 (4H, m, H-8, H-9), 7.46 (2H, t, *J* = 8.0 Hz, H-12), 3.34–3.30 (4H, m, H₂-15), 2.95–2.91 (8H, m, H₂-2, H₂-17), 2.68–2.61 (8H, m, H₂-3, H₂-19), 1.86–1.79 (4H, m, H₂-16), 1.47–1.40 (4H, m, H₂-20), 1.14–1.08 (12H, m, H₂-21, H₂-22, H₂-23); ¹³C NMR (CD₃OD, 100 MHz) $\delta$ 176.3 (C-1), 174.2 (C-4), 135.8 (C-6), 134.4 (C-10a), 130.1 (C-6a), 129.5 (C-7), 127.5 (C-13), 127.34 (C-8/C-9), 127.26 (C-8/C-9), 126.5 (C-12), 123.7 (C-11), 123.6 (C-10), 49.0 (C-19), 46.1(C-17), 36.6 (C-15), 32.0 (C-2), 31.6 (C-3), 30.3 (C-23), 30.1 (C-22), 27.8 (C-16), 27.4 (C-20/C-21), 27.2 (C-20/C-21); (+)-HRESIMS m/z 737.4699 [M+H]⁺ (calcd for C₄₄H₆₁N₆O₄, 737.4749).

4.2.15. $N^1$, $N^{12}$-Bis(3-(4-(Naphthalen-1-ylamino)-4-oxobutanamido)propyl)dodecane-1,12-diaminium 2,2,2-trifluoroacetate (18f)

Following general procedure B, the reaction of carboxylic acid 9 (58 mg, 0.24 mmol), di-tert-butyl dodecane-1,12-diylbis((3-aminopropyl)carbamate) (16f) (57 mg, 0.11 mmol), EDC·HCl (52 mg, 0.27 mmol), and DMAP (60 mg, 0.49 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl dodecane-1,12-diylbis((3-(4-(naphthalen-1-ylamino)-4-oxobutanamido)propyl)carbamate) as a colorless oil (62 mg, 58%). Following general procedure C, the reaction of a sub-sample of this material (26 mg, 0.027 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **18f** as a pale-yellow oil after purification (20 mg, 75%). $R_f = 0.20$ (RP-18, MeOH:10% HCl, 7:3); IR (ATR) $v_{max}$ 3083, 2927, 1667, 1537, 1201, 1132, 800, 775 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) $\delta$ 8.05 (2H, dd, *J* = 8.0, 1.5 Hz, H-10), 7.88 (2H, dd, *J* = 7.5, 2.0 Hz, H-7), 7.75 (2H, d, *J* = 8.0 Hz, H-13), 7.61 (2H, dd, *J* = 7.5, 1.0 Hz, H-11), 7.56–7.50 (4H, m, H-8, H-9), 7.46 (2H, t, *J* = 7.8 Hz, H-12), 3.34–3.30 (4H, m, H₂-15), 2.95–2.91 (8H, m, H₂-2, H₂-17), 2.68–2.62 (8H, m, H₂-3, H₂-19), 1.86–1.80 (4H, m, H₂-16), 1.48–1.41 (4H, m, H₂-20), 1.21–1.08 (16H, m, H₂-21, H₂-22, H₂-23, H₂-24); ¹³C NMR (CD₃OD, 100 MHz) $\delta$ 176.2 (C-1), 174.2 (C-4), 135.7 (C-6), 134.3 (C-10a), 130.0 (C-6a) 129.4 (C-7), 127.5 (C-13), 127.3 (C-8/C-9), 127.2 (C-8/C-9), 126.5 (C-12), 123.7 (C-11), 123.5 (C-10), 49.0 (C-19), 46.0 (C-17), 36.6 (C-15), 32.0 (C-2), 31.6 (C-3), 30.5 (C-22/C-23/C-24), 30.4 (C-22/C-23/C-24), 30.1 (C-22/C-23/C-24), 27.7 (C-16), 27.3 (C-20/C-21), 27.2 (C-20/C-21); (+)-HRESIMS [M+2H]⁺ m/z 383.2575 (calcd for C₄₆H₆₆N₆O₄, 383.2567).

4.2.16. $N^1$, $N^4$-Bis(3-(2-naphthamido)propyl)butane-1,4-diaminium 2,2,2-trifluoroacetate (19a)

Following general procedure A, the reaction of 2-napthoic acid (10) (94 mg, 0.55 mmol), di-tert-butyl butane-1,4-diylbis((3-aminopropyl)carbamate) (16a) (100 mg, 0.25 mmol), EDC·HCl (124 mg, 0.65 mmol), HOBt (87 mg, 0.64 mmol), and DIPEA (0.26 mL, 1.49 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl butane-1,4-diylbis((3-(2-naphthamido)propyl)carbamate) (91 mg, 51%) as a white solid. Following general procedure C, the reaction of a sub-sample of this material (72 mg, 0.10 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **19a** as a beige solid after purification (71 mg, 96%). $R_f = 0.33$ (RP-18, MeOH:10% HCl, 7:3); m.p. 132–135 °C; IR (ATR) $v_{max}$ 3332, 2948, 2835, 1674, 1639, 1544, 1435, 1313, 1201, 1133, 1018, 721 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) $\delta$ 8.38 (2H, br s, H-3), 7.96–7.87 (8H, m, H-4, H-7, H-8, H-9), 7.61–7.53 (4H, m, H-5, H-6), 3.57 (4H, t, *J* = 6.4 Hz, H₂-11), 3.14–3.10 (8H, m, H₂-13, H₂-15), 2.08–2.01 (4H, m, H₂-12), 1.90–1.87 (4H, m, H₂-16); ¹³C NMR (CD₃OD,
100 MHz) δ 171.2 (C-1), 136.4 (C-7a), 134.0 (C-3a), 132.2 (C-2), 130.0 (C-4), 129.5 (C-8), 129.1 (C-3/C-6), 129.0 (C-3/C-6), 128.8 (C-7), 128.0 (C-5), 124.8 (C-9), 48.2 (C-15), 46.5 (C-13), 37.5 (C-11), 27.9 (C-12), 24.4 (C-16); (+)-HRESIMS *m/z* 511.3071 [M+H]⁺ (calcd for C₃₂H₃₉N₄O₂, 511.3068).

### 4.2.17. *N*¹,*N*⁶-Bis(3-(2-naphthamido)propyl)hexane-1,6-diaminium 2,2,2-trifluoroacetate (**19b**)

Following general procedure A, the reaction of 2-naphthoic acid (10) (44.0 mg, 0.256 mmol), di-tert-butyl hexane-1,6-diylbis((3-aminopropyl)carbamate) (16b) (50.0 mg, 0.12 mmol), EDC·HCl (57.9 mg, 0.302 mmol), HOBT (40.8 mg, 0.30 mmol), and DIPEA (0.12 mL, 0.69 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl hexane-1,6-diylbis((3-(2-naphthamido)propyl)carbamate) as a colorless oil (48.0 mg, 54%). Following general procedure C, the reaction of a sub-sample of this material (6 mg, 0.0081 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **19b** as a colorless gum (6 mg, 97%) with no further purification required. Rf = 0.43 (RP-18, MeOH:10% HCl, 7:3); IR (ATR) νmax 3747, 3325, 2922, 2853, 2354, 1635, 1541, 1465, 1199 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.39 (2H, br s, H-3), 7.98–7.88 (8H, m, H-4, H-7, H-8, H-9), 7.62–7.55 (4H, m, H-5, H-6), 3.57 (4H, t, *J* = 6.5 Hz, H₂-11), 3.09 (4H, t, *J* = 7.2 Hz, H₂-13), 3.05 (4H, t, *J* = 8.0 Hz, H₂-15), 2.06–2.99 (4H, m, H₂-12), 1.80–1.74 (4H, m, H₂-16), 1.54–1.50 (4H, m, H₂-17); ¹³C NMR (CD₃OD, 100 MHz) δ 171.3 (C-1), 136.5 (C-7a), 134.1 (C-3a), 131.5 (C-2), 130.0 (C-4), 129.5 (C-8), 129.1 (C-3/C-6), 129.0 (C-3/C-6), 128.9 (C-7), 128.0 (C-5), 124.7 (C-9), 49.0 (C-15), 46.4 (C-13), 37.5 (C-11), 28.0 (C-12), 27.2 (C-16/C-17), 27.1 (C-16/C-17); (+)-HRESIMS *m/z* 539.3387[M+H]⁺ (calcd for C₃₄H₄₃N₄O₂, 539.3381).

### 4.2.18. *N*¹,*N*⁷-Bis(3-(2-naphthamido)propyl)heptane-1,7-diaminium 2,2,2-trifluoroacetate (**19c**)

Following general procedure A, the reaction of 2-naphthoic acid (10) (42.6 mg, 0.247 mmol), di-tert-butyl heptane-1,7-diylbis((3-aminopropyl)carbamate) (16c) (50 mg, 0.11 mmol), EDC·HCl (56.1 mg, 0.293 mmol), HOBT (39.6 mg, 0.29 mmol), and DIPEA (0.118 mL, 0.677 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl heptane-1,7-diylbis((3-(2-naphthamido)propyl)carbamate) as a colorless oil (48 mg, 58%). Following general procedure C, the reaction of a sub-sample of this material (12 mg, 0.016 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **19c** as a colorless gum after purification (6 mg, 48%). Rf = 0.33 (RP-18, MeOH:10% HCl, 7:3); IR (ATR) νmax 3311, 2927, 2857, 1674, 1639, 1544, 1505, 1434, 1312, 1200, 1179, 1131, 876, 832, 799, 780, 762, 721 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.43 (2H, s, H-3), 8.03–7.90 (8H, m, H-4, H-7, H-8, H-9), 7.66–7.56 (4H, m, H-5, H-6), 3.59 (4H, t, *J* = 6.5 Hz, H₂-11), 3.11 (4H, t, *J* = 7.0 Hz, H₂-13), 3.05 (4H, t, *J* = 7.5 Hz, H₂-15), 2.09–2.02 (4H, m, H₂-12), 1.81–1.73 (4H, m, H₂-16), 1.51–1.47 (6H, m, H₂-17, H₂-18); ¹³C NMR (CD₃OD, 100 MHz) δ 171.2 (C-1), 136.4 (C-7a), 134.1 (C-3a), 132.2 (C-2), 130.0 (C-4), 129.5 (C-8), 129.1 (C-3/C-6), 129.0 (C-3/C-6), 128.8 (C-7), 128.0 (C-5), 124.8 (C-9), 49.0 (C-15), 46.4 (C-13), 37.5 (C-11), 29.7 (C-18), 27.9 (C-12), 27.3 (C-16/C-17), 27.2 (C-16/C-17); (+)-HRESIMS *m/z* 553.3520 [M+H]⁺ (calcd for C₃₅H₄₅N₄O₂, 553.3537).

### 4.2.19. *N*¹,*N*⁸-Bis(3-(2-naphthamido)propyl)octane-1,8-diaminium 2,2,2-trifluoroacetate (**19d**)

Following general procedure A, the reaction of 2-naphthoic acid (10) (41.3 mg, 0.240 mmol), di-tert-butyl octane-1,8-diylbis((3-aminopropyl)carbamate) (16d) (50 mg, 0.11 mmol), EDC·HCl (54.3 mg, 0.283 mmol), HOBT (38.3 mg, 0.28 mmol), and DIPEA (0.114 mL, 0.653 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl octane-1,8-diylbis((3-(2-naphthamido)propyl)carbamate) as a colorless oil (44 mg, 52%). Following general procedure C, the reaction of a sub-sample of this material (18 mg, 0.024 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **19d** as a colorless gum after purification (16 mg, 84%). Rf = 0.33 (RP-18, MeOH:10% HCl, 7:3); IR (ATR) νmax 3716, 2927, 2343, 1739, 1463, 1263, 801 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.40 (2H, s, H-3), 7.99–7.88 (8H, m, H-4, H-7, H-8, H-9), 7.62–7.56 (4H, m, H-5, H-6), 3.57 (4H, t, *J* = 6.5 Hz, H₂-11), 3.09 (4H, t, *J* = 7.4 Hz, H₂-13), 3.02 (4H, t, *J* = 7.8 Hz, H₂-15), 2.10–1.99 (4H, m, H₂-12), 1.80–1.69 (4H, m, H₂-16), 1.50–1.43 (8H, m, H₂-17, H₂-18); ¹³C NMR (CD₃OD, 100 MHz) δ 171.2 (C-1), 136.4 (C-7a), 134.1 (C-3a), 132.2 (C-2), 130.0
(C-4), 129.5 (C-8), 129.1 (C-3/C-6), 129.0 (C-3/C-6), 128.9 (C-7), 128.0 (C-5), 124.7 (C-9), 49.0 (C-15), 46.4 (C-13), 37.5 (C-11), 30.0 (C-18), 27.9 (C-12), 27.5 (C-16/C-17), 27.4 (C-16/C-17); (+)-HRESIMS *m/z* 567.3691 [M+H]$^+$ (calcd for C₃₆H₄₇N₄O₂, 567.3694).

### 4.2.20. $N^1,N^{10}$-Bis(3-(2-naphthamido)propyl)decane-1,10-diaminium 2,2,2-trifluoroacetate (19e)

Following general procedure A, the reaction of 2-naphthoic acid (10) (78 mg, 0.45 mmol), di-tert-butyl decane-1,10-diylbis((3-aminopropyl)carbamate) (16e) (100 mg, 0.21 mmol), EDC·HCl (103 mg, 0.54 mmol), HOBt (72 mg, 0.53 mmol), and DIPEA (0.22 mL, 1.26 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl decane-1,10-diylbis((3-(2-naphthamido)propyl)carbamate) (99 mg, 59%) as a colorless oil. Following general procedure C, the reaction of a sub-sample of this material (78 mg, 0.098 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt 19e (76 mg, 94%) as a yellow oil with no further purification required. Rf = 0.14 (RP-18, MeOH:10% HCl, 7:3); IR (ATR) vmax 3307,2944, 2832, 1685, 1448, 1115, 1022 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.40 (2H, br s, H-3), 7.98–7.89 (8H, m, H-4, H-7, H-8, H-9), 7.62–7.54 (4H, m, H-5, H-6), 3.57 (4H, t, *J* = 6.5 Hz, H₂-11), 3.08 (4H, t, *J* = 7.2 Hz, H₂-13), 3.01 (4H, t, *J* = 7.7 Hz, H₂-15), 2.07–2.00 (4H, m, H₂-12), 1.75–1.67 (4H, m, H₂-16), 1.43–1.34 (12H, m, H₂-17, H₂-18, H₂-19); ¹³C NMR (CD₃OD, 100 MHz) δ 171.1 (C-1), 136.4 (C-7a), 134.1 (C-3a), 132.2 (C-2), 130.1 (C-4), 129.5 (C-8), 129.1 (C-3/C-6), 129.0 (C-3/C-6), 128.8 (C-7), 128.0 (C-5), 124.8 (C-9), 49.0 (C-15), 46.4 (C-13), 37.6 (C-11), 30.4 (C-18/C-19), 30.2 (C-18/C-19), 27.8 (C-12), 27.5 (C-17), 27.4 (C-16); (+)-HRESIMS *m/z* 595.3993 [M+H]$^+$ (calcd for C₃₈H₅₁N₄O₂, 595.4007).

### 4.2.21. $N^1,N^{12}$-Bis(3-(2-naphthamido)propyl)dodecane-1,12-diaminium 2,2,2-trifluoroacetate (19f)

Following general procedure A, the reaction of 2-naphthoic acid (10) (55 mg, 0.32 mmol), di-tert-butyl dodecane-1,12-diylbis((3-aminopropyl)carbamate) (16f) (75 mg, 0.15 mmol), EDC·HCl (73 mg, 0.38 mmol), HOBt (51 mg, 0.38 mmol), and DIPEA (0.15 mL, 0.86 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl dodecane-1,12-diylbis((3-(2-naphthamido)propyl)carbamate) (35 mg, 28%) as a colorless oil. Following general procedure C, the reaction of a sub-sample of this material (20 mg, 0.024 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt 19f (16 mg, 78%) as an orange oil with no further purification required. Rf = 0.12 (RP-18, MeOH:10% HCl, 7:3); IR (ATR) vmax 3308, 2945, 2833, 1655, 1450, 1246, 1115, 1022 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.43 (2H, s, H-3), 8.01–7.91 (8H, m, H-4, H-7, H-8, H-9), 7.65–7.57 (4H, m, H-5, H-6), 3.59 (4H, t, *J* = 6.5 Hz, H₂-11), 3.11 (4H, t, *J* = 7.3 Hz, H₂-13), 3.04 (4H, t, *J* = 7.8 Hz, H₂-15), 2.08–2.02 (4H, m, H₂-12), 1.77–1.70 (4H, m, H₂-16) 1.46–1.32 (16H, m, H₂-17, H₂-18, H₂-19, H₂-20); ¹³C NMR (CD₃OD, 100 MHz) δ 171.2 (C-1), 136.4 (C-7a), 134.1 (C-3a), 132.2 (C-2), 130.0 (C-4), 129.5 (C-8), 129.1 (C-3/C-6), 129.0 (C-3/C-6), 128.8 (C-7), 128.0 (C-5), 124.7 (C-9), 49.1 (C-15), 46.4 (C-13), 37.5 (C-11), 30.7 (C-18/C-19/C-20), 30.5 (C-18/C-19/C-20), 30.3 (C-18/C-19/C-20), 27.9 (C-12), 27.5 (C-17), 27.4 (C-16); (+)-HRESIMS *m/z* 623.4306 [M+H]$^+$ (calcd for C₄₀H₅₅N₄O₂, 623.4320).

### 4.2.22. $N^1,N^4$-Bis(3-(4-(naphthalen-2-ylamino)-4-oxobutanamido)propyl)butane-1,4-diaminium 2,2,2-trifluoroacetate (20a)

Following general procedure B, the reaction of carboxylic acid 11 (62 mg, 0.25 mmol), di-tert-butyl butane-1,4-diylbis((3-aminopropyl)carbamate) (16a) (48 mg, 0.12 mmol), EDC·HCl (55 mg, 0.29 mmol), and DMAP (62 mg, 0.51 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl butane-1,4-diylbis((3-(4-(naphthalen-2-ylamino)-4-oxobutanamido)propyl)carbamate) as a pale-pink oil (84 mg, 82%). Following general procedure C, the reaction of a sub-sample of this material (16 mg, 0.019 mmol) in CH₂Cl₂ (2.0 mL) with TFA (0.2 mL) created the di-TFA salt 20a as a colorless oil after purification (15 mg, 90%). Rf = 0.28 (RP-18, MeOH:10% HCl, 7:3); IR (ATR) vmax 3278, 1676, 1202, 1160, 799, 766 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.18 (2H, d, *J* = 2.0 Hz, H-7), 7.80–7.73 (6H, m, H-8, H-11, H-12), 7.54 (2H, dd, *J* = 9.0, 2.0 Hz, H-13), 7.46–7.42 (2H, m, H-9), 7.40–7.36 (2H, m, H-10), 3.32–3.28 (4H, m, H₂-15), 2.87 (4H, t, *J* = 7.0 Hz, H₂-17), 2.80–2.77 (4H, m, H₂-2), 2.70–2.66 (4H, m, H₂-19), 2.61–2.58 (4H, m, H₂-3), 1.84–1.77 (4H, m, H₂-16), 1.46–1.42 (4H, m, H₂-20); ¹³C NMR (CD₃OD, 100 MHz)
δ 176.5 (C-1), 173.2 (C-4), 137.5 (C-6), 135.2 (C-7a), 131.9 (C-11a), 129.7 (C-12), 128.7 (C-11), 128.4 (C-8), 127.6 (C-9), 126.0, (C-10), 121.2 (C-13), 117.4 (C-7), 47.9 (C-19), 45.8 (C-17), 36.4 (C-15), 32.4 (C-2), 31.3 (C-3), 27.8 (C-16), 24.0 (C-20); (+)-HRESIMS *m/z* 653.3823 [M+H]<sup>+</sup> (calcd for C<sub>38</sub>H<sub>49</sub>N<sub>6</sub>O<sub>4</sub>, 653.3810).

### 4.2.23. *N*¹,*N*⁶-Bis(3-(4-(naphthalen-2-ylamino)-4-oxobutanamido)propyl)hexane-1,6-diaminium 2,2,2-trifluoroacetate (**20b**)

Following general procedure B, the reaction of carboxylic acid **11** (71 mg, 0.29 mmol), di-tert-butyl hexane-1,6-diylbis((3-aminopropyl)carbamate) (**16b**) (50 mg, 0.12 mmol), EDC·HCl (62 mg, 0.32 mmol), and DMAP (71 mg, 0.58 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butylhexane-1,6-diylbis((3-(4-(naphthalen-2-ylamino)-4-oxobutanamido)propyl)carbamate) as a pale brown oil (53 mg, 50%). Following general procedure C, the reaction of a sub-sample of this material (26 mg, 0.030 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **20b** as a yellow oil after purification (24 mg, 88%). R_f = 0.32 (RP-18, MeOH:10% HCl, 7:3); IR (ATR) *v*max 3279, 1671, 1542, 1201, 1132, 800, 777 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.20 (2H, d, *J* = 2.0 Hz, H-7), 7.78-7.71 (6H, m, H-8, H-11, H-12), 7.54 (2H, dd, *J* = 8.5, 2.0 Hz, H-13), 7.43 (2H, td, *J* = 7.5, 1.5 Hz, H-9), 7.37 (2H, td, *J* = 7.5, 1.5 Hz, H-10), 3.35-3.30 (4H, m, H₂-15), 2.96 (4H, t, *J* = 6.8 Hz, H₂-17), 2.80 (4H, t, *J* = 6.5 Hz, H₂-2), 2.63-2.59 (8H, m, H₂-3, H₂-19), 1.88-1.82 (4H, m, H₂-16), 1.31-1.27 (4H, m, H₂-20), 0.83-0.81 (4H, m, H₂-21); ¹³C NMR (CD₃OD, 100 MHz) δ 176.5 (C-1), 173.2 (C-4), 137.6 (C-6), 135.3 (C-7a), 131.9 (C-11a), 129.6 (C-12), 128.7 (C-11), 128.5 (C-8), 127.6 (C-9), 126.0, (C-10), 121.1 (C-13), 117.3 (C-7), 48.7 (C-19), 45.8 (C-17), 36.4 (C-15), 32.4 (C-2), 31.2 (C-3), 27.9 (C-16), 26.8 (C-20/C-21), 26.6 (C-20/C-21); (+)-HRESIMS [M+H]<sup>+</sup> *m/z* 681.4106 (calcd for C₄₀H₅₃N₆O₄, 681.4123).

### 4.2.24. *N*¹,*N*⁷-Bis(3-(4-(naphthalen-2-ylamino)-4-oxobutanamido)propyl)heptane-1,7-diaminium 2,2,2-trifluoroacetate (**20c**)

Following general procedure B, the reaction of carboxylic acid **11** (68 mg, 0.29 mmol), di-tert-butyl heptane-1,7-diylbis((3-aminopropyl)carbamate) (**16c**) (50 mg, 0.11 mmol), EDC·HCl (60 mg, 0.31 mmol), and DMAP (69 mg, 0.57 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl heptane-1,7-diylbis((3-(4-(naphthalen-2-ylamino)-4-oxobutanamido)propyl)carbamate) as a colorless oil (64 mg, 65%). Following general procedure C, the reaction of a sub-sample of this material (44 mg, 0.049 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **20c** as a colorless oil after purification (42 mg, 93%). R_f = 0.29 (RP-18, MeOH:10% HCl, 7:3); IR (ATR) *v*max 3289, 3027 1666, 1537, 1201, 1131, 800, 723 cm⁻¹; ¹H NMR (CD₃OD, 400 MHz) δ 8.20 (2H, d, *J* = 2.0 Hz, H-7), 7.77-7.71 (6H, m, H-8, H-11, H-12), 7.54 (2H, dd, *J* = 9.0, 2.0 Hz, H-13), 7.42 (2H, td, *J* = 7.5, 1.3 Hz, H-9), 7.36 (2H, td, *J* = 8.3, 1.5 Hz, H-10), 3.35-3.30 (4H, m, H₂-15), 3.00 (4H, t, *J* = 7.0 Hz, H₂-17) 2.81-2.78 (4H, m, H₂-2), 2.67 (4H, t, *J* = 8.0 Hz, H₂-19), 2.62-2.59 (4H, m, H₂-3), 1.89-1.83 (4H, m, H₂-16), 1.37-1.29 (4H, m, H₂-20), 0.81-0.76 (6H, m, H₂-21, H₂-22); ¹³C NMR (CD₃OD, 100 MHz) δ 176.6 (C-1), 173.2 (C-4), 137.6 (C-6), 135.3 (C-7a), 131.9 (C-11a), 129.6 (C-12), 128.6 (C-8/C-11), 128.5 (C-8/C-11), 127.6 (C-9), 126.0, (C-10), 121.0 (C-13), 117.2 (C-7), 48.9 (C-19), 45.8 (C-17), 36.4 (C-15), 32.4 (C-2), 31.2 (C-3), 29.4 (C-22), 27.9 (C-16), 27.01 (C-20/C-21), 26.96 (C-20/C-21); (+)-HRESIMS [M+H]<sup>+</sup> *m/z* 695.4283 (calcd for C₄₁H₅₅N₆O₄, 695.4279).

### 4.2.25. *N*¹,*N*⁸-Bis(3-(4-(naphthalen-2-ylamino)-4-oxobutanamido)propyl)octane-1,8-diaminium 2,2,2-trifluoroacetate (**20d**)

Following general procedure B, the reaction of carboxylic acid **11** (67 mg, 0.27 mmol), di-tert-butyl octane-1,8-diylbis((3-aminopropyl)carbamate) (**16d**) (50 mg, 0.11 mmol), EDC·HCl (59 mg, 0.31 mmol) and DMAP (67 mg, 0.55 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl octane-1,8-diylbis((3-(4-(naphthalen-2-ylamino)-4-oxobutanamido)propyl)carbamate) as a colorless oil (40 mg, 40%). Following general procedure C, the reaction of this material (40 mg, 0.044 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **20d** as a pale purple oil after purification (37 mg, 90%). R_f = 0.28 (RP-18, MeOH:10% HCl, 7:3); IR
(ATR) $v_{max}$ 3288, 3061 1669, 1553, 1200, 1132, 800, 721 cm$^{-1}$; $^1$H NMR (CD$_3$OD, 400 MHz) $\delta$ 8.20 (2H, d, $J = 2.0$ Hz, H-7), 7.77-7.71 (6H, m, H-8, H-11, H-12), 7.55 (2H, dd, $J = 9.0$, 2.0 Hz, H-13), 7.44-7.40 (2H, m, H-9), 7.39-7.34 (2H, m, H-10), 3.36-3.30 (4H, m, H$_2$-15), 3.01 (4H, t, $J = 7.0$ Hz, H$_2$-17), 2.82-2.78 (4H, m, H$_2$-2), 2.71 (4H, t, $J = 8.0$ Hz, H$_2$-19), 2.62-2.59 (4H, m, H$_2$-3), 1.90-1.84 (4H, m, H$_2$-16), 1.42-1.36 (4H, m, H$_2$-20), 0.85-0.80 (8H, m, H$_2$-21, H$_2$-22); $^{13}$C NMR (CD$_3$OD, 100 MHz) $\delta$ 176.5 (C-1), 173.2 (C-4), 137.6 (C-6), 135.3 (C-7a), 131.9 (C-11a), 129.6 (C-12), 128.6 (C-8/C-11), 128.4 (C-8/C-11), 127.5 (C-9), 125.9 (C-10), 121.0 (C-13), 117.2 (C-7), 48.9 (C-19), 45.8 (C-17), 36.3 (C-15), 32.3 (C-2), 31.2 (C-3), 29.7 (C-22), 27.9 (C-16), 27.14 (C-20/C-21), 27.07 (C-20/C-21); (+)-HRESIMS [M+2H]$^{2+}$ m/z 355.2252 (calcd for C$_{42}$H$_{58}$N$_6$O$_4$, 355.2254).

### 4.2.26. $N^1,N^{10}$-Bis(3-(4-(naphthalen-2-ylamino)-4-oxobutanamido)propyl)decane-1,10-diaminium 2,2,2-trifluoroacetate (20e)

Following general procedure B, the reaction of carboxylic acid 11 (63 mg, 0.26 mmol), di-tert-butyl decane-1,10-diylbis((3-aminopropyl)carbamate) (16e) (50 mg, 0.10 mmol), EDC·HCl (55 mg, 0.29 mmol), and DMAP (63 mg, 0.52 mmol) in CH$_2$Cl$_2$ (1.5 mL) created di-tert-butyl decane-1,10-diylbis((3-(4-(naphthalen-2-ylamino)-4-oxobutanamido)propyl)carbamate) as a colorless oil (78 mg, 83%). Following general procedure C, the reaction of a sub-sample of this material (41 mg, 0.044 mmol) in CH$_2$Cl$_2$ (2.0 mL) with TFA (0.2 mL) created the di-TFA salt 20e as a colorless oil after purification (38 mg, 89%). $R_f = 0.17$ (RP-18, MeOH: 10% HCl, 7:3); IR (ATR) $v_{max}$ 3293, 1679, 1538, 1202, 1132, 721 cm$^{-1}$; $^1$H NMR (CD$_3$OD, 400 MHz) $\delta$ 8.21 (2H, d, $J = 2.0$ Hz, H-7), 7.78-7.72 (6H, m, H-8, H-11, H-12), 7.55 (2H, dd, $J = 8.5$, 2.0 Hz, H-13), 7.44-7.39 (2H, m, H-9), 7.37-7.33 (2H, m, H-10), 3.36-3.30 (4H, m, H$_2$-15), 3.02 (4H, t, $J = 7.0$ Hz, H$_2$-17), 2.81-2.74 (8H, m, H$_2$-2, H$_2$-19), 2.62-2.59 (4H, m, H$_2$-3), 1.90-1.83 (4H, m, H$_2$-16), 1.49-1.41 (4H, m, H$_2$-20), 0.96-0.88 (12H, m, H$_2$-21, H$_2$-22, H$_2$-23); $^{13}$C NMR (CD$_3$OD, 100 MHz) $\delta$ 176.5 (C-1), 173.2 (C-4), 137.7 (C-6), 135.3 (C-7a), 132.0 (C-11a), 129.7 (C-12), 128.7 (C-11), 128.5 (C-8), 127.6 (C-9), 126.0 (C-10), 121.1 (C-13), 117.3 (C-7), 49.1 (C-19), 45.9 (C-17), 36.4 (C-15), 32.4 (C-2), 31.3 (C-3), 30.2 (C-23), 30.0 (C-22), 27.9 (C-16), 27.32 (C-20/C-21), 27.28 (C-20/C-21); (+)-HRESIMS m/z 737.4736 [M+H]$^+$ (calcd for C$_{44}$H$_{61}$N$_6$O$_4$, 737.4749).

### 4.2.27. $N^1,N^{12}$-Bis(3-(4-(naphthalen-2-ylamino)-4-oxobutanamido)propyl)dodecane-1, 12-diaminium 2,2,2-trifluoroacetate (20f)

Following general procedure B, the reaction of carboxylic acid 11 (58 mg, 0.24 mmol), di-tert-butyl dodecane-1,12-diylbis((3-aminopropyl)carbamate) (16f) (57 mg, 0.11 mmol), EDC·HCl (52 mg, 0.27 mmol), and DMAP (60 mg, 0.49 mmol) in CH$_2$Cl$_2$ (1.5 mL) created di-tert-butyl dodecane-1,12-diylbis((3-(4-(naphthalen-2-ylamino)-4-oxobutanamido)propyl)carbamate) as a colorless oil (81 mg, 76%). Following general procedure C, the reaction of a sub-sample of this material (28 mg, 0.029 mmol) in CH$_2$Cl$_2$ (2 mL) with TFA (0.2 mL) created the di-TFA salt 20f as a colorless oil after purification (26 mg, 90%). $R_f = 0.13$ (RP-18, MeOH:10% HCl, 7:3); IR (ATR) $v_{max}$ 2916, 1769, 1671, 1503, 1202, 1037, 802 cm$^{-1}$; $^1$H NMR (CD$_3$OD, 400 MHz) $\delta$ 8.21 (2H, d, $J = 1.5$ Hz, H-7), 7.79-7.72 (6H, m, H-8, H-11, H-12), 7.56 (2H, dd, $J = 9.0$, 2.0 Hz, H-13), 7.44-7.40 (2H, m, H-9), 7.38-7.34 (2H, m, H-10), 3.36-3.30 (4H, m, H$_2$-15), 3.02 (4H, t, $J = 7.0$ Hz, H$_2$-17), 2.81-2.75 (4H, m, H$_2$-2, H$_2$-19), 2.62-2.59 (4H, m, H$_2$-3), 1.90-1.84 (4H, m, H$_2$-16), 1.51-1.44 (4H, m, H$_2$-20), 1.04-0.99 (16H, m, H$_2$-21, H$_2$-22, H$_2$-23, H$_2$-24); $^{13}$C NMR (CD$_3$OD, 100 MHz) $\delta$ 176.5 (C-1), 173.2 (C-4), 137.6 (C-6), 135.3 (C-7a), 131.9 (C-11a), 129.6 (C-12), 128.6 (C-8/C-11), 128.4 (C-8/C-11), 127.5 (C-9), 125.9 (C-10), 121.0 (C-13), 117.2 (C-7), 49.1 (C-19), 45.8 (C-17), 36.4 (C-15), 32.4 (C-2), 31.2 (C-3), 30.4 (C-22/C-23/C-24), 30.3 (C-22/C-23/C-24), 30.1 (C-22/C-23/C-24), 27.9 (C-16), 27.3 (C-20/C-21), 27.2 (C-20/C-21); (+)-HRESIMS [M+2H]$^{2+}$ m/z 383.2578 (calcd for C$_{46}$H$_{66}$N$_6$O$_4$, 383.2567).
4.2.28. $N^1,N^4$-Bis(3-([1,1'-biphenyl]-4-ylamino)-4-oxobutanamido)propyl)butane-1,4-diaminium 2,2,2-trifluoroacetate (21a)

Following general procedure A, the reaction of carboxylic acid 12 (74 mg, 0.27 mmol) with di-tert-butyl butane-1,4-diylbis((3-aminopropyl)carbamate) (16a) (50 mg, 0.12 mmol), EDC·HCl (62 mg, 0.32 mmol), HOBT (44 mg, 0.32 mmol), and DIPEA (0.13 mL, 0.75 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl butane-1,4-diylbis((3-([1,1'-biphenyl]-4-ylamino)-4-oxobutanamido)propyl)carbamate) as a pink solid (65 mg, 60%). Following general procedure C, the reaction of a sub-sample of this material (20 mg, 0.022 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt 21a as a yellow solid after purification (15 mg, 73%). $R_f = 0.37$ (RP-18, MeOH:10% HCl, 5:1); m.p. 203–205 °C; IR (ATR) $v_{max}$ 3290, 3099, 3033, 2831, 1669, 1599, 1531, 1200, 1178, 1130, 835, 764, 720 cm⁻¹; ¹H NMR (DMSO-d₆, 400 MHz) δ 10.08 (2H, br s, NH-5), 8.61–8.47 (4H, m, NH₂-18), 8.11 (2H, t, *J* = 6.0 Hz, NH-14), 7.71–7.68 (4H, m, H-7), 7.65–7.58 (8H, m, H-8, H-11), 7.46–7.40 (4H, m, H-12), 7.35–7.29 (2H, m, H-13), 3.13 (4H, dt, *J* = 6.4, 6.2 Hz, H₂-15), 2.93–2.82 (8H, m, H₂-17, H₂-19), 2.61 (4H, t, *J* = 7.0 Hz, H₂-2/H₂-3), 2.43 (4H, t, *J* = 7.0 Hz, H₂-2/H₂-3), 1.72 (4H, tt, *J* = 7.4, 6.4 Hz, H₂-16), 1.63–1.54 (4H, m, H₂-20); ¹³C NMR (DMSO-d₆, 100 MHz) δ 172.0 (C-1), 170.5 (C-4), 139.7 (C-10), 138.8 (C-6), 134.6 (C-9), 128.9 (C-12), 127.0 (C-13), 126.8 (C-8), 126.2 (C-11), 119.3 (C-7), 46.1 (C-19), 44.5 (C-17), 35.5 (C-15), 31.5 (C-2/C-3), 30.1 (C-2/C-3), 26.1 (C-16), 22.6 (C-20); (+)-HRESIMS *m/z* 705.4118 [M+H]⁺ (calcd for C₄₂H₅₃N₆O₄, 705.4123).

4.2.29. $N^1,N^6$-Bis(3-([1,1'-biphenyl]-4-ylamino)-4-oxobutanamido)propyl)hexane-1,6-diaminium 2,2,2-trifluoroacetate (21b)

Following general procedure A, the reaction of carboxylic acid 12 (69 mg, 0.26 mmol) with di-tert-butyl hexane-1,6-diylbis((3-aminopropyl)carbamate) (16b) (50 mg, 0.12 mmol), EDC·HCl (58 mg, 0.30 mmol), HOBT (41 mg, 0.30 mmol), and DIPEA (0.12 mL, 0.69 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl hexane-1,6-diylbis((3-([1,1'-biphenyl]-4-ylamino)-4-oxobutanamido)propyl)carbamate) as a pink solid (54 mg, 48%). Following general procedure C, the reaction of a sub-sample of this material (20 mg, 0.021 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt 21b as a yellow solid after purification (15 mg, 74%). $R_f = 0.43$ (RP-18, MeOH:10% HCl, 5:1); m.p. 200–202 °C; IR (ATR) $v_{max}$ 3296, 3031, 2947, 2832, 2528, 1681, 1657, 1637, 1529, 1198, 1173, 1123, 1000, 759, 718 cm⁻¹; ¹H NMR (DMSO-d₆, 400 MHz) δ 10.08 (2H, br s, NH-5), 8.54–8.29 (4H, m, NH₂-18), 8.12 (2H, t, *J* = 5.8 Hz, NH-14), 7.71–7.65 (4H, m, H-7), 7.65–7.58 (8H, m, H-8, H-11), 7.46–7.40 (4H, m, H-12), 7.35–7.29 (2H, m, H-13), 3.14 (4H, dt, *J* = 6.4, 6.2 Hz, H₂-15), 2.86 (4H, t, *J* = 7.2 Hz, H₂-17), 2.77 (4H, t, *J* = 7.8 Hz, H₂-19), 2.61 (4H, t, *J* = 6.8 Hz, H₂-2/H₂-3), 2.44 (4H, t, *J* = 6.8 Hz, H₂-2/H₂-3), 1.71 (4H, tt, *J* = 7.2, 6.7 Hz, H₂-16), 1.53–1.43 (4H, m, H₂-20), 1.23–1.15 (4H, m, H₂-21); ¹³C NMR (DMSO-d₆, 100 MHz) δ 172.1 (C-1), 170.6 (C-4), 139.7 (C-10), 138.8 (C-6), 134.5 (C-9), 128.9 (C-12), 127.0 (C-13), 126.8 (C-8), 126.1 (C-11), 119.2 (C-7), 46.7 (C-19), 44.5 (C-17), 35.4 (C-15), 31.4 (C-2/C-3), 30.1 (C-2/C-3), 26.2 (C-16), 25.4 (C-21), 25.3 (C-20); (+)-HRESIMS *m/z* 733.4415 [M+H]⁺ (calcd for C₄₄H₅₇N₆O₄, 733.4436).

4.2.30. $N^1,N^7$-Bis(3-([1,1'-biphenyl]-4-ylamino)-4-oxobutanamido)propyl)heptane-1,7-diaminium 2,2,2-trifluoroacetate (21c)

Following general procedure A, the reaction of carboxylic acid 12 (66 mg, 0.25 mmol) with di-tert-butyl heptane-1,7-diylbis((3-aminopropyl)carbamate) (16c) (50 mg, 0.11 mmol), EDC·HCl (56 mg, 0.29 mmol), HOBT (39 mg, 0.29 mmol), and DIPEA (0.12 mL, 0.69 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl heptane-1,7-diylbis((3-([1,1'-biphenyl]-4-ylamino)-4-oxobutanamido)propyl)carbamate) as a pink solid (52 mg, 50%). Following general procedure C, the reaction of a sub-sample of this material (20 mg, 0.021 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt 21c as a yellow solid after purification (14 mg, 68%). $R_f = 0.51$ (RP-18, MeOH:10% HCl, 5:1); m.p. 178–180 °C; IR (ATR) $v_{max}$ 3288, 3034, 2939, 2859, 2527, 1658, 1637, 1533, 1198, 1173, 1134, 763, 719 cm⁻¹; ¹H NMR (DMSO-d₆, 400 MHz) δ 10.08 (2H, br s, NH-5), 8.48–8.33 (4H, m, NH₂-18), 8.12 (2H, t, *J* = 5.8
Hz, NH-14), 7.71–7.65 (4H, m, H-7), 7.65–7.57 (8H, m, H-8, H-11), 7.46–7.40 (4H, m, H-12), 7.35–7.29 (2H, m, H-13), 3.14 (4H, dt, *J* = 6.4, 6.2 Hz, H₂-15), 2.86 (4H, t, *J* = 7.0 Hz, H₂-17), 2.75 (4H, t, *J* = 7.0 Hz, H₂-19), 2.61 (4H, t, *J* = 6.6 Hz, H₂-2/H₂-3), 2.44 (4H, t, *J* = 6.6 Hz, H₂-2/H₂-3), 1.71 (4H, tt, *J* = 7.0, 6.4 Hz, H₂-16), 1.53–1.42 (4H, m, H₂-20), 1.20–1.10 (6H, m, H₂-21, H₂-22); ¹³C NMR (DMSO-d₆, 100 MHz) δ 172.3 (C-1), 170.6 (C-4), 139.7 (C-10), 138.8 (C-6), 134.5 (C-9), 128.9 (C-12), 127.0 (C-13), 126.8 (C-8), 126.1 (C-11), 119.2 (C-7), 46.7 (C-19), 44.4 (C-17), 35.4 (C-15), 31.4 (C-2/C-3), 30.1 (C-2/C-3), 28.0 (C-21/C-22), 26.2 (C-16), 25.7 (C-21/C-22), 25.4 (C-20); (+)-HRESIMS *m/z* 747.4566 [M+H]⁺ (calcd for C₄₅H₅₉N₆O₄, 747.4592).

### 4.2.31. *N*¹,*N*⁸-Bis(3-([1,1'-biphenyl]-4-ylamino)-4-oxobutanamido)propyl)octane-1,8-diaminium 2,2,2-trifluoroacetate (**21d**)

Following general procedure A, the reaction of carboxylic acid **12** (65 mg, 0.24 mmol) with di-tert-butyl octane-1,8-diylbis((3-aminopropyl)carbamate) (**16d**) (50 mg, 0.11 mmol), EDC·HCl (54 mg, 0.28 mmol), HOBt (38 mg, 0.28 mmol), and DIPEA (0.11 mL, 0.63 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl octane-1,8-diylbis((3-([1,1'-biphenyl]-4-ylamino)-4-oxobutanamido)propyl)carbamate) as a pink solid (56 mg, 53%). Following general procedure C, the reaction of a sub-sample of this material (20 mg, 0.021 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **21d** as a yellow solid after purification (14 mg, 67%). R_f = 0.51 (RP-18, MeOH:10% HCl, 5:1); m.p. 182–184 °C; IR (ATR) *v*max 3411, 3292, 3049, 2937, 2860, 2255, 1674, 1534, 1200, 1173, 1129, 1024, 1003, 764, 719 cm⁻¹; ¹H NMR (DMSO-d₆, 400 MHz) δ 10.08 (2H, br s, NH-5), 8.48–8.34 (4H, m, NH₂-18), 8.13 (2H, t, *J* = 6.0 Hz, NH-14), 7.71–7.65 (4H, m, H-7), 7.65–7.57 (8H, m, H-8, H-11), 7.46–7.40 (4H, m, H-12), 7.35–7.29 (2H, m, H-13), 3.15 (4H, dt, *J* = 6.4, 6.0 Hz, H₂-15), 2.87 (4H, t, *J* = 7.0 Hz, H₂-17), 2.76 (4H, t, *J* = 7.5 Hz, H₂-19), 2.61 (4H, t, *J* = 6.8 Hz, H₂-2/H₂-3), 2.43 (4H, t, *J* = 6.8 Hz, H₂-2/H₂-3), 1.71 (4H, tt, *J* = 7.0, 6.4 Hz, H₂-16), 1.53–1.41 (4H, m, H₂-20), 1.19–1.08 (8H, m, H₂-21, H₂-22); ¹³C NMR (DMSO-d₆, 100 MHz) δ 172.2 (C-1), 170.6 (C-4), 139.7 (C-10), 138.8 (C-6), 134.5 (C-9), 128.9 (C-12), 127.0 (C-13), 126.8 (C-8), 126.1 (C-11), 119.2 (C-7), 46.8 (C-19), 44.4 (C-17), 35.4 (C-15), 31.4 (C-2/C-3), 30.0 (C-2/C-3), 28.3 (C-21/C-22), 26.2 (C-16), 25.8 (C-21/C-22), 25.4 (C-20); (+)-HRESIMS *m/z* 761.4739 [M+H]⁺ (calcd for C₄₆H₆₁N₆O₄, 761.4749).

### 4.2.32. *N*¹,*N*¹⁰-Bis(3-([1,1'-biphenyl]-4-ylamino)-4-oxobutanamido)propyl)decane-1, 10-diaminium 2,2,2-trifluoroacetate (**21e**)

Following general procedure A, the reaction of carboxylic acid **12** (61 mg, 0.23 mmol) with di-tert-butyl decane-1,10-diylbis((3-aminopropyl)carbamate) (**16e**) (50 mg, 0.10 mmol), EDC·HCl (51 mg, 0.27 mmol), HOBt (36 mg, 0.27 mmol), and DIPEA (0.11 mL, 0.63 mmol) in CH₂Cl₂ (1.5 mL) created di-tert-butyl decane-1,10-diylbis((3-([1,1'-biphenyl]-4-ylamino)-4-oxobutanamido)propyl)carbamate) as a pale yellow solid (56 mg, 57%). Following general procedure C, the reaction of a sub-sample of this material (20 mg, 0.020 mmol) in CH₂Cl₂ (2 mL) with TFA (0.2 mL) created the di-TFA salt **21e** as a yellow solid after purification (15 mg, 74%). R_f = 0.34 (RP-18, MeOH:10% HCl, 5:1); m.p. 184–186 °C; IR (ATR) *v*max 3287, 3099, 3033, 2930, 2854, 1668, 1599, 1533, 1200, 1175, 1130, 764, 720 cm⁻¹; ¹H NMR (DMSO-d₆, 400 MHz) δ 10.09 (2H, br s, NH-5), 8.49–8.37 (4H, m, NH₂-18), 8.14 (2H, t, *J* = 6.0 Hz, NH-14), 7.71–7.66 (4H, m, H-7), 7.64–7.57 (8H, m, H-8, H-11), 7.46–7.39 (4H, m, H-12), 7.34–7.28 (2H, m, H-13), 3.15 (4H, dt, *J* = 6.4, 6.2 Hz, H₂-15), 2.93–2.83 (4H, m, H₂-17), 2.82–2.72 (4H, m, H₂-19), 2.62 (4H, t, *J* = 6.8 Hz, H₂-2/H₂-3), 2.44 (4H, t, *J* = 6.8 Hz, H₂-2/H₂-3), 1.72 (4H, tt, *J* = 7.0, 6.4 Hz, H₂-16), 1.53–1.42 (4H, m, H₂-20), 1.20–1.07 (12H, m, H₂-21, H₂-22, H₂-23); ¹³C NMR (DMSO-d₆, 100 MHz) δ 172.3 (C-1), 170.6 (C-4), 139.7 (C-10), 138.8 (C-6), 134.5 (C-9), 128.9 (C-12), 127.0 (C-13), 126.8 (C-8), 126.1 (C-11), 119.2 (C-7), 46.9 (C-19), 44.4 (C-17), 35.4 (C-15), 31.4 (C-2/C-3), 30.1 (C-2/C-3), 28.8 (C-21/C-22/C-23), 28.5 (C-21/C-22/C-23), 26.2 (C-16), 25.9 (C-21/C-22/C-23), 25.5 (C-20); (+)-HRESIMS *m/z* 789.5055 [M+H]⁺ (calcd for C₄₈H₆₅N₆O₄, 789.5062).
### 4.3. Antimicrobial Assays

The susceptibility of bacterial strains *S. aureus* (ATCC 25,923 or 29213), *E. coli* (ATCC 25922), and *P. aeruginosa* (ATCC 27853) to antibiotics and compounds was determined according to previously reported protocols [27]. Additional antimicrobial evaluation against MRSA (ATCC 43300), *Klebsiella pneumoniae* (ATCC 700603), *Acinetobacter baumannii* (ATCC 19606), *Candida albicans* (ATCC 90028), and *Cryptococcus neoformans* (ATCC 208821) was undertaken at the Community for Open Antimicrobial Drug Discovery at The University of Queensland (Australia) according to their standard protocols as reported previously [27,36].

### 4.4. Determination of the MICs of Antibiotics in the Presence of Synergizing Compounds

Restoring enhancer concentrations were determined using previously reported protocols [27].

### 4.5. Cytotoxicity Assays

Cytotoxicity assays were conducted using the protocols previously reported [27,36].

### 4.6. Hemolytic Assays

Hemolysis assays were conducted using the protocols previously reported [27,36].

### 4.7. Real-Time Growth Curves

Solutions of compound 20f at concentrations of 2, 4, and 16 µg/mL were each tested in triplicate against *S. aureus* (ATCC 25923), MRSA (CF-Marseille), and *E. coli* (ATCC 25922) following previously reported protocols [27].

### 4.8. Minimum Bactericidal Concentration Test

MBC's were determined following previously reported protocols [27].

## 5. Conclusions

A series of α,ω-disubstituted polyamines bearing naphthyl and biphenyl capping groups were prepared and evaluated for antimicrobial properties, as well as for the ability to enhance the action of doxycycline and erythromycin towards Gram-negative bacteria. Several analogues were identified as exhibiting pronounced antibacterial activity towards MRSA, with some examples also possessing antifungal activity towards *C. neoformans*. One particular analogue, 20f, was found to act as a bactericide. In contrast to previously reported structurally related disubstituted polyamines, the naphthyl-containing analogues were able to restore the action of legacy antibiotics with two examples, enhancing activity over 32-fold. These current results suggest that naphthyl capped polyamines may represent a particularly useful scaffold to further explore in the search for non-toxic antibiotic enhancers.

**Supplementary Materials:** The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/antibiotics12061014/s1, Figure S1 ¹H NMR (DMSO-d₆, 400 MHz) and ¹³C NMR (DMSO-d₆, 100 MHz) spectra for 9; Figure S2 ¹H NMR (DMSO-d₆, 400 MHz) and ¹³C NMR (DMSO-d₆, 100 MHz) spectra for 11; Figure S3 ¹H NMR (DMSO-d₆, 400 MHz) and ¹³C NMR (DMSO-d₆, 100 MHz) spectra for 12; Figure S4 ¹H NMR (DMSO-d₆, 400 MHz) and ¹³C NMR (DMSO-d₆, 100 MHz) spectra for 17a; Figure S5 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for 17b; Figure S6 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for 17c; Figure S7 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for 17d; Figure S8 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for 17e; Figure S9 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for 17f; Figure S10 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for 18a; Figure S11 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for 18b; Figure S12 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for 18c; Figure S13 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for 18d; Figure S14 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for 18e; Figure S15 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for 18f; Figure S16 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR
(CD₃OD, 100 MHz) spectra for **19a**; Figure S17 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for **19b**; Figure S18 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for **19c**; Figure S19 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for **19d**; Figure S20 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for **19e**; Figure S21 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for **19f**; Figure S22 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for **20a**; Figure S23 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for **20b**; Figure S24 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for **20c**; Figure S25 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for **20d**; Figure S26 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for **20e**; Figure S27 ¹H NMR (CD₃OD, 400 MHz) and ¹³C NMR (CD₃OD, 100 MHz) spectra for **20f**; Figure S28 ¹H NMR (DMSO-d₆, 400 MHz) and ¹³C NMR (DMSO-d₆, 100 MHz) spectra for **21a**; Figure S29 ¹H NMR (DMSO-d₆, 400 MHz) and ¹³C NMR (DMSO-d₆, 100 MHz) spectra for **21b**; Figure S30 ¹H NMR (DMSO-d₆, 400 MHz) and ¹³C NMR (DMSO-d₆, 100 MHz) spectra for **21c**; Figure S31 ¹H NMR (DMSO-d₆, 400 MHz) and ¹³C NMR (DMSO-d₆, 100 MHz) spectra for **21d**; Figure S32 ¹H NMR (DMSO-d₆, 400 MHz) and ¹³C NMR (DMSO-d₆, 100 MHz) spectra for **21e**.

**Author Contributions:** Conceptualization, B.R.C.; methodology, D.C., L.R.E., E.S.G., K.F. and F.R.; formal analysis, B.R.C. and J.M.B.; investigation, M.M.C., D.C., L.R.E., E.S.G., K.F., F.R., M.-L.B.-K., J.M.B. and B.R.C.; resources, B.R.C. and J.M.B.; data curation, B.R.C.; writing—original draft preparation, B.R.C. and M.M.C.; writing—review and editing, B.R.C., M.M.C., M.-L.B.-K. and J.M.B.; supervision, B.R.C., M.M.C. and J.M.B.; project administration, B.R.C. and M.M.C.; funding acquisition, B.R.C., M.M.C., M.-L.B.-K. and J.M.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Catalyst: Seeding Dumont d'Urville NZ-France Science and Technology Support Programme (19-UOA-057-DDU) provided by the New Zealand Ministry of Business, Innovation and Employment and administered by the Royal Society Te Apārangi, and the Maurice and Phyllis Paykel Trust (3718919).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data are contained within the article or Supplementary Materials.

**Acknowledgments:** We thank Michael Schmitz and Mansa Nair for their assistance with NMR and mass spectrometric data. Some of the antimicrobial screening was performed by CO-ADD (The Community for Antimicrobial Drug Discovery), funded by the Wellcome Trust (UK) and The University of Queensland (Australia).

**Conflicts of Interest:** The authors declare no conflict of interest.

## References

1. Mookherjee, N.; Anderson, M.A.; Haagsman, H.P.; Davidson, D.J. Antimicrobial Host Defence Peptides: Functions and Clinical Potential. *Nat. Rev. Drug Discov.* **2020**, *19*, 311–332. [CrossRef] [PubMed]

2. Ali, W.; Elsahn, A.; Ting, D.S.J.; Dua, H.S.; Mohammed, I. Host Defence Peptides: A Potent Alternative to Combat Antimicrobial Resistance in the Era of the COVID-19 Pandemic. *Antibiotics* **2022**, *11*, 475. [CrossRef] [PubMed]

3. D'Andrea, L.D.; Romanelli, A. Temporins: Multifunctional Peptides from Frog Skin. *Int. J. Mol. Sci.* **2023**, *24*, 5426. [CrossRef] [PubMed]

4. Bellotti, D.; Remelli, M. Lights and Shadows on the Therapeutic Use of Antimicrobial Peptides. *Molecules* **2022**, *27*, 4584. [CrossRef]

5. Hancock, R.E.W.; Alford, M.A.; Haney, E.F. Antibiofilm activity of host defence peptides: complexity provides opportunities. *Nat. Rev. Microbiol.* **2021**, *19*, 786–797. [CrossRef]

6. Neshani, A.; Sedighian, H.; Mirhosseini, S.A.; Ghazvini, K.; Zare, H.; Jahangiri, A. Antimicrobial peptides as a promising treatment option against *Acinetobacter baumannii* infections. *Microb. Pathogenesis* **2020**, *146*, 104238. [CrossRef]

7. Gan, B.H.; Gaynord, J.; Rowe, S.M.; Deingruber, T.; Spring, D.R. The Multifaceted Nature of Antimicrobial Peptides: Current Synthetic Chemistry Approaches and Future Directions. *Chem. Soc. Rev.* **2021**, *50*, 7820–7880. [CrossRef]

8. Chen, C.H.; Lu, T.K. Development and Challenges of Antimicrobial Peptides for Therapeutic Applications. *Antibiotics* **2020**, *9*, 24. [CrossRef]
9. Hemmingsen, L.M.; Giordani, B.; Paulsen, M.H.; Vanić, Ž.; Flaten, G.E.; Vitali, B.; Basnet, P.; Bayer, A.; Strøm, M.B.; Škalko-Basnet, N. Tailored anti-biofilm activity—Liposomal delivery for mimic of small antimicrobial peptide. *Biomater. Adv.* **2023**, *145*, 213238.
[CrossRef]

10. Langer, M.K.; Rahman, A.; Dey, H.; Anderssen, T.; Blencke, H.-M.; Haug, T.; Stensvåg, K.; Strøm, M.B.; Bayer, A. Investigation of tetrasubstituted heterocycles reveals hydantoins as a promising scaffold for development of novel antimicrobials with membranolytic properties. *Eur. J. Med. Chem.* **2023**, *249*, 115147. [CrossRef]

11. Langer, M.K.; Rahman, A.; Dey, H.; Anderssen, T.; Zilioli, F.; Haug, T.; Blencke, H.-M.; Stensvåg, K.; Strøm, M.B.; Bayer, A. A concise SAR-analysis of antimicrobial cationic amphipathic barbiturates for an improved activity-toxicity profile. *Eur. J. Med. Chem.* **2022**, *241*, 114632. [CrossRef] [PubMed]

12. Kopiasz, R.J.; Zabost, A.; Myszka, M.; Kuźmińska, A.; Drężek, K.; Mierzejewska, J.; Tomaszewski, W.; Iwańska, A.; Augustynowicz-Kopeć, E.; Ciachc, T.; et al. Main-chain flexibility and hydrophobicity of ionenes strongly impact their antimicrobial activity: an extended study on drug resistance strains and *Mycobacterium*. *RSC Adv.* **2022**, *12*, 26220–26232. [CrossRef] [PubMed]

13. Jiang, Y.; Chen, Y.; Song, Z.; Tan, Z.; Cheng, J. Recent advances in design of antimicrobial peptides and polypeptides toward clinical translation. *Adv. Drug Deliver. Rev.* **2021**, *170*, 261–280. [CrossRef]

14. Tyagi, A.; Mishra, A. Methacrylamide based antibiotic polymers with no detectable bacterial resistance. *Soft Matter* **2021**, *17*, 3404–3416. [CrossRef] [PubMed]

15. Ghosh, C.; Haldar, J. Membrane-Active Small Molecules: Designs Inspired by Antimicrobial Peptides. *ChemMedChem* **2015**, *10*, 1606–1624. [CrossRef]

16. Isaksson, J.; Brandsdal, B.O.; Engqvist, M.; Flaten, G.E.; Svendsen, J.S.M.; Stensen, W. A Synthetic Antimicrobial Peptidomimetic (LTX 109): Stereochemical Impact on Membrane Disruption. *J. Med. Chem.* **2011**, *54*, 5786–5795. [CrossRef]

17. Zhou, M.; Zheng, M.; Cai, J. Small Molecules with Membrane-Active Antibacterial Activity. *ACS Appl. Mater. Interfaces* **2020**, *12*, 21292–21299. [CrossRef]

18. Alhanout, K.; Malesinki, S.; Vidal, N.; Peyrot, V.; Rolain, J.M.; Brunel, J.M. New Insights into the Antibacterial Mechanism of Action of Squalamine. *J. Antimicrob. Chemother.* **2010**, *65*, 1688–1693. [CrossRef]

19. Su, M.; Xia, D.; Teng, P.; Nimmagadda, A.; Zhang, C.; Odom, T.; Cao, A.; Hu, Y.; Cai, J. Membrane-Active Hydantoin Derivatives as Antibiotic Agents. *J. Med. Chem.* **2017**, *60*, 8456–8465. [CrossRef]

20. Dijksteel, G.S.; Ulrich, M.M.W.; Middelkoop, E.; Boekema, B.K.H.L. Review: Lessons Learned From Clinical Trials Using Antimicrobial Peptides (AMPs). *Front. Microbiol.* **2021**, *12*, 616979. [CrossRef]

21. Moore, K.S.; Wehrli, S.; Roder, H.; Rogers, M.; Forrest, J.N.; McCrimmon, D.; Zasloff, M. Squalamine: An Aminosterol Antibiotic from the Shark. *Proc. Natl. Acad. Sci. USA* **1993**, *90*, 1354–1358. [CrossRef] [PubMed]

22. Douafer, H.; Andrieu, V.; Phanstiel, O.; Brunel, J.M. Antibiotic Adjuvants: Make Antibiotics Great Again! *J. Med. Chem.* **2019**, *62*, 8665–8681. [CrossRef] [PubMed]

23. Xu, M.; Davis, R.A.; Feng, Y.; Sykes, M.L.; Shelper, T.; Avery, V.M.; Camp, D.; Quinn, R.J. Ianthelliformisamines A–C, Antibacterial Bromotyrosine-Derived Metabolites from the Marine Sponge *Suberea ianthelliformis*. *J. Nat. Prod.* **2012**, *75*, 1001–1005. [CrossRef] [PubMed]

24. Pieri, C.; Borselli, D.; Di Giorgio, C.; De Méo, M.; Bolla, J.-M.; Vidal, N.; Combes, S.; Brunel, J.M. New Ianthelliformisamine Derivatives as Antibiotic Enhancers against Resistant Gram-Negative Bacteria. *J. Med. Chem.* **2014**, *57*, 4263–4272. [CrossRef] [PubMed]

25. Khan, F.A.; Ahmad, S.; Kodipelli, N.; Shivange, G.; Anindya, R. Syntheses of a Library of Molecules on the Marine Natural Product Ianthelliformisamines Platform and Their Biological Evaluation. *Org. Biomol. Chem.* **2014**, *12*, 3847. [CrossRef] [PubMed]

26. Blanchet, M.; Borselli, D.; Brunel, J.M. Polyamine Derivatives: A Revival of an Old Neglected Scaffold to Fight Resistant Gram-Negative Bacteria? *Future Med. Chem.* **2016**, *8*, 963–973. [CrossRef]

27. Chen, D.; Cadelis, M.M.; Rouvier, F.; Troia, T.; Edmeades, L.R.; Fraser, K.; Gill, E.S.; Bourguet-Kondracki, M.-L.; Brunel, J.M.; Copp, B.R. α,ω-Diacyl-Substituted Analogues of Natural and Unnatural Polyamines: Identification of Potent Bactericides That Selectively Target Bacterial Membranes. *Int. J. Mol. Sci.* **2023**, *24*, 5882. [CrossRef]

28. Glukhov, E.; Burrows, L.L.; Deber, C.M. Membrane Interactions of Designed Cationic Antimicrobial Peptides: The Two Thresholds. *Biopolymers* **2008**, *89*, 360–371. [CrossRef]

29. Pearce, A.N.; Kaiser, M.; Copp, B.R. Synthesis and Antimalarial Evaluation of Artesunate-Polyamine and Trioxolane-Polyamine Conjugates. *Eur. J. Med. Chem.* **2017**, *140*, 595–603. [CrossRef]

30. Klenke, B.; Gilbert, I.H. Nitrile Reduction in the Presence of Boc-Protected Amino Groups by Catalytic Hydrogenation over Palladium-Activated Raney-Nickel. *J. Org. Chem.* **2001**, *66*, 2480–2483. [CrossRef]

31. Klenke, B.; Stewart, M.; Barrett, M.P.; Brun, R.; Gilbert, I.H. Synthesis and Biological Evaluation of s -Triazine Substituted Polyamines as Potential New Anti-Trypanosomal Drugs. *J. Med. Chem.* **2001**, *44*, 3440–3452. [CrossRef] [PubMed]

32. Israel, M.; Rosenfield, J.S.; Modest, E.J. Analogs of Spermine and Spermidine. I. Synthesis of Polymethylenepolyamines by Reduction of Cyanoethylated α,ℓ-Alkylenediamines1,2. *J. Med. Chem.* **1964**, *7*, 710–716. [CrossRef] [PubMed]

33. Sander, T.; Freyss, J.; von Korff, M.; Rufener, C. DataWarrior: An Open-Source Program For Chemistry Aware Data Visualization And Analysis. *J. Chem. Inf. Model.* **2015**, *55*, 460–473. [CrossRef] [PubMed]
34. Rolain, J.-M.; Francois, P.; Hernandez, D.; Bittar, F.; Richet, H.; Fournous, G.; Mattenberger, Y.; Bosdure, E.; Stremler, N.; Dubus, J.-C.; et al. Genomic Analysis of an Emerging Multiresistant *Staphylococcus aureus* Strain Rapidly Spreading in Cystic Fibrosis Patients Revealed the Presence of an Antibiotic Inducible Bacteriophage. *Biol. Direct* **2009**, *4*, 1. [CrossRef]

35. Yasuda, K.; Ohmizo, C.; Katsu, T. Mode of Action of Novel Polyamines Increasing the Permeability of Bacterial Outer Membrane. *Int. J. Antimicrob. Agents* **2004**, *24*, 67–71. [CrossRef]

36. Blaskovich, M.A.T.; Zuegg, J.; Elliott, A.G.; Cooper, M.A. Helping Chemists Discover New Antibiotics. *ACS Infect. Dis.* **2015**, *1*, 285–287. [CrossRef]

**Disclaimer/Publisher's Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.