# Synthesis of 2-aminopyridine Lactones and Studies of Their Antioxidant, Antibacterial and Antifungal Properties

Fadila Salhi, Nawel Cheikh, Didier Villemin, Nathalie Bar

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Fadila Salhi, Nawel Cheikh, Didier Villemin, Nathalie Bar. Synthesis of 2-aminopyridine Lactones and Studies of Their Antioxidant, Antibacterial and Antifungal Properties. Chemistry Proceedings, 2022, This article belongs to the Proceedings of The 25th International Electronic Conference on Synthetic Organic Chemistry, 6 (1), pp.9. 10.3390/ecsoc-25-11709. http://hal-03790910

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# Synthesis of 2-aminopyridine Lactones and Studies of Their Antioxidant, Antibacterial and Antifungal Properties †

Fadila Salhi <fnref n="1" />, Nawel Cheikh <fnref n="2" />, Didier Villemin <fnref n="1" />,* and Nathalie Bar <fnref n="1" />

**Abstract:** In the present work, the synthesis and biological activities of substituted 2-aminopyridine δ-lactone derivatives were achieved. 4,6,6-trimethyl-2-oxo-5,6-dihydro-2H-pyran-3-carbonitrile was synthesised from 4-hydroxy-4-methylpentan-2-one, followed by its transformation in enaminonitrile with DMFDMA. The antioxidant effects of substituted 2-aminopyridine δ-lactone derivatives were evaluated through DPPH assay and revealed a great antioxidant capacity. The antifungal and antibacterial activities were investigated by disc diffusion method against clinical Gram-negative bacteria and against clinical fungi. The study shows moderate to very good antibacterial and antifungal activities for the new substituted 2-aminopyridine δ-lactone derivatives.

**Keywords:** 2-aminopyridines; bis-2-aminopyridines; antioxidant; DPPH; radical scavenger; antibacterial activity; antifungal activity

## 1. Introduction

Substituted 2-aminopyridine δ-lactone derivatives were achieved. 4,6,6-trimethyl-2-oxo-5,6-dihydro-2H-pyran-3-carbonitrile (1) was synthesised from 4-hydroxy-4-methylpentan-2-one [1] (Figure 1), followed by its transformation in enaminonitrile with DMFDMA [1].

<figure><img src="image_2.png" /><figcaption>**Figure 1.** Synthesis of 4,6,6-trimethyl-2-oxo-5,6-dihydro-2H-pyran-3-carbonitrile 1.</figcaption></figure>

The compound 3 was prepared by the reaction of δ-lactone nitrile «4,6,6-trimethyl-2-oxo-5,6-dihydro-2H-pyran-3-carbonitrile » 1 with dimethylformamide dimethylacetal DMFDMA in stoichiometric amounts. The reaction was performed at room temperature during 24 h and afforded good overall yield (72%) [1] according to the Figure 2.

The reaction of enaminolactone nitrile 3 and primary amines 4a–f in refluxed DMF according to our previous work [1] results in new substituted 2-aminopyridines 5a–f, according Figure 3, results are reported in Table 1.

<footnote n="1">¹ Normandie Université France, ENSICAEN, LCMT, UMR CNRS 6507, INC3 M, FR 3038, Labex EMC3, LabexSynOrg, 6 Bd Maréchal Juin, 14050 Caen, France; salhifdila@gmail.com (F.S.); nathalie.bar@ensicaen.fr (N.B.)</footnote>

<footnote n="2">² Laboratoire de Catalyse et Synthèse en Chimie Organique, Faculté des Sciences, Université Abou-Bakr Belkaid, BP 119, Tlemcen 13000, Algeria; n Cheikh@yahoo.fr</footnote>

<footnote>* Correspondence: didier.villemin@ensicaen.fr; Tel.: +33-231-452840</footnote>

<footnote>† Presented at the 25th International Electronic Conference on Synthetic Organic Chemistry, 15–30 November 2021. Available online: https://ecsoc-25.sciforum.net/.</footnote>
<figure><img src="image_3.png" /><figcaption>Figure 2. Synthesis of enaminolactone nitrile 3.</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Figure 3. Synthesis of 2-aminopyridines 5a-f from enaminolactone nitrile 3.</figcaption></figure>

The reactions between 1 equiv of diamines 6a-c with 2 equiv of enaminolactone nitrile 3 were performed. The mixture was refluxed in DMF during 6 h. After removing of the solvent and purification by column chromatography, we afforded the new original bis-(2-aminopyridines) 7a-c in moderate to good yields (Figure 4, Table 2).

<figure><img src="image_5.png" /><figcaption>Figure 4. Synthesis of new bis-(2-aminopyridines) 7a-c.</figcaption></figure>

The structure of the compounds 7a-c was confirmed by spectral data (IR, ¹H NMR and ¹³CNMR).
<table><caption>**Table 1.** Synthesis of 2-aminopyridine lactones.</caption><thead><tr><th>Entry</th><th>Enaminolactone</th><th>RNH<sub>2</sub></th><th>Product</th><th>Yield (%)</th></tr></thead><tbody><tr><td>1</td><td>3</td><td>CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub><sub>4a</sub></td><td>5a</td><td>95</td></tr><tr><td>2</td><td>3</td><td>CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub><sub>4b</sub></td><td>5b</td><td>87</td></tr><tr><td>3</td><td>3</td><td>CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub><sub>4c</sub></td><td>5c</td><td>92</td></tr><tr><td>4</td><td>3</td><td>CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub><sub>4d</sub></td><td>5d</td><td>96</td></tr><tr><td>5</td><td>3</td><td>CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub><sub>4e</sub></td><td>5e</td><td>95</td></tr><tr><td>6</td><td>3</td><td>CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub><sub>4f</sub></td><td>5f</td><td>96</td></tr></tbody></table>

The structure of substituted 2-aminopyridine δ-lactones were characterised by spectroscopic methods (IR, ¹H NMR, ¹³C NMR and MS).
<table><caption>**Table 2.** Synthesis of bis-2-aminopyridine lactones.</caption><thead><tr><th>Entry</th><th>RNH<sub>2</sub></th><th>Product</th><th>Yield (%)</th></tr></thead><tbody><tr><td>1</td><td>H<sub>2</sub>N-<b>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub></b><sup>6a</sup></td><td><b>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH</b><sub>2</sub><b>-CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH</b><sub>2</sub><b>-CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH</b><sub>2</sub><sup>7a</sup></td><td>57</td></tr><tr><td>2</td><td>H<sub>2</sub>N-<b>(CH<sub>2</sub>)<sub>10</sub>CH<sub>2</sub>NH<sub>2</sub></b><sup>6b</sup></td><td><b>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH</b><sub>2</sub><b>-CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH</b><sub>2</sub><b>-CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH</b><sub>2</sub><sup>7b</sup></td><td>60</td></tr><tr><td>3</td><td>H<sub>2</sub>N-<b>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH</b><sub>2</sub><sup>6c</sup></td><td><b>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH</b><sub>2</sub><b>-CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH</b><sub>2</sub><b>-CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH</b><sub>2</sub><sup>7c</sup></td><td>89</td></tr></tbody></table>

## 2. Antioxidant Effects

The antioxidant effects of substituted 2-aminopyridine δ-lactone derivatives were evaluated through DPPH assay and revealed a great antioxidant capacity.

For initial screening of antioxidant activity DPPH on TLC was employed [2]. After the qualitative confirmation of antioxidant potential, spectroscopic measurements were made through DPPH assay. The antioxidant proprieties were measured and evidenced in terms of their efficient concentration $IC_{50}$, as well as their reduction kinetics [3]. Evaluation of the antioxydant activity by the test of DPPH, revealed a great antioxydant capacity for the most of compounds tested with a variation of $IC_{50}$ between 1.30–3.61 mg/mL and times of reaction of 30 min.

## 3. Antifungal and Antibacterial Activities

The antifungal and antibacterial activities of 2-aminopyridines and bis-2-aminopyridines were investigated in vitro in order to evaluate their efficacy. The antibacterial activity of the compounds was determined by the disc diffusion method [4,5] against clinical Gram-negative bacteria: *Escherichia coli*, *Pseudomonas aeruginosa* and Gram-positive bacteria: *Staphylococcus aureus*, *Listeria monocytogenes* and *Bacillus cereus*. The antifungal activity of the compounds was determined by using a direct-contact and agar diffusion test [4] against clinical fungi *Aspergillus flavus* and *Aspergillus ochraceus*. The compounds showed moderate to very good antibacterial and antifungal activities, that the **5b**, **5d**, **5e** and **5f** presents a best minimal inhibitory concentration (MIC) with 62.5 µg/mL. The *Aspergillus ochraceus* strain revealed a stronger sensitivity than *Aspergillus flavus* to all compounds tested, While that the **7c** and **7b** showed a broad-spectrum antifungal activity again pathogenic *Aspergillus ochraceus* with an inhibition percentage of 77% and 78%, respectively. Based our results, the compounds of 2-aminopyridines and bis-2-aminopyridines can be considered as a source of novel antibiotic and antifungal.

## 4. Experimental

In the supplementary informations:

(A) Synthesis and Screening of Antioxidant Potential

(B) Screening of antibacterial and antifungal properties of the compounds.
**5. Conclusions**

The study shows moderate to very good antibacterial and antifungal activities for the
new substituted 2-aminopyridine δ-lactone derivatives.

**Supplementary Materials:** The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/ecsoc-25-11709/s1.

**Author Contributions:** Conceptualization, D.V.; Investigation, F.S. and N.B.; Writing—Original draft, N.B. and D.V.; Writing—Review and editing, N.C., N.B. and D.V. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Supplementary Informations in English (parts A and B) https://hal-normandie-univ-archives-ouvertes-fr.ezproxy.u-pec.fr/hal-03510414/document.

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

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