CC BY ND NC 4.0 · SynOpen 2017; 01(01): 0050-0058
DOI: 10.1055/s-0036-1590800
paper
Copyright with the author

Efficient Synthesis of Pyrazinoic Acid Hybrid Conjugates

Siva S. Panda*a, Abdullah M. Asirib, Mohamed Elagawanyc, Devan D. Buchanana, Behrad Torkiana, Keerthana Bathalaa, Sean J. Thomasa, Jason E. Capitoa, Muhammad N. Arshadb, Abeer N. Al-Romaizanb
  • aDepartment of Chemistry & Physics, Augusta University, Augusta, GA 30912, USA
  • bChemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, 21589, Saudi Arabia
  • cDepartment of Pharmaceutical Chemistry, faculty of pharmacy, Damanhour University, Damanhour, Egypt   Email: sspanda12@gmail.com   Email: sipanda@augusta.edu
Further Information

Publication History

Received: 05 April 2017

Accepted after revision: 31 May 2017

Publication Date:
06 July 2017 (online)

 

Abstract

Benzotriazole-activated pyrazinoic acid was utilized as a versatile building block for the efficient and convenient synthesis of novel hybrid conjugates of pyrazinoic acid with secondary amines via amino acid linkers in high yields.


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Tuberculosis (TB) is a bacterial pathogen caused by Mycobacterium­ tuberculosis, which is known to cause pulmonary infection and to become extremely pervasive within the lungs.[1] [2] [3] TB is considered to be one of the world’s deadliest communicable diseases because of its high virulence and the ability of M. tuberculosis to enter into a dormant­ ­­state, then subsequently undergo reactivation.[3] [4] [5] Pyrazinamide (PZA) is a first-line antituberculosis prodrug that is often used in combinational therapy with drugs such as isoniazide, ethambutol, streptomycin, and rifampicin (Figure [1]).[6–8]

Zoom Image
Figure 1 Current antituberculosis drugs

PZA is perceived to inhibit vital ribosomal proteins after being converted into its active constituent, pyrazinoic acid (POA), by the tuberculosis enzyme, pyrazinamidase (PZAase) (Scheme [1]).[9] It may lower the pH of the area surrounding M. tuberculosis to such an extent that the organism is unable to grow. Due to its low lipophilicity, POA cannot be absorbed by the gastrointestinal tract. Fortunately, the drug can be absorbed in the pyrazinamide configuration.

Zoom Image
Scheme 1 PZA is converted into POA in the presence of PZAase

One of the drawbacks of using PZA to treat TB is that it inhibits protein synthesis. With prolonged administration of the recommended dose, harmful side effects such as hepatitis, acute hypertension, thrombocytopenia, and gastrointestinal discomfort have been reported.[10] To overcome these issues, several molecular hybridization approaches have been reported for the development of potential antitubercular agents. Most hybridized structures include clinically used drugs such as rifamycin, ethambutol and isoniazid coupled with other hydrophobic structures such as cinnamic acid derivatives.[11] [12] [13] [14] Unfortunately the most promising prodrugs of POA are not stable.[15]

Secondary amines such morpholine, piperidine, N-methylpiperazine, and pyrrolidine are important scaffolds for potential biological molecules. Structural activity relationships (SARs) suggest that these secondary amines play an important role in bioactive molecules.[16] Drug–amino acid conjugates are used to enhance drug delivery and to increase tissue cell penetration. In addition to acting as carriers of these agents, amino acids also amplify their bioavailability while maintaining their bioactive integrity. Recently, we have synthesized and reported several bioconjugates with enhanced biological properties and increased lipophilicity.[17] [18] [19] [20]

In a continuation of our interest in synthesizing amino acid–peptide conjugates with biological significance, we report herein an efficient synthesis of pyrazimide hybrid conjugates, which contain various amino acids and secondary amines, that may decrease the dose of PZA required to fight TB, increase the drug’s lipophilicity and decrease adverse effects.

Table 1 Boc-Protected Amino Acid–Secondary Amine Conjugates 11at

Entry

Product 11

Yield (%)

Mp (°C)

[α] d 20 (c 1.0 in MeOH)

1

Boc-Gly-Mor

11a

62

114–116

2

Boc-l-Ala-Mor

11b

67

oil

–20.3

3

Boc-dl-Ala-Mor

11b′

74

oil

racemic

4

Boc-l-Val-Mor

11c

75

135–137

–17.5

5

Boc-l-Ile-Mor

11d

81

oil

–23.6

6

Boc-l-Phe-Mor

11e

84

129–131

–15.0

7

Boc-Gly-Pip

11f

90

oil

8

Boc-l-Ala-Pip

11g

97

oil

–19.6

9

Boc-l-Val-Pip

11h

78

oil

–20.6

10

Boc-l-Ile-Pip

11i

79

oil

–21.8

11

Boc-l-Phe-Pip

11j

81

122–124

–18.5

12

Boc-Gly-NMP

11k

76

oil

13

Boc-l-Ala-NMP

11l

81

oil

–20.0

14

Boc-l-Val-NMP

11m

84

oil

–14.3

15

Boc-l-Ile-NMP

11n

69

oil

–19.6

16

Boc-l-Phe-NMP

11o

83

111–113

–16.5

17

Boc-Gly-Pyr

11p

89

oil

18

Boc-l-Ala-Pyr

11q

83

oil

–21.1

19

Boc-l-Val-Pyr

11r

67

oil

–22.3

20

Boc-l-Ile-Pyr

11s

72

oil

–18.6

21

Boc-l-Phe-Pyr

11t

78

126–128

–24.0

POA was activated as its benzotriazolide derivative 1 by following the previously reported procedure[21] and coupled with free amino acids 2 in a mixture of acetonitrile and water (7:3) at 20 °C for 2 h in the presence of 1.5 equivalents of triethylamine to give compounds 3. Attempts to prepare benzotriazole derivatives of POA–amino acid conjugates failed. We were also unsuccessful in coupling compounds 3 with secondary amines using different coupling reagents and ended up with mixtures of compounds as evidenced by TLC (Scheme [2]). We therefore decided to redesign our approach and synthesize bis-conjugates of POA–secondary amines by coupling Boc-protected aminoacylbenzotriazoles[22] with secondary amines. After removing the Boc group with dioxane–HCl, the unprotected conjugates were coupled with benzotriazole-activated POA to produce the desired products in good yields (Scheme [3]). Boc-protected aminoacylbenzotriazoles 6ad were treated with secondary amines 710 in the presence of triethylamine in acetonitrile at 20 °C for 2 h to obtain the conjugates in good yields without loss of chiral integrity (Scheme [3], Table [1]).

Zoom Image
Scheme 2 Synthesis of POA hybrid conjugates with secondary heterocyclic amines and amino acid (Route I)
Zoom Image
Scheme 3 Synthesis of Boc-protected amino acid–secondary heterocyclic amine conjugates

Boc-protected amino acid–secondary amine conjugates 11at were deprotected using a dioxane–HCl mixture at 20 °C for 1 h to give unprotected amino acid–secondary amine conjugates 12at. These compounds were then used in the next step without further characterization. The target compounds 5at were prepared by coupling the unprotected amino acid–secondary amine conjugates with POA-benzotriazolide 1 in the presence of triethylamine in acetonitrile at 20 °C for 3 h (Scheme [4], Table [2]). All compounds were fully characterized by NMR spectroscopy, HRMS and specific rotation. X-ray diffraction analysis of compound 5a further confirmed the formation of the hybrid conjugate (Figure [2]).

Table 2 POA Hybrid Conjugates 5at

Entry

Product 5

Yield (%)

Mp (°C)

[α] d 20 (c 1.0 in MeOH)

1

POA-Gly-Mor

5a

75

180–181

2

POA-l-Ala-Mor

5b

69

sticky

–25.4

3

POA-dl-Ala-Mor

5b′

72

oil

racemic

4

POA-l-Val-Mor

5c

76

oil

–19.2

5

POA-l-Ile-Mor

5d

70

oil

–20.3

6

POA-l-Phe-Mor

5e

78

sticky

–25.6

7

POA-Gly-Pip

5f

74

123–125

8

POA-l-Ala-Pip

5g

75

oil

–19.9

9

POA-l-Val-Pip

5h

81

oil

–23.6

10

POA-l-Ile-Pip

5i

64

sticky

–22.0

11

POA-l-Phe-Pip

5j

79

oil

–20.1

12

POA-Gly-NMP

5k

69

sticky

13

POA-l-Ala-NMP

5l

73

oil

–26.5

14

POA-l-Val-NMP

5m

62

oil

–20.9

15

POA-l-Ile-NMP

5n

64

oil

–23.0

16

POA-l-Phe-NMP

5o

71

oil

–28.1

17

POA-Gly-Pyr

5p

81

148–150

18

POA-l-Ala-Pyr

5q

79

oil

–23.0

19

POA-l-Val-Pyr

5r

82

oil

–28.5

20

POA-l-Ile-Pyr

5s

74

oil

–26.6

21

POA-l-Phe-Pyr

5t

73

oil

–25.1

Zoom Image
Figure 2 ORTEP diagram of POA-Gly-Mor (5a)
Zoom Image
Scheme 4 Synthesis of POA hybrid conjugates with secondary heterocyclic amines and amino acid (Route II)

In conclusion, benzotriazole-activated pyrazinoic acid has been used as a precursor for the efficient synthesis of pyrazinoic acid hybrid conjugates. The hybrid conjugates may be candidates for the development of new antituberculosis agents.

Melting points were determined with a capillary melting-point apparatus equipped with a digital thermometer. Reactions were monitored by using thin-layer chromatography (TLC) on 0.2 mm silica gel F254 plates (Merck). The chemical structures of final products and intermediates were characterized by 1H and 13C NMR spectroscopy with a Bruker NMR spectrometer (500 MHz, 125 MHz). 13C NMR spectra were fully decoupled. Chemical shifts are reported in parts per million (ppm) using the deuterated solvent peak or tetramethylsilane as an internal standard. Mass spectrometric analysis was carried out with a high-resolution Biosystems QStar Elite time-of-flight electrospray mass spectrometer or an Agilent 6210 instrument using time-of-flight mass spectrometry (TOF-MS) with electrospray ionization (ESI). Specific rotation measurements were carried out with an Autopol IV polarimeter.


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Synthesis of (1H-benzo[d][1,2,3]triazol-1-yl)(pyrazin-2-yl)methanone (POA-Bt, 1)[21]

1H-Benzotriazole (4.0 equiv) was dissolved in anhydrous methylene chloride. Thionyl chloride (1.2 equiv) was added and the mixture was stirred for 30 min. Pyrazinoic acid (1.0 equiv) was added and the reaction mixture was stirred for 2–3 h at r.t. Upon completion of the reaction, 20% aqueous sodium bicarbonate was added and the organic layer was extracted twice with the alkaline solution, washed with brine, and dried over anhydrous magnesium sulfate. After filtration, the solvent was evaporated and the residue crystallized from diethyl ether to yield 1 in good yield.


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Synthesis of Secondary Amine–Amino Acid Conjugates 11a–t; General Procedure

A 50 mL round-bottom flask containing a small stir bar was charged with N-(Boc-aminoacyl)benzotriazole 6ae (1.0 equiv) and secondary amine (morpholine, piperidine, N-methylpiperazine, pyrrolidine) (1.0 equiv) dissolved in acetonitrile (10 mL) along with triethylamine (1.5 equiv). The reaction mixture was stirred at r.t. for 3–4 h and the progress of the reaction was monitored by TLC. After completion of the reaction, the acetonitrile was evaporated under reduced pressure and the residue was extracted with EtOAc. The organic layer was washed with aqueous sodium carbonate and dried over sodium sulfate. After filtration, the EtOAc was evaporated under reduced pressure to obtain the desired amino acid–secondary amine conjugate in good yield.


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tert-Butyl (2-Morpholino-2-oxoethyl)carbamate (Boc-Gly-Mor, 11a)

Yield: 62%; colorless microcrystals; mp 114–116 °C.

1H NMR (500 MHz, CDCl3): δ = 5.50 (br s, 1 H), 3.95 (d, J=3.5 Hz, 2 H), 3.70–3.62 (m, 6 H), 3.40 (t, J=4.4 Hz, 2 H), 1.45 (s, 9 H).

13C NMR (125 MHz, CDCl3): δ = 167.5, 156.0, 80.0, 66.9, 66.5, 45.0, 42.4, 42.3, 28.5.

HRMS (ESI): m/z[M + H]+ calcd for C11H20N2O4: 244.1424; found: 244.1425.


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tert-Butyl (S)-(1-Morpholino-1-oxopropan-2-yl)carbamate (Boc-l-Ala-Mor, 11b)

Yield: 67%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.51 (br s, 1 H), 4.59 (br s, 1 H), 3.67–3.47 (m, 8 H), 1.43 (s, 9 H), 1.29 (d, J=5.8 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 171.5, 155.3, 79.8, 67.0, 66.8, 46.1, 42.6, 28.6, 19.5.

HRMS (ESI): m/z[M + H]+ calcd for C12H22N2O4: 258.1584; found: 258.1580.


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tert-Butyl (1-Morpholino-1-oxopropan-2-yl)carbamate (Boc-dl-Ala-Mor, 11b′)

Yield: 74%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.57 (d, J=5.8 Hz, 1 H), 4.54 (d, J=5.8 Hz, 1 H), 3.62–3.40 (m, 8 H), 1.37 (s, 9 H), 1.24 (d, J=7 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 171.4, 155.1, 79.6, 66.8, 66.6, 46.0, 42.4, 28.4, 19.2.

HRMS (ESI): m/z[M + H]+ calcd for C12H22N2O4: 258.1584; found: 258.1582.


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tert-Butyl (S)-(3-Methyl-1-morpholino-1-oxobutan-2-yl)carbamate (Boc-l-Val-Mor, 11c)

Yield: 75%; colorless microcrystals; mp 135–137 °C.

1H NMR (500 MHz, CDCl3): δ = 5.37 (d, J=7.9 Hz, 1 H), 4.34 (t, J=7.9 Hz, 1 H), 3.64–3.48 (m, 8 H), 1.89–1.83 (m, 1 H), 1.36 (s, 9 H), 0.88 (d, J=6.6 Hz, 3 H), 0.83 (d, J=6.6 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 170.8, 155.9, 79.4, 66.9, 66.7, 54.6, 46.3, 42.4, 31.4, 28.3, 19.6, 17.3.

HRMS (ESI): m/z[M + H]+ calcd for C14H26N2O4: 286.1896; found: 286.1894.


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tert-Butyl ((2S,3S)-3-Methyl-1-morpholino-1-oxopentan-2-yl)carbamate (Boc-l-Ile-Mor, 11d)

Yield: 81%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.32 (d, J=7.9 Hz, 1 H), 4.39 (t, J=7.9 Hz, 1 H), 3.68–3.48 (m, 8 H), 2.30–2.23 (m, 1 H), 1.65–1.64 (m, 1 H), 1.50–1.45 (m, 1 H), 1.38 (s, 9 H), 0.88–0.81 (m, 6 H).

13C NMR (125 MHz, CDCl3): δ = 171.1, 155.9, 79.6, 66.9, 66.8, 54.0, 46.5, 42.5, 38.1, 28.4, 24.1, 15.9, 11.4.

HRMS (ESI): m/z[M + H]+ calcd for C15H28N2O4: 300.2049; found: 300.2054.


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tert-Butyl (S)-(1-Morpholino-1-oxo-3-phenylpropan-2-yl)carbamate (Boc-l-Phe-Mor, 11e)

Yield: 84%; colorless microcrystals; mp 129–131 °C.

1H NMR (500 MHz, CDCl3): δ = 7.29–7.19 (m, 5 H), 5.44 (d, J=7.5 Hz, 1 H), 4.82–4.78 (m, 1 H), 3.62–3.28 (m, 6 H), 3.05–2.89 (m, 4 H), 1.43 (s, 9 H).

13C NMR (125 MHz, CDCl3): δ = 170.5, 155.2, 136.5, 129.7, 128.8, 127.3, 80.0, 66.7, 66.3, 51.0, 46.2, 42.4, 40.7, 28.5.

HRMS (ESI): m/z[M + H]+ calcd for C18H26N2O4: 334.1898; found: 334.1909.


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tert-Butyl (2-Oxo-2-(piperidin-1-yl)ethyl)carbamate (Boc-Gly-Pip, 11f)

Yield: 90%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.56 (br s, 1 H), 3.94 (d, J=3.5 Hz, 2 H), 3.56 (t, J=5 Hz, 2 H), 3.31 (t, J=5 Hz, 2 H), 1.65–1.63 (m, 6 H), 1.45 (s, 9 H).

13C NMR (125 MHz, CDCl3): δ = 167.9, 164.3, 79.6, 45.9, 44.2, 41.9, 28.4, 25.9, 24.8, 24.6.

HRMS (ESI): m/z[M + H]+ calcd for C12H22N2O3: 242.1633; found: 242.1641.


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tert-Butyl (S)-(1-Oxo-1-(piperidin-1-yl)propan-2-yl)carbamate (Boc-l-Ala-Pip, 11g)

Yield: 97%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.61 (d, J=8.4 Hz,1 H), 4.64–4.58 (m, 1 H), 3.62–3.38 (m, 4 H), 1.68–1.53 (m, 6 H), 1.44 (s, 9 H), 1.29 (d, J=6.7 Hz, 1 H).

13C NMR (125 MHz, CDCl3): δ = 171.0, 155.3, 79.5, 46.6, 46.4, 43.4, 28.6, 28.6, 28.5, 26.6, 25.7, 24.7, 19.7

HRMS (ESI): m/z[M + H]+ calcd for C13H24N2O3: 256.1787; found: 256.1792.


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tert-Butyl (S)-(3-Methyl-1-oxo-1-(piperidin-1-yl)butan-2-yl)carbamate (Boc-l-Val-Pip, 11h)

Yield: 78%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.37 (d, J=7.5 Hz, 1 H), 4.42 (t, J=7.5 Hz, 1 H), 3.54–3.41 (m, 4 H), 1.89–1.84 (m, 1 H), 1.60–1.45 (m, 6 H), 1.37 (s, 9 H), 0.90 (d, J=6.7 Hz, 3 H), 0.81 (d, J=6.7 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 170.8, 155.9, 79.4, 66.9, 66.7, 54.6, 46.3, 42.4, 31.4. 28.3, 19.6, 17.3.

HRMS (ESI): m/z[M + H]+ calcd for C15H28N2O3: 284.2105; found: 284.2100.


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tert-Butyl ((2S,3S)-3-Methyl-1-oxo-1-(piperidin-1-yl)pentan-2-yl)carbamate (Boc-l-Ile-Pip, 11i)

Yield: 79%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.33 (d, J=7.9 Hz, 1 H), 4.50 (t, J=7.9 Hz, 1 H), 3.59–3.49 (m, 4 H), 3.20–3.17 (m, 1 H), 1.70–1.53 (m, 8 H), 1.43 (s, 9 H), 0.93 (d, J=5.8 Hz, 3 H), 0.88 (t, J=7.5 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 170.7, 156.1, 79.5, 54.4, 47.1, 43.3, 38.5, 28.6, 26.8, 25.8, 24.7, 24.0, 16.2, 11.7.

HRMS (ESI): m/z[M + H]+ calcd for C16H30N2O3: 298.2260; found: 298.2258.


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tert-Butyl (S)-(1-Oxo-3-phenyl-1-(piperidin-1-yl)propan-2-yl)carbamate (Boc-l-Phe-Pip, 11j)

Yield: 81%; colorless microcrystals; mp 122–124 °C.

1H NMR (500 MHz, CDCl3): δ = 7.30–7.20 (m, 5 H), 5.48 (d, J=8.5 Hz, 1 H), 4.89–4.85 (m, 1 H), 3.52–3.48 (m, 2 H), 3.28–3.23 (m, 1 H), 3.06–2.97 (m, 3 H), 1.51–1.42 (m, 15 H).

13C NMR (125 MHz, CDCl3): δ = 169.9, 155.2, 136.8, 129.8, 128.6, 127.0, 79.7, 51.1, 46.7, 43.2, 40.5, 28.5, 26.1, 25.5, 24.5.

HRMS (ESI): m/z[M + H]+ calcd for C19H28N2O3: 332.2100; found: 332.2104.


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tert-Butyl (2-(4-Methylpiperazin-1-yl)-2-oxoethyl)carbamate (Boc-Gly-NMP, 11k)

Yield: 76%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.54 (br s, 1 H), 3.95 (d, J=4 Hz, 2 H), 3.64 (t, J=4.7 Hz, 2 H), 3.40 (t, J=4.7 Hz, 2 H), 2.41–2.38 (m, 4 H), 1.45 (s, 9 H).

13C NMR (125 MHz, CDCl3): δ = 169.7, 164.4, 79.4, 54.7, 54.5, 45.9, 44.2, 42.2, 41.9, 28.4.

HRMS (ESI): m/z[M + H]+ calcd for C12H23N3O3: 257.1739; found: 257.1740.


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tert-Butyl (S)-(1-(4-Methylpiperazin-1-yl)-1-oxopropan-2-yl)carbamate (Boc-l-Ala-NMP, 11l)

Yield: 81%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.53 (d, J=7.6 Hz,1 H), 4.55–4.50 (m, 1 H), 3.63–3.40 (m, 4 H), 2.35–2.30 (m, 4 H), 2.23 (s, 3 H), 1.36 (s, 9 H), 1.22 (d, J=6.9 Hz, 1 H).

13C NMR (125 MHz, CDCl3): δ = 171.2, 155.2, 79.6, 55.1, 54.7, 46.2, 46.0, 45.4, 42.0, 28.5, 19.5.

HRMS (ESI): m/z[M + H]+ calcd for C13H25N3O3: 271.1896; found: 271.1899.


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tert-Butyl (S)-(3-Methyl-1-(4-methylpiperazin-1-yl)-1-oxobutan-2-yl)carbamate (Boc-l-Val-NMP, 11m)

Yield: 84%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.34 (d, J=7.2 Hz, 1 H), 4.30 (d, J=7.2 Hz, 1 H), 3.53–3.39 (m, 4 H), 2.27–2.22 (m, 4 H), 2.15 (s, 3 H), 1.82–1.76 (m, 1 H), 1.29 (s, 9 H), 0.81 (d, J=6.7 Hz, 3 H), 0.74 (d, J=6.7 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 170.4, 155.8, 79.3, 55.2, 54.7, 45.9, 45.6, 41.9, 31.5, 28.3, 19.7, 17.1.

HRMS (ESI): m/z[M + H]+ calcd for C15H29N3O3: 299.2211; found: 299.2208.


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tert-Butyl ((2S,3S)-3-Methyl-1-(4-methylpiperazin-1-yl)-1-oxopentan-2-yl)carbamate (Boc-l-Ile-NMP, 11n)

Yield: 69%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.26 (d, J=8.2 Hz, 1 H), 4.41 (t, J=8.2 Hz, 1 H), 3.66–3.46 (m, 4 H), 2.35–2.32 (m, 4 H), 2.24 (s, 3 H), 2.15–2.10 (m, 1 H), 1.65–1.60 (m, 1 H), 1.49–1.45 (m, 1 H), 1.29 (s, 9 H), 0.91–0.80 (m, 6 H).

13C NMR (125 MHz, CDCl3): δ = 170.9, 156.0, 79.6, 55.4, 54.9, 54.3, 46.1, 45.9, 42.1, 38.4, 28.5, 24.1, 16.1, 11.6.

HRMS (ESI): m/z[M + H]+ calcd for C16H31N3O3: 313.2365; found: 313.2366.


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tert-Butyl (S)-(1-(4-Methylpiperazin-1-yl)-1-oxo-3-phenylpropan-2-yl)carbamate (Boc-l-Phe-NMP, 11o)

Yield: 83%; white microcrystals; mp 111–113 °C.

1H NMR (500 MHz, CDCl3): δ = 7.29–7.18 (m, 5 H), 5.45 (d, J=8.2 Hz, 1 H), 4.85–4.80 (m, 1 H), 3.60–3.52 (m, 2 H), 3.34–3.28 (m, 1 H), 2.99–2.92 (m, 3 H), 2.33–2.17 (m, 7 H), 1.42 (m, 9 H).

13C NMR (125 MHz, CDCl3): δ = 170.2, 155.2, 136.6, 129.8, 128.7, 127.2, 79.9, 54.7, 54.5, 51.1, 46.0, 45.6, 42.0, 40.7, 28.6.

HRMS (ESI): m/z[M + H]+ calcd for C19H29N3O3: 347.2211; found: 347.2220.


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tert-Butyl (2-Oxo-2-(pyrrolidin-1-yl)ethyl)carbamate (Boc-Gly-Pyr, 11p)

Yield: 89%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.38 (br s, 1 H), 4.07 (d, J=4.3 Hz, 2 H), 3.56–3.38 (m, 4 H), 2.03–1.84 (m, 4 H).

13C NMR (125 MHz, CDCl3): δ = 168.3, 163.1, 79.6, 46.9, 46.3, 43.1, 28.5, 26.3, 24.5.

HRMS (ESI): m/z[M + H]+ calcd for C11H20N2O3: 228.1475; found: 228.1477.


#

tert-Butyl (S)-(1-Oxo-1-(pyrrolidin-1-yl)propan-2-yl)carbamate (Boc-l-Ala-Pyr, 11q)

Yield: 83%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.48 (br s, 1 H), 4.47–4.42 (m, 1 H), 3.63–3.40 (m, 4 H), 1.99–1.86 (m, 4 H), 1.43 (s, 9 H), 1.31 (d, J=6.7 Hz, 1 H).

13C NMR (125 MHz, CDCl3): δ = 171.4, 155.3, 79.6, 48.0, 46.5, 46.1, 28.6, 26.2, 24.3, 18.9.

HRMS (ESI): m/z[M + H]+ calcd for C12H22N2O3: 242.1630; found: 242.1637.


#

tert-Butyl (S)-(3-Methyl-1-oxo-1-(pyrrolidin-1-yl)butan-2-yl)carbamate (Boc-l-Val-Pyr, 11r)

Yield: 67%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.26 (d, J=7.8 Hz, 1 H), 4.15 (t, J=7.8 Hz, 1 H), 3.60–3.30 (m, 4 H), 1.87–1.75 (m, 5 H), 1.37 (s, 9 H), 0.86 (d, J=6.7 Hz, 3 H), 0.83 (d, J=6.7 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 170.7, 155.8, 79.2, 57.0, 46.6, 45.7, 31.3, 28.3, 26.0, 24.1, 19.5, 17.5.

HRMS (ESI): m/z[M + H]+ calcd for C14H26N2O3: 270.1945; found: 270.1946.


#

tert-Butyl ((2S,3S)-3-Methyl-1-oxo-1-(pyrrolidin-1-yl)pentan-2-yl)carbamate (Boc-l-Ile-Pyr, 11s)

Yield: 72%; oil.

1H NMR (500 MHz, CDCl3): δ = 5.23 (d, J=8.5 Hz, 1 H), 4.27 (t, J=8.5 Hz, 1 H), 3.74–3.69 (m, 1 H), 3.56–3.20 (m, 4 H), 1.67–1.86 (m, 4 H), 1.73–1.55 (m, 2 H), 1.43 (s, 9 H), 0.93–0.86 (m, 6 H).

13C NMR (125 MHz, CDCl3): δ = 171.2, 156.0, 79.6, 56.6, 48.1, 46.9, 46.0, 38.2, 28.6, 26.2, 24.4, 15.8, 11.5.

HRMS (ESI): m/z[M + H]+ calcd for C15H28N2O3: 284.2101; found: 284.2111.


#

tert-Butyl (S)-(1-Oxo-3-phenyl-1-(pyrrolidin-1-yl)propan-2-yl)carbamate (Boc-l-Phe-Pyr, 11t)

Yield: 78%; colorless microcrystals; mp 126–128 °C.

1H NMR (500 MHz, CDCl3): δ = 7.29–7.22 (m, 5 H), 5.43 (d, J=7.8 Hz, 1 H), 4.63–4.58 (m, 1 H), 3.48–3.33 (m, 3 H), 3.28–3.23 (m, 1 H), 3.01–2.94 (m, 2 H), 2.63–2.57 (m, 1 H), 1.82–1.56 (m, 4 H), 1.44 (m, 9 H).

13C NMR (125 MHz, CDCl3): δ = 170.1, 155.3, 136.8, 129.7, 128.5, 127.0, 79.8, 53.8, 46.4, 45.9, 40.5, 28.6, 26.0, 24.2.

HRMS (ESI): m/z[M + H]+ calcd for C18H26N2O3: 318.1944; found: 318.1943.


#

Synthesis of Bisconjugates 5a–t; General Procedure

The secondary amine–amino acid conjugate was stirred in 4 M HCl–dioxane solution for 1 h. The dioxane was evaporated under reduced pressure and the residue was treated with diethyl ether. The resulting solid was treated without further purification with the benzotriazole derivative of pyrazinoic acid in the presence of triethylamine (1.5 equiv) in acetonitrile (10 mL). The reaction mixture was stirred at 20 °C for 4–6 h, monitoring by TLC. Upon completion of reaction, the acetonitrile was evaporated and the residue was extracted with EtOAc. The organic layer was washed with aqueous sodium carbonate and dried over anhydrous sodium sulfate. After filtration, the EtOAc was evaporated under reduced pressure to obtain the desired conjugates in good yields.


#

N-(2-Morpholino-2-oxoethyl)pyrazine-2-carboxamide (POA-Gly-Mor, 5a)

Yield: 75%; colorless microcrystals; mp 180–181 °C.

1H NMR (500 MHz, CDCl3): δ = 9.32 (s, 1 H), 8.70 (br s, 1 H), 8.65 (br s, 1 H), 8.53 (br s, 1 H), 4.23 (d, J=4.3 Hz, 2 H), 3.68–3.63 (m, 6 H), 3.46–3.44 (m, 2 H).

13C NMR (125 MHz, CDCl3): δ = 166.4, 163.3, 147.5, 144.3, 143.1, 66.8, 66.5, 45.1, 42.5. 41.2.

HRMS (ESI): m/z[M + H]+ calcd for C11H14N4O3: 250.1068; found: 250.1074.


#

(S)-N-(1-Morpholino-1-oxopropan-2-yl)pyrazine-2-carboxamide (POA-l-Ala-Mor, 5b)

Yield: 68%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.34 (s, 1 H), 8.74–8.70 (m, 2 H), 8.50 (br s, 1 H), 5.13–5.08 (m, 1 H), 3.69–3.53 (m, 8 H), 1.45 (d, J=6.9 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 170.8, 162.6, 147.5, 144.3, 143.0, 66.9, 66.7, 46.2, 45.4, 42.8, 19.0.

HRMS (ESI): m/z[M + H]+ calcd for C12H16N4O3: 264.1221; found: 264.1225.


#

(S)-N-(1-Morpholino-1-oxopropan-2-yl)pyrazine-2-carboxamide (POA-dl-Ala-Mor, 5b′)

Yield: 72%; gum.

1H NMR (500 MHz, CDCl3): δ = 9.33 (s, 1 H), 8.74–8.68 (m, 2 H), 8.50 (br s, 1 H), 5.16–5.07 (m, 1 H), 3.69–3.55 (m, 8 H), 1.44 (d, J=6.9 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 170.8, 162.4, 147.5, 145.0, 143.1, 66.9, 66.7, 46.2, 45.5, 42.7, 19.0.

HRMS (ESI): m/z[M + H]+ calcd for C12H16N4O3: 264.1221; found: 264.1222.


#

(S)-N-(3-Methyl-1-morpholino-1-oxobutan-2-yl)pyrazine-2-carboxamide (POA-l-Val-Mor, 5c)

Yield: 76%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.37 (s, 1 H), 8.76 (br s, 1 H), 8.58 (br s, 1 H), 8.50 (d, J=8.7 Hz, 1 H), 5.00–4.97 (m, 1 H), 3.77–3.60 (m, 8 H),2.19–2.13 (m, 1 H), 1.05 (d, J=6.6 Hz, 3 H), 1.00 (d, J=6.6 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 169.8, 163.0, 147.3¸ 144.3, 142.7, 66.7, 66.6, 53.2, 46.3, 42.4, 31.7, 19.7, 17.5.

HRMS (ESI): m/z[M + H]+ calcd for C14H20N4O3: 292.1535; found: 292.1534.


#

N-((2S,3S)-3-Methyl-1-morpholino-1-oxopentan-2-yl)pyrazine-2-carboxamide (POA-l-Ile-Mor, 5d)

Yield: 70%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.37 (s, 1 H), 8.76 (br s, 1 H), 8.57 (br s, 1 H), 8.46 (d, J=7.9 Hz, 1 H), 5.02 (t, J=7.9 H, 1 H), 3.76–3.52 (m, 8 H), 1.94–1.93 (m, 1 H), 1.64–1.59 (m, 1 H), 1.23–1.16 (m, 1 H), 1.02–0.91 (m, 6 H).

13C NMR (125 MHz, CDCl3): δ = 170.3, 163.0, 147.5, 144.5, 142.9, 67.0, 66.9, 52.8, 46.7, 42.7, 38.4, 24.4, 16.1, 11.4.

HRMS (ESI): m/z[M + H]+ calcd for C15H22N4O3: 306.1694; found: 306.1692.


#

(S)-N-(1-Morpholino-1-oxo-3-phenylpropan-2-yl)pyrazine-2-carboxamide (POA-l-Phe-Mor, 5e)

Yield: 78%; gum.

1H NMR (500 MHz, CDCl3): δ = 9.36 (s, 1 H), 8.75 (br s, 1 H), 8.59–856 (m, 2 H), 7.33–7.26 (m, 5 H), 5.35–5.30 (m, 1 H), 3.61–3.32 (m, 6 H), 3.20–3.09 (m, 2 H), 3.00–2.89 (m, 2 H).

13C NMR (125 MHz, CDCl3): δ = 169.7, 162.6, 147.6, 144.5, 143.0, 136.2, 129.8, 128.9, 127.6, 66.7, 66.2, 49.8, 46.3, 42.5, 40.4.

HRMS (ESI): m/z[M + H]+ calcd for C18H20N4O3: 340.1536; found: 340.1535.


#

N-(2-Oxo-2-(piperidin-1-yl)ethyl)pyrazine-2-carboxamide (POA-Gly-Pip, 5f)

Yield: 74%; colorless microcrystals; mp 123–125 °C.

1H NMR (500 MHz, CDCl3): δ = 9.38 (s, 1 H), 8.77–8.74 (m, 2 H), 8.58 (br s, 1 H), 4.27 (d, J=4.3 Hz, 2 H), 3.63 (t, J=5.2 Hz, 2 H), 3.41 (t, J=5.2 Hz, 2 H), 1.69–1.59 (m, 6 H).

13C NMR (125 MHz, CDCl3): δ = 165.8, 163.3, 147.5, 144.4, 143.1, 45.8, 43.4, 41.4, 41.4, 26.4, 25.6, 24.6.

HRMS (ESI): m/z[M + H]+ calcd for C12H16N4O2: 248.1273; found: 248.1275.


#

(S)-N-(1-Oxo-1-(piperidin-1-yl)propan-2-yl)pyrazine-2-carboxamide (POA-l-Ala-Pip, 5g)

Yield: 75%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.28 (s, 1 H), 8.74 (d, J=7.2 Hz, 1 H), 8.66 (br s, 1 H), 8.50 (br s, 1 H), 5.04–4.98 (m, 1 H), 3.61–3.38 (m, 4 H), 1.61–1.45 (m, 6 H), 1.37 (d, J=6.9 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 169.9, 162.1, 147.2, 144.1, 142.8, 46.5, 45.3, 43.3, 26.4, 25.5, 24.4, 19.0.

HRMS (ESI): m/z[M + H]+ calcd for C13H18N4O2: 262.1429; found: 262.1431.


#

(S)-N-(3-Methyl-1-oxo-1-(piperidin-1-yl)butan-2-yl)pyrazine-2-carboxamide (POA-l-Val-Pip, 5h)

Yield: 81%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.31 (s, 1 H), 8.68 (br s, 1 H), 8.52–8.49 (m, 2 H), 5.00–4.97 (m, 1 H), 3.59–3.51 (m, 4 H), 2.12–2.05 (m, 1 H), 1.61–150 (m, 6 H), 0.98 (d, J=6.6 Hz, 3 H), 0.91 (d, J=6.6 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 169.5, 163.0, 147.3, 144.5, 142.9, 53.5, 47.1, 43.4, 32.1, 26.7, 25.7, 24.6, 20.0, 17.5.

HRMS (ESI): m/z[M + H]+ calcd for C15H22N4O2: 290.1742; found: 290.1749.


#

N-((2S,3S)-3-Methyl-1-oxo-1-(piperidin-1-yl)pentan-2-yl)pyrazine-2-carboxamide (POA-l-Ile-Pip, 5i)

Yield: 64%; gum.

1H NMR (500 MHz, CDCl3): δ = 9.32 (s, 1 H), 8.73 (br s, 1 H), 8.52 (br s, 1 H), 8.43 (d, J=7.9 Hz, 1 H), 5.04 (t, J=7.9 H, 1 H), 3.54–3.49 (m, 4 H),1.87–1.85 (m, 1 H), 1.15–1.08 (m, 8 H), 0.92 (d, J=7.3 Hz, 1 H), 0.79 (d, J=7.3 Hz, 1 H).

13C NMR (125 MHz, CDCl3): δ = 170.6, 163.3, 147.5, 144.7, 142.6, 53.2, 47.3, 43.6, 38.4, 26.5, 25.6, 24.3, 24.0, 16.0, 11.4.

HRMS (ESI): m/z[M + H]+ calcd for C16H24N4O2: 304.1896; found: 304.1899.


#

(S)-N-(1-Oxo-3-phenyl-1-(piperidin-1-yl)propan-2-yl)pyrazine-2-carboxamide (POA-l-Phe-Pip, 5j)

Yield: 79%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.35 (s, 1 H), 8.73 (br s, 1 H), 8.62–8.56 (m, 2 H), 7.34–7.24 (m, 5 H), 5.40–5.35 (m, 1 H), 3.57–3.47 (m, 4 H), 2.94–2.78 (m, 2 H), 1.54–1.43 (m, 6 H).

13C NMR (125 MHz, CDCl3): δ = 169.1, 162.4, 147.4, 144.4, 142.9, 138.0, 129.5, 128.6, 127.2, 52.5, 49.9, 46.3, 43.2, 26.2, 25.6, 24.4.

HRMS (ESI): m/z[M + H]+ calcd for C19H22N4O2: 338.1743; found: 338.1746.


#

N-(2-(4-Methylpiperazin-1-yl)-2-oxoethyl)pyrazine-2-carboxamide (POA-Gly-NMP, 5k)

Yield: 69%; gum.

1H NMR (500 MHz, CDCl3): δ = 9.34 (s, 1 H), 8.71 (br s, 1 H), 8.68 (br s, 1 H), 8.54 (br s, 1 H), 4.26 (d, J=4.3 Hz, 2 H), 3.75–3.60 (m, 4 H), 2.42–2.35 (m, 4 H), 2.31 (s, 3 H).

13C NMR (125 MHz, CDCl3): δ = 169.4, 163.3, 147.8, 144.5, 143.4, 55.3, 54.8, 46.4, 46.1, 45.9, 40.8.

HRMS (ESI): m/z[M + H]+ calcd for C12H17N5O2: 263.1385; found: 263.1386.


#

(S)-N-(1-(4-Methylpiperazin-1-yl)-1-oxopropan-2-yl)pyrazine-2-carboxamide (POA-l-Ala-NMP, 5l)

Yield: 73%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.32 (s, 1 H), 8.72–8.70 (m, 2 H), 8.53 (br s, 1 H), 5.07–5.04 (m, 1 H), 3.72–3.51 (m, 4 H), 2.44–2.34 (m, 4 H), 2.27 (s, 3 H), 1.42 (d, J=6.7 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 170.3, 162.3, 147.4, 144.3, 142.9, 55.1, 54.6, 46.0, 45.4, 45.3, 42.2, 19.1.

HRMS (ESI): m/z[M + H]+ calcd for C13H19N5O2: 277.1536; found: 277.1541.


#

(S)-N-(3-Methyl-1-(4-methylpiperazin-1-yl)-1-oxobutan-2-yl)pyrazine-2-carboxamide (POA-l-Val-NMP, 5m)

Yield: 62%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.37 (s, 1 H), 8.75 (br s, 1 H), 8.57 (br s, 1 H), 8.52 (d, J=8.9 Hz, 1 H), 5.03–5.00 (m, 1 H), 3.76–3.61 (m, 4 H), 2.46–2.38 (m, 4 H), 2.31 (s, 3 H), 2.17–2.13 (m, 1 H), 1.04 (d, J=6.7 Hz, 3 H), 0.98 (d, J=6.7 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 169.8, 163.3, 147.5, 144.4, 143.0, 55.4, 54.9, 53.6, 46.2, 46.0, 42.3, 32.1, 20.1, 17.7.

HRMS (ESI): m/z[M + H]+ calcd for C15H23N5O2: 305.1852; found: 305.1860.


#

N-((2S,3S)-3-Methyl-1-(4-methylpiperazin-1-yl)-1-oxopentan-2-yl)pyrazine-2-carboxamide (POA-l-Ile-NMP, 5n)

Yield: 64%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.32 (s, 1 H), 8.70 (br s, 1 H), 8.52 (br s, 1 H), 8.45 (d, J=7.8 Hz, 1 H), 5.01 (t, J=7.8 H, 1 H), 3.72–3.60 (m, 4 H), 2.42–2.36 (m, 4 H), 2.27 (s, 3 H), 1.89–1.88 (m, 1 H), 1.57–1.53 (m, 1 H), 1.18–1.13 (m, 1 H), 0.98–0.86 (m, 6 H).

13C NMR (125 MHz, CDCl3): δ = 169.9, 162.9, 147.4, 144.4, 142.9, 55.3, 54.7, 52.9, 46.0, 42.2, 38.4, 24.3, 16.1, 11.4.

HRMS (ESI): m/z[M + H]+ calcd for C16H25N5O2: 319.2005; found: 319.2000.


#

(S)-N-(1-(4-Methylpiperazin-1-yl)-1-oxo-3-phenylpropan-2-yl)pyrazine-2-carboxamide (POA-l-Phe-NMP, 5o)

Yield: 71%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.34 (s, 1 H), 8.73 (br s, 1 H), 8.58–854 (m, 2 H), 7.30–7.19 (m, 5 H), 5.30–5.24 (m, 1 H), 3.72–3.61 (m, 4 H), 3.20–3.09 (m, 2 H), 2.47–2.38 (m, 4 H), 2.24 (s, 3 H).

13C NMR (125 MHz, CDCl3): δ = 170.1, 162.8, 147.5, 144.7, 143.2, 136.5, 129.3, 128.7, 127.2, 55.3, 54.7, 53.5, 46.5, 46.2, 42.6, 40.8.

HRMS (ESI): m/z[M + H]+ calcd for C19H23N5O2: 353.1853; found: 353.1850.


#

N-(2-Oxo-2-(pyrrolidin-1-yl)ethyl)pyrazine-2-carboxamide (POA-Gly-Pyr, 5p)

Yield: 81%; colorless microcrystals; mp 148–150 °C.

1H NMR (500 MHz, CDCl3): δ = 9.31 (s, 1 H), 8.68–8.64 (m, 2 H), 8.52 (br s, 1 H), 4.15 (d, J=4.3 Hz, 2 H), 3.50–3.40 (m, 4 H), 2.00–1.78 (m, 4 H).

13C NMR (125 MHz, CDCl3): δ = 166.1, 163.3, 147.4, 144.3, 143.0, 68.1, 46.2, 45.7, 42.1, 26.1, 24.3.

HRMS (ESI): m/z[M + H]+ calcd for C11H14N4O2: 234.1117; found: 234.1121.


#

(S)-N-(1-Oxo-1-(pyrrolidin-1-yl)propan-2-yl)pyrazine-2-carboxamide (POA-l-Ala-Pyr, 5q)

Yield: 79%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.29 (s, 1 H), 8.67 (br s, 1 H), 8.59 (br s, 1 H), 8.49 (br s, 1 H), 4.89–4.85 (m, 1 H), 3.64–3.40 (m, 4 H), 1.97–1.82 (m, 4 H), 1.41 (d, J=6.4 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 170.4, 162.4, 147.3, 144.3, 142.9, 47.0, 46.6, 46.2, 26.2, 24.2, 18.4.

HRMS (ESI): m/z[M + H]+ calcd for C12H16N4O2: 248.1271; found: 248.1279.


#

(S)-N-(3-Methyl-1-oxo-1-(pyrrolidin-1-yl)butan-2-yl)pyrazine-2-carboxamide (POA-l-Val-Pyr, 5r)

Yield: 82%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.32 (s, 1 H), 8.69 (br s, 1 H), 8.52 (br s, 1 H), 8.38 (d, J=8.2 Hz, 1 H), 4.74 (t, J=8.2 Hz, 1 H), 3.77–3.39 (m, 4 H), 2.18–2.11 (m, 1 H), 1.98–1.82 (m, 4 H), 1.00 (d, J=6.6 Hz, 3 H), 0.97 (d, J=6.6 Hz, 3 H).

13C NMR (125 MHz, CDCl3): δ = 169.9, 163.0, 147.4, 144.5, 142.9, 56.1, 47.0, 46.1, 31.8, 26.2, 24.4, 19.8, 18.1.

HRMS (ESI): m/z[M + H]+ calcd for C14H20N4O2: 276.1586; found: 276.1582.


#

N-((2S,3S)-3-Methyl-1-oxo-1-(pyrrolidin-1-yl)pentan-2-yl)pyrazine-2-carboxamide (POA-l-Ile-Pyr, 5s)

Yield: 74%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.34 (s, 1 H), 8.68 (br s, 1 H), 8.57 (br s, 1 H), 8.49 (d, J=7.8 Hz, 1 H), 5.04 (t, J=7.8 H, 1 H), 3.66–3.42 (m, 4 H), 2.01–1.88 (m, 5 H), 1.62–1.58 (m, 1 H), 1.17–1.12 (m, 1 H), 1.01–0.89 (m, 6 H).

13C NMR (125 MHz, CDCl3): δ = 170.3, 163.1, 147.6, 144.2, 142.5, 52.9, 45.7, 42.6, 38.1, 25.0, 24.8, 24.5, 16.2, 11.7.

HRMS (ESI): m/z[M + H]+ calcd for C15H22N4O2: 290.1743; found: 290.1746.


#

(S)-N-(1-Oxo-3-phenyl-1-(pyrrolidin-1-yl)propan-2-yl)pyrazine-2-carboxamide (POA-l-Phe-Pyr, 5t)

Yield: 73%; oil.

1H NMR (500 MHz, CDCl3): δ = 9.33 (s, 1 H), 8.73 (br s, 1 H), 8.59–855 (m, 2 H), 7.35–7.23 (m, 5 H), 5.14–5.09 (m, 1 H), 3.75–3.34 (m, 4 H), 3.03–2.93 (m, 2 H), 2.03–1.72 (m, 4 H).

13C NMR (125 MHz, CDCl3): δ = 169.0, 162.3, 147.3, 144.2, 142.8, 136.2, 129.2, 128.3, 126.6, 52.5, 45.9, 45.8, 39.7, 24.0, 23.8.

HRMS (ESI): m/z[M + H]+ calcd for C18H20N4O2: 324.1588; found: 324.1585.


#
#

Acknowledgment

We thank the Augusta University and Pamplin Student Research & Travel Fund for financial support.

Supporting Information

  • References

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  • 4 World Health Organization. Global Tuberculosis, Report 2013. WHO/HTM/TB/ 2013, 11.
  • 5 Goletti D. Weissman D. Jackson RW. Graham NM. Vlahov D. Klein RS. Munsiff SS. L’Ortona L. Cauda R. Fauci AS. J. Immunol. 1996; 157: 1271
  • 6 Ma Z. Ginsberg AM. Spigelman M. Antimycobacterium agents, In Comprehensive Medicinal Chemistry II . Taylor JB. Triggle DJ. Elsevier; Oxford; 2006. Vol. 7, 699
  • 7 Kremer L. Besra GS. Expert Opin. Invest. Drugs 2002; 11: 1033
  • 8 World Health Organization (WHO), WHO Report 2010: Global Tuberculosis Control, 2010.
  • 9 Zhang Y. Mitchison D. Int. J. Tuberc. Lung Dis. 2003; 7: 6
  • 10 Van den Boogaard J. Kibiki GS. Kisanga ER. Boeree MJ. Aarnoutse RE. Antimicrob. Agents Chemother. 2009; 53: 849
  • 11 Reddy VM. Nadadhur G. Daneluzzi D. Dimova V. Gangadharam PR. Antimicrob. Agents Chemother. 1995; 39: 2320
  • 12 Chitre TS. Asgaonkar KD. Miniyar PB. Dharme AB. Arkile MA. Yeware A. Sarkar D. Khedkar VM. Jha PC. Bioorg. Med. Chem. Lett. 2016; 26: 2224
  • 13 Jardosh HH. Patel MP. Eur. J. Med. Chem. 2013; 65: 348
  • 14 Saha R. Alam MM. Akhter M. RSC Adv. 2015; 5: 12807
  • 15 Simoes MF. Valente E. Gomez MJ. R. Anes E. Constantino L. Eur. J. Pharm. Sci. 2009; 37: 257
  • 16 Mohamed T. Zhao X. Habib LK. Yang J. Rao PP. N. Bioorg. Med. Chem. 2011; 19: 2269
  • 17 Panda SS. Bajaj K. Meyers MJ. Sverdrup FM. Katritzky AR. Org. Biomol. Chem. 2012; 10: 8985
  • 18 Ibrahim MA. Panda SS. Birs AS. Serrano JC. Gonzalez CF. Alamry KA. Katritzky AR. Bioorg. Med. Chem. Lett. 2014; 24: 1856
  • 19 Panda SS. Naumov RN. Asiri AM. Katritzky AR. Synthesis 2014; 46: 1511
  • 20 Panda SS. Liaqat S. Girgis AS. Samir A. Hall CD. Katritzky AR. Bioorg. Med. Chem. Lett. 2015; 25: 3816
  • 21 Panda SS. Detistov OS. Girgis AS. Mohapatra PP. Samir A. Katritzky AR. Bioorg. Med. Chem. Lett. 2016; 26: 2198
  • 22 Panda SS. Hall CD. Scriven E. Katritzky AR. Aldrichimica Acta 2013; 46: 43

  • References

  • 1 Mitchison DA. Tubercle 1985; 66: 219
  • 2 Joshi RR. Barchha A. Khedkar VM. Pissurlenkar RR. S. Sarkar S. Sarkar D. Joshi RR. Joshi RA. Shah AK. Coutinho EC. Chem. Biol. Drug Des. 2015; 85: 201
  • 3 Rivers EC. R. Mancera L. Drug Discovery Today 2008; 13: 1090
  • 4 World Health Organization. Global Tuberculosis, Report 2013. WHO/HTM/TB/ 2013, 11.
  • 5 Goletti D. Weissman D. Jackson RW. Graham NM. Vlahov D. Klein RS. Munsiff SS. L’Ortona L. Cauda R. Fauci AS. J. Immunol. 1996; 157: 1271
  • 6 Ma Z. Ginsberg AM. Spigelman M. Antimycobacterium agents, In Comprehensive Medicinal Chemistry II . Taylor JB. Triggle DJ. Elsevier; Oxford; 2006. Vol. 7, 699
  • 7 Kremer L. Besra GS. Expert Opin. Invest. Drugs 2002; 11: 1033
  • 8 World Health Organization (WHO), WHO Report 2010: Global Tuberculosis Control, 2010.
  • 9 Zhang Y. Mitchison D. Int. J. Tuberc. Lung Dis. 2003; 7: 6
  • 10 Van den Boogaard J. Kibiki GS. Kisanga ER. Boeree MJ. Aarnoutse RE. Antimicrob. Agents Chemother. 2009; 53: 849
  • 11 Reddy VM. Nadadhur G. Daneluzzi D. Dimova V. Gangadharam PR. Antimicrob. Agents Chemother. 1995; 39: 2320
  • 12 Chitre TS. Asgaonkar KD. Miniyar PB. Dharme AB. Arkile MA. Yeware A. Sarkar D. Khedkar VM. Jha PC. Bioorg. Med. Chem. Lett. 2016; 26: 2224
  • 13 Jardosh HH. Patel MP. Eur. J. Med. Chem. 2013; 65: 348
  • 14 Saha R. Alam MM. Akhter M. RSC Adv. 2015; 5: 12807
  • 15 Simoes MF. Valente E. Gomez MJ. R. Anes E. Constantino L. Eur. J. Pharm. Sci. 2009; 37: 257
  • 16 Mohamed T. Zhao X. Habib LK. Yang J. Rao PP. N. Bioorg. Med. Chem. 2011; 19: 2269
  • 17 Panda SS. Bajaj K. Meyers MJ. Sverdrup FM. Katritzky AR. Org. Biomol. Chem. 2012; 10: 8985
  • 18 Ibrahim MA. Panda SS. Birs AS. Serrano JC. Gonzalez CF. Alamry KA. Katritzky AR. Bioorg. Med. Chem. Lett. 2014; 24: 1856
  • 19 Panda SS. Naumov RN. Asiri AM. Katritzky AR. Synthesis 2014; 46: 1511
  • 20 Panda SS. Liaqat S. Girgis AS. Samir A. Hall CD. Katritzky AR. Bioorg. Med. Chem. Lett. 2015; 25: 3816
  • 21 Panda SS. Detistov OS. Girgis AS. Mohapatra PP. Samir A. Katritzky AR. Bioorg. Med. Chem. Lett. 2016; 26: 2198
  • 22 Panda SS. Hall CD. Scriven E. Katritzky AR. Aldrichimica Acta 2013; 46: 43

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Figure 1 Current antituberculosis drugs
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Scheme 1 PZA is converted into POA in the presence of PZAase
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Scheme 2 Synthesis of POA hybrid conjugates with secondary heterocyclic amines and amino acid (Route I)
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Scheme 3 Synthesis of Boc-protected amino acid–secondary heterocyclic amine conjugates
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Figure 2 ORTEP diagram of POA-Gly-Mor (5a)
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Scheme 4 Synthesis of POA hybrid conjugates with secondary heterocyclic amines and amino acid (Route II)