A new class of dihaloquinolones bearing N'-aldehydoglycosylhydrazides, mercapto-1,2,4-triazole, oxadiazoline and a-amino ester precursors: synthesis and antimicrobial activity

ARTICLE

A new class of dihaloquinolones bearing N'-aldehydoglycosylhydrazides, mercapto-1,2,4-triazole, oxadiazoline and a-amino ester precursors: synthesis and antimicrobial activity

Yaseen A. Al-Soud^I; Najim A. Al-MasoudiII, ^*

^IDepartment of Chemistry, College of Science, University of Al al-Bayt, Al-Mafraq, Jordan

^IIFachbereich Chemie, Universität Konstanz, Postfach 5560, D-78457 Konstanz, Germany

ABSTRACT

Reaction of the quinolones 6-8 with hydrazine afforded the hydrazide 9-11 in moderate yields. Condensation of 9 and 11 with CS₂ /KOH furnished the potassium salts 13 and 14, respectively, which spontaneously afforded the 3-(1,2,4-triazolyl)-quinolones 15 and 16, respectively, on treatment with hydrazine. Reaction of 9 in refluxing CS₂ /KOH gave the 3-(1,2,4-oxadiazolyl)-quinolone 17. Alternatively, 15 was prepared from 17. The azide derivative 12, obtained from 10, furnished the a-amino ester derivative 18, on reaction with the glycine ethyl ester. Coupling of 10 with various sugars gave the N'-aldehydoglycosyl-quinolone-3-yl)carbohydrazides 19a-e. The newly synthesized compounds were screened for their antibacterial activity.

Keywords: antimicrobial activity, hydrazides, quinolones

RESUMO

A reação das quinolonas 6-8 com hidrazina forneceu as hidrazidas 9-11 em rendimentos moderados. A condensação de 9 e 11 com CS₂/KOH rendeu os sais de potássio 13 e 14, respectivamente, que espontaneamente forneceram as 3-(1,2,4-triazolil)-quinolonas 15 e 16, respectivamente, quando tratadas com hidrazina. A reação de 9 com CS₂/KOH sob refluxo resultou na 3-(1,2,4-oxadiazolil)-quinolona 17. Alternativamente, 15 foi preparado a partir de 17. O derivado 12, obtido a partir de 10, forneceu o derivado a-amino ester 18 mediante reação com o éster etílico da glicina. O acoplamento de 10 com vários açúcares forneceu as N'-(aldeidoglicosil-quinolona-3-il)carbohidrazidas 19a-e. Os novos compostos sintetizados foram avaliados quanto a sua atividade antibacteriana.

Introduction

The second generation of fluoroquinolones^1-3 such as norfloxacin⁴2, the modified analogue of nalidixic acid⁵1, ciprofloxacin⁶3, ofloxacin⁷4, and sparfloxacin⁸5 are known as a major class of antibacterial agents and widely used to treat patient with infections. In recent years, and due to the increasing of resistance of many infections by gram negative and gram positive bacteria to these quinolones, several studies⁹ described various modifications in the quinolone ring, for example: substitution with different groups at aromatic ring,^10-13 replacement of the same ring by thiophene moiety,^13,14 introduction of amido group^14,15 at C-3, as well as substitution at N-1 by sugar^16-19 or acyclic moieties.²⁰

Nevertheless, some quinolones cause injury to the chromosome of eukaryotic cells.^21,22 These findings prompted us to optimize the substituent at C-3, by introduction of heterocyclic, a-amino acid ester precursors or N'-aldehydoglycosylcarbohydrazide moities to evaluate the effect of these groups on the antibacterial activity. It had been reported²³ that heterocycles such as oxadiazoles, thiadiazoles and mercaptotriazoles are themselves important chemotherapeutic agents and exhibit antitubercular, bacteriostatic, hypoglycemic, antiviral, antifungal, antithyroid, carcinostatic and strong herbicidal activity. Some reported mercaptotriazole derivatives showed potent activity²⁴ more than streptomycin against Candida albicans, whereas derivatives of 5-substituted 1,2,4-oxadiazole-2-thiones are known to possess interesting pharmacodynamic property and some have exhibited remarkable activity²⁵ against Mycobacterium tuberculosis. Recently, bactericidal and/or fungicidal or antimicrobial activity was reported for oxadiazolidinethiones.²⁶ Furthermore, a number of 1,2,4-triazole derivatives are angiotensin II receptor antagonists. To the best of our knowledge, only two examples of quinolone 3-hydrazides are reported: 1-phenyl-²⁷ and 1-methyl-4-oxo-1,4-dihydroquinoline-3-carboxylic acid hydrazides.²⁸

Experimental

General procedures

Melting points are uncorrected. The ¹H-NMR and ¹³C-NMR spectra were recorded on DRX 600, VRX 200 and UNITY 300 spectrometers with tetramethylsilane as an internal standard (d scale in ppm and coupling constants in Hz). The signal assignments in the ¹H-NMR spectra were confirmed by selective proton decoupling or by COSY spectra. Heteronuclear assignments were verified by ¹H-¹³C COSY or HMQC experiments. EI and FAB mass were measured on an MAT 312 mass spectrometer using 3-nitrophenol (NBOH) or glycerol as matrix.

Preparation of 6-chloro-1-ethyl- and 6,7-dihalo-1,4-dihydro-4-oxoquinoline-3-carboxylic acid hydrazides (9-11)

To a stirred suspension of 6-8 (10 mmol) in MeOH (50 mL) was added hydrated hydrazine (2.5 g, 50 mmol) at 23 °C. After stirring with EtOH (70 mL) for 72 h, the suspension was evaporated to dryness and the residue was washed with diethyl ether (50 mL), filtered and recrystallized from EtOH to give the desired products 9-11, respectively, as yellow crystals.

6,7-Dichloro-1-ethyl-1,4-dihydro-4-oxoquinoline-3 -carboxylic acid hydrazide (9)

From 6 (3.14 g). Yield: 2.01 g (67%); mp 204-206 °C; ¹H-NMR (DMSO-d₆) d 11.64 (s,br, 3H, NH, NH₂); 8.99 (s, 1H, H-2); 8.38 (s, 1H, H-8); 8.38 (s, 1H, H-5); 4.45 (q, J 7.0 Hz, 2H, CH₂CH₃); 1.60 (t, 3H, CH₂CH₃). ¹³C-NMR (DMSO-d₆) d 175.0 (C-9); 164.8 (C-4); 149.8 (H-2); 140.4 (C-7); 137.8 (C-8a); 132.7 (C-6); 128.5 (C-5); 126.2 (4a); 118.8 (C-8); 108.8 (C-3); 50.8 (CH₂CH₃); 14.2 (CH₂CH₃); MS m/z (EI, relative abundance %) 300/302 (M^+•, 38/24).

6-Chloro-1-ethyl-7-fluoro-1,4-dihydro-4-oxoquinoline-3 -carboxylic acid hydrazide (10)

From 7 (2.98 g). Yield: 1.50 g (53%) as a yellow crystals; mp 263–264 °C; ¹H-NMR (DMSO-d₆) d 10.43 (s, 1H, NH); 8.85 (s, 1H, H-2); 8.24 (d, 1H, J_H8-F 5.5 Hz, H-8); 8.11 (d, 1H, J_H5-F 8.3 Hz, H-5); 7.20 (s, br, 2H, NH₂); 4.52 (q, 2H, J 7.1 Hz, CH₂CH₃); 1.38 (t, 3H, J 7.1 Hz, CH₂CH₃); ¹³C-NMR (DMSO-d₆) d 173.5 (C-9); 163.1 (C-4); 154.2 (d, J_C6-F 247.7 Hz, H-6); 147.6 (C-2); 135.6 (C-8a); 127.3 (d, J_C4a-F 5.5 Hz, C-4a); 125.9 (d, J_C7-F 20.4 Hz, C-7); 120.0 (C-8); 112.1 (d, J_C5-F 22.6 Hz, C-5); 110.6 (C-3); 48.6 (CH₂CH₃); 14.4 (CH₂CH₃); Anal. calc. for C₁₂H₁₁FClN₃O₂ : C, 50.81; H, 3.91; N, 14.81. Found: C, 50.70; H, 3.87; N, 14.70; MS m/z (EI, relative abundance %) 283/285 (M^+•, 50/19).

6-Chloro-1-ethyl-1,4-dihydro-4-oxoquinoline-3 -carboxylic acid hydrazide (11)

From 8 (2.80 g). Yield: 1.72 g (65%); mp 224-226 °C; ¹H-NMR (DMSO-d₆) d 11.64 (s, br, 3H, NH, NH₂); 8.99 (s, 1H, H-2); 8.38 (dd, 1H, J_H7-8 9.5 Hz, H-8); 8.28 (d, 1H, J_H5-7 3.0 Hz, H-5); 7.92 (m, 1H, H-7); 4.45 (q, 2H, J 7.0 Hz, CH₂CH₃); 1.60 (t, 3H, J 7.0 Hz, CH₂CH₃); ¹³C-NMR (DMSO-d₆) d 175.0 (C-9); 164.8 (C-4); 149.8 (H-2); 140.4 (C-7); 137.8 (C-8a); 132.7 (C-6); 128.5 (C-5); 126.2 (4a); 118.8 (C-8); 108.8 (C-3); 50.8 (CH₂CH₃); 14.2 (CH₂CH₃); Anal. calc. for C₁₂H₁₂ClN₃O₂ : C, 54.25; H, 4.55; N, 15.81. Found: C, 54.10; H, 4.49; N, 15.67; MS m/z (EI, relative abundance %) 264/266 (M^+•, 45/24).

3-(4-Amino-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-3-yl)-6 -chloro-1-ethyl-1,4-dihydro-4-oxoquinoline (15)

Method A. A solution of KOH (0.38 g, 6.77 mmol) in EtOH (25 mL) was added stepwise to a mixture of CS₂ (0.52 g, 6.83 mmol) and hydrazide 9 (1.35 g, 4.50 mmol). The mixture was stirred at 23 °C for 72 h, then evaporated to dryness. The residue was washed with Et₂O (50 mL) to give the potassium salt 13, which was used directly for the next step without purification. To a solution of 4.0 mmol of the salt in H₂O (25 mL) was added 95% hydrated hydrazine (0.26 g, 5.19 mmol) and the mixture was heated under reflux for 18 h. After cooling, the solution was acidified with concentrated HCl, and the precipitate was filtered . The product was washed with H₂O (100 mL), dried and recrystallized from MeOH-EtOH 1:1 to afford 15 (0.96 g, 60%); mp 239-240 °C; ¹H-NMR (DMSO-d₆) d 13.20 (s, 1H, NH); 8.54 (s, 1H, H-2); 8.22 (d, 1H, J_H5-8 < 1.0 Hz, H-5); 7.98 (d, 1H, J_H8-5 < 1.0 Hz, H-8); 6.67 (s, br, 2H, NH₂); 4.43 (q, 2H, J 7.1 Hz, 2H, CH₂CH₃); 1.40 (t, 3H, J 7.1 Hz, CH₂CH₃); ¹³C-NMR (DMSO-d₆) d 172.6 [C-12, (C=S)]; 163.7 (C-4); 146.6 (C-9); 145.9 (H-2); 137.6 (H-8a); 132.6 (C-6); 129.6 (C-5); 127.5 (C-4a); 124.9 (C-7); 119.8 (C-8); 107.4 (C-3); 48.00 (CH₂CH₃); 14.3 (CH₂CH₃); Anal. calc. for C₁₃H₁₁Cl₂N₅ SO: C, 43.83; H, 3.11; N, 19.66. Found: C, 43.61; H, 3.02; N, 19.38; MS m/z (EI, relative abundance %) 355/357 (M^+•, 35/30).

Method B. A solution of 17 (1.00 g, 3.42 mmol), H₂O (3 mL) and 95% N₂H₄ (1.60 g) was heated under reflux for 4 h. After cooling, the solution was diluted with cold H₂O (20 mL), acidified by dropwise addition of concentrated HCl, and filtered. The solid was washed with a minimium of cold H₂O, dried and recrystallized from 1:1 EtOH:H₂O to give 15 (0.70 g, 57%). The product had identical mp, mixed mp (238-240 °C) and other physical properties for those of the authentic sample prepared in method A.

3-(4-Amino-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-3-yl) -6,7-dichloro-1-ethyl-1,4-dihydro-4-oxoquinoline (16)

This compound was prepared from 11 (1.20 g, 4.52 mmol) in a similar manner as desribed for the preparation of 15 (method A) via salt 14. Yield: 1.20 g, (83%); mp 235-238 °C; ¹H-NMR (DMSO-d₆) d 13.81 (s, 1H, NH); 8.55 (s, 1H, H-2); 8.7 (s, 1H, H-5); 8.20 (s, 1H, H-8); 5.68 (s, br, 2H, NH₂); 4.33 (q, 2H, J 7.0 Hz, CH₂CH₃); 1.40 (t, 3H, J 7.0 Hz, CH₂CH₃); ¹³C-NMR (DMSO-d₆) d 172.9 [C-12, (C=S)]; 163.8 (C-4); 150.8 (C-2); 145.9 (C-9); 138.9 (C-7); 136.8 (H-8a); 128.6 (C-6); 127.8 (C-5); 126.6 (C-4a); 118.5 (C-8); 108.5 (C-3); 48.8 (CH₂CH₃); 15.0 (CH₂CH₃); Anal. calc. for C₁₃H₁₂ClN₅SO: C, 48.52; H, 3.76; N, 21.76. Found: C, 48.36; H, 3.67; N, 21.49; MS m/z (EI, relative abundance %) 321/323 (M^+•, 100/45).

6,7-Dichloro-1-ethyl-4-dihydro-3-(5-thioxo-1H-1,3,4 -oxadiazol-3-yl)-4-oxoquinoline (17)

To a solution containing EtOH (20 mL) and KOH (5.00 mmol) dissolved in H₂O (5 mL), the hydrazide 9 (1.50 g, 5.00 mmol) was added. After solution occurred, CS₂ (0.42 g, 5.51 mmol) was added and the mixture was heated under reflux for 3 h. After concentration of the solution to a small volume, the residue was dissolved in H₂O (10 mL). A precipitate was obtained by adding the solution to ice containing concentrated HCl. The solid was filtered off and dried. Recrystallization from EtOH gave the title compound 17 (1.00 g, 58%); mp 227-229 °C; ¹H-NMR (DMSO-d₆) d 11.05 (s, 1H, NH); 9.045 (s, 1H, H-2); 8.47 (s, 1H, H-5); 7.88 (s, 1H, H-8); 4.50 (q, 2H, J 7.0 Hz, CH₂CH₃); 1.65 (t, 3H, J 7.0 Hz, CH₂CH₃); ¹³C-NMR (DMSO-d₆) d 175.2 (C=S); 165.0 (C-4); 150.0 (C-2); 141.0 (C-9); 138.0 (C-7); 133.4 (H-8a); 128.6 (C-6); 126.2 (C-5); 121.6 (C-4a); 119.1 (C-8); 108.7 (C-3); 51.2 (CH₂CH₃); 14.4 (CH₂CH₃); Anal. calc. for C₁₃H₉Cl₂N₃ SO₂: C, 45.63; H, 2.65; N, 12.28. Found: C, 45.42; H, 2.56; N, 12.02; MS m/z (EI, relative abundance %) 341/343 (M^+•, 20/14).

7-Chloro-1-ethyl-6-fluoro-1,4-dihydro-4-oxoquinoline-3 -carboxylic acid azide (12)

To compound 10 (1.00 g, 2.84 mmol) was added a mixture of 2.0 mol L^-1 HCl (12 mL, 40 mmol) and AcOH (2 mL, 80 mmol) at – 10 °C with stirring, followed by addition of NaNO₂ solution (0.40 g in 3 mL H₂O). After additional 15 min stirring between 0 °C and – 10 °C, the yellow azide product 12 was collected, washed with cold H₂O and used immediately for the preparation of 18. The title azide 12 is rather unstable, and starts to decompose in the solid state at 23 °C within two days. However, this azide is stable when stored as solid at – 10 °C: IR n_max/cm^-1: 2100 (azide group), (KBr); ¹H-NMR (DMSO-d₆) d 8.74 (s, 1H, H-2); 8.14 (d, 1H, J_8,F 5.4 Hz, H-8); 8.02 (d, 1H, J_5,F 8.1 Hz, H-5); 4.48 (q, 2H, J 7.0 Hz, CH₂CH₃); 1.32 (t, 3H, J 7.0 Hz, CH₂CH₃); MS m/z (FAB, relative abundance %) 293/295 (MNa^+•, 87/25).

(7-Chloro-1-ethyl-6-fluoro-1,4-dihydro-4-oxoquinolino-3 -yl)-a-amino acetic acid ethyl ester (18)

To a solution of 12 (1.20 g, 4.07 mmol) in DMF (40 mL) was added glycine ethyl ester (0.70 g, 6.79 mmol) at – 10 °C, followed by slow addition of Et₃N (0.60 g, 5.93 mmol). After stirring at 0 to 5 °C for 1 h, the mixture was added to an ice-cold water (150 ml) and the precipitate was filtered, dried and recrystallized from CHCl₃ to give 18 (0.72 g, 50%); mp 258-260 °C; ¹H-NMR (CDCl₃) d 10.10 (s, 1H, NH); 8.80 (s, 1H, H-2); 8.20 (d, 1H, J_5,F 8.5 Hz, H-5); 7.51 (d, J_8,F 5.8 Hz, 1H, H-8); 4.19 (m, 6H, 3xCH₂); 1.58, 1.22 (m, 6H, 2xCH₂CH₃); d_C (DMSO-d₆): 175.1, 175.0, 169.8 (C=O); 164.8 (C-4); 155.4 (d, J_5,F 251.1; C-5); 147.6 (C-2); 135.5 (d, J_8a,F 1.6 Hz, C-8a); 128.2 (d, J_4a,F 6.3 Hz, C-4a); 127.7 (d, J_7,F 21.6 Hz, C-7); 118.3 C-8); 113.7 (d, J_5,F 23.6 Hz, C-5); 111.5 (C-3); 61.3 (C-10); 49.5 (NCH₂CH₃); 41.5 (OCH₂CH₃); 14.5 (OCH₂CH₃); 14.2 (NCH₂CH₃); Anal. calc. for C₁₆H₁₆FClN₂O₄ : C, 54.17; H, 4.55; N, 7.90. Found: C, 53.95; H, 4.50; N, 7.78; MS m/z (EI, relative abundance %) 354/356 (M^+•, 25/10).

N'-D-Aldehydoglycosyl-(7-chloro-l-ethyl-6-fluoro-1,4 -dihydro-4-oxoquinolin-3-yl)carbohydrazide (19a-e)

A suspension of 10 (1.40 g, 4.93 mmol) in EtOH (50 mL) and the sugar moiety (5.20 mmol) was heated under reflux for 4-6 h. After cooling, the product was collected and recrystallized from EtOH to afford the desired product 19.

N'-D-Aldehydoarabinosyl-(7-chloro-l-ethyl-6-fluoro-1,4 -dihydro-4-oxoquinolin-3-yl)carbohydrazide (19a)

From D-arabinose (0.78 g). Yield: 2.01 g (98%); mp 225 °C; ¹H-NMR (600 MHz, HMQC, DMSO-d₆) d 12.69 (s,1H, NH); 8.99 (s,1H, H-2); 8.32 (d, 1H, J_H8-F 5.4 Hz, H-8); 8.15 (d, 1H, J_H5-F 8.4 Hz, H-5); 7.65 (d, 1H, J 5.5 Hz, OH, exchangable with D₂O); 4.99 (d, 1H, J 5.5 Hz, OH); 4.64 (m, 5H, H-1', CH₂CH₃, 2xOH, exchangable with D₂O); 4.38 (dd, 1H, J 8.0 Hz, J 3.2 Hz, H-2'); 4.30 (dd, 1H, J 3.2 Hz, J 8.3 Hz, H-3'); 3.60 (m, 2H, H-4', H-5'); 3.46 (dd, 1H, J_H5',H5" 12.0 Hz, H-5"); 1.42 (t, 3H, J 7.1 Hz, CH₂CH₃); ¹³C-NMR (DMSO-d₆) d 173.9 (C-9); 160.3 (C-4); 155.9 (d, J_C6-F 180.3 Hz, C-6); 151.9 (N=CH-1'); 148.7 (C-2); 135.7(C-8a); 127.3 (d, J_C4a-F 5.4 Hz, C-4a); 126.2 (d, J_C7-F 20.3 Hz, C-7); 120.2 (C-8); 112.2 (d, J_C5-F 22.3 Hz, C-5); 110.3 (C-3); 73.3 (C-3'); 70.9 (C-4'); 70.3 (C-2'); 63.3 (C-5'); 48.8 (CH₂CH₃); 14.4 (CH₂CH₃); Anal. calc. for C₁₇H₁₉FClN₃O₆ : C, 49.11; H, 4.61; N, 10.11. Found: C, 49.00; H, 4.50; N, 9.85; MS m/z (FAB, relative abundance %) 438/440 (MNa^+•, 100/36).

N'-D-Aldehydoxylosyl-(7-chloro-l-ethyl-6-fluoro-1,4 -dihydro-4-oxoquinolin-3-yl)carbohydrazide (19b)

From D-xylose (0.78 g). Yield: 1.90 g (93%); mp 131 °C, decomposed; ¹H-NMR (DMSO-d₆) d 10.92 (s, 1H, NH); 8.90 (s,1H, H-2); 8.28 (d, 1H, J_H8-F 5.3 Hz, H-8); 8.15 (d, 1H, J_H5-F 8.5 Hz, H-5); 6.00 (t, 1H, J_OH-H5',H5" 5.5 Hz, C_5'-OH, exchangable with D₂O); 5.05 (s, br, 1H, OH, exchangable with D₂O); 4.92 (m, 2H, 2xOH, exchangable with D₂O); 4.54 (m, 4H, H-1', H-2', CH₂CH₃); 4.34 (m, 1H, H-3'); 3.84 (m, 1H, H-4'); 3.55 (m, 1H, H-5'); 3.42 (m, 1H, H-5"); 1.40 (t, 3H, J 7.0 Hz, CH₂CH₃); ¹³C-NMR (DMSO-d₆) d 173.6 (C-9); 163.5 (C-4); 154.5 (d, J_C6-F 195.2 Hz, H-6); 149.0 (N=CH-1'); 148.1 (C-2); 135.7(C-8a); 127.3 (d, J_C4a-F 6.1 Hz, C-4a); 125.8 (d, J_C7-F 20.0 Hz, C-7); 120.1 (C-8); 112.2 (d, J_C5-F 23.0 Hz, C-5); 110.0 (C-3); 76.5 (C-3'); 70.7 (C-4'); 69.7 (C-2'); 67.1 (C-5'); 48.7 (CH₂CH₃); 14.4 (CH₂CH₃); Anal. calc. for C₁₇H₁₉FClN₃O₆ : C, 49.11; H, 4.61; N, 10.11. Found: C, 48.82; H, 4.52; N, 9.89; MS m/z (FAB, relative abundance %) 438/440 (MNa^+•,86/38).

N'-D-Aldehydoribosyl-(7-chloro-l-ethyl-6-fluoro-1,4 -dihydro-4-oxoquinolin-3-yl)carbohydrazide (19c)

From D-ribose (0.78 g). Yield: 1.80 g (88%); mp 168-171 °C; ¹H-NMR (DMSO-d₆) d 12.58 (s, 1H, NH); 8.97 (s,1H, H-2); 8.32 (d, 1H, J_H8-F 6.0 Hz, H-8); 8.17 (d, 1H, J_C5-F 9.4 Hz, H-5); 6.15 (t, 1H, J_OH-H5',H5" 5.3 Hz, C_5'-OH, exchangable with D₂O); 5.50-4.65 (m, 3H, 3xOH, exchangable with D₂O); 4.56 (m, 4H, H-1', H-2', CH₂CH₃); 3.40-3.33 (m, 3H, H-3', H-4', H-5'); 3.37 (dd, 1H, J 12.1 Hz, J 4.4 Hz, H-5"); 1.42 (t, 3H, J 7.1 Hz, CH₂CH₃); Anal. calc. for C₁₇H₁₉FClN₃O₆ : C, 49.11; H, 4.61; N, 10.11. Found: C, 48.87; H, 4.52; N, 9.87; MS m/z (FAB, relative abundance %) 438/440 (MNa^+•, 100/36).

N'-D-Aldehydomannosyl-(7-chloro-l-ethyl-6-fluoro-1,4 -dihydro-4-oxoquinolin-3-yl)carbo-hydrazide (19d)

From D-mannose (0.94 g).Yield: 2.1 g (95%); mp 88-90 °C; ¹H-NMR (DMSO-d₆) d 10.92 (d, 1H, J_NH,1' 1.2 Hz, NH); 8.88 (s,1H, H-2); 8.28 (d, 1H, J_H8-F 5.2 Hz, H-8); 8.12 (d, 1H, J_H5-F 8.3 Hz, H-5); 4.76-4.51 (m, 3H, 3xOH, exchangable with D₂O); 4.59 (m, 5H, H-1', H-2', CH₂CH₃, OH); 4.54 (s, br, 1H, OH, exchangable with D₂O); 4.20 (dd, 1H, J_H2'-H3' 9.2 Hz, J_H3'-H4' 1.2 Hz, H-3'); 3.76 (dd, 1H, J_H3'-H4' 1.2 Hz J_H4'-H5' 9.1 Hz, H-4'); 3.64 (dd, 1H, J_H5'-H6' 5.3 Hz, J_H6'-H6" 12.0 Hz H-6'); 3.50 (dt, 1H, J_H5'-H.6' 5.3 Hz, J_H5'-H.6" 3.0 Hz, H-5'); 3.36 (d, 1H, J_H6'-H6" 12.0 Hz, H-6"); 1.38 (t, 3H, J 7.1 Hz, CH₂CH₃); ¹³C-NMR (DMSO-d₆) d 173.5 (C-9); 161.8 (C-4); 154.5 (d, J_C6-F 210.2 Hz, H-6); 152.6 (N=CH-1'); 147.9 (C-2); 135.6 (C-8a); 127.3 (d, J_C4a-F 6.1 Hz, C-4a); 125.0 (d, J_C7-F 20.4 Hz, C-7); 120.1 (C-8); 112.1 (d, J_C5-F 23.5 Hz, C-5); 110.8 (C-3); 78.2 (C-3'); 74.2 (C-5'); 69.9 (C-4'); 67.2 (C-2'); 61.4 (C-6'); 48.6 (CH₂CH₃); 14.4 (CH₂CH₃); Anal. calc. for C₁₈H₂₁FClN₃O₇: C, 48.49; H, 4.75; N, 9.43. Found: C, 48.31; H, 4.64; N, 9.21; MS m/z (FAB, relative abundance %) 468/470 (MNa^+•, 100/38).

N'-D-Aldehydogalactosyl-(7-chloro-l-ethyl-6-fluoro-1,4 -dihydro-4-oxoquinolin-3-yl)carbohydrazide (19e)

From D-galactose (0.94 g). Yield: 1.90 g (86%); mp 114-117 °C; ¹H-NMR (DMSO-d₆) d 10.78 (d, 1H, J_NH,1' 2.0 Hz, NH); 8.78 (s,1H, H-2); 8.28 (d, 1H, J_H8-F 5.1 Hz, H-8); 8.13 (d, 1H, J_H5-F 8.4 Hz, H-5); 5.98 (t, 1H, J_OH-H6',H6" 2.0 Hz, C_6'-OH, exchangable with D₂O); 4.88-4.72 (m, 3H, 3xOH, exchangable with D₂O); 4.66 (s, br, 1H, H-1'); 4.57 (m, 4H, H-2', CH₂CH₃, OH, exchangable with D₂O); 3.82 (dd, 1H, J_H2'-H3' 1.3 Hz J_H3'-H4' 8.5 Hz, H-3'); 3.69 (dd, 1H, J_H3'-H4' 8.5 Hz; J_H4'-H5' 2.5 Hz, H-4'); 3.55 (dd, 1H, J_H5'-H6' 5.6 Hz, J_H6'-H6" 12.2 Hz, H-6'); 3.45 (dt, 1H, J_H5'-H6' 5.6 Hz, J_H5'-H6" 3.5 Hz, H-5'); 3.38 (d, 1H, J_H6'-H6" 12.2 Hz, H-6"); 1.39 (t, 3H, J 7.0 Hz, CH₂CH₃); ¹³C-NMR (DMSO-d₆) d 173.6 (C-9); 163.8 (C-4); 155.0 (d, J_C6-F 212.8 Hz, H-6); 151.8 (N=CH-1'); 148.2 (C-2); 135.7 (C-8a); 127.3 (d, J_C4a-F 6.1 Hz, C-4a); 126.1 (d, J_C7-F 20.3 Hz, C-7); 120.1 (C-8); 112.2 (d, J_C5-F 22.3 Hz, C-5); 110.0 (C-3); 76.7 (C-3'); 73.3 (C-5'); 68.3 (C-4'); 68.0 (C-2'); 60.5 (C-6'); 48.7 (CH₂CH₃); 14.4 (CH₂CH₃); Anal. calc. for C₁₈H₂₁FClN₃O₇ : C, 48.49; H, 4.75; N, 9.43. Found: C, 48.29; H, 4.61; N, 9.32; MS m/z (FAB, relative abundance %) 468/470 (MNa^+•, 100/40).

Results and Discussion

Hydrazides 9-11 were prepared in 67, 53 and 65% yield, respectively, as key intermediates for the synthesis of the target molecules from reaction of the quinolones 6-8 with the hydrated hydrazine at 23 °C for 72 h (Scheme 1). Condensation of the carboxylic acid hydrazides 9 and 11 with CS₂ in ethanolic KOH afforded the unseparable potassium 3-quinolonodithio-carbazates 13 and 14, respectively. These salts were cyclized, at refluxing temperature, with hydrazine followed by acidification with conc. HCl to furnish triazoles 15 and 16 in 60 and 83% yield, respectively. The 1,3,4-oxadiazole-2-thione derivative 17 was prepared from 9, following Young and Wood²⁹ in 58% yield. Alternatively, 17 could be converted with hydrazine into the triazole 15 in 57% yield. Treatment of 10 with with NaNO₂ in the presence of 2 mol L^-1 HCl and AcOH mixture at – 10 °C afforded the unstable carboxylic acid azide derivative 12, which was used immediately for the next step. Condensation of the azide derivative 12 with glycine ethyl ester in the presence of base at – 10 °C for 1 h afforded the ethyl ester derivative 18 in 50% yield (Scheme 1). The structures of the newly compounds were confirmed by homo- and heteronuclear NMR spectroscopy methods and mass spectrometry. The proton spin systems of compounds 13-16 were elucidated from their DQF-COSY³⁰ spectra (chemical shifts are listed in experimental section). Compound 18 was selected for further NMR studies via gradient selected HMBC³¹ spectrum: the carbonyl group (C-9) at d_C 169.8 shows a ³J_C,H correlation to CH₂-11 at d_H 4.19, meanwhile C-2 at d_C 147.6 shows the same correlation to N¹-CH₂CH₃ at d_H 4.19.

Derivatization of the carboxylic group of the quinolone bases was extended next. The hydrazide key intermediate was used here for the synthesis of the 3-carbohydrazide-sugar compounds as promising antibacterial agents. Thus, boiling of 10 with five aldehydosugars (D-arabinose, D- xylose, D-ribose, D-mannose and D-galactose) for 2-4 h afforded, after purification, the yellowish 3-carbohydrazide derivatives 19a-e in 86-98% yield (Scheme 2). The structures of these compounds were confirmed on the basis of their NMR spectra, which were characterized by the presence of a singlet in the region d_H 8.99 – 8.78 (H-2) and two doublets at d_H 8.32 – 8.24 with large coupling constant (J_H8-F ~ 8.5 Hz), and at d_H 8.15 – 8.11 with small coupling constant (J_H5-F ~ 5.5 Hz), assigned to H-8 and H-5, respectively. The protons of the carbohydrate moiety were resolved, after exchanging the hydroxyl groups with D₂O, and comparison of their coupling constants with those of the corresponding free sugars. The proton spin system of 19a,c was further confirmed from DFQ-COSY spectrum: H-1' of 19a appeared as doublet at d_H 4.99, while H-2' – H-5' in the region d_H 4.64 – 3.46, and these protons correlated to the signals at d_C 151.9, 70.3, 73.3, 70.9 and 63.3 for C-1' – C-5', respectively. Similarly, both protons and carbons of 19b-d were identified, whereas the ¹³C-NMR signals of the quinolone residue in 19a-e were analysed by comparison to those of the previously reported quinolone nucleosides.³²

Bioassay

Two factors influence the Minimal Inhibitory Concentration (MIC) of fluoroquinolones: the rate of penetration into bacterial cell and its inhibitory activity of DNA gyrase.³³ Although, most of the studies proposed that a substituent at 7-position of the quinoline ring is related to the binding site with enzyme through electrostatic interactions,^34,35 our aim here was to study the influence of the structural change of the carboxylic group of the quinolone ring by N'-aldehydoglycosyl-carbohydrazides as well as a new heterocycle and a-amino acid ester groups on the antibacterial activity. The in vitro antimicrobial activity of compounds 15-18 and 19a-e was tested by using the Escherichia coli K 12 wild-type strain D10, a gram negative bacterium, and wild-type Bacillius subtilius, a gram-positive bacterium, as well as Staphylococcus aureus. 10⁴ Cells x mL^-1 were incubated into LB medium containing the indicated amount of a given compond. After growth overnight at 37 °C, the optical density of the culture was determined. The minimal inhibitory concentrations (MIC) of 13-19 were determined by assaying the effect of each compound at concentrations of 0.1, 0.5, 1, 10, 50, 100, 200 and 500 mg x mL^-1, and none of them showed significant activity. The screening results of compounds 19a-e are summarized in Table 1, using ciprofloxacine (CPR), as standard, for comparison.

The above data showed that the newly prepared compounds have slightly or no activity against the mentioned organisms, except 19a which exhibited slight activity against E. coli. In conclusion, the substitution of the carboxylic group of the quinolones by 1,2,4-triazolyl, 1,3,4-oxadiazolyl, a-amino ester or hydrazide derivatives of aldehydosugars does not influence the antibacterial activity, since the new compounds are nearly inactive.

Acknowledgments

We thank Mrs. A. Friemel for the NMR (DFQ-COSY, ROESY, HMQC) experiments, Dr. M. Eherman, Fakultät für Biologie, Universität Konstanz, Germany, for the antibacterial screening, and Mr. K. Hägele for the mass spectra. We thank also Professor A. El Ashry of Alxanderia University, Egypt, for supporting the sugar compounds.

References

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Received: January 31, 2002

Published on the web: September 1, 2003

Publication Dates

• Publication in this collection
  04 Feb 2004
• Date of issue
  Oct 2003

History

• Accepted
  01 Sept 2003
• Received
  31 Jan 2002