Synthesis of amino acid derivatives of quinolone antibiotics

Article abstract of DOI:10.1039/b900762h

Optically pure conjugates of quinolone antibiotics with naturally occurring amino acids are synthesized in 40-98% yields. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b900762h

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Synthesis of amino acid derivatives of quinolone antibiotics†
Alan R. Katritzky,* Munawar Ali Munawar, Judit Kovacs and Levan Khelashvili
Received 14th January 2009, Accepted 17th February 2009
First published as an Advance Article on the web 31st March 2009
DOI: 10.1039/b900762h
Optically pure conjugates of quinolone antibiotics with naturally occurring amino acids are synthesized
in 40–98% yields.
Introduction
The broad-spectrum quinolone antibiotics act on topoisomerase
II (DNA gyrase usually of Gram-negative) or on topoisomerase
IV enzyme (of Gram-positive bacteria) to inhibit DNA replication
and transcription.1–2
Porins (b-barrel proteins) mediate the entry of quinolones into
cells, and quinolone antibiotics are often used to treat intracellular
pathogens such as Legionella pneumophila and Mycoplasma
pneumoniae.3
Oxolinic acid 1, nalidixic acid 2, cinoxacin 3, and flumequine
4 (Fig. 1), all first-generation agents, are currently widely used
to treat Gram-negative bacteria (e.g. urinary tract infections and
Scheme
conjugates.
1 Literature preparation of quinolone amino acid ester
psoriasis) by dermal delivery.4 However, a major drawback is that
their prolonged oral use causes gastrointestinal disturbances.
pared from N-protected a-amino acids were successfully utilized
for synthesis of di- and tripeptides.17
We now report syntheses of amino acid conjugates of quinolones
1–4 by coupling the free amino acids 9–23, as well as dipeptide
Gly–Gly 24 with benzotriazole-activated oxolinic acid 5, nalidixic
acid 6, cinoxacin 7 and flumequine 8.
Fig. 1 Quinolone antibiotics.
Results and discussion
Prodrugs formed from quinolone acids and amino acid esters
are more lipophilic than the parent drugs,4a,5 and show enhanced
in vivo antibacterial properties6,8,9 with pronounced therapeutic
effects against Pseudomonas aeruginosa,10–11 Escherichia coli,12
Staphylococcus aureus12 and Salmonella typhi,9 in addition to
other wide-ranging biological activities comprising anti-allergic,7
antihypertensive,7 bronchodilating,7 and binding to bovine serum
albumin.4a
Preparation of benzotriazole derivatives of quinolone antibiotics
Oxolinic 1 and nalidixic 2 acids, cinoxacin 3 and flumequine 4 were
converted to their corresponding benzotriazole derivatives using
a standard method.17b Compounds 5–8 were obtained in 75–90%
yields (Table 1), and are stable indefinitely at 20 ◦C.
Table 1 Preparation of acid benzotriazolides 5–8
Literature preparations of quinolone amino acid conjugates
include the use of ethyl chloroformate,4a,7,8,10,11 acid chlorides5,8
and mixed anhydrides (Scheme 1).9 Utilizing amino acid esters
as coupling reagents, these methods provide quinolone–amino
acid ester conjugates (yields range 50–95%) in reaction times of
5–24 h. However, coupling with free amino acids gave the target
compounds in lower yields (20–50%).8
Entry
Reactant
Product
Yield (%)
Mp (◦C)
1
2
3
4
Oxolinic acid 1
Nalidixic acid 2
Cinoxacin 3
5
6
7
8
75
90
80
81
229–232
169–171
221–223
218–219
Flumequine 4
N-Acylbenzotriazoles13 are efficient coupling reagents for
N-,14 C-15 and O-acylation.16 N-(Aminoacyl)benzotriazoles pre-
Preparation of oxolinic–amino acid conjugates
The coupling of 5 with free amino acids 9–23 in aqueous MeCN
in the presence of Et3N in 3 h resulted in the formation of
oxolinic–amino acid conjugates 25–39 in 58–96% yields (Table 2).
Benzotriazole-activated oxolinic acid 5 reacted with free dipeptide
Gly–Gly 24 giving oxolinic–dipeptide conjugate 40 in 90% yield
Center for Heterocyclic Compounds, Department of Chemistry, University
of Florida, Gainesville, FL 32611-7200, USA. E-mail: katritzky@
chem.ufl.edu; Fax: +1 352-392-9199; Tel: +1 352-392-0554
† Electronic supplementary information (ESI) available: Experimental
details for compounds 6–8, 25–29 and 31–56. See DOI: 10.1039/b900762h
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Table 2 Preparation of oxolinic–amino acid conjugates
Entry
Reactant
Product
Overall yield (%)
Mp (◦C)
Lit. overall yield (%)
Lit. mp (◦C)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Gly 9
25
26
27
28b
29c
30
31
32
33
34
35
36
37
38
39
40
78
82
71
72
75
74
75
78
61
54
75
82
61
77
49
77
296–298
257–259
257–259
213–215
248–249
193–194
219–221
225–228
167–171
246–248
218–220
238–239
225–227
292–293
234–236
282–284
4410
188
258
300
267–269
266–268
—
—
—
204
—
—
247
—
221
—
L-Ala 10
DL-Ala 11
L-Phe 12
DL-Phe 13
L-Met 14
L-Leu 15
L-Ile 16
a
—
—
a
a
—
4010
a
—
a
L-Trp 17
L-Ser 18
L-Cys 19
L-Asp 20
L-Val 21
L-Tyr 22
Cystine 23
Gly–Gly 24
—
4210
a
—
407
a
—
—
—
a
—
—
—
a
a
—
a Compound is novel. b Retention time for 28 = 9.02 min. c Retention time for 29 = 9.16 and 9.68 min.
Table 3 Preparation of nalidixic–amino acid conjugates
Entry
Reactant
Product
Overall yield (%)
Mp (◦C)
Lit. overall yield (%)
5410
Lit. mp (◦C)
1
2
3
4
5
6
7
8
9
Gly 9
41
42
43
44
45
46
47
48
49
50
51
75
81
88
86
58
60
69
39
54
70
59
259–260
251–253
252–254
213–215
164–165
171–172
159–160
238–239
182–185
140–142
246–247
276
—
253–255
—
—
168
—
207
—
—
a
L-Ala 10
DL-Ala 11
L-Phe 12
L-Met 14
L-Leu 15
L-Ile 16
—
508
a
—
—
a
2810
a
—
L-Asp 20
L-Val 21
L-Tyr 22
Gly–Gly 24
547
a
—
—
—
a
10
11
a
—
a Compound is novel.
(Table 2). All novel compounds were characterized by 1H-NMR,
13C-NMR and elemental analysis.
Preparation of nalidixic–amino acid conjugates
HPLC (detection at 220 nm, flow rate 0.5 mL/min, and 50%
MeOH as solvent) showed a single peak for 28. By contrast
two peaks were observed for the corresponding racemic mixture
29,confirming the enantiopurity of oxolyl-L-Phe 28.
In the literature, oxolinic–amino acid conjugates were prepared
either by (a) coupling of ester-activated oxolinic acid with amino
acid esters (52–66%), followed by ester hydrolysis (66–90%)7,10
or (b) reaction of oxolinic acid chloride with free amino acids
(18–25%) (Table 2).8 Our methodology allows the synthesis of
oxolinic–amino acid conjugates in higher overall yields (average
of 71% for 16 compounds vs literature average yield of 35% for
6 compounds), uses simple preparative and purification proce-
dures, does not require anhydrous conditions, and is cost-effective.
Similarly, the coupling of 6 with 9–12, 14–16, and 20–22 afforded
nalidixic–amino acid conjugates 41–50 in 40–98% yields (Table 3).
The reaction of 6 with Gly–Gly 24 resulted in the formation
of nalidixic–dipeptide conjugate 51 in 66% yield (Table 3).
All products were characterized by 1H-NMR, 13C-NMR and
elemental analysis.
Previously, nalidixic–amino acid conjugates were prepared
either (a) in three steps by the active ester method7,10 or (b) in
two steps by the acid chloride method.8 Our two-step approach
provides nalidixic–amino acid conjugates in better overall yields
compared to those reported in the literature (Table 3) (average
of 67% for 11 compounds vs literature average yield of 46% for
4 compounds).
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3H). 13C NMR (75 MHz, DMSO-d6) d: 171.7, 164.9, 152.5, 146.8,
Table 4 Preparation of cinoxacin– and flumequine–amino acid conju-
gatesa
146.2, 145.4, 136.1, 130.9, 126.2, 123.3, 119.9, 113.6, 113.1, 102.8,
1
2
102.7, 97.0, 48.7, 14.5. C19H14N4O4· H2O, Calculated: C, 61.45;
H, 4.07; N, 15.09, Found: C, 61.19; H, 3.73; N, 15.27.
General procedure for oxolinic–amino acid conjugates (25–40)
A mixture of 7-(1H-benzo[d][1,2,3]triazole-1-carbonyl)-5-ethyl-
[1,3]dioxolo[4,5-g]quinolin-8(5H)-one 5 (181 mg, 0.5 mmol),
amino acid (0.5 mmol) and triethylamine (101 mg, 0.13 mL, 1.0
mmol) in acetonitrile–water mixture (3.5 mL +1.5 mL) was stirred
at room temperature for three hours. The acetonitrile was removed
under vacuum and the residue was acidified with concentrated
HCl. The precipitate was filtered, washed with cold water, dried
under reduced pressure and recrystallized from aq. ethanol to gave
the corresponding product.
Overall
Entry Reactant
Quinolone Product yield (%) Mp (◦C)
1
2
3
4
5
L-Ala-OH 10
7
7
7
8
8
52
53
54
55
56
66
66
58
43
45
236–238
266–268
179–181
175–176
200–202
(S)-2-(5-Ethyl-8-oxodihydro-[1,3]dioxolo[4,5-g]quinoline-7-car-
boxamido)-4-methylsulfanylbutanoate (30). (170 mg, 87%), mp
193–194 ◦C. 1H NMR (300 MHz, DMSO-d6) d: 1.34 (t, J = 7.2 Hz,
3H), 1.93–2.13 (m, 5H), 2.50 (m, 2H), 4.43 (q, J = 7.2 Hz, 2H),
4.59–4.66 (m, 1H), 6.24 (s, 2H), 7.50 (s, 1H), 7.63 (s, 1H), 8.71 (s,
1H), 8.90 (bs, 1H), 10.53 (d, J = 7.7 Hz, 1H). 13C NMR (75 MHz,
DMSO-d6) d: 14.6, 29.5, 31.6, 48.9, 50.8, 96.7, 102.6, 102.8, 110.1,
123.1, 136.1, 146.2, 146.3, 152.6, 164.3, 173.2, 174.1. C18H20N2O6S,
Calculated: C, 55.09; H, 5.14; N, 7.14, Found: C, 54.89; H, 5.06;
N, 6.75.
DL-Phe-OH 13
L-Trp-OH 17
L-Phe-OH 14
L-Trp-OH 17
a All compounds are novel.
Preparation of cinoxacin– and flumequine–amino acid conjugates
In order to show the generality of benzotriazole methodology,
we coupled amino acids with two other quinolone antibiotics:
cinoxacin 3 and flumequine 4. Cinoxacin–amino acid conjugates
52–54 were obtained in 73–82% yields by reacting 7 with 10, 13,
17 in aqueous acetonitrile for 3 h (Table 4).
Acknowledgements
We thank the Higher Education Commission of Pakistan for
financial support to Dr. Munawar Ali Munawar, a post-doc fellow
from the University of the Punjab, Pakistan.
Under the same reaction procedure the coupling of
benzotriazole-activated flumequine
8 with 14, 17 afforded
flumequine–amino acid conjugates 55–56 in 53 and 56% yields,
respectively (Table 4).
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