Quinine bis-conjugates with quinolone antibiotics and peptides: Synthesis and antimalarial bioassay

Article abstract of DOI:10.1039/c2ob26439k

Benzotriazole-mediated syntheses led to novel bis-conjugates of quinine with quinolone antibiotics and amino acid linkers which were successfully prepared by two alternative routes with excellent yields and retention of chirality. These bis conjugates ret

Full text of DOI:10.1039/c2ob26439k

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PAPER
Quinine bis-conjugates with quinolone antibiotics and peptides: synthesis and
antimalarial bioassay†
Siva S. Panda,a Kiran Bajaj,a Marvin J. Meyers,b Francis M. Sverdrupb and Alan R. Katritzky*a,c
Received 23rd July 2012, Accepted 14th September 2012
DOI: 10.1039/c2ob26439k
Benzotriazole-mediated syntheses led to novel bis-conjugates of quinine with quinolone antibiotics and
amino acid linkers which were successfully prepared by two alternative routes with excellent yields and
retention of chirality. These bis conjugates retain in vitro antimalarial activity with IC50 values ranging
from 12 to 207 nM, similar to quinine itself.
found widespread clinical use in the treatment of urinary tract
Introduction
infections.6,7 Levofloxacin 2c (a highly potent antibacterial) and
Quinolines derivatives occur in numerous natural products,
however quinoline and quinolone derivatives possess interesting
biological and pharmaceutical properties.1 Originating from the
bark of cinchona tree and first brought to Europe from Peru in
the 17th century, quinine (1) has a unique therapeutic heritage;
its exceptional pharmacological efficacy as an antimalarial agent
led to the claim that it is “the drug that has relieved more human
suffering than any other in history” (Fig. 1).2 Quinine analogs
act as calcitonin gene-related peptide receptor antagonists.3
Quinine derivatives have also been used successfully as chiral
catalysts in a wide variety of synthetic transformations.4,5
enrofloxacin 2d are fluoroquinolones used for the treatment of
cystic fibrosis and bacterial infections. These antibiotics are pre-
scribed worldwide for the treatment of life-threatening bacterial
infections especially those that have failed to respond to other
classes of antibiotic.8 Enrofloxacin 2d is used for the treatment
of pets and domestic animals and poultry (Fig. 2).9 Quinolones
and fluoroquinolones have also been proposed for treatment of
malaria since these drugs have in vitro antimalarial activity
against
chloroquine-sensitive
and
chloroquine-resistant
P. falciparum.10–12 Activities of 25 quinolones and fluoroquino-
lones studied in vitro against erythrocytic and liver stages of Plas-
modium falciparum showed all to inhibit both chloroquine-sensitive
and chloroquine-resistant P. falciparum grown in red blood cells.13
Dangerous deterioration of the efficacy of the classical anti-
malarial drugs has resulted in increasing resistance of the malaria
parasite Plasmodium falciparum. Considerable concomitant
bacteraemia, septicaemia or localized bacterial infections was
Synthetic quinolone-derived antimicrobial agents include oxo-
linic acid 2a and nalidixic acid 2b (a naphthyridine), which have
Fig. 1 Quinine.
aCenter for Heterocyclic Compounds, Department of Chemistry,
University of Florida, Gainesville, FL 32611-7200, USA.
E-mail: katritzky@chem.ufl.edu
bCenter for World Health & Medicine, Saint Louis University,
Saint Louis, MO 63104, USA
cDepartment of Chemistry, King Abdulaziz University, Jeddah, 21589,
Saudi Arabia
†Electronic supplementary information (ESI) available: 1H, 13C NMR,
CHN/HRMS for all compounds. Antimalarial bioassay graphical data
for 8a–k are provided. See DOI: 10.1039/c2ob26439k
Fig. 2 Quinolone antibiotics.
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revealed in patients with severe malaria14 but the administration
of combination therapy was often successful. The potential value
of malaria therapy using combinations of drugs15,16 is identified
as a strategic and viable option to improve the efficacy and delay-
ing the development and selection of resistant parasites. Combi-
nation therapy (CT) drugs utilize the simultaneous administration
of two or more blood schizontocidal antimalarial drugs with inde-
pendent modes of action and different biochemical targets in the
parasite. Successful treatment with a high cure rate has been rea-
lized with combined use of the antibiotic tetracycline and
quinine.17 However, due to side effects, this combination cannot
be used for children or pregnant women. Over 90% of adult
Gabonese patients with Plasmodium falciparum malaria were
cured by using quinine-clindamycin and quinine-doxycycline.18
Several reports show that quinine amino acid conjugates can
exhibit significant antimalarial activity19 and that quinolone anti-
biotic conjugates with amino acids can possess anti-allergic20
and antibacterial activities.21,22 Since amino acids have been
used as carriers for drugs because of their ability to transplant
into mammalian tissue, we have synthesized novel conjugates of
quinine linked by amino acid residues to quinolone antibiotics as
potential enhancers of the antimalarial activity.
Table 1 Preparation of quinolone antibiotic benzotriazolides 4a–d
Entry
Product 4
Yield (%)
Mp (°C)
Lit Mp (°C)
1
2
3
4
Oxolinic-Bt 4a
Nalidixic-Bt 4b
Levofloxacin-Bt 4c
Enrofloxacin-Bt 4d
96
82
79
76
230–231
171–172
231–233
210–212
229–23223
171–17223
Novel
Novel
Results and discussion
Preparation of quinolone antibiotic benzotriazolides 4a–d
The carboxylic groups of quinolone antibiotics were activated in
high yields (76–96%) by benzotriazole 3 using previously
reported methods (Scheme 1, Table 1).23
Syntheses of quinine bis-conjugates with quinolone antibiotic
and a peptidic fragment
Quinine bis-conjugates with antibiotics and amino acid as linker
were prepared by using two routes depending on the nature of
antibiotics.
Scheme 2 Synthesis of quinine bis-conjugates with quinolone anti-
biotics and peptides 8a–f (Route I).
Route I: Route I utilizes amino acid–antibiotic conjugates
6a–f prepared by our previously reported method (Scheme 2).23
The carboxyl groups of amino acid–antibiotic conjugates 6a–f
were activated by conversion to the corresponding acyl-benzo-
triazolides 7a–f in high yields (76–90%) (Scheme 2, Table 2).
The reactive intermediates 7a–f were utilized for O-acylation
of quinine 1 to give target compounds 8a–f in the presence of
potassium carbonate in anhydrous DMF under microwave
irradiation at 50 °C and 20 W for 5–10 min in good yields
(68–72%). Initially, compounds 8b and 8e were synthesized in
Scheme 1 Preparation of quinolone antibiotic benzotriazolides 4a–d.
8986 | Org. Biomol. Chem., 2012, 10, 8985–8993
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Table 2 Preparation of antibiotics-amino acyl benzotriazolides 7a–f
Entry
Product 7
Yield (%)
Mp (°C)
1
2
3
4
5
6
Oxolinic-Phe-Bt 7a
Oxolinic-Ala-Bt 7b
Oxolinic-Val-Bt 7c
Nalidixic-Gly-Bt 7d
Nalidixic-Leu-Bt 7e
Nalidixic-Ala-Bt 7f
89
86
78
90
76
80
248–249
199–200
240–242
255–257
92–93
208–210
Table 3 Preparation of quinine bis-conjugates 8a–f with antibiotics
and peptidic fragment
Yield (%)
Time
Entry Product 8 Conv. MW Conv. (h) MW (min) Mp (°C)
1
2
3
4
5
6
8a
8b
8c
8d
8e
8f
—
51
—
—
50
—
70
72
68
70
69
70
—
7
—
—
8
5
5
5
10
10
10
125–127
224–226
160–162
173–175
109–111
112–113
—
the presence of potassium carbonate in anhydrous DMF at room
temperature for 8 h and then switched to microwave irradiation,
which showed better yields in less reaction time (Scheme 2,
Table 3).
Route II: an alternative method to the preparation of quinine
bis-conjugates with antibiotics and peptide fragment. Route I
failed to prepare the amino acid–levofloxacin/enrofloxacin conju-
gates due to the presence of the piperazine nucleus in levofoxa-
cin and enrofloxacin, which leads to the formation of water
soluble hydrochloride salts. To overcome this problem we syn-
thesized the Boc-protected amino acid–quinine conjugates
10a–d by O-acylation of quinine 1 with Boc-aminoacylbenzo-
triazoles 9a–d using similar conditions used in route I for O-acy-
lation. (Scheme 3, Table 4) Boc group deprotection with
dioxane/HCl mixture at 20 °C for 1 h gave unprotected amino
acid–quinine conjugates, which were further used for the next
step without characterization. The target compounds 8g–k were
Table 4 Preparation of Boc-protected amino acid–quinine conjugates
10a–d
Entry
Product 10
Yield (%)
Mp (°C)
1
2
3
4
Boc-Gly-quinine 10a
Boc-Ala-quinine 10b
Boc-Phe-quinine 10c
Boc-Ile-quinine 10d
86
81
80
90
74–76
110–112
166–168
68–70
Scheme 3 Synthesis of quinine bis-conjugates 8g–k with quinolone
antibiotics and peptides (Route II).
prepared by coupling unprotected amino acid–quinine conjugates
with antibiotic–benzotriazolides 4c–d in the presence of triethyl-
amine at 20 °C for 2 h in good yields (71–88%) (Scheme 3,
Table 5).
Table 5 Preparation of quinine bis-conjugates 8g–k with antibiotics
and peptidic fragments
Entry
Product 8
Yield (%)
Time (h)
Mp (°C)
1
2
3
4
5
8g
8h
8i
8j
8k
88
78
72
83
71
2.5
2.5
2.5
2
115–117
145–146
161–163
104–106
128–129
Antimalarial bioassay
In vitro activity of compounds against Plasmodium falciparum.
To determine if the conjugates between quinine and antibiotics
2
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Table 6 In vitro antimalarial activities of compounds against the
chloroquine-sensitive 3D7 strain of P. falciparum
J = 7.8 Hz, 1H), 7.55 (t, J = 7.5 Hz, 1H), 7.47–7.39 (m, 2H),
4.54 (d, J = 9.0 Hz, 2H), 4.39 (d, J = 11.1 Hz, 1H), 3.38 (m,
4H), 2.58 (m, 4H), 2.39 (s, 3H), 1.61 (d, J = 6.3 Hz, 3H); 13C
NMR (CDCl3): δ 172.7, 164.1, 157.3, 154.0, 146.0, 145.4,
139.7, 132.4, 132.2, 131.7, 130.1, 126.0, 123.9, 122.3, 120.0,
114.3, 112.2, 105.6, 105.2, 68.3, 55.9, 55.1, 50.8, 46.6, 18.5.
Anal. calcd for C24H23FN6O3: C, 62.33; H, 5.01; N, 18.17.
Found: C, 62.19; H, 5.15; N, 18.21.
Compound
IC50 a (nM)
Oxolinic-Phe-quinine 8a
Oxolinic-Ala-quinine 8b
Oxolinic-Val-quinine 8c
Nalidixic-Gly-quinine 8d
Nalidixic-Leu-quinine 8e
Nalidixic-Ala-quinine 8f
Levofloxacin-Gly-quinine 8g
Levofloxacin-Ala-quinine 8h
Levofloxacin-Phe-quinine 8i
Enrofloxacin-Gly-quinine 8j
Enrofloxacin-Ile-quinine 8k
Quinine 1
115 (65–200)
29 (18–46)
183 (108–313)
46 (19–108)
50 (31–82)
16 (9–27)
12 (9–16)
3-(1H-Benzo[d][1,2,3]triazole-1-carbonyl)-1-cyclopropyl-7-
(4-ethylpiperazin-1-yl)-6-fluoroquinolin-4(1H)-one (4d). Light
yellow microcrystals (76%); mp 210–212 °C; 1H NMR (CDCl3):
δ 8.42 (s, 1H), 8.25 (d, J = 7.5 Hz, 1H), 8.06 (d, J = 8.1 Hz,
1H), 7.99–7.90 (m, 1H), 7.61 (t, J = 6.9 Hz, 1H), 7.46 (t, J =
7.5 Hz, 1H), 7.31–7.28 (m, 1H), 3.61–3.45 (m, 1H), 3.36 (br s,
4H), 2.75 (br s, 4H), 2.62–2.55 (m, 2H), 1.35–1.30 (m, 2H),
1.25–1.16 (m, 5H); 13C NMR (CDCl3): δ 173.0, 164.3, 155.1,
151.8, 147.8, 146.1, 145.0, 144.9, 138.2, 131.8, 130.2, 126.1,
120.1, 114.5, 113.3, 105.2, 52.6, 52.5, 49.8, 35.0, 12.0, 8.4.
Anal. calcd for C25H25FN6O2: C, 65.20; H, 5.47; N, 18.25.
Found: C, 64.95; H, 5.90; N, 18.17.
33 (20–53)
48 (35–65)
28 (19–44)
207 (163–263)
18 (11–30)
>10 000
Oxolinic acid 2a
Naladixic acid 2b
Levofloxacin 2c
>20 000
>20 000
a Mean value (95% confidence intervals).
described here retained antimalarial activity, the bis-conjugates
(compounds 8a–k) as well as the parent compounds were tested
against the blood stage of P. falciparum strain 3D7 in vitro.
Table 6 gives the IC50 values determined 72 h after compound
addition. Quinine was extremely potent (IC50 = 18 nM) as
expected. The parent antibiotics were less active (IC50s >
10 μM), consistent with previous work.13 The bis-conjugates
were all active with IC50s ranging from 12 to 207 nM, indicating
that conjugation did not interfere with antimalarial activity
(Table 6).
General procedure for the preparation of quinoline
antibiotic–amino acid conjugates 6a–f
Compounds 6a–f were synthesized by the established
procedure.23
General procedure for the synthesis of antibiotic–
aminoacylbenzotriazolides 7a–f
1-H-Benzotriazole (4.0 eq.) was dissolved in anhydrous methy-
lene chloride. Thionyl chloride (1.2 eq.) was added and stirred
for 30 min, and then the solution was cooled down to −15 °C.
Antibiotic–amino acid conjugate (1.0 eq.) was added and the
reaction mixture was stirred for 4 h at −15 °C. Upon completion
of the reaction, 5% solution of sodium bicarbonate was added
and the organic layer was extracted twice with the alkaline solu-
tion, washed with brine and dried over anhydrous magnesium
sulfate. The solvent was evaporated and crystallized from diethyl
ether to yield antibiotic–aminoacylbenzotriazolides.
Experimental section
General
Melting points were determined on a capillary point apparatus
equipped with a digital thermometer. NMR spectra were
recorded in CDCl3 on Mercury or Gemini NMR spectrometers
operating at 300 MHz for 1H (with TMS as an internal standard)
and 75 MHz for 13C. Elemental analyses were performed on a
Carlo Erba-EA1108 instrument. All microwave assisted reactions
were carried out with a single mode cavity Discover Microwave
Synthesizer (CEM Corporation, NC). The reaction mixtures were
transferred into a 10 mL glass pressure microwave tube equipped
with a magnetic stirrer bar. The tube was closed with a silicon
septum and the reaction mixture was subjected to microwave
irradiation (Discover mode; run time: 60 s; Power Max-cooling
mode).
(S)-N-(1-(1H-Benzo[d][1,2,3]triazol-1-yl)-1-oxo-3-phenylpro-
pan-2-yl)-5-ethyl-8-oxo-5,8-dihydro-[1,3]dioxolo[4,5-g]quinoline-
7-carboxamide
(7a). While
microcrystals
(89%);
mp
1
248–249 °C; H NMR (CDCl3): δ 10.97 (d, J = 6.9 Hz, 1H),
8.36 (s, 1H), 8.30 (d, J = 8.4 Hz, 1H), 8.14 (d, J = 8.1 Hz, 1H),
7.76 (s, 1H), 7.65 (t, J = 7.8 Hz, 1H), 7.52 (t, J = 7.8 Hz, 1H),
7.40 (d, J = 7.8 Hz, 2H), 7.31–7.16 (m, 3H), 6.66 (s, 1H),
6.45–6.37 (m, 1H), 6.10 (d, J = 10.5 Hz, 2H), 4.16–4.03 (m,
2H), 3.57 (dd, J = 13.5, 4.2 Hz, 1H), 3.31 (dd, J = 13.7, 9.5 Hz,
1H), 1.43 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3): δ 175.1,
171.3, 165.6, 153.0, 146.9, 146.2, 145.4, 136.3, 136.0, 131.4,
131.4, 130.7, 129.7, 128.8, 127.3, 126.5, 123.9, 120.4, 114.8,
110.4, 104.0, 102.9, 95.4, 54.9, 49.8, 38.7, 14.6. Anal. calcd for
C28H23N5O5: C, 66.00; H, 4.55; N, 13.74. Found: C, 65.78; H,
4.40; N, 13.64.
General preparation for benzotriazole derivatives of quinolone
antibiotics (4a–d)
Compounds 4a–d were synthesized by a reported procedure23
(Table 1).
(S)-6-(1H-Benzo[d][1,2,3]triazole-1-carbonyl)-9-fluoro-3-methyl-
10-(4-methyl-piperazin-1-yl)-2H-[1,4]oxazino[2,3,4-ij]quinolin-7(3H)-
one (4c). Light yellow microcrystals (79%); mp 231–233 °C; H
NMR (CDCl3): δ 8.26 (s, 1H), 8.13 (d, J = 8.1 Hz, 1H), 8.03 (d,
8988 | Org. Biomol. Chem., 2012, 10, 8985–8993
1
(S)-N-(1-(1H-Benzo[d][1,2,3]triazol-1-yl)-1-oxopropan-2-yl)-5-
ethyl-8-oxo-5,8-dihydro-[1,3]dioxolo[4,5-g]quinoline-7-
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1
carboxamide (7b). Beige powder (86%); mp 199–200 °C; H
NMR (CDCl3): δ 177.1, 172.2, 164.9, 163.6, 148.7, 146.2,
136.5, 131.5, 130.7, 126.5, 121.6, 120.6, 120.4, 114.8, 112.3,
49.3, 47.1, 25.4, 18.6, 15.4. Anal. calcd for C21H20N6O3: C,
62.37; H, 4.98; N, 20.78. Found: C, 62.03; H, 5.02; N, 20.67.
NMR (CDCl3): δ 10.91 (d, J = 6.0 Hz, 1H), 8.58 (s, 1H), 8.33
(d, J = 8.4 Hz, 1H), 8.15 (d, J = 8.1 Hz, 1H), 7.86 (s, 1H), 7.66
(t, J = 7.6 Hz, 1H), 7.52 (t, J = 7.8 Hz, 1H), 6.92 (s, 1H), 6.15
(s, 2H), 4.23 (q, J = 7.2 Hz, 2H), 1.84 (m, 4H), 1.51 (t, J = 7.2,
3H); 13C NMR (CDCl3): δ 175.2, 172.3, 165.4, 153.1, 146.8,
146.1, 145.7, 136.2, 131.5, 130.7, 126.5, 124.1, 120.3, 114.7,
110.7, 104.2, 102.8, 95.4, 50.0, 49.2, 18.6, 14.6. HRMS
(+ESI-TOF) m/z for C22H19N5O5 [M + Na]+ calcd 456.1278,
found 456.1289.
General procedure for the synthesis of quinine bis-conjugates
8a–f
A dried heavy-walled Pyrex tube containing a small stir bar was
charged with benzotriazole intermediate (1.0 eq.) and quinine
(1.0 eq.) dissolved in DMF along with anhydrous potassium car-
bonate (2.0 eq.). The reaction mixture was exposed to microwave
irradiation (20 W) at a temperature of 50 °C for specified times.
Each mixture was allowed to cool through an inbuilt system until
the temperature had fallen below 30 °C (ca. 10 min). Each reac-
tion mixture was quenched with ice cold water and the solid
obtained was filtered and washed with 10% Na2CO3 and water
to give the desired compound.
(S)-N-(1-(1H-Benzo[d][1,2,3]triazol-1-yl)-3-methyl-1-oxobutan-
2-yl)-5-ethyl-8-oxo-5,8-dihydro-[1,3]dioxolo[4,5-g]quinoline-7-
carboxamide (7c). White solid (78%); mp 240–242 °C; 1H
NMR (CDCl3): δ 11.01 (d, J = 6.9 Hz, 1H), 8.59 (s, 1H), 8.34
(d, J = 8.1 Hz, 1H), 8.15 (d, J = 8.4 Hz, 1H), 7.91 (s, 1H), 7.65
(t, J = 7.5 Hz, 1H), 7.52 (t, J = 7.7 Hz, 1H), 6.91 (s, 1H), 6.15
(s, 2H), 6.14–6.10 (m, 1H), 4.22 (q, J = 7.1 Hz, 2H), 2.67–2.63
(m, 1H), 1.51 (t, J = 7.1 Hz, 3H), 1.22 (d, J = 6.9 Hz, 3H), 1.18
(d, J = 6.9 Hz, 3H); 13C NMR (CDCl3): δ 175.4, 171.6, 166.0,
153.0, 146.9, 146.2, 145.7, 136.1, 130.6, 126.4, 125.6, 124.0,
114.8, 110.9, 104.3, 102.8, 95.4, 48.1, 50.0, 31.4, 20.3, 17.9,
14.7. HRMS (+ESI-TOF) m/z for C24H23N5O5 [M + Na]+ calcd
484.1591, found 484.1604.
Conventional method. Quinine (1.0 eq.) dissolved in DMF
along with anhydrous potassium carbonate (2.0 eq.) in a round
bottom flask. Benzotriazole intermediate (1.0 eq.) was added to
the solution and the mixture was stirred at room temperature for
6–8 h. After completion of the reaction, the reaction mixture was
quenched with ice cold water and the solid obtained was filtered
and washed with 10% Na2CO3 and water to give the desired
compound.
N-(2-(1H-Benzo[d][1,2,3]triazol-1-yl)-2-oxoethyl)-1-ethyl-7-
methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxamide
(7d). Beige powder (90%); mp 255–257 °C; 1H NMR (CDCl3):
δ 10.70–10.64 (m, 1H), 8.91 (s, 1H), 8.67 (d, J = 8.1 Hz, 1H),
8.26 (d, J = 7.8 Hz, 1H), 8.12 (d, J = 8.4 Hz, 1H), 7.63 (t, J =
7.8 Hz, 1H), 7.49 (t, J = 7.7 Hz, 1H), 7.29 (d, J = 8.1 Hz, 1H),
5.34 (d, J = 5.8 Hz, 2H), 4.54 (q, J = 7.2 Hz, 2H), 2.68 (s, 3H),
1.48 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3): δ 179.1, 177.2,
168.3, 165.8, 163.6, 148.8, 147.8, 146.2, 136.6, 131.4, 130.8,
126.6, 121.6, 120.5, 114.5, 112.4, 47.1, 43.6, 25.5, 15.5. Anal.
calcd for C20H18N6O3: C, 61.53; H, 4.65; N, 21.53. Found: C,
61.16; H, 4.65; N, 21.25.
(2S)-(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)-
methyl 2-(5-ethyl-8-oxo-5,8-dihydro-[1,3]dioxolo[4,5-g]quinoline-
7-carboxamido)-3-phenylpropanoate (8a). White solid (70%);
mp 125–127 °C; 1H NMR (CDCl3): δ 10.98 (d, J = 6.9 Hz, 1H),
8.68–8.65 (m, 1H), 8.53 (s, 1H), 8.35–8.28 (m, 1H), 8.02–7.96
(m, 1H), 7.90–7.85 (m, 1H), 7.67–7.62 (m, 1H), 7.54–7.49 (m,
1H), 7.45–7.35 (m, 2H), 7.24–7.17 (m, 2H), 7.09 (d, J = 9.3 Hz,
2H), 6.87 (d, J = 14.7 Hz, 1H), 6.44–6.36 (m, 1H), 6.14 (s, 2H),
5.84–5.77 (m, 1H), 5.58–5.56 (m, 1H), 5.04–5.86 (m, 2H),
4.21–4.15 (m, 2H), 3.89 (s, 3H), 3.61–3.57 (m, 1H), 3.39–3.16
(m, 4H), 2.60–2.45 (m, 2H), 2.57–1.71 (m, 4H), 1.52–1.39 (m,
4H); 13C NMR (CDCl3): δ 175.1, 171.3, 165.3, 158.0, 152.9,
147.7, 146.7, 145.5, 143.3, 142.0, 136.1, 136.0, 131.7, 129.5,
129.4, 128.6, 127.0, 124.1, 122.0, 114.6, 110.9, 104.4, 102.7,
101.6, 95.3, 70.5, 59.3, 56.7, 55.8, 54.4, 49.8, 42.5, 40.0, 38.1,
27.7, 24.5, 14.7. HRMS (+ESI-TOF) m/z for C42H42N4O7 for
[M + 1]+ calcd 715.3126, found 715.3130.
(S)-N-(1-(1H-Benzo[d][1,2,3]triazol-1-yl)-4-methyl-1-oxopentan-
2-yl)-1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-car-
1
boxamide (7e). Yellow microcrystals (76%); mp 92–93 °C; H
NMR (CDCl3): δ 10.64 (d, J = 6.3 Hz, 1H), 8.88 (s, 1H), 8.70
(d, J = 8.4 Hz, 1H), 8.31 (d, J = 7.8 Hz, 1H), 8.15 (d, J = 8.1
Hz, 1H), 7.66–7.62 (m, 1H), 7.54–7.48 (m, 1H), 7.33 (d, J = 8.4
Hz, 1H), 6.26–6.18 (m, 1H), 4.53 (q, J = 7.2 Hz, 2H), 2.71 (s,
3H), 2.08–1.96 (m, 3H), 1.49 (t, J = 7.1 Hz, 3H), 1.15 (d, J =
6.0 Hz, 3H), 1.04 (d, J = 6.0 Hz, 3H); 13C NMR (CDCl3): δ
177.1, 172.2, 165.1, 163.5, 148.6, 147.6, 146.1, 136.4, 131.4,
130.5, 126.3, 121.5, 120.5, 120.3, 114.7, 112.3, 52.0, 47.0, 41.3,
25.7, 25.4, 23.6, 21.5, 15.4. HRMS (+ESI-TOF) m/z for
C24H26N6O3 [M + Na]+ calcd 469.1959, found 469.1970.
(2S)-(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)-
methyl 2-(5-ethyl-8-oxo-5,8-dihydro-[1,3]dioxolo[4,5-g]quinoline-
7-carboxamido)propanoate (8b). White solid (72%); mp
1
224–226 °C; H NMR (CDCl3): δ 10.69 (d, J = 7.2 Hz, 1H),
8.81 (s, 1H), 8.68 (s, 1H), 8.30 (d, J = 9.3 Hz, 1H), 7.68 (s, 1H),
7.99 (s, 1H), 7.51–7.46 (m, 2H), 6.93 (s, 1H), 6.13 (s, 2H),
5.69–5.53 (m, 1H), 5.07–5.00 (m, 2H), 4.75 (br s, 1H),
4.30–4.26 (m, 3H), 4.19 (s, 3H), 4.05–4.01 (m, 1H), 3.61–3.42
(m, 2H), 3.29–3.22 (m, 1H), 3.20–3.11 (m, 1H), 2.76–2.36 (m,
1H), 2.31–2.14 (m, 2H), 1.99–1.83 (m, 1H), 1.75–1.68 (m, 1H),
1.61 (d, J = 6.6 Hz, 3H), 1.58–1.49 (m, 3H); 13C NMR
(CDCl3): δ 175.1, 170.8, 165.8, 160.8, 153.1, 146.8, 146.0,
145.2, 143.2, 140.0, 137.0, 136.2, 128.1, 127.0, 126.3, 123.9,
118.1, 117.8, 110.4, 104.1, 102.8, 101.7, 95.6, 70.2, 58.5, 58.4,
(S)-N-(1-(1H-Benzo[d][1,2,3]triazol-1-yl)-1-oxopropan-2-yl)-1-
ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carbox-
1
amide (7f). Beige powder (80%); mp 208–210 °C; H NMR
(CDCl3): δ 10.68 (d, J = 5.1 Hz, 1H), 8.88 (s, 1H), 8.71 (d, J =
8.1 Hz, 1H), 8.33 (d, J = 8.4 Hz, 1H), 8.16 (d, J = 7.8 Hz, 1H),
7.67 (t, J = 7.7 Hz, 1H), 7.53 (t, J = 7.8 Hz, 1H), 7.34 (d, J =
8.1 Hz, 1H), 6.20–6.11 (m, 1H), 4.58–4.53 (m, 2H), 2.71 (s,
3H), 1.85 (d, J = 6.9 Hz, 3H), 1.49 (t, J = 7.1 Hz, 3H); 13C
This journal is © The Royal Society of Chemistry 2012
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(2S)-(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)-
methyl-2-(1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-
3-carboxamido)propanoate (8f). White power (70%); mp
54.9, 50.2, 48.8, 43.7, 36.9, 27.1, 24.4, 19.9, 17.4, 14.8. HRMS
(+ESI-TOF) m/z for C36H38N4O7 [M + 1]+ calcd 639.2813,
found 639.2815.
1
112–113 °C; H NMR (CDCl3): δ 10.38 (d, J = 6.6 Hz, 1H),
8.78 (s, 1H), 8.71 (d, J = 3.6 Hz, 1H), 8.62 (d, J = 7.8 Hz, 1H),
7.97 (d, J = 9.3 Hz, 1H), 7.43–7.35 (m, 2H), 7.30–7.26 (m, 2H),
6.54–6.51 (m, 1H), 5.90–5.73 (m, 1H), 4.99 (d, J = 7.8 Hz, 1H),
4.95 (s, 1H), 4.86–4.70 (m, 1H), 4.60–4.40 (m, 2H), 3.91 (s,
3H), 3.48–3.32 (m, 1H), 3.20–3.08 (m, 1H), 3.01 (t, J =
12.0 Hz, 1H), 2.68 (s, 3H), 2.65–2.50 (m, 2H), 2.30–2.20 (m,
1H), 1.96–1.62 (m, 5H), 1.50–1.46 (m, 6H); 13C NMR (CDCl3):
δ 176.9, 172.2, 164.6, 163.5, 158.0, 148.6, 147.5, 147.4, 144.8,
143.6, 141.9, 136.4, 131.8, 127.1, 122.0, 121.5, 120.5, 119.1,
114.6, 112.3, 101.5, 74.9, 59.4, 56.7, 55.8, 48.6, 47.0, 42.6,
39.9, 27.8, 27.7, 25.4, 24.5, 17.9, 15.4. HRMS (+ESI-TOF) m/z
for C35H39N5O5 [M + Na]+ calcd 632.2843, found 632.2850.
(2S)-(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)-
methyl 2-(5-ethyl-8-oxo-5,8-dihydro-[1,3]dioxolo[4,5-g]quinoline-
7-carboxamido)-3-methylbutanoate (8c). White powder (68%);
mp 160–162 °C; 1H NMR (CDCl3): δ 10.74 (d, J = 7.5 Hz, 1H),
8.70 (d, J = 4.2 Hz, 1H), 8.49 (s, 1H), 7.96 (d, J = 9.0 Hz, 1H),
7.81 (d, J = 4.2 Hz, 1H), 7.46–7.39 (m, 2H), 6.89 (s, 1H),
6.56–6.52 (m, 1H), 6.12 (s, 2H), 5.89–5.80 (m, 1H), 5.03 (d, J =
4.2 Hz, 1H), 4.98 (s, 1H), 4.73–4.70 (m, 1H), 4.19–4.17 (m,
2H), 3.92 (s, 3H), 3.47–3.41 (m, 1H), 3.22–2.97 (m, 2H),
2.70–2.55 (m, 3H), 2.39–2.20 (m, 3H), 2.02–1.92 (m, 1H),
1.80–1.75 (m, 1H), 1.61–1.40 (m, 4H), 1.30–1.20 (m, 1H), 1.01
(d, J = 5.7 Hz, 3H), 0.90 (d, J = 5.7 Hz, 3H); 13C NMR
(CDCl3): δ 175.2, 171.4, 165.6, 157.9, 152.9, 147.5, 146.6,
145.5, 144.8, 143.7, 141.9, 136.0, 131.6, 127.2, 124.0, 121.9,
114.6, 111.0, 104.3, 102.7, 101.6, 95.3, 59.4, 58.1, 56.6, 55.8,
49.8, 42.5, 39.9, 30.8, 27.8, 27.6, 24.8, 19.7, 18.0, 14.6. Anal.
calcd for C38H42N4O7: C, 68.45; H, 6.35; N, 8.40. Found: C,
68.05; H, 6.67; N, 8.23.
General procedure for the preparation of N-(Boc-aminoacyl)-
benzotriazoles 9a–d
Compounds 9a–d were synthesized by irradiating an equimolar
amount of Boc protected amino acid with 1-(methylsulfonyl)-
1H-benzo[d][1,2,3]triazole (BtSO2Me) in the presence of 2.0 eq.
of triethylamine for 2 min run time and 30 min hold time at
70 °C and 50 W irradiation power. Completion of the reaction
was monitored by TLC. After completion of the reaction, the
mixture was quenched with water. The precipitate obtained was
washed with saturated solution of sodium carbonate and water to
afford compound 9a–d (Table 7).
(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)methyl
2-(1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-car-
boxamido)acetate (8d). White microcrystals (70%); mp
1
173–175 °C; H NMR (CDCl3): δ 10.41 (t, J = 5.3 Hz, 1H),
8.84 (s, 1H), 8.74 (d, J = 4.8 Hz, 1H), 8.64 (d, J = 7.8 Hz, 1H),
7.99 (d, J = 9.0 Hz, 1H), 7.43–7.40 (m, 2H), 7.36–7.25 (m, 2H),
6.57 (d, J = 6.9 Hz, 1H), 5.90–5.76 (m, 1H), 5.03–4.94 (m, 2H),
4.60–4.47 (m, 2H), 4.42–4.20 (m, 2H), 3.94 (s, 3H), 3.45–3.35
(m, 1H), 3.17–2.98 (m, 2H), 2.69 (s, 3H), 2.65–2.55 (m, 2H),
2.30–2.20 (m, 1H), 1.95–1.80 (m, 4H), 1.78–1.67 (m, 1H),
1.61–1.56 (m, 1H), 1.49 (t, J = 6.9, 7.2 Hz, 3H); 13C NMR
(CDCl3): δ 177.0, 169.4, 165.4, 163.5, 158.1, 148.7, 147.7,
147.6, 144.9, 143.4, 142.0, 136.6, 132.0, 127.2, 122.0, 121.5,
120.3, 119.2, 114.6, 112.4, 101.6, 74.9, 59.4, 56.8, 55.9, 47.0,
42.7, 41.8, 39.9, 27.9, 27.7, 25.4, 24.4, 15.4. HRMS
(+ESI-TOF) m/z for C34H37N5O5 [M + Na]+ calcd 618.2687,
found 618.2694.
Table 7 Preparation of N-(Pg-aminoacyl)benzotriazoles 9a–d
Entry
Products
Yield (%)
Mp (°C)
Lit Mp (°C)
1
2
3
4
Boc-Gly-Bt 9a
Boc-Ala-Bt 9b
Boc-Phe-Bt 9c
Boc-Ile-Bt 9d
75
54
59
85
68–70
145–146
86–88
68–6924
144–14524
85–8624
100–101
Novel
tert-Butyl ((2S,3S)-1-(1H-benzo[d][1,2,3]triazol-1-yl)-3-methyl-
1-oxopentan-2-yl)carbamate (9d). White solid (85%); mp
100–101 °C; 1H NMR (CDCl3): δ 8.30 (d, J = 8.1 Hz, 1H), 8.15
(d, J = 8.1 Hz, 1H), 7.68 (t, J = 7.7 Hz, 1H), 7.53 (t, J = 7.7 Hz,
1H), 5.67 (br s, 1H), 5.36 (br s, 1H), 2.20 (br s, 1H), 1.61–1.42
(m, 2H), 1.45 (s, 9H), 1.07 (d, J = 6.6 Hz, 3H), 0.90 (t, J =
7.4 Hz, 3H); 13C NMR (CDCl3): δ 172.3, 155.8, 146.2, 131.2,
130.7, 126.6, 120.5, 114.6, 80.4, 59.0, 38.3, 28.5, 24.4, 16.2,
11.5. Anal. calcd for C17H24N4O3: C, 61.43; H, 7.28; N, 16.85.
Found: C, 61.22; H, 7.34; N, 16.73.
(2S)-(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)-
methyl-2-(1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-
carboxamido)-4-methylpentanoate (8e). White microcrystals
(69%); mp 109–111 °C; 1H NMR (CDCl3): δ 10.22 (d, J =
6.9 Hz, 1H), 8.68 (s, 1H), 8.61 (d, J = 4.2 Hz, 1H), 8.56 (dd, J =
8.1, 1.2 Hz, 1H), 7.87 (d, J = 9.0 Hz, 1H), 7.36–7.30 (m, 2H),
7.26–7.16 (m, 3H), 6.44 (d, J = 7.5 Hz, 1H), 5.82–5.70 (m, 1H),
4.94 (dd, J = 7.2, 1.2 Hz, 1H), 4.89 (s, 1H), 4.74–4.68 (m, 1H),
4.52–4.30 (m, 2H), 3.83 (s, 3H), 3.40–3.28 (m, 1H), 3.16–3.00
(m, 1H), 2.98–2.85 (m, 1H), 2.62 (s, 3H), 2.58–2.42 (m, 2H),
2.22–2.12 (m, 1H), 1.93–1.80 (m, 1H), 1.75–1.48 (m, 6H), 1.41
(t, J = 7.2 Hz, 3H), 0.86–0.81 (m, 6H); 13C NMR (CDCl3): δ
177.0, 172.2, 164.9, 163.5, 157.9, 148.7, 147.6, 147.5, 144.9,
143.6, 142.1, 136.4, 131.8, 127.2, 121.9, 121.5, 120.5, 119.6,
114.6, 112.4, 101.7, 74.3, 59.4, 56.8, 55.8, 51.5, 47.0, 42.6,
40.8, 40.0, 27.9, 27.7, 25.4, 25.2, 24.8, 23.2, 21.9, 15.5. Anal.
calcd for C38H45N5O5: C, 70.02; H, 6.96; N, 10.74. Found C,
69.72; H, 7.15; N, 10.54.
General procedure for the synthesis of quinine–aminoacid
conjugates 10a–d
A dried heavy-walled Pyrex tube containing a small stir bar was
charged with N-(Boc-aminoacyl)benzotriazoles (1.0 eq.) and
quinine (1.0 eq.) dissolved in DMF along with anhydrous pot-
assium carbonate (2.0 eq.). The reaction mixture was exposed to
microwave irradiation (20 W) at 50 °C for 10 min. Each mixture
was allowed to cool through an inbuilt system until the
8990 | Org. Biomol. Chem., 2012, 10, 8985–8993
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temperature fell below 30 °C (ca. 10 min). Each reaction mixture
was quenched with ice cold water and the solid obtained was
filtered and washed with 10% Na2CO3 and water to give the
desired compound.
143.4, 141.9, 132.0, 127.1, 122.0, 119.1, 114.7, 101.5, 80.1,
75.0, 59.4, 58.3, 56.8, 55.8, 42.6, 39.8, 37.8, 28.5, 27.9, 27.6,
25.0, 24.5, 15.8, 11.5. HRMS (+ESI-TOF) m/z for C31H43N3O5
[M + 1]+ calcd 538.3275, found 538.3258.
(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)methyl
2-((tert-butoxycarbonyl)amino)acetate (10a). White microcrys-
tals (86%); mp 74–76 °C; 1H NMR (CDCl3): δ 8.72 (d, J =
4.8 Hz, 1H), 8.07 (d, J = 9.3 Hz, 1H), 7.78 (d, J = 2.1 Hz, 1H),
7.45–7.41 (m, 3H), 5.72–5.64 (m, 1H), 5.64–5.52 (m, 1H), 5.09
(s, 1H), 5.04 (d, J = 4.8 Hz, 1H), 4.17 (s, 3H), 4.09 (dd, J = 9.4,
6.0 Hz, 2H), 3.85–3.75 (m, 1H), 3.66–3.57 (m, 1H), 3.51–3.44
(m, 1H), 3.33–3.28 (m, 1H), 3.14–3.07 (m, 1H), 2.78–2.72 (m,
1H), 2.21–2.10 (m, 3H), 1.99–1.90 (m, 1H), 1.70–1.60 (m, 1H),
1.43 (s, 9H); 13C NMR (CDCl3): δ 169.2, 159.7, 156.3, 146.9,
144.2, 140.4, 137.1, 131.6, 125.9, 123.9, 118.0, 117.8, 101.1,
80.4, 70.9, 58.4, 58.1, 54.9, 43.8, 43.3, 36.9, 28.6, 27.1, 24.4,
20.0. HRMS (+ESI-TOF) m/z for C27H35N3O5 [M + 1]+ calcd
482.2649, found 482.2655.
General procedure for the synthesis of quinine bis-conjugates
8g–k
Quinine–amino acid conjugate was stirred in HCl gas saturated
dioxane for 1 h. Dioxane was evaporated under reduced pressure
and the residue was treated with diethyl ether. The resultant
sticky solid was treated without further purification with benzo-
triazole derivatives of quinolone antibiotic in the presence of tri-
ethylamine (2.0 eq.) in acetonitrile–water mixture (3.5 mL +
1.5 mL) and stirred at room temperature for 3 h. Acetonitrile was
removed under vacuum and the residue quenched in ice cold
water. The reaction was then extracted with ethyl actetae (3 ×
20 mL). The organic layer was dried over anhydrous MgSO4 and
subjected to column chromatography in a methanol/dichloro-
methane gradient to obtain the desired product.
(2S)-(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)-
methyl 2-((tert-butoxycarbonyl)amino)propanoate (10b). White
1
microcrystals (81%); mp 110–112 °C; H NMR (CDCl3): δ 8.73
(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)methyl
2-((S)-9-fluoro-3-methyl-10-(4-methylpiperazin-1-yl)-7-oxo-3,7-
dihydro-2H-[1,4]oxazino[2,3,4-ij]quinoline-6-carboxamido)-
acetate (8g). White microcrystals (88%); mp 115–117 °C; 1H
NMR (CDCl3): δ 10.49 (t, J = 5.4 Hz, 1H), 8.75 (d, J = 4.8 Hz,
1H), 8.46 (s, 1H), 8.00 (d, J = 9.3 Hz, 1H), 7.57 (d, J = 12.6 Hz,
1H), 7.45–7.32 (m, 3H), 6.56 (d, J = 6.9 Hz, 1H), 5.89–5.77 (m,
1H), 5.03–5.00 (m, 2H), 4.35–4.28 (m, 4H), 3.94 (s, 3H),
3.40–3.29 (m, 5H), 3.13–2.99 (m, 3H), 2.69–2.62 (m, 2H),
2.57–2.52 (m, 4H), 2.35 (s, 3H), 1.95–1.85 (m, 2H), 1.76–1.68
(m, 1H), 1.63–1.52 (m, 3H), 1.45–1.42 (m, 3H); 13C NMR
(CDCl3): δ 175.2, 169.4, 165.5, 158.0, 157.4, 154.2, 147.6,
144.8, 144.0, 143.4, 141.8, 139.5, 132.1, 131.9, 127.0, 124.3,
122.3, 122.2, 122.0, 119.1, 114.6, 110.3, 105.3, 105.0, 101.4,
74.9, 68.2, 59.4, 56.8, 55.8, 55.0, 50.7, 46.6, 42.7, 41.7, 39.9,
27.8, 27.6, 24.3, 18.3. HRMS (+ESI-TOF) m/z for
C40H45FN6O6 [M + Na]+ calcd 747.3277, found 747.3286.
(d, J = 4.8 Hz, 1H), 8.01 (d, J = 8.7 Hz, 1H), 7.39–7.30 (m,
4H), 6.50–6.47 (m, 1H), 5.89–5.76 (m, 1H), 5.04–4.95 (m, 3H),
4.43–4.39 (m, 1H), 3.95 (s, 3H), 3.40–3.31 (m, 1H), 3.10–2.99
(m, 2H), 2.70–2.57 (m, 2H), 2.56–2.39 (m, 1H), 2.32–2.27 (m,
1H), 1.90–1.47 (m, 3H), 1.43 (s, 9H), 1.33 (d, J = 7.2 Hz, 3H);
13C NMR (CDCl3) δ 172.7, 158.1, 155.2, 147.6, 144.9, 143.2,
141.8, 132.0, 127.1, 122.1, 119.0, 114.8, 101.4, 80.2, 75.1, 59.4,
56.8, 55.9, 49.4, 42.7, 39.8, 28.5, 28.0, 27.7, 24.5, 18.4. HRMS
(+ESI-TOF) m/z for C28H37N3O5 [M + 1]+ calcd 496.2806,
found 496.2815.
(2S)-(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)-
methyl 2-((tert-butoxycarbonyl)amino)-3-phenylpropanoate
(10c). Off white microcrystals (80%); mp 166–168 °C; 1H
NMR (CDCl3): δ 8.67 (t, J = 4.7 Hz, 1H), 8.08–8.00 (m, 1H),
7.40–7.26 (m, 2H), 7.20–7.03 (m, 4H), 6.87 (d, J = 6.9 Hz, 2H),
6.60–6.54 (m, 1H), 5.86–5.68 (m, 1H), 5.06–4.94 (m, 3H),
4.72–4.63 (m, 1H), 3.92 (s, 3H), 3.42–3.28 (m, 1H), 3.08–2.80
(m, 5H), 2.68–2.53 (m, 2H), 2.34–2.22 (m, 1H), 1.86–1.60 (m,
3H), 1.49–1.38 (m, 10H); 13C NMR (CDCl3): δ 171.5, 158.3,
155.3, 147.6, 144.9, 142.5, 141.3, 135.5, 132.0, 129.3, 128.7,
127.3, 127.0, 122.2, 119.0, 115.1, 101.4, 80.4, 74.6, 58.8, 56.3,
56.0, 54.6, 42.5, 39.5, 38.1, 28.5, 27.6, 23.7. HRMS
(+ESI-TOF) m/z for C34H41N3O5 [M + Na]+ calcd 594.2938,
found 594.2939.
(2S)-(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)-
methyl 2-((S)-9-fluoro-3-methyl-10-(4-methylpiperazin-1-yl)-7-
oxo-3,7-dihydro-2H-[1,4]oxazino[2,3,4-ij]quinoline-6-carboxamido)-
propanoate (8h). White microcrystals (78%); mp 145–146 °C;
1H NMR (CDCl3): δ 10.49 (d, J = 6.9 Hz, 1H), 8.70 (d, J =
4.5 Hz, 1H), 8.53 (s, 1H), 7.98 (d, J = 9.3 Hz, 1H), 7.70 (d, J =
12.6 Hz, 1H), 7.43–7.38 (m, 2H), 7.32 (dd, J = 9.3, 2.7 Hz, 1H),
6.54 (d, J = 6.9 Hz, 1H), 5.90–5.77 (m, 1H), 5.03–5.00 (m, 1H),
4.97 (d, J = 0.6 Hz, 1H), 4.78 (p, J = 7.1 Hz, 1H), 4.42–4.25
(m, 3H), 3.93 (s, 3H), 3.44–3.32 (m, 5H), 3.20–3.09 (m, 1H),
3.07–2.98 (m, 1H), 2.69–2.60 (m, 2H), 2.57–2.53 (m, 4H), 2.36
(s, 3H), 2.39–2.20 (m, 3H), 1.98–1.88 (m, 1H), 1.87–1.82 (m,
1H), 1.80–1.65 (m, 1H), 1.55 (d, J = 6.9 Hz, 3H), 1.50 (d, J =
7.2 Hz, 3H); 13C NMR (CDCl3): δ 175.4, 172.2, 164.9, 158.0,
157.9, 154.3, 147.5, 144.8, 143.9, 143.7, 142.0, 139.6, 131.9,
131.8, 127.1, 124.4, 122.4, 122.0, 119.1, 114.6, 110.5, 105.6,
105.2, 101.5, 74.5, 68.3, 59.5, 56.8, 55.9, 55.1, 50.8, 48.6, 46.6,
42.4, 40.0, 27.9, 27.7, 24.5, 18.4, 17.9. HRMS (+ESI-TOF) m/z
for C41H47FN6O6 [M + 1]+ calcd 739.3614, found 739.3613.
(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)methyl
2-((tert-butoxycarbonyl)amino)-3-methylpentanoate (10d). White
1
solid (90%); mp 68–70 °C; H NMR (CDCl3): δ 8.73 (d, J =
4.5 Hz, 1H), 8.01 (d, J = 9.3 Hz, 1H), 7.43 (s, 1H), 7.39–7.35
(m, 2H), 6.51–6.49 (m, 1H), 5.87–5.79 (m, 1H), 5.04 (d, J =
4.8 Hz, 1H), 4.99 (s, 1H), 4.95–4.90 (m, 1H), 4.37–4.32 (m,
1H), 3.96 (s, 3H), 3.41–3.38 (m, 1H), 3.06–2.98 (m, 2H),
2.68–2.55 (m, 2H), 2.28–2.25 (m, 1H), 2.00–1.86 (m, 3H),
1.77–1.68 (m, 1H), 1.53–1.47 (m, 2H), 1.46–1.36 (m, 10H),
0.94–0.92 (m, 2H), 0.83 (d, J = 10.5 Hz, 3H), 0.67–0.65 (m,
2H); 13C NMR (CDCl3): δ 172.2, 158.1, 155.8, 147.4, 145.0,
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(2S)-(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)-
methyl 2-((S)-9-fluoro-3-methyl-10-(4-methylpiperazin-1-yl)-7-
oxo-3,7-dihydro-2H-[1,4]oxazino[2,3,4-ij]quinoline-6-carbox-
amido)-3-phenylpropanoate (8i). White microcrystals (72%);
mp 161–163 °C; 1H NMR (CDCl3): δ 10.62 (d, J = 7.2 Hz, 1H),
8.72–8.62 (m, 1H), 8.50 (s, 1H), 7.98 (d, J = 9.0 Hz, 1H), 7.65
(d, J = 12.6 Hz, 1H), 7.43–7.26 (m, 2H), 7.22 (d, J = 7.5 Hz,
1H), 7.14–7.06 (m, 5H), 6.53–6.48 (m, 1H), 5.88–5.40 (m, 1H),
5.18–4.88 (m, 3H), 4.38–4.21 (m, 3H), 3.89 (s, 3H), 3.43–3.28
(m, 5H), 3.23–2.94 (m, 4H), 2.66–2.48 (m, 6H), 2.36 (s, 3H),
1.80–1.66 (m, 4H), 1.50 (overlapped d, J = 6.6 Hz, 3H),
1.50–1.41 (m, 2H); 13C NMR (CDCl3): δ 175.2, 171.1,
165.0, 157.9, 157.4, 154.2, 147.5, 144.8, 143.9, 143.1,
141.8, 139.5, 136.1, 132.1, 131.9, 131.7, 129.3, 128.5,
127.1, 127.0, 124.3, 122.3, 121.9, 119.4, 114.6, 110.4,
105.4, 105.1, 101.5, 74.4, 68.2, 59.2, 56.5, 55.8, 54.9, 54.2,
50.6, 46.5, 42.4, 39.8, 38.3, 38.0, 27.6, 24.4, 18.3. HRMS
(+ESI-TOF) m/z for C47H51FN6O6 [M + Na]+ calcd 837.3746,
found 837.3738.
Antimalarial activity assay
P. falciparum strain 3D7 was cultured according to the method
of Trager and Jensen25 with minor modifications. Parasites were
grown in human erythrocytes (2% hematocrit) in an atmosphere
of 5% CO2, 5% O2, 90% N2 in RPMI1640 medium (Gibco) sup-
plemented with 25 mM Hepes buffer (Sigma), 25 mg L−1 genta-
micin (Gibco), 1 mM Sodium pyruvate (Sigma), 50 mg L−1
hypoxanthine (Sigma), 2 g L−1 glucose (Sigma), 2.52 g L−1
sodium bicarbonate (Sigma) and 5 g L−1 Albumax 1 (Gibco).
In vitro antimalarial activity was determined by the SYBR Green
I method described by Smilkstein et al.26 with modifications.27
Stock solutions of each compound were prepared in DMSO at a
concentration 10 mM and 3-fold serial dilutions prepared in
DMSO. Drugs were then diluted 250-fold into culture medium
in 96-well storage plates to create 2X drug solutions. Drug solu-
tions (50 μl per well) were transferred in quadruplicate to para-
site cultures (50 μl) in 96-well black tissue culture plates for a
total volume of 100 μl at 2% hematocrit, 0.2% parasitemia and
0.2% DMSO final concentrations. The plates were then incu-
bated for 72 h at 37 °C. After incubation, 100 μl of lysis buffer
containing 0.2 μl ml−1 SYBR Green I was added to each well.
After incubation for 1 h at room temperature in the dark, plates
were read on a Safire2 (Tecan) plate reader with excitation and
emission wavelengths of 497 and 520 nM, respectively. The
50% inhibitory concentrations (IC50s) were determined by non-
linear regression using a four parameter logistic equation (Graph-
Pad Prism software).
(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)methyl
2-(1-cyclopropyl-7-(4-ethylpiperazin-1-yl)-6-fluoro-4-oxo-1,4-di-
hydroquinoline-3-carboxamido)acetate (8j). White microcrystals
(83%); mp 104–106 °C; 1H NMR (CDCl3): δ 10.53 (t, J =
7.2 Hz, 1H), 8.74 (d, J = 4.5 Hz, 1H), 8.73 (s, 1H), 8.01 (d, J =
5.1 Hz, 1H), 7.98 (s, 1H), 7.41 (s, 1H), 7.40 (s, 1H), 7.36–7.30
(m, 2H), 6.56 (d, J = 7.2 Hz, 1H), 5.91–5.75 (m, 1H), 5.01
(d, J = 9.3 Hz, 1H), 4.33 (dd, J = 18.0, 5.7 Hz, 1H), 4.24 (dd,
J = 17.9, 5.6 Hz, 1H), 3.93 (s, 3H), 3.48–3.38 (m, 2H), 3.32 (t,
J = 4.3 Hz, 4H), 3.18–2.99 (m, 2H), 2.68 (t, J = 4.8 Hz, 4H),
2.56–2.48 (m, 2H), 2.32–2.21 (m, 2H), 1.90–1.83 (m, 2H),
1.61–1.49 (m, 2H), 1.35–1.25 (m, 4H), 1.17–1.12 (m, 5H);
13C NMR (CDCl3) δ 175.0, 169.4, 165.6, 158.0, 155.1,
152.1, 147.7, 146.8, 145.3, 144.9, 143.4, 142.0, 138.6,
131.9, 127.1, 122.0, 119.2, 114.6, 112.9, 112.6, 110.7,
104.9, 101.5, 74.8, 59.4, 56.8, 55.9, 52.7, 52.5, 50.2, 42.7,
41.8, 40.0, 34.9, 27.9, 27.7, 24.5, 12.2, 8.4. HRMS (+ESI-TOF)
m/z for C41H47FN6O5 [M + 1]+ calcd 723.3665, found
723.3663.
Conclusion
In conclusion, we have developed convenient benzotriazole-
mediated efficient syntheses of quinine bis conjugates incorpor-
ated with quinolone (or fluoroquinolone) antibiotic and peptide
fragments via two alternative routes and have demonstrated that
some of these bis-conjugates retain antimalarial activity similar
to quinine (IC50 values ranging from 12 to 207 nM).
Acknowledgements
(2S,3S)-(1R)-(6-Methoxyquinolin-4-yl)(5-vinylquinuclidin-2-yl)-
We thank the University of Florida, The Kenan Foundation,
King Abdulaziz University, Jeddah, Saudi Arabia. We also thank
Dr Hall for English checking.
methyl
2-(1-cyclopropyl-7-(4-ethylpiperazin-1-yl)-6-fluoro-4-
oxo-1,4-dihydroquinoline-3-carboxamido)-3-methylpentanoate
(8k). White solid (71%); mp 128–129 °C; H NMR (CDCl3): δ
1
10.57 (d, J = 7.8 Hz, 1H), 8.74–8.66 (m, 2H), 8.06–7.92 (m,
2H), 7.45–7.30 (m, 4H), 6.60–6.42 (m, 1H), 5.92–5.80 (m, 1H),
5.03–5.01 (m, 1H), 4.98 (s, 1H), 3.96–3.95 (m, 1H), 3.91 (s,
3H), 3.47–3.40 (m, 2H), 3.34–3.26 (m, 4H), 3.25–2.95 (m, 2H),
2.70–2.60 (m, 4H), 2.51 (q, J = 7.2 Hz, 2H), 2.31–2.18 (m, 1H),
2.08–1.92 (m, 2H), 1.84–1.67 (m, 2H), 1.60–1.43 (m, 3H),
1.31–1.20 (m, 5H), 1.17–1.12 (m, 5H), 0.98–0.94 (m, 4H),
0.85–0.74 (m, 2H); 13C NMR (CDCl3): δ 175.5, 171.5,
171.3, 165.3, 157.8, 155.2, 151.9, 147.4, 146.7, 145.1,
145.0, 144.8, 143.7, 141.9, 141.8, 138.5, 131.6, 127.2,
121.9, 119.3, 114.5, 112.8, 112.5, 110.7, 104.7, 101.6,
74.2, 59.3, 57.6, 56.6, 55.7, 52.6, 52.4, 50.0, 42.4, 39.9,
37.7, 37.2, 34.8, 27.8, 27.6, 25.0, 16.1, 12.1, 11.5, 8.2.
HRMS (+ESI-TOF) m/z for C41H47FN6O6 [M + 1]+ calcd
779.4291, found 779.4286.
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