Synthesis of 5-oxyquinoline derivatives for reversal of multidrug resistance

Article abstract of DOI:10.3762/bjoc.8.193

The inhibition of ABC (ATP binding cassette) transporters is considered a powerful tool to reverse multidrug resistance. Zosuquidar featuring a difluorocyclopropyl-annulated dibenzosuberyl moiety has been found to be an inhibitor of the P-glycoprotein, one of the best-studied multidrug efflux pumps. Twelve 5-oxyisoquinoline derivatives, which are analogues of zosuquidar wherein the dibenzosuberyl-piperazine moiety is replaced by either a diarylaminopiperidine or a piperidone-derived acetal or thioacetal group, have been synthesized as pure enantiomers. Their inhibitory power has been evaluated for the bacterial multidrugresistance ABC transporter LmrCD and fungal Pdr5. Four of the newly synthesized compounds reduced the transport activity to a higher degree than zosuquidar, being up to fourfold more efficient than the lead compound in the case of LmrCD and about two times better for Pdr5.

Full text of DOI:10.3762/bjoc.8.193

Synthesis of 5-oxyquinoline derivatives for
reversal of multidrug resistance
Torsten Dittrich1, Nils Hanekop2, Nacera Infed2, Lutz Schmitt2
and Manfred Braun*1
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2012, 8, 1700–1704.
1Institute of Organic and Macromolecular Chemistry, University of
Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany and
2Institute of Biochemistry, University of Düsseldorf, Universitätsstr. 1,
D-40225 Düsseldorf, Germany
doi:10.3762/bjoc.8.193
Received: 21 June 2012
Accepted: 31 August 2012
Published: 05 October 2012
Email:
Manfred Braun* - braunm@hhu.de
Associate Editor: S. Bräse
* Corresponding author
© 2012 Dittrich et al; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
acetals; enantiopure compounds; heterocycles; inhibitor; multidrug
resistance
Abstract
The inhibition of ABC (ATP binding cassette) transporters is considered a powerful tool to reverse multidrug resistance.
Zosuquidar featuring a difluorocyclopropyl-annulated dibenzosuberyl moiety has been found to be an inhibitor of the P-glyco-
protein, one of the best-studied multidrug efflux pumps. Twelve 5-oxyisoquinoline derivatives, which are analogues of zosuquidar
wherein the dibenzosuberyl-piperazine moiety is replaced by either a diarylaminopiperidine or a piperidone-derived acetal or
thioacetal group, have been synthesized as pure enantiomers. Their inhibitory power has been evaluated for the bacterial multidrug-
resistance ABC transporter LmrCD and fungal Pdr5. Four of the newly synthesized compounds reduced the transport activity to a
higher degree than zosuquidar, being up to fourfold more efficient than the lead compound in the case of LmrCD and about two
times better for Pdr5.
Introduction
The treatment of cancer is often severely hampered by efflux been investigated most intensively [2]. As P-glycoprotein is
pumps, which are responsible for the extrusion of various considered to be a major player in multidrug resistance and has
chemotherapeutics from the tumor cell, an effect termed been found to be over expressed in tumor cells [3,4], consider-
“multidrug resistance”. Various transporters of the ATP-binding able attempts have been made to develop inhibitors of P-glyco-
cassette family, so called ABC transporters, have been shown to protein in order to reverse multidrug resistance. These efforts
be responsible for multidrug resistance [1]. Among these were pursued for a longer period leading to a variety of small-
multidrug-resistance ABC transporters, the P-glycoprotein has molecular compounds with different structures that act as
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Beilstein J. Org. Chem. 2012, 8, 1700–1704.
Results and Discussion
P-glycoprotein inhibitors [5]. The drug zosuquidar (1a)
emerged as the most promising among them [6-9]; however, Synthesis
so far it has not made its way into routine clinical application As extended studies on modifications of zosuquidar (1a) had
[10].
revealed both the 5-oxyquinoline and the hydroxypropane
spacer as being crucial for inhibitory activity on P-glycoprotein
Apart from their role in multidrug resistance of tumor cells, [14-18], our strategy was based on modification or replacement
ABC-type efflux pumps are also involved in multidrug resis- of the dibenzosuberyl and the piperazine moieties, whereas the
tance of pathogenic Gram-positive bacteria and fungi for which above-mentioned “southern part” of zosuquidar (1a) was
inhibitors have only rarely been studied. Therefore, we were planned to be maintained, including the absolute configuration
interested in developing inhibitors of efflux pumps from bacte- of the stereogenic carbinol center. Thus, we replaced the piper-
rial and fungal organisms, namely LmrCD from Lactococcus azine motif in 1 by a piperidine ring carrying either nitrogen or
lactis and Pdr5 from Saccharomyces cerevisiae [11,12]. Thus, oxygen as a hetero substituent(s) in the 4-position. Therefore,
we synthesized, guided by the lead structure zosuquidar (1a), a an initial series of 4-aminopiperidines 2a–4a and, in a second
series of compounds that were evaluated as potential inhibitors approach, new spirocyclic acetals 5a–12a as well as the thioac-
of LmrCD and Pdr5. Whereas biochemical studies with the etal 13a were synthesized. All the new compounds, shown in
novel compounds will be disclosed separately [13], we present Scheme 1, were obtained in enantiomerically pure form, with
in this article the synthesis, in detail, of twelve new compounds the stereogenic carbinol center adopting (R) configuration. The
that may provide reversal of multidrug-resistant activity.
acetals 8a and 9a formed as mixtures of diastereomers, whereas
Scheme 1: Lead structure of zosuquidar (1a) and new inhibitors 2–13 (series a); precursors 2–13 (series b); precursors 6–13 (series c).
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Beilstein J. Org. Chem. 2012, 8, 1700–1704.
Scheme 2: Synthetic route to compounds 2a–13a. Reagents and conditions: (a) K3PO4, CH2Cl2, reflux, 3 h; then triethylamine, 0 °C, 1 h; then:
3-nitrobenzenesulfonyl chloride, 0 to 25 °C, 1 h; 72%. (b) 5-hydroxyquinoline, K2CO3, DMF, 25 °C, 20 h; 67%. (c) EtOH, reflux, 3 h; 2a: 72%; 3a:
72%; 4a: 69%; 5a: 83%; 6a: 79%; 7a: 77%; 8a: 98%; 9a: 61%; 10a: 83%; 11a: 72%; 12a: 90%; 13a: 29%.
compound 10a was enantiomerically and diastereomerically The spirocyclic compounds 6c–13c were obtained by standard
pure.
acid-catalyzed reaction with the corresponding diols for the for-
mation of acetals 6c–12c and propanedithiol for 13c, starting
The commercially available chiral building block (S)-3-chloro- from N-acetyl-4-piperidone. Basic hydrolysis was found to be
1,2-propanediol (14) was chosen as the starting material. It was appropriate for the removal of the N-protecting group. Again,
converted to (R)-nosylate 15 in three steps by following a modi- the free amines 6b–13b were used as crude products for the
fied procedure [19], as shown in Scheme 2. The subsequent reaction with the oxirane (R)-16 to give the series of new com-
treatment with 5-hydroxyquinoline [20] led to the epoxide (R)- pounds. Spiroacetal 5b was commercially available.
16, serving as the chiral building bloc in the final key step,
which involves the nucleophilic attack of the secondary amino Biochemical studies
group of the precursors 2b–13b to the epoxide 16, to deliver the The transport activity [13] of the compounds 2a–13a and the
final products 2a–13a. The yields of the final coupling step are reference compound zosuquidar (1a) was determined for the
given in Scheme 2.
ABC transporters LmrCD and Pdr5. The results are given in
Table 1, which restricts itself to those compounds that displayed
The precursor 2c was obtained by an N-arylation, as described a significantly enhanced activity compared to that of 1a. The
in the literature.[21] A modified Buchwald–Hartwig amination activity of the individual transporters in the absence of either
reaction using tri-tert-butylphosphane as a ligand at palladium zosuquidar (1a) or any of the new compounds 2a–13a is
[22] was applied in order to couple 4-methylphenyl bromide assigned as 100%, meaning that those substances that show a
and 4-fluorophenyl bromide with Boc-protected amino- lower relative transport activity than zosuquidar (1a) are consid-
piperidines 17 and 18, respectively. Thus, diarylaminopiperi- ered as potential improvements. Various new 5-oxyquinoline
dine 3c and 4c became readily accessible, as outlined in derivatives show activity that is comparable or inferior to that of
Scheme 3. The cleavage of the protecting group occurred 1a. For reasons of clarity, only those results are included in
according to standard protocols by treatment with trifluoro- Table 1 that indicate a substantially higher reduction of trans-
acetic acid to liberate the amines 2b–4b, which were used port activity than that for zosuquidar (1a). It turns out that, at
without further purification in the coupling reaction with the transporter LmrCD (first column), a derivative with a
epoxide (R)-16.
4-aminopiperidine skeleton, compound 3a, was distinctly more
Scheme 3: Preparation of N-Boc-protected 4-aminopiperidines 3c and 4c. Reagents and conditions: (a) NaOt-Bu, Pd(OAc)2, t-Bu3P, toluene, reflux,
16 h; 3c: 76%; 4c: 41%.
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Beilstein J. Org. Chem. 2012, 8, 1700–1704.
Table 1: Relative transport activity of LmrCD and Pdr5 in the presence of zosuquidar (1a) and selected new 5-oxyquinoline derivatives (2a–13a).a
Compound / Relative transport activity at LmrCD
Compound / Relative transport activity at Pdr5
1a / 42.4%
3a / 19.8%
10a / 11.2%
1a / 23.7%
2a / 14.0%
11a / 12.5%
a100% activity corresponds to the transport activity in the absence of either zosuquidar (1a) or any 5-oxyquinoline derivative. The reported values
represent the average of three independent measurements.
General procedure for the reaction of
active than zosuquidar (1a). Moreover, the acetal derivative 10a
was found to be about four times more active than the lead com- piperidines 2b–13b with (R)-16
pound 1. For the fungal transporter Pdr5 (second column), one A solution of (R)-16 (0.101 g, 0.50 mmol) and a piperidine
compound of the 4-aminopiperidine series, 2a, is about twice as 2b–13b (0.50 mmol) in ethanol (10 mL) was heated under
active as zosuquidar (1a). Similar activity is provided by reflux in a 25 mL flask for 3 h. After cooling to room tempera-
catechol-derived acetal 13a, whereas, at this transporter, the ture, the solvent was removed in a rotary evaporator, and the
acetals derived from 1,2-diphenylethanediol, are still active as residue was purified by column chromatography on silica gel
transport inhibitors, but their activity is slightly lower than (chloroform/methanol, 10:1). Thus, the products 2a–13a were
that of zosuquidar (31% relative transport activity). The full obtained as white or yellowish solids or oils.
details of the results of transport inhibition for all the com-
General procedure for the preparation of
pounds 1a and 2a through 13a are given in a separate communi-
cation [13].
acetals 6c–12c
Under nitrogen, a mixture of N-acetyl-4-piperidinone (1.13 g,
Conclusion
8.0 mmol), the corresponding diol (or dithiol), and p-toluenesul-
The replacement of the benzosuberyl moiety of zosuquidar (1a) fonic acid monohydrate (0.095 g, 0.5 mmol) in chloroform
by diarylamino or acetal groups lead to a series of twelve new (60 mL) was heated under reflux in a 100 mL flask, equipped
compounds, which have been tested as potential inhibitors of with a Soxhlet extraction apparatus, which was filled with
the multidrug-resistance ABC transporters LmrCD and Pdr5. As molecular sieves (4 Å). After heating under reflux for 10 to
a result, four of the new compounds were identified as being 15 h, the mixture was cooled to room temperature, a saturated
superior to zosuquidar in terms of transport reduction. The com- aqueous solution of sodium hydrogen carbonate (20 mL) was
pound 10a, which was found to be the most efficient of all, added, and the mixture was stirred for 10 min at room tempera-
features a cyclic acetal moiety derived from (R,R)-1,2-diphenyl- ture. The aqueous layer was removed, and the organic layer was
1,2-ethanediol.
dried with sodium sulfate. After removal of the solvent in a
rotary evaporator, the residue was purified by flash chromatog-
raphy. For the preparation of catechol-derived acetals 11c and
Experimental
General: Melting points were determined with a Büchi 540 12c, toluene was used instead of chloroform, and trifluoro-
melting point apparatus and are not corrected. NMR spectra methanesulfonic acid instead of p-toluenesulfonic acid.
were recorded in CDCl3 with a Bruker Avance DRX 200 and a
General procedure for the N-arylation of
Bruker Avance DRX 500 spectrometer. IR spectra were
measured with a Bruker Vector 22 spectrometer. Mass spectra N-Boc-4-arylaminopiperidines 17 and 18
were recorded on a Thermo Finnigan Trace DSQ apparatus A 25 mL two-necked flask, equipped with a magnetic stirrer
(GCMS), an ion-trap API mass spectrometer Finnigan LCQ and a connection to a combined argon/vacuum line was charged
Deca (ESI), a triple-quadrupole-mass spectrometer Finnigan with piperidine 19 or 20 (3.6 mmol), the corresponding aryl
TSQ 7000 (EI), and a sector field mass spectrometer Finnigan bromide (3.6 mmol), sodium tert-butoxide (0.43 g, 4.5 mmol)
MAT 8200 (EI, 70 eV). High-resolution mass spectroscopy was and palladium acetate (10.1 mg, 0.045 mmol). The flask was
carried out on Bruker FT-ICR APEX III (7.0 T) (MALDI) at the closed with a septum and the air in the flask was replaced by
University of Bielefeld. Column chromatography was nitrogen. Dry toluene (5 mL) was added, and the mixture was
performed with Fluka silica gel 60 (230–400 mesh), and thin- stirred at room temperature for 30 min. Then, a solution of tri-
layer chromatography was carried out by using Merck TLC tert-butylphosphane (0.12 mL, 0.5 mmol) in toluene (1 mL) was
silicagel 60 F254 aluminium sheets. Toluene was freshly added, and the mixture was refluxed for 16 h under argon. After
distilled from sodium under nitrogen.
cooling to room temperature, water (10 mL) was added, and the
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Supporting Information
Supporting Information File 1
Procedures. Spectroscopic and analytical data.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-8-193-S1.pdf]
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