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EHOOPrAHH^ECKAa XHMH3, 2012, moM 38, № 4, c. 489-495
SYNTHESIS OF SOME QUINOLINYL CHALCONE ANALOGUES
AND INVESTIGATION OF THEIR ANTICANCER AND SYNERGISTIC ANTICANCER EFFECT WITH DOXORUBICIN
© 2012 Mohamed R. E. Alyfl #, El-Sayed I. Ibrahim4, Fakher A. El Shahed4, Hamdy A. Soliman4, Zein S. Ibrahimc, and Samir A. M. El-Shazly*
aChemistry Department, Faculty of Science, Taif University, Taif, Alhawyia, Kingdom of Saudi Arabia Chemistry Department, Faculty of Applied Science, Port Said University, Port Said-Egypt bChemistry Department, Faculty of Science, Suez Canal University, Ismailia-Egypt cPhysiology Department, Faculty of Medicine, Taif University, Taif-KSA Department of Physiology, Faculty of Veterinary Medicine, KaferelSheikh University, Egypt dBiotechnology Department, Faculty of Science, Taif University, Taif-KSA Department of Biochemistry, Faculty of Veterinary Medicine, KaferelSheikh University, Egypt Received May 18, 2011; in final form July 27, 2011
Two derivatives of 2-(4-acetylanilino)quinolines (IIIa, b) were synthesized as scaffolds for synthesis of open chalcone analogues (\&—f) through Claisen-Schmidt condensation with a set of aromatic aldehydes (I\&—d). Derivatives (\a, b) were further manipulated into cyclic a, P-unsaturated ketones by Michael-addition of acety-lacetone and ethylacetoacetate affording derivatives (VI—VII). Deethoxycarboxylation of derivatives (VIIa, b) afforded cyclohexenons (VIIIa, b) allowing formation of a mini library of a, P-unsaturated ketones for screening their anticancer and synergistic anticancer effect with doxorubicin using colon cancer cell line (Caco-2). Two open enones, (Vb) and (Ve), showed significant anticancer activity with IC50 of 5.0 and 2.5 p.M respectively. Only one cyclic enone, (VIa) showed synergistic anticancer activity with doxorubicin at 10 p.M.
Keywords: quinoline, chalcones, doxorubicin, antiproliferative effect, synergistic effect.
INTRODUCTION
Chalcones, i.e. 1,3-diaryl-2-propen-1-ones (Fig.1) are important class of natural products belonging to the flavonoid and isoflavonoid families [1]. They are easily accessible via Claisen-Schmidt condensation of acety-lated aryls with aldehydes, therefore, an endless number of chalcone derivatives is continually reported.
The wide diversity of the periphery around the enone core (Fig. 1) gave the chalcones the potency to have a reported broad spectrum ofbiological activities as anticancer [2], antioxidant [2], anti-inflammatory-analgesic-antipyretic [3], antimicrobial [4], antiparasitic [5], anti-hepatotoxic [3], antiallergic [6], antihyperglycemic [7], NO-synthase inhibitors [8], antifertility [9], antinociceptive [10], as immunomodulators [11], anticonvulsant [12], antiangial [3b], anticataracts [13] and as probes for in vivo imaging of P-amyloid plaques in Alzheimer's disease [14]. In bioorganic chemistry, they served as tags for glycoconjugates involved as thiol-specific carbohydrate reagents utilized in affinity separation of protein-type toxins as well as posttranslation of free-cysteine containing proteins [15]. The enone core was reported to be responsible for eliciting the biological activity of chalcones
# Corresponding author (phone: 00966562694753; e-mail: mrea34@hotmail.com).
through targeting specific host enzymes if the periphery of this core is optimum for the recognition event [1a, 16].
One of the emerging discoveries in the role of chalcones in cancer therapy, even if they have no own cytotoxicity, is their synergistic effect with the anticancer natural product doxorubicin. Thus, chalcones with specific basic periphery were reported to enhance the curative potency of this drug through inhibition of the drug-efflux protein Pgps characteristic for cancer cells and responsible for their drug resistance response [17].
Therefore, we initiated a program to trace this encouraging discovery, at this stage, to synthesize a set of quinoline-containg chalcone analogues to investigate their own anticancer activity as well as their synergistic anticancer potency with doxorubicin taking colon-cancer cell line (Caco-2) as cancer module. Quinoline was elected both for its basic nature and its known pharmacophore activities [18], besides, the designed series sustains a p-imino group relative to the enone moiety which is necessary for protonation under physiological pH to ensue the potential activity.
RESULTS AND DISCUSSION
Chemistry
2-(p-Acetylanilino)quinolines (IIIa, b) were synthesized from the relevant 2-chloroquinolines (Ia, b)
and ^-acetylaniline (II) in refluxing EtOH containing drops of conc. HCl as described by Ashour et al. for (Ilia) [19]. Compound (Illb) showed a broad band for
the NH+ at 3375 cm-1, IR spectrum, as well as a ba-thochromic shifted band at 1660 cm-1 for the aromatic C=O group. In the 1H NMR spectrum, the NH+ signal was downfield shifted out of scale at 5 10.87 ppm due to the quaternary nature of the nitrogen atom. Claisen-Schmidt condensation of quinolines (IIIa, b) with a set of aldehydes (IVi-d) (Scheme & table), afforded the required first set of cinnamoylquinolines (Va-f) in very good yields, most of the case. IR-spectra showed clearly the existence of the characteristic
stretching vibration bands of the enone moiety at v 1652-1642 cm-1 for the C=O and 1609-1599 cm-1 for the olefinic groups. The expected bathochromic-shift of the carbonyl groups refers to their conjugation with the olefinic double bond. The last group, i.e. the olefinic protons in the 1H NMR spectra could not be assigned due to overlap of its protons with aromatic protons at 5 « 8.20-6.90 ppm while the NH signal appeared clearly downfield as broad singlet at 5 « 9.80 ppm. In all next derivatives, the N-H signal was observed at nearly the same value and it was D2O exchangeable. In 13C NMR, the C=O signal was observed in compound (Ve) at 5 186.67 ppm.
R
O
N Cl (Ia, b)
N
N
H.HCl (IIIa, b)
R
OHC
(IVa-d) O
N N
H (Va-f)
N i
H
(VIa, b)
N i
H (VIIa, b)
N i
H
(VIIIa, b)
Scheme. Reagents and conditions: (a) EtOH, HCl, rfx; (b) NaOH, EtOH-H2O, rt; (c) (Va) or (Vb), acetylacetone, NaOMe, MeOH, rfx; (d) (Va) or (Vb), ethylacetoacetate, NaOMe, MeOH, rfx; (e) NaOH, aq. EtOH, rfx.
b
Chalcone analogues (M, b) were further manipulated to be converted into cyclic enones with side chain diversity to have a mini library of the required class. To this endeavor, Michael-addition of acetylac-etone and ethylacetoacetate with compounds (Va, b) in refluxing EtOH containing NaOMe afforded cyclic enones with acetyl, (VIa, b) and ethyloxycarbonyl, (VIIa, b) side chains in good yields. In the IR-spectra of these compounds, clear NH stretching vibration bands appeared at v « 3333 cm-1 as for derivatives (M-f). Furthermore, a second C=O band arose at the ordinary frequency v « 1720 cm-1 due to the acetyl and ester side chains besides the enone's C=O stretching vibration band at v « 1650 cm-1. In the 1H NMR spectra of compounds (VIa, b) a signal at 5 6.48 ppm was observed in both compounds which might refer to the single olefinic proton of the cyclohexene ring. This proton appeared as doublet with coupling constant less than 1.0 Hz in enone (VIa) and 1.8 Hz for enone (VIb). This coupling is due to the allylic-like coupling with H4 protons. For the cyclohexenone protons at C4, C5 and C6 atoms, the 1H NMR of compound (VIb) was much clear than for compound (VIa), thus, the common coupling of 1.8 Hz for the four-doublet signal at 5 2.94 ppm assigned it to be one of the diaste-reotopic protons of C4 methylene protons. Other common coupling of 17.4 Hz in the previous signal with the doublet-of-doublet at 5 3.07 ppm assigned the later to be the other diastereotopic proton of the same methylene group. The multiplet at 5 3.44 ppm, which was deoverlaped from the H2O signal of DMSO by D2O labeling, was assigned for the cyclohexenone's H5 while the doublet-of-doublet at 5 2.76 is for H6 of the same ring. A multiplicity of doublet-of-doublet rather than a doublet for H6 might be attributed to the racemic nature of this compound. Both compounds showed one signal for both carbonyl groups at 5 « 198.4 ppm in the 13C NMR.
In the 1H NMR spectra of compounds (VIIa, b) the ethyl group's signals appeared normally as triplet for the -CH3 and a quartet for the -CH2- groups at 5^ 0.90 and 3.90 ppm respectively. The cyclohex-enone ring showed the diastereotopic C6 methylene protons as doublet-of-doublet for each one at 5 « 4.11 and 2.78 ppm. Proton H5 appeared as multiplet at 5 « 3.60 ppm, while, the methine proton, i.e. H4, appeared as doublet at 5 « 3.00 ppm.
The labile ethyloxycarbonyl side chains of derivatives (VIIa, b) could be easily removed by treatment with NaOH in refluxing aqueous EtOH to afford a third variety of cyclic enones (VIIIa, b). The IR spectra revealed disappearance of the C=O band at v « 1720 cm-1 ,while, disappearance of the ethyl protons signals in the 1H NMR spectra were good evidences for this elimination. Compound (VIIIb) showed a smooth spectrum as compound (VIb). Mass-spectra as well as elemental analysis were in good
Enone Core
O
Diverse Perifery
Fig. 1. Chemical structure of chalcones.
agreement with the molecular formulas of all compounds.
The anti-proliferative effect of 10 of the synthesized enones (Fig. 2) was examined using Caco-2 colon cancer cells and MTT assay [20]. Moreover the synergetic effects of these derivatives in combination with the drug Doxorubicin were also examined. The results revealed that highly significant, p < 0.001, anti-proliferative effect were observed with compounds having open enone moieties including compounds (Vb) and (Ve) with inhibition potency of 54 and 58% and IC50 at 5.0 ^M and 2.5 ^M respectively. These results, might roughly, exhibiting the relevance of the p-chloro substitution on ring B in nonmethylated quinolyl derivatives and the basic p-NMe2 group on
Side chain variations and yields of compounds (I)-(VIII)
Compd R R' R" Yield (%)
(
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