Chemistry around imidazopyrazine and ibuprofen - UCL-Bruxelles ...

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Table 4 pI50 values of 1,3-dithiane derivatives and references (from three independent experiments). Entry among other templates, substrate analogues, lipophilic b-lactams (azetidin-2-ones), and heterocycle-based inhibitors [43,53e55]. The assay is a competitive hydrolytic experiment using the radiolabelled substrate (anandamide ¼ arachidonoylethanolamide, AEA) to measure FAAH activity. Briefly, recombinant human FAAH in buffer (pH 7.4) is added to glass tubes that contain either the drug in DMSO or DMSO alone (control). Hydrolysis is initiated by adding [ 3 H]-AEA solution and the tubes are incubated at 37 C. Tubes containing buffer only are used as controls for chemical hydrolysis (blank) and this value is systematically subtracted. Reactions are stopped by adding ice-cold MeOH/CHCl3, the radiolabelled ethanolamine is extracted and the radioactivity is measured by liquid scintillation counting (LSC). The selectivity vs. monoacylglycerol lipase (MGL) was similarly assayed, using the [ 3 H]-labelled 2oleoylglycerol (2-OG) as competitive substrate [43,53e55]. The inhibition results expressed as FAAH activity (% of control) vs. drug concentration are shown in Fig. 4. From those experimental dose-response curves, the pI50 (i.e. log IC50) values were calculated (Table 3). The results clearly show that all tested ibuprofen derivatives are more active than the parent carboxylate (sodium salt) and behave as selective inhibitors of FAAH vs. MGL, another hydrolytic enzyme of the endocannabinoid system. We recorded the following decreasing order of activity: 4a (entry 4, R ¼ 1,3-dithian-2-yl), 11a (entry 7, R ¼ chloromethyl), 2a (entry 2, R ¼ benzotriazolyl), 6a (entry 5, R ¼ nitromethyl), 7a (entry 6, R ¼ N-(hydroxy)imino), 3a (entry 3, R ¼ N-(methoxy)methylamino), and 1a (entry 1, ibuprofen from commercial source). The most active compound 4a (1-(1,3dithian-2-yl)-2-(4-isobutylphenyl)-propan-1-one) was compared to related dithiane derivatives featuring fewer alkyl substituents, namely 4b (1-(1,3-dithian-2-yl)-2-phenylpropan-1-one) and 4c (1- (1,3-dithian-2-yl)-2-phenylethan-1-one). We found that the ibuprofen core significantly enhances the activity compared to the simple benzyl derivatives (Table 4, compare entry 3 with entries 4 and 5). The same effect was visible when comparing ibuprofen 1a (acid, entry 1) with 2-methyl-phenylacetic acid (1b, entry 3). 3. Conclusion R 2 R 1 O Our idea to construct an original ibuprofen prodrug based on the in situ oxidation of an imidazopyrazinone precursor (E) could R pI50 (hFAAH) Cmpd R 1 R 2 R 1 1a Me i-Bu OH 3.55 [48] 2 1b Me H OH 2.91 0.04 3 4a Me i-Bu S 4 4b Me H S 5 4c H H S 6 Ibu-am5 Me i-Bu F. De Wael et al. / European Journal of Medicinal Chemistry 45 (2010) 3564e3574 3569 H N S S S N Me 5.86 0.03 4.00 0.03 4.33 0.06 5.08 0.08 [52] not be applied because the required ibuprofen-synthon (F) was synthetically inaccessible. However during our Holy Grail quest, we discovered a novel imidazopyrazine framework, presumably the imine compounds 18 (X ¼ H) (and not the corresponding oximes (X ¼ OH)). The p-hydroxyphenyl derivative 18b is endowed with antioxidant and anti-inflammatory activities and appears even more active than the related imidazopyrazinone 17b. Nevertheless, this result is rather difficult to exploit further due to the uncertainty about the structural assignment and the high synthetic challenge. Ibuprofen (1a) showed only a poor anti-inflammatory effect on the IL-8 secretion by the inflamed intestinal cells. This can be explained as the anti-inflammatory mechanism of NSAIDs implicates another target of the inflammation cascade i.e. the inhibition of pro-inflammatory enzymes, the cyclooxygenases (COX-1 and COX-2) [56]. However, some ibuprofen derivatives with masked acid function (2a, 3a) exhibited a significant activity. Knowing that the cannabinoid system can contribute to the pharmacological effects of NSAIDs [52], we evaluated the ibuprofen derivatives against FAAH. The loss of activity of this enzyme has been shown to provide beneficial effects in models of inflammation due to the increased levels of N-acyl-ethanolamines [57]. Interestingly, we disclosed novel FAAH inhibitors among the series of ibuprofen derivatives synthesized as precursors of the synthon F. In particular, the best FAAH inhibitor 4a is more active than N-(6-(methyl)pyridin-2-yl)-ibuprofen-amide (Table 4, entry 6, Ibu-am5) recently selected by Fowler et al. [52] as “lead” to explore the potential analgesic effect of compounds combining COX- and FAAH-inhibitory properties. Even if 4a is devoid of antiinflammatory action in our cellular test, its unique activity against FAAH is of interest. Indeed, the recognized therapeutic promise of FAAH inhibition for the treatment of anxiety, eating and sleep disorders, among others [50], nowadays, stimulates the research of novel inhibitors by structure-based design or high-throughput screening [58]. Our present work provides an unexpected entry in this field with the 1,3-dithian-2-yl ketone derived from ibuprofen as a novel “hit”. 4. Experimental protocols 4.1. Materials and methods Anhydrous solvents were provided by Fluka. All reagents were obtained from AldricheFluka, Acros or ROCC and used as received. 1 H(300MHz)and 13 C (75 MHz) NMR spectra were recorded on a BRUCKER AVANCE-300 spectrometer. 1 H(500MHz)and 13 C (125 MHz) NMR spectra were recorded on a BRUCKER AM-500 spectrometer. The attributions were established by homonuclear and heteronuclear correlations or by selective decoupling experiments. Chemical shifts are reported as d values (in ppm) downfield from TMS for 1 Hand 13 C or from CFCl3 for 19 F. The mass spectra were obtained using a Finnigan-MAT TSQ-7000 instrument (FAB, EI and CI modes) or an LCQ Finnigan-MAT LCQ instrument (APCI and ESI modes). HRMS analyses were obtained at the Université Mons-Hainaut, Mass spectroscopy laboratory, Pr. Flammang or at the University College of London (UK), chemistry department, Dr. L. D. Harris laboratory. UV spectra were recorded on a UV-vis-NIR Varian-Cary spectrophotometer (l given in nm). IR spectra were determined using a Shimadzu FTIR-8400S apparatus. Thin-layer chromatography was carried out on silica gel 60 plates F254 (Merck, 0.2 mm); product visualization was effected with UV light (l ¼ 254 nm), KMnO4 or I2. For flash chromatography we used Merck silica gel 60 of 230e400 mesh ASTM. Melting points were determined on an electro-thermal apparatus BUCHI Melting Point B-540.
3570 4.2. Organic chemistry 4.2.1. 1-(Benzotriazol-1-yl)-2-(4-isobutylphenyl)propan-1-one (2a) To a solution of ibuprofen (398 mg, 1.93 mmol) in dry THF (4 mL, 2 mL/mmol) were added BtMs (420 mg, 2.13 mmol) and TEA (300 mL, 2.14 mmol) under Ar atmosphere. The solution was heated overnight to reflux. The mixture was cooled to RT and evaporated to dryness. The residue was dissolved in ethyl acetate, washed with HCl 0.33 M, Na2CO3 (sat.), brine, dried over MgSO4, filtered and evaporated under vacuum. We obtained 573 mg (97%) of a white solid. Rf 0.73 (hexane/AcOEt 5:2); m.p. 52e55 C; 1 H NMR (300 MHz, CDCl3) d 0.86 (d, 3 J ¼ 6.6 Hz, 6H), 1.74 (d, 3 J ¼ 7.1 Hz, 3H), 1.80 (m, 1H), 2.40 (d, 3 J ¼ 7.2 Hz, 2H), 5.40 (q, 3 J ¼ 7.1 Hz, 1H), 7.09 (d, 3 J ¼ 8.1 Hz, 2H), 7.41 (d, 3 J ¼ 8.1 Hz, 2H), 7.48 (dd, 3 J ¼ 7.2 Hz, 3 J ¼ 8.2 Hz,1H), 7.63 (dd, 3 J ¼ 7.2 Hz, 3 J ¼ 8.2 Hz, 1H), 8.08 (d, 3 J ¼ 8.2 Hz, 1H), 8.29 (d, 3 J ¼ 8.2 Hz, 1H); 13 C NMR (125 MHz, CDCl3) d 18.9, 22.7, 30.4, 44.7, 45.3, 114.9, 120.4, 126.4, 128.1, 129.9, 131.7, 131.6, 136.7, 141.4, 146.5, 173.9; FT-IR (ATR-SeZn, cm 1 ) n 2954 (s), 1734 (s), 1450(m), 1380 (s), 1166 (m), 948 (s), 750 (m); MS (APCI) m/z: 308 [Mþ H] þ ,120 [Bt þ H] þ ;HRMScalcdforC19H21N3ONa: 330.1582, found: 330.1571. 4.2.2. N-Methoxy-N-methyl-2-(4-isobutylphenyl)propanamide (3a) To a solution of N-methoxy-N-methylamine hydrochloride (350 mg, 3.59 mmol) and TEA (500 mL, 3.56 mmol) in dry THF (5 mL) was added 1-(benzotriazol-1-yl)-2-(4-isobutylphenyl) propan-1-one (1 g, 3.25 mmol) under Ar atmosphere. The mixture was stirred overnight at RT, then evaporated to dryness and the residue was diluted in ethyl acetate (25 mL). The organic layer was washed with HCl (0.33 M), Na2CO3 (sat.), brine, dried over MgSO4, filtered and concentrated under vacuum. The residue was purified by flash chromatography (hexane/ethyl acetate 7:1) and 491 mg (61%) of pale yellow oil were obtained. Rf 0.54 (hexane/ethyl acetate 5:2); 1 H NMR (300 MHz, CDCl3) d 0.88 (d, 3 J ¼ 6.6 Hz, 6H), 1.42 (d, 3 J ¼ 7.0 Hz, 3H), 1.83 (m, 1H), 2.43 (d, 3 J ¼ 7.2 Hz, 2H), 3.16 (s, 3H), 3.40 (s, 3H), 4.10 (q, 3 J ¼ 7.0 Hz, 1H), 7.07 (d, 3 J ¼ 8.1 Hz, 2H), 7.20 (d, 3 J ¼ 8.1 Hz, 2H); 13 C NMR (125 MHz, CDCl3) d 19.8, 22.6, 30.4, 32.6, 41.9, 45.3, 61.4, 127.6, 129.6, 139.4, 140.4, 175.9; FT-IR (ATR-SeZn, cm 1 ) n 2954 (s), 1660 (s), 1510 (m), 1462 (s), 1379 (s), 1173 (m), 1119 (m), 1069 (m), 987 (s), 848 (m), 806 (w), 773 (w); MS (ESI) m/z: 521 [2M þ Na] þ ,272[Mþ Na] þ , 250 [M þ H] þ , 161 [M C3H6NO2] þ ; HRMS calcd for C15H24NO2: 250.1807, found: 250.1814. 4.2.3. N-Methoxy-N-methyl-2-phenylpropionamide (3b) To a solution of 2-phenylpropionic acid (2.14 mL, 14.3 mmol) in dry THF (60 mL) were added dropwise TEA (6.3 mL, 45.2 mmol) and mesyl chloride (1.3 mL,16.5 mmol) under Aratmosphere at 0 C. After 10 min, N-methoxy-N-methyl ammonium chloride (2.25 g, 23.1 mmol) was added and the mixture was stirred 1 h at RT. The mixture was diluted with water (30 mL) and diethyl ether (30 mL). The two layers were separated and the aqueous layer was extracted (2 ) with diethyl ether. The combined organic layers were washed with HCl (1 M), NaOH (1 M) and brine, dried over MgSO4, filtered and concentrated under vacuum to obtain 1.653 g (60%) of yellow oil. 1 H NMR (300 MHz, CDCl3) d 1.44 (d, 3 J ¼ 6.9 Hz, 3H), 3.16 (s, 3H), 3.40 (s, 3H), 4.12 (m, 1H), 7.29 (m, 5H); 13 C NMR (125 MHz, CDCl3) d 19.9, 32.7, 42.3, 61.4, 127.0, 127.9, 128.9, 142.2, 177.3; FT-IR (NaCl, cm 1 ) n 2935 (m), 1662 (s), 1452 (m), 1380 (m), 1176 (w), 986 (m), 754 (w), 700 (m); MS (ESI) m/z: 194 [M þ H] þ . 4.2.4. N-Methoxy-N-methyl-2-phenylacetamide (3c) To a solution of 2-phenylacetyl chloride (870 mL, 6.45 mmol) in dry CH2Cl2 (10 mL) were added N-methoxy-N-methyl ammonium chloride (690 mg, 7.07 mmol) and dropwise TEA (2 mL, 14.3 mmol) F. De Wael et al. / European Journal of Medicinal Chemistry 45 (2010) 3564e3574 under Ar atmosphere at 0 C. The mixture was stirred 1 h at RT. The mixture was diluted with water (5 mL) and acidified with HCl 2 M (5 mL). The two layers were separated, the organic layer was washed with NaHCO3 (sat.) and brine, dried over MgSO4, filtered and concentrated under vacuum. The residue was purified by flash chromatography (cyclohexane/ethyl acetate 5:1) and 740 mg (64%) of yellow oil were obtained. Rf 0.17 (cyclohexane/ethyl acetate 5:1); 1 H NMR (300 MHz, CDCl3) d 3.18 (s, 3H), 3.59 (s, 3H), 3.77 (s, 2H), 7.29 (m, 5H); 13 C NMR (75 MHz, CDCl3) d 32.2, 39.4, 61.2, 127.1, 128.9, 129.7, 134.8, 172.2; FT-IR (NaCl, cm 1 ) n 2939 (m), 1645 (s), 1455 (w), 1246 (w), 1187 (w), 1032 (w), 730 (w); MS (APCI) m/z: 180 [M þ H] þ ,91[C7H7] þ . 4.2.5. 1-(1,3-Dithian-2-yl)-2-(4-isobutylphenyl)-propan-1-one (4a) To a solution of 1,3-dithiane (135 mg,1.12 mmol) in dry THF (2 mL, 2 mL/mmol) was added dropwise n-BuLi (440 mL, 2.5 M in hexane) at 35 C under Ar atmosphere. The mixture was stirred vigorously for 1 h between 30 Cand 20 C and was added dropwise to a solution of N-methoxy-N-methyl-2-(4-isobutylphenyl)propanamide (245 mg, 0.98 mmol) in dry THF (3 mL) at 78 CunderAr atmosphere. The mixture was warmed to RT in 4 h and NH4Cl (sat., 5 mL) was added to quench the reaction. The mixture was extracted with diethyl ether (3 10 mL), the organic layers were combined, dried over MgSO4, filtered and concentrated under vacuum. The residue was purified by flash chromatography (hexane/ethyl acetate 10:1) and 174 mg (57%) of yellow oil were obtained. Rf 0.75 (hexane/ethyl acetate 10:1); 1 H NMR (300 MHz, CDCl3) d 0.88 (d, 3 J ¼ 6.6 Hz, 6H), 1.44 (d, 3 J ¼ 6.9 Hz, 3H), 1.84 (m, 1H), 1.99 (m, 1H), 2.09 (m, 1H), 2.44 (d, 3 J ¼ 7.1 Hz, 2H), 2.50 and 2.59 (m, 2H), 3.04 (ddd, 3 J ¼ 14.0 Hz, 3 J ¼ 11.5 Hz, 3 J ¼ 2.6 Hz, 1H), 3.51 (ddd, 3 J ¼ 13.8 Hz, 3 J ¼ 11.8 Hz, 3 J ¼ 2.9 Hz, 1H), 4.19 (s, 1H), 4.19 (q, 3 J ¼ 6.9 Hz, 1H), 7.09 (d, 3 J ¼ 8.3 Hz, 2H), 7.19 (d, 3 J ¼ 8.3 Hz, 2H); 13 C NMR (75 MHz, CDCl3) d 18.7, 22.7, 25.4, 26.1, 26.3, 30.4, 44.6, 45.3, 49.7, 128.0, 130.1, 137.4, 141.2, 203.1; FT-IR (ATR-SeZn, cm 1 ) n 2956 (s), 1709 (s), 1423 (s), 1242 (m), 1029 (s), 848 (w); MS (ESI) m/z:347 [M þ K] þ , 331 [Mþ Na] þ , 309 [M þ H] þ ; HRMS calcd for C17H24ONaS2: 331.1166, found: 331.1155. 4.2.6. 1-(1,3-Dithian-2-yl)-2-phenylpropan-1-one (4b) The protocol described for 4a was applied. Yield: 55%; Rf 0.23 (cyclohexane/ethyl acetate 95:5); 1 H NMR (300 MHz, CDCl3) d 1.46 (d, 3 J ¼ 6.9 Hz, 3H), 2.02 (m, 2H), 2.53 (m, 2H), 3.04 (ddd, 3 J ¼ 14.4 Hz, 3 J ¼ 11.4 Hz, 3 J ¼ 2.1 Hz, 1H), 3.48 (ddd, 3 J ¼ 14.4 Hz, 3 J ¼ 11.2 Hz, 3 J ¼ 2.7 Hz, 1H), 4.18 (s, 1H), 4.23 (q, 3 J ¼ 6.9 Hz, 1H), 7.27 (m, 5H); 13 C NMR (125 MHz, CDCl3) d 18.3, 25.0, 25.7, 25.9, 44.4, 49.8, 127.3, 127.9, 128.9, 139.9, 202.6; FT-IR (NaCl, cm 1 ) n 2929 (m), 1708 (s), 1493 (m), 1452 (m), 1423 (m), 1261 (w), 1066 (w), 1028 (m), 912 (w), 742 (w), 700 (s); MS (APCI, positive mode) m/z: 253 [M þ H] þ , 217, 215; MS (APCI, negative mode) m/z: 251[M H] , 209, 179, 175. 4.2.7. 1-(1,3-Dithian-2-yl)-2-phenylethan-1-one (4c) The protocol described for 4a was applied. Yield: 50%; Rf 0.32 (cyclohexane/ethyl acetate 95:5); 1 H NMR (300 MHz, CDCl3) d 2.02 (m, 2H), 2.57 (m, 2H), 3.24 (ddd, 2 J ¼ 14.3 Hz, 3 J ¼ 11.1 Hz, 3 J ¼ 2.7 Hz, 2H), 3.96 (s, 2H), 4.26 (s, 1H), 7.27 (m, 5H); 13 C NMR (125 MHz, CDCl3) d 25.0, 25.8, 45.3, 46.7, 127.1, 128.6, 129.4, 133.6, 199.8; FT-IR (NaCl, cm 1 ) n 2916 (m), 1708 (s), 1496 (w), 1425 (w), 1315 (m), 1257 (m), 1049 (m), 754 (m), 704 (s); MS (APCI) m/z: 239 [M þ H] þ , 163 [C6H11OS2] þ ,149[C5H9OS2] þ . 4.2.8. 3-(4-Isobutylphenyl)-1-nitrobutan-2-one (6a) To a vigorously stirred solution of nitromethane (36 mL, 0.66 mmol) in dry DMSO (3.5 mL, 5 mL/mmol) at 10 C was added t-BuOK (164 mg, 1.46 mmol) under Ar atmosphere. The mixture
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