MAGNETIC RESONANCE IN CHEMISTRYMagn. Reson. Chem. 2006; 44: 856–860Published online 20 June 2006 in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/mrc.1863

NMR spectroscopic structure elucidation of theproducts of the reaction of 3-(3-aryl-3-oxopropenyl)-chromen-4-ones with 1,2-phenylenediamine†

Gabor Toth,1,4∗ Andras Simon,1 Tımea Gondos,1 Albert Levai,2 Jozsef Jeko,3 andFerenc Andrasi4

1 Institute for General and Analytical Chemistry, Budapest University of Technology and Economics, Szent Gellert ter 4, H-1111 Budapest, Hungary2 Department of Organic Chemistry, University of Debrecen, P.O. Box 20, H-4010 Debrecen, Hungary3 Department of Chemistry, College of Nyıregyhaza, Sostoi u. 31/b, H-4400 Nyıregyhaza, Hungary4 Drug Research Institute Ltd., Berlini u. 47-49, H-1045 Budapest, Hungary

Received 6 April 2006; Revised 10 May 2006; Accepted 12 May 2006

The reaction of 3-(3-aryl-3-oxopropenyl)chromen-4-ones with 1,2-phenylenediamine resulted in theunexpected formation of 10a-aryl-1,2,10,10a-tetrahydrobenzo-[4,5]-imidazo[1,2-a]pyridin-3-yl(2-hydroxy-phenyl)-1-methanones. Their structure elucidation and complete 1H and 13C assignments have beenperformed by a combination of various one- and two-dimensional NMR experiments. Copyright 2006John Wiley & Sons, Ltd.

KEYWORDS: NMR; 1H; 13C; 15N; stereo structure; new 10a-aryl-1,2,10,-10a-tetrahydrobenzo[4,5]imidazo[1,2-a]pyridin-3-yl(2-hydroxyphenyl)-1-methanones

INTRODUCTION

Owing to their activity on the central nervous system,benzodiazepines are the active ingredients of severalimportant and popular medicines. Simple and conve-nient methods have been introduced for the preparationof 1,5-benzodiazepines and numerous representatives ofthese compounds have become easily available for bio-logical and pharmaceutical trials. Different series of 2,3-dihydro-1H-1,5-benzodiazepines were synthesized by thereaction of ˛,ˇ-unsaturated ketones1 and exocyclic ˛,ˇ-unsaturated ketones2 with 1,2-phenylenediamine or related1,2-diamino compounds.3 In continuation of our previousstudies on the chemical transformations of 3-(3-aryl-3-oxopropenyl)chromen-4-ones,4 the aim of our present workwas to try to synthesize 2,3-dihydro-4-aryl-2-(3-chromonyl)-1H-1,5-benzodiazepines by the reaction of these chromonederivatives with 1,2-phenylenediamine.

RESULTS AND DISCUSSION

3-(3-Aryl-3-oxopropenyl)chromen-4-ones,5 1a–f, were allo-wed to react with 1,2-phenylenediamine in hot ethanolin the presence of acetic acid. On the basis of publishedliterature data about the synthesis of 2,3-dihydro-1H-1,5-benzodiazepines by the reaction of 1,2-phenylenediamine

ŁCorrespondence to: Gabor Toth, Institute for General andAnalytical Chemistry, Budapest University of Technology andEconomics, Szent Gellert ter 4, H-1111 Budapest, Hungary.E-mail: gabor.toth@mail.bme.hu†This contribution is dedicated to Prof. Dr Helmut Duddeck,Hannover, Germany, on the occasion of his 60th birthday.

with ˛,ˇ-unsaturated ketones under similar reaction condi-tions, the formation of 2,3-dihydro-4-aryl-2-(3-chromonyl)-1H-1,5-benzodiazepines, 2a–f, was expected.1 Structures ofthe isolated yellow crystalline major products were analyzedby NMR and mass spectroscopic measurements. 70 eV EImass spectra revealed molecular ions that were higher by2 Daltons than those of the compounds 2a–f (Scheme 1).Since this available information suggested that the iso-lated substances cannot be the 1,5-benzodiazepines thatwere expected, one-dimensional 1H, 13C, APT, DEPT-135and two-dimensional gradient selected 1H,1H-COSY, HSQC,HMQC, HMQC-TOCSY, HMBC and 1H,1H-NOESY spectrawere run for structure elucidation and 1H/13C NMR signalassignment. Structure elucidation and NMR signal assign-ment were performed using widely accepted strategies.6

The 1H,1H-COSY spectra proved the proton–proton con-nectivities within the spin systems, the HMQC and HSQCmeasurements assigned the one-bond coupled 1H and 13Cnuclei, whereas the HMBC measurement supported the cor-relations between 1H and 13C atoms over two and threebonds. The chemical shifts are shown in Tables 1 and 2.

Assignment of the 1H and 13C NMR spectra of compound3d (Scheme 1) will be considered in detail (Fig. 1). For othercompounds, analyses were carried out in a similar way.

The compound 3d exhibited in the EI MS spectrum [M]C

ions at 446/448 m/z, corresponding to a molecular formulaof C24H19N2O2Br. The 1H, DEPT-135 and HSQC spectrashowed two CH2 groups, which immediately ruled outthe existence of type 2 structures. The assignment of thepeak at 192.2 in the 13C NMR spectrum to a conjugatedC O group is straightforward. Seven quaternary sp2 carbon

Copyright 2006 John Wiley & Sons, Ltd.

NMR of 10a-aryl-1,2,10,10a-tetrahydrobenzo-[4,5]-imidazo[1,2-a]pyridin-3-yl(2-hydroxyphenyl)-1-methanones 857

Scheme 1. Reaction route and atomic numbering of products3a–f.

Table 1. 1H chemical shifts of compounds 3a–f (in CDCl3)

3a 3b 3c 3d 3e 3f

1 ax 2.15 2.13 2.14 2.14 2.13 2.12– eq 2.78 2.87 2.73 2.72 2.73 2.75

2 ax 1.86 1.87 1.85 1.85 1.85 1.89– eq 2.95 2.95 2.95 2.95 2.95 2.93

4 – 7.87 7.86 7.84 7.83 7.84 7.856 – 6.86 6.86 6.86 6.86 6.86 6.867 – 6.80 6.79 6.81 6.82 6.81 6.798 – 6.83 6.83 6.85 6.84 6.84 6.839 – 6.60 6.60 6.62 6.62 6.62 6.6030 – 7.04 7.04 7.04 7.03 7.04 7.0340 – 7.44 7.44 7.44 7.44 7.44 7.4350 – 6.95 6.94 6.94 6.94 6.95 6.9360 – 7.58 7.57 7.55 7.55 7.56 7.56200 – 7.39 7.27 7.32 7.26 7.35 7.29300 – 7.41 7.22 7.37 7.53 7.08 6.92400 – 7.33 – – – – –500 – 7.41 7.22 7.37 7.53 7.08 6.92600 – 7.39 7.27 7.32 7.26 7.35 7.29R – – 2.35 – – – 3.78OH – 11.25a 11.25a 11.20a 11.21 11.25a 11.31a

– – – – 10.10b 10.06b – 10.11b

NH – 4.39a 4.35a 7.05b 4.36a 4.30a 4.38a

– – – – – 7.05b – –

a Broad.b Measured in DMSO–d6.

signals were observed between 157–111 ppm, whereas onlyone quaternary sp3 carbon signal was observed at 82.2. Theappearance of nine CH signals and an addition of two

CH signals with double intensity (characteristic for para-substituted phenyl group) proved that two hydrogen atomsare attached to one oxygen atom and one nitrogen atom,respectively. The high chemical shift, υ D 10.06, of the OHgroup indicates a strong intramolecular hydrogen bonding.The OH and NH signals were rather sharp in the spectrataken in DMSO-d6, therefore we preferred this solvent forthe HMBC experiments.

Table 2. 13C chemical shifts of compounds 3a–f (in CDCl3)

3a 3b 3c 3d 3e 3f

1 32.5 32.5 32.3 32.3 32.5 32.52 18.8 18.9 18.8 18.8 18.8 18.93 111.6 111.6 11.6 111.6 111.5 111.64 139.6 139.6 139.5 139.5 139.6 139.65a 133.4 133.4 133.4 133.4 133.4 133.46 108.0 107.9 108.1 108.1 108.0 107.97 120.8 120.7 121.1 121.2 121.0 120.88 123.9 123.8 124.0 124.0 124.0 123.99 111.3 111.3 111.6 111.6 111.5 111.49a 139.4 139.4 139.0 139.0 139.1 139.510a 83.2 83.1 82.6 82.7 82.6 82.910 121.1 121.1 120.9 120.9 121.0 121.120 160.8 160.8 160.8 160.9 160.8 160.830 117.9 117.9 118.1 118.0 118.0 117.940 133.6 133.6 133.7 133.8 133.7 133.650 118.2 118.2 118.3 118.3 118.2 118.260 130.7 130.8 130.7 130.7 130.7 130.7100 142.3 139.4 140.9 141.5 138.3 134.4200 123.9 123.8 125.6 125.9 126.0 125.3300 129.3 129.9 129.4 132.4 116.1 114.6400 128.5 138.4 134.4 122.6 162.5 159.6500 129.3 129.9 128.5 132.4 116.1 114.6600 123.9 123.8 125.6 125.9 126.0 125.3C O 195.1 195.1 195.2 195.2 195.1 195.1R – 21.0 – – – 55.3

The 1H,1H-COSY measurement revealed the presenceof five separated spin systems, i.e. two 1,2-disubstituted(6.84d, 6.58t, 6.72t, 6.46d and 7.27d, 6.89t, 7.31t, 6.92d, respec-tively) one 1,4-disubstituted phenyl (7.58 2H, 7.33 2H) rings,one –CH2 —CH2 – moiety, and one separated N–CH(υH-4 D 7.67s) spin. The characteristic HMBC and NOESYresponses of compound 3d are summarized in Table 3.

The connections of the five isolated 1H spin systemsidentified in the COSY should be revealed on the basis of thetwo- and three-bond J(C,H) couplings (Table 3).

H-200,600 (υ D 7.33) atoms of the p-substituted phenyl ringgive over three bonds strong HMBC cross-peaks with the sp3

quaternary carbon atom C-10a (82.2), which is connected totwo nitrogens. The –CH2 —CH2 – moiety is also connectedto C-10a, and the cross-peaks at 1.98/82.2 and 1.98/142.3give rise to the assignment of this hydrogen to H-1. Onthe basis of the 1.56/111.5 correlation the C-2 methyleneis attached to an enamine group (C-3 D C-4 � N-5),which forms the six-membered piperidine ring with theC-2 � C-1 � C-10a moiety. On the basis of the H-4/C OHMBC response (7.67/192.2), the carbonyl group is attachedto C-3 atom, whereas the H-60/C O response elucidated itsother neighbor, the ortho-disubstituted phenyl ring with theOH group. The sharp appearance and the high chemicalshift of the OH signal indicate a chelate bonding withthe carbonyl. The H-4/C-5a coupling gave evidence of thejunction of the remaining ortho-disubstituted phenyl ring,which should be a benzimidazo group. Taking into accountthe cross-peaks of the NH hydrogen with C-5a, C-9a and

Copyright 2006 John Wiley & Sons, Ltd. Magn. Reson. Chem. 2006; 44: 856–860DOI: 10.1002/mrc

858 G. Toth et al.

Figure 1. Sections of the HMBC spectrum of compound 3d (DMDO–d6).

C-10a atoms, respectively, the assignment of this ring alsobecame straightforward.

Stereo structureThe H-200,600/Heq-1, H-200,600/NH and H-200,600/Hax-2 cross-peaks in the NOESY spectrum indicated the axial positionof the p-Br-phenyl group. Considering the high value of theJ�Hax-1,Hax-2� D 12.9 Hz coupling, these hydrogen atomsshould be antiperiplanar, which arrangement is in accor-dance with a sofa-type conformation of the six-memberedpiperydine ring. The results of the semiempirical PM3 calcu-lation (HyperChem 7.0) also supported this stereo structure.The H-4/H-6 cross-peak marked out the H-6 signal, butthe other NOESY response of H-4 with H-60 revealed thesteric proximity of these atoms, which can be achieved bysupposing a free rotation around the O C–C-3 bond.

The presence of two nitrogen atoms in position 5 and10 was proven with a 1H,15N-gs-HMBC measurement onsample 3f. The H-6, H-4 and Heq-1 hydrogen atoms showedHMBC cross-peaks at �256.9 ppm and gave the assignmentof υ N-5. According to the stereo structure depicted inFig. 2, Heq-1 and N-5 atoms are antiperiplanar. At the samemeasurement, the Hax-1 atom resulted in a cross-peak at�289.6 ppm with the gauche arranged N-10 atom. These datagave further support of the structure and stereo structure.

Pharmacological investigationsThe chemical structure and novelty of compound 3 promptedus to investigate compounds 3a–c and 3f in vitro on the P-170efflux pump. This 170 kDa ATPase enzyme extrudes severallarge lipophilic xenobiotics from the mammalian cells andthus, when over-expressed, is the cause of drug-resistancein cancer cells. The activity of the enzyme was enhanced by40 µM verapamil, and the inhibition was investigated at 10and 100 µM concentrations of the test molecules. Compounds3a–c and 3f showed 56%, 58%, 54% and 49% inhibition,respectively, at 10 µM.

The in vivo biological activity was tested in male CD1-type mice with a dose of 100 mg kg�1 (intraperitonealapplication). The molecules showed mild tranquilizingactivity (the spontaneous locomotor activity was diminished)that lasted for 2 h. This dose was atoxic.

CONCLUSIONS

We have observed an unprecedented formation of 10a-aryl-1,2,10,10a-tetrahydrobenzo-[4,5]imidazo[1,2-a]pyridin-3-yl(2-hydroxyphenyl)-1-methanones by the reaction of 3-(3-aryl-3-oxopropenyl)chromen-4-ones with 1,2-phenylene-diamine. Analogous fused nitrogen-containing ring system

Copyright 2006 John Wiley & Sons, Ltd. Magn. Reson. Chem. 2006; 44: 856–860DOI: 10.1002/mrc

NMR of 10a-aryl-1,2,10,10a-tetrahydrobenzo-[4,5]-imidazo[1,2-a]pyridin-3-yl(2-hydroxyphenyl)-1-methanones 859

Table 3. 1H and 13C chemical shifts, J(H,H) couplings, characteristic HMBC and NOESY responses of compound 3d inDMSO–d6

1H J(Hz) 13C HMBC NOESY

1 ax 1.98 12.9, 4.8 (td) 31.7 C-3, C-10a, C-100 Hax-2– eq 2.66 – – C-3 H-200,600

2 ax 1.56 18.0,12.9, 4.8(ddd) 18.2 C-3, C-10a, C-100 Hax-1, H-200,600

– eq 2.66 – – C-10a –3 – – – 111.5 – –4 – 7.67 – 139.7 C-2, C-3, C-5a, C-10a, C O H-6, H-60

5a – – – 132.4 – –6 – 6.84 7.6 (d) 107.9 C-8, C-9a H-4, H-77 – 6.58 7.6 (t) 118.6 C-5a, C-8, C-9 H-6, H-88 – 6.72 7.6 (t) 123.5 C-6, C-9a H-7, H-99 – 6.46 7.6 (d) 109.1 C-5a, C-7 H-8, NH9a – – – 140.1 – –10a – – – 82.2 – –10 – – – 126.1 – –20 – – – 155.7 – –30 – 6.92 8.1 (d) 116.4 C-10, C-50 OH40 – 7.31 8.1, 7.5, 1.6 (ddd) 131.0 C-20, C-60 H-50

50 – 6.89 7.5 (t) 118.7 C-10, C-30 H-40, H-60, H-200,600

60 – 7.27 7.5, 1.6 (dd) 129.6 C-20, C-40, C O H-4, H-50

C O – – – 192.2 – –100 – – – 142.3 – –200,600 – 7.33 8.6 (d) 126.9 C-10a, C-400, C-300,500 Heq-1, Hax-2, NH, H-300,500

300,500 – 7.58 8.6 (d) 131.5 C-100, C-200,600, C-400 H-200,600

400 – – – 121.1 – –OH – 10.06 – – C-10, C-20, C-30 H-30

NH – 7.05 – – C-5a, C-9a, C-10a H-9, H-200,600

has been synthesized only in one case by the reaction of 1,5-diketones with 1,2-phenylene-diamine.7 Stereo structure ofcompounds 3 along with full NMR signal assignments, weredetermined. Compounds 3 exhibited interesting anticanceractivity.

EXPERIMENTAL

Synthesis of compounds 3a–fA mixture of 3-(3-aryl-3-oxopropenyl)chromen-4-one4 (1a–f,1.0 g), 1,2-phenylene-diamine (2.0 g), ethanol (50.0 ml) andacetic acid (5.0 ml) was refluxed for 7 h, then the solventwas evaporated under reduced pressure. The major productwas separated by silica gel column chromatography byusing 1,2-dichloroethane as eluent to afford compounds3a–f (Scheme 1). All compounds gave satisfactory elementalanalysis data.

10a-Phenyl-1,2,10,10a-tetrahydrobenzo[4,5]imidazo[1,2-a]pyri-din-3-yl(2-hydroxyphenyl)-1-methanone (3a): m.p. 199–200 °C; yield 40%, ms (m/z) 368 (MC, 29), 339 (35), 291(100), 195 (73).

10a-(4-Methylphenyl)-1,2,10,10a-tetrahydrobenzo[4,5]imidazo[1,2-a]pyridin-3-yl(2-hydroxyphenyl)-1-methanone (3b): m.p.98–99 °C; yield 36%; ms (m/z) 382 (MC, 45), 353 (38), 291(91), 209 (100).

10a-(4-Chlorophenyl)-1,2,10,10a-tetrahydrobenzo[4,5]imidazo[1,2-a]pyridin-3-yl(2-hydroxyphenyl)-1-methanone (3c): m.p.

101–102 °C; yield 39%; ms (m/z) 402 (MC, 24), 373 (21),291 (64), 229 (100).

10a-(4-Bromophenyl)-1,2,10,10a-tetrahydrobenzo[4,5]imidazo[1,2-a]pyridin-3-yl(2-hydroxyphenyl)-1-methanone (3d): m.p.126–127 °C; yield 35%; ms (m/z) 446/448 (MC, 16/16),417/419 (13/13), 291 (100), 273/275 (82/82).

10a-(4-Fluorophenyl)-1,2,10,10a-tetrahydrobenzo[4,5]imidazo[1,2-a]pyridin-3-yl(2-hydroxyphenyl)-1-methanone (3e): m.p.195–196 °C; yield 35%; ms (m/z) 386 (MC, 26), 357 (25),291 (60), 213 (100).

10a-(4-Methoxyphenyl)-1,2,10,10a-tetrahydrobenzo[4,5]imidazo[1,2-a]pyridin-3-yl(2-hydroxyphenyl)-1-methanone (3f): m.p.105–106 °C; yield 34%; ms (m/z) 398 (MC, 53), 369 (52),291 (100), 225 (98).

NMR spectroscopyNMR spectra were recorded on a Bruker Avance-500spectrometer in CDCl3 and DMSO-d6 at 300 K. Chemicalshifts are given on the υ scale and referenced to TMS asthe internal standard in the 1H and 13C measurements.The 15N chemical shifts were detected by 1H,15N-gs-HMBCmethod optimized for J(N,H) D 5 Hz long-range couplingsand referenced to υMeNO2 D 0 as external standard. Theone-dimensional (1H,13C, ATP and DEPT-135) and two-dimensional (1H,1H-gs-COSY, gs-HSQC, gs-HMQC, gs-HMQC-TOCSY, gs-HMBC, and 1H,1H-NOESY with mixingtime D 300 m s�1 and relaxation delay of 2 s) measurements

Copyright 2006 John Wiley & Sons, Ltd. Magn. Reson. Chem. 2006; 44: 856–860DOI: 10.1002/mrc

860 G. Toth et al.

Figure 2. Stereo structure (HyperChem 7) of compound 3d.

were utilized with acquisition and processing parameters asdescribed in our previous publications.8 The pulse programswere taken from the Buker software library.

AcknowledgementsThis study was sponsored by the Hungarian Scientific Research Fund(Grant Nos OTKA T046127 and T049468). The technical assistanceof Mrs. M. Nagy is highly appreciated. A.S. is grateful for theVarga/Rohr fellowship.

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Copyright 2006 John Wiley & Sons, Ltd. Magn. Reson. Chem. 2006; 44: 856–860DOI: 10.1002/mrc