Abstract
A series of benzo[b][1, 8]naphthyridines has been synthesized by Friedländer condensation of 2-aminoquinoline-3-carbaldehyde 1 (o-aminoaldehyde) with active methylenes in basic medium. The fluorescence spectroscopic properties of some representative compounds has been studied in different organic solvents; moreover interaction with bovine serum albumin (BSA) in phosphate buffer was examined by UV–vis and fluorescence spectroscopy. The effect of electron donor-acceptor substituents on fluorescence properties of benzo[b][1, 8]naphthyridines 13(a-n) has been investigated along with their fluorescent quantum yields.
Synthesis and fluorescence investigation of benzo[b][1,8]naphthyridines
Avoid common mistakes on your manuscript.
Introduction
In recent years, carbon rich organic compounds with a high degree of π-conjugation has received much attention because of their unique property as an ideal materials for advanced electronic and photonic applications, such as organic light-emitting diodes (OLEDs), liquid-crystal displays, thin-film transistors, solar cell and optical storage devices [1–19]. Large π-electron donor-acceptor compounds like ADMS, 9-(4-N,N-dimethylaminophenyl)-anthracene, has been the subject of intensive investigations during past decade. Recently, several donor and/or acceptor substituted compounds related to carbazoles, acridines etc. were synthesized and photoinduced charged separation has been intensively studied [20–22]. The 4-N,N-dimethylaminophenyl derivatives of bis-pyrazolo[3,4-b;4’3’-e]pyridine and pyrazolo[3,4-b]quinoline are further representatives of bulky π-electron donor-acceptor compounds and were recently investigated in some detail both experimentally [23–28] as well as semiempirically [26, 29–31]. These are highly emissive in non-polar solvents and shows charge separation and dual fluorescence in polar protic solvents. The donor-acceptor diphenylpolyenes capable of fluorescing from their charge-transfer excited states and were studied for microenvironment of micelles and proteins [32–35]. From literature, it was observed that the photophysical properties of heterocyclic compounds in different organic solvents were little explored. Prompted with these literature reports, we undertook the synthesis and study photophysical properties of benzonaphthyridines obtained from 2-aminoquinoline-3-carbaldehyde (o-aminoaldehyde) 1. The construction of ring structures from orthoaminoaldehyde as a starting material has wide applicability for the annulation of various heterocyclic systems [36–56].
In our earlier communications [57–61], we have reported the synthetic utility of heterocyclic o-aminoaldehyde in which annulation of heterocyclic system on pyrazole and pyrazolopyridine nucleus were performed and recently [62] synthesis of fluorescent benzo[b][1, 8]naphthyridine-3-carbonitrile using 1 has been reported. In this communication, we extend the work towards the synthesis of several linear polycyclic heterocycles from 1 and studied their photophysical properties. We also studied the effect of specific solvent-fluorophore interaction on absorption and emission of flurophore 13k, 15b as well as fluorescence properties of 13d, 13k, 15a and 15b in aqueous buffer and in bovine serum albumin (BSA) (a well known protein responsible for transport of a variety of ligands [63]) are studied. Photophysical properties of 13(a-n) are also studied and compared absorption and emission maxima with reference to donor and acceptor substituents on D ring (Fig. 1). The substituent effect on the performance of 13(a-n) and 15(a-d) are studied by calculating HOMO, LUMO energies and electron hole gap by using MOPAC-2009 to investigate the fluorescence properties of 13 and 15.
3D picture of benzo[b][1, 8]naphthyridine 13(a-g) and 13(h-n)
Result and Discussion
In continuation of our efforts to explore the synthetic applicability of o-aminoaldehyde 1 [62], we report herein condensation of 1 with different reactive methylenes to obtained polycyclic heterocycles. Thus, Friedländer condensation of 1a or 1b with active methylene nitriles such as malononitrile/cyanoacetamide in ethanol using piperidine as a base under reflux yielded 2-aminobenzo[b][1, 8]naphthyridine-3-carbonitrile 3(a-b) and 2-aminobenzo[b][1, 8]naphthyridine-3-carboxymide 5(a-b) respectively in 83-87% yield. In this cyclization, the reactive methylene undergoes Aldol condensation with carbonyl of 1 then intramolecular attack of amino on nitrile to yield 3 or 5. However, the course of reaction of 1 with cyanoacetic ester 6a or diethyl malonate 6b is different under similar reaction conditions in which Aldol type condensation of aldehyde carbonyl of 1 with active methylene, then SN2 attack of –NH2 functionality on to ester, displacing ethoxy group. This cyclocondensation furnished tricyclic benzo[b][1, 8]naphthyridine derivatives 7(a-d) in good yield. It was interesting to observe that when condensation partner of 1 is acetoacetic ester 8 then Friedländer condensation occur via usual combined Schiff base formation and then Aldol condensation to furnished 9(a-b) in 83-84% yield. Surprisingly, ester functionality in 7(c-d) and 9(a-b) remains intact in the product, under basic reaction condition. Cyclocondensation of 1a or 1b with aliphatic ketones 10(a-b) and substituted acetophenones 12(a-g) under similar reaction condition smoothly yielded benzo[b][1, 8]naphthyridine 11(a-d) and 13(a-n) respectively in excellent yield.
Reactions of o-aminoaldehyde 1 (2-aminoquinoline-3-carbaldehyde) with cyclic ketones are especially valuable for the construction of polycondensed heterocyclic rings. The synthesis of pentacyclic linear heterocycles can be achieved by condensation of 1a or 1b with indanone 14(a-b). However, this condensation was unsuccessful under mild base such as piperidine, hence; this cyclocondensation was achieved by using strong base such as ethanolic KOH. Thus, condensation of 1a or 1b with indanone 14(a-b) yielded 9,10-dimethoxy-7H-benzo[b]indeno[1,2-g][1, 8]naphthyridine 15(a-d) in 80–89% yield (Scheme 1). Substituents of 13(a-n) and 15(a-d) are summarized in Tables 1 and 4. Synthesised compounds were characterized by spectroscopic and analytical methods. The spectroscopic data of 15b is discussed here. The 1 H NMR of 15b shows three singlet at 3.88, 3.96 and 4.05 ppm corresponds to protons of three methoxy groups, singlet at 3.75 ppm corresponds to methylene protons. All aromatic protons shows expected chemical shifts and splitting patterns which resembles with the structure of 15b. The mass spectrum of 15b reveals a molecular ion peak m/z at 358. The 13 C NMR spectrum of this compound in agreement with the structure proposed. (Scheme 1)
Synthesis of Benzo[b][1,8]naphthyridines
Semi-empirical study of Benzo[b][1, 8]naphthyridine 13(a-n) and 2,9,10-trimethoxy-7H-benzo[b]indeno[1,2-g][1, 8]naphthyridine 15(a-d)
The heterocycles which are useful as Organic Light Emitting Diodes (OLED) should fluoresces between 400–700 nm and HOMO/LUMO or ‘electron-hole’ gap in the range 2.7–3.0 eV i.e. low gap [64]. Prompted with these quotations, we have calculated HOMO-LUMO energies, electron hole gap of compounds 13 and 15 by using MOPAC-2009 (Version 8.331) [65, 66] and are summarized in Table 1. The charge is more concentrated on ring D as compared to ring A, B and C (Fig. 1). The donor chromophores (-CF3,-OCH3 groups) on ring D plays an important role in increasing the electron density and lowering electron hole gap. Compounds 13c, 13d, 13e, 13j, 13k, 13l and 13m shows low GAP values indicating higher overlapping of HOMO or LUMO orbitals which shows red shift and high quantum yields. On the other hand, HOMO-LUMO energies of compound 13g and 13n shows increase in GAP values due to presence of inductively and mesomerically electron withdrawing chromophore (-NO2) i.e. lower overlapping of atomic orbitals, this shows blue shift and low quantum yields. Among 15, methoxy substituted derivatives 15a and 15b shows low GAP values, it fluoresces at longer wavelength and high quantum yields as compared to 15c and 15d. (Table 1)
Photophysical Properties
Effect of Solvent
The effects of solvents on fluorescence spectra are the result of specific interactions between the solvent and the fluorophore. Specific interactions are produced by one or a few neighboring molecules and are determined by specific chemical properties of both the fluorophore and the solvent [67, 68]. Specific effects can be due to hydrogen bonding, acid–base chemistry or charge-transfer interactions, to name a few of the possible origins. The emission spectra of fluorophore are depends both on orientation polarizability of the solvent and chemical structure of fluorophore and solvent. Therefore solvent effect can cause large change in emission of fluorophore and hence more easily observed spectral shifts. The solvent-fluorophore interactions can be studied by examining the UV/vis and fluorescence spectra of fluorophore in variety of solvents. Thus, absorption and emission spectra of 13k and 15b were undertaken in variety of solvents such as non-polar aprotic (n-Hexane), polar aprotic (THF, DMF, acetonitrile, acetone) and polar protic (Methanol, Ethanol) at room temperature at same concentration i.e. 1.0 × 10-3 M. The absorption and fluorescence spectral data of 13k and 15b in different organic solvents are summarized in Table 2 and graphically represented in Fig. 2. The fluorescence maxima of these compounds are greatly affected by the solvent polarity. Such a behavior indicates that the fluorescent state is not the same as the initially populated locally excited state (LE state), but it is a polar state with a charge transfer character. We observed that as the solvent polarity is increased further, the emission spectra continue to shift to longer wavelength and each monomer shows a certain solvatochromism in both the absorption and the emission spectrum. The λabs. max. and λem. max. of fluorophore 13k and 15b are significantly red-shifted as the solvent polarity is increased from n-Hexane to acetonitrile. In non-polar aprotic solvents (such as n-Hexane), the fluorescence intensities are weak as well as a shift of the emission spectrum to shorter wavelength. It has been reported that in nitrogen heterocycles (e.g. quinoline, isoquinoline and acridine) there is a 1nπ* state very close to the π-π* state [69, 70]. In fact, in hydrocarbon solvents, the lowest excited singlet state in these molecules is of 1n, π* type. Most of these nitrogen heterocycles are weakly or non-fluorescent in non-polar and aprotic solvents. However, in polar-aprotic and protic solvents, they become strongly fluorescent due to a reversal of n, π* and π, π* states [69, 70]. Thus, π- π* is the lowest energy transition in these molecules in protic solvents. In protic solvents, the energy gap between 1n, π* and 1π, π* (lowest excited singlet state) is probably very small. In general, in the emission spectra, the emission bands are found to be similar in acetonitrile and DMF. On the other hand, in ethanol and methanol, the emission band shifts to the blue it may be due to intramolecular hydrogen bond interaction between solvent and fluorophore. As the absorption band shifts to the blue, the emission band also shifts to the local emission from the hydrogen bonded clusters. Thus, intramolecular hydrogen bonding between solvent-fluorophore interaction can often be identified by examining the emission spectra in different concentration of methanol. We thought that, fluorescence may increases as solvent polarity increases by increasing % of water, but surprisingly, we observed that intensity of this emission band to gradually increases and we noted that emission corresponding to only the monomer at 476 nm of 13k (Fig. 3). We observed that, emission is maximum in acetone because of acetone have keto-enol tautomerism due to this, conjugation increases as a result fluorophore may be fluoresces to longer wavelength in acetone. Thus UV/vis and fluorescence spectra of compounds 3(a-b), 5(a-b), 7(a-d), 9(a-b), 11(a-d), 13(a-n) and 15(a-d) are taken in acetone. Fluorescence quantum yield of each were determined by standard literature procedure using quinine sulphate as a reference standard [71, 72] and are given in Tables 2, 3 and 4.
UV–vis absorption (λabs. max.) and fluorescence (λem. max.) spectra of 13k in solvents of different polarity
Fluorescence emission spectra of 13k in methanol to which water was added. The % of water in the solvent were 1) 10% 2) 20% 3) 30% 4) 40%
Effect of Concentration
We also examined the effect of concentration on the fluorescence emission of 13k in acetone. By increasing the concentration from 1.0 × 10-7 M (Fig. 4, line 1) to 1.0× 10-3 M (Fig. 4, line 4), we observed that intensity of this emission band to gradually increases, and we noted that the emission corresponding to only the monomer at 550 nm (Fig. 4).
Effect of concentration on the fluorescence emission spectra of 13k recorded in acetone at room temperature (1) 1.0 × 10-7 M, (2) 1.0× 10-6 M, (3) 1.0× 10-5 M, (4) 1.0× 10-3
Effect of Electron Donor-Acceptor Substituents
From the Table 4, it was observed that fluorescence maxima of the compound 13(h-n) are larger than 13(a-g) may be due to presence of strong π-electron donor group i.e. -OCH3 on the A ring except 13d (Fig. 1). The 3D picture of the benzonaphthyridines 13(a-n) is depicted in Fig. 1. From the Table 4, it was noted that compound 13c, 13d, 13e, 13j, 13k and 13l shows fluorescence band appearing at longer wavelength was substantially bathochromically shifted, we ascribe to the increased π-electron density on the D ring, arising from the electron donating nature of -CF3 group (σ-π electron donor) at C3 & C5 position (13c, 13j) and -OCH3 group (π-electron donor) at para position (13d, 13k), at C3 & C4 position (13e, 13l) respectively. Among 13, the 13d and 13k displayed the largest bathochromic shift of absorption and fluorescence bands, which could be attributed to the methoxy group at para position on ring D having strongest electron donating ability having different substituents. On the other hand, blue shift was observed in 13g and 13n due to presence of electron acceptor group i.e. -NO2 group at para position on ring D. Another interesting feature was that halo substituted molecules (compounds 13a, 13b, 13h and 13i) shows less fluorescence, quantum yield than methoxy substituted compounds (ϕ F = 0.39-0.44). This may be due to the quenching of fluorescence with halogen atoms as the substitution. The comparative absorption and emission spectra of compounds 13j, 13k and 13n are graphically presented in Fig. 5. We also noted that among 15, the methoxy substituted compounds i.e. 15(a-b) shows more fluorescence and quantum yields as compare to 15(c-d) may be due to presence of -OCH3 group in 15(a-b) [R1 = R2 = OCH3] (Table 4).
The comparative absorption (UV λMax.) and fluorescence (Em λMax.) spectra of compounds 13j, 13k and 13n respectively
The Effect of BSA on the Fluorescence Emission of Compounds 13d, 13k, 15a and 15b in Phosphate Buffer
In order to examine the interaction of 13d, 13k, 15a and 15b with bovine serum albumin (BSA), the fluorescence titrations with BSA, was carried out in phosphate buffer of pH 7.4. The absorption and fluorescent spectral data of 13d, 13k, 15a and 15b are collected in Table 5 and λem. max. is graphically presented in Fig. 6. We observed the blue shift of λem. max. for 13d, 13k, 15a and 15b. We also examined the effect of increasing BSA concentration on fluorescence emission and noted that gradually increase in the concentration of BSA in the solutions of 13k in phosphate buffer results in an enhancement of the fluorescence emission and quantum yield (ϕF) (Fig. 7). The blue shift in the λem. max. suggests that the polarities of the protein environments in which the benzo[b][1, 8]naphthyridines are located are less that the polarity of the bulk aqueous phase since similar blue shifts are observed in less polar organic solvents. This shows the binding of the probes to a hydrophobic site of the protein.
Comparative fluorescence (Em λMax.) spectra of 13d, 13k, 15a and 15b: A] In Phosphate Buffer, B] In BSA
Fluorescence emission spectra of 13k with increasing BSA concentration; curves a-e correspond to [BSA] 1.0, 2.0, 3.0, 4.0 and 5.0 (x 10-6 mol L-1), respectively
Conclusion
In summary, the tetracyclic and pentacyclic linear heterocycles are synthesized by Friedländer condensation of activemethylene nitrile, active methylene and cyclic ketone such as indanone with 1. Our methods have several additional advantages such as milder reaction condition, shorter reaction time, scalable and lack of side product. UV–vis absorption and emission spectroscopic studies of 13k and 15b have been done in three types of solvents i.e. non-polar aprotic, polar aprotic, polar protic and it exhibit solvatochromic fluorescence emission in organic solvents. The interaction of 13d, 13k, 15a and 15b with BSA have been investigated by UV–vis absorption and fluorescence spectroscopy and observed that the λem. max. gets blue-shifted upon binding with BSA. However the fluorescence intensity enhancement is linear with the increasing in BSA concentration (13k). The fluorescence properties of benzo[b][1, 8]naphthyridines 13(a-n) depend upon the nature of substituents present on ring D. Thus, benzo[b][1, 8]naphthyridines 13(a-n) bearing electron-releasing group i.e. substituents like di-CF3 and -OMe (Compound 13c, 13j, 13d, 13e, 13k and 13l) on ring D (Fig. 1) fluoresces at longer wavelength as compared with the electron-withdrawing group like -NO2 (Compound 13g, 13n) on ring D (Fig. 1) at the para position. From empirical calculations, we revels that benzo[b][1, 8]naphthyridines (13a-n and 15a-d) which shows low electron hole gap values (e.g. 13c, 13d, 13e, 13j, 13k, 13l, 13m, 15a and 15b) are fluoresces at longer wavelength and have high quantum yields, while compounds with higher electron hole gap (e.g. 13b, 13g, 13h and 13n) are fluoresces at shorter wavelength with low quantum yields and are in agreement with theoretical observations. This study has brought out interesting substituent and solvent-dependent fluorescence properties of benzonaphthyridines. The efficient blue light emission and physical and chemical stability makes these benzonaphthyridine derivatives as a promising family of materials which may be useful in photophysical applications. All these synthesized compounds are addition to the library of new heterocyclic compounds.
Experimental
General
Bovine serum albumin (BSA) and Quinine sulphate was purchased from HiMedia Laboratories Pvt. Ltd. Mumbai (India) and Research-Lab Fine Chem Industries, Mumbai (India) respectively. All other chemicals, reagents and solvents were obtained from LOBA Chemie. Pvt. Ltd., Mumbai (India), Spectrochem, Mumbai (India) and E. Merck (India). All AR-grade organic solvents were dried and freshly distilled prior to use. The UV-grade solvents were used for spectral studies. Melting points were determined on a Gallenkamp melting point apparatus, Mod. MFB595 in open capillary tubes and are uncorrected. Fourier transform infrared (FTIR) spectra in KBr disk were measured on a Shimadzu FTIR-408 spectrophotometer. 1 H NMR and 13 C NMR spectra were recorded on a Varian XL-300 MHz spectrometer using tetramethylsilane (TMS) as internal standard and solvents are deuterio-chloroform (CDCl3) and deuterio-dimethylsulphoxide (DMSO-d 6 ). Chemical shifts are reported in ppm from internal tetramethylsilane standard and are given in δ-units. High-resolution mass spectra are obtained with a Mat 112 Varian Mat Bremen (70 eV) mass spectrometer. Elemental analyses are performed on a Hosli CH-Analyzer and are within ± 0.3 of the theoretical percentage. The absorption spectra were measured using a Shimadzu UV-1601 UV–VIS spectrophotometer. The fluorescence spectra were recorded on a RF-5301 PC spectrofluorophotometer by exciting the samples at their absorption maximum (λabs. max.). Compounds for UV and fluorescence measurements are dissolved in acetone, UV and fluorescence scan are recorded from 200 to 600 nm. The Фf relative to quinine sulphate in 1.0 × 10-3 mol L-1 H2SO4 (Фf = 0.57) was measured at room temperature by standard literature procedure [73–75]. Both samples and standard were excited at the same excitation wavelength and the optical density (OD) of the standard and the sample was adjusted to be nearly equal. For all electronic spectroscopic studies (absorption, fluorescence excitation and emission) 1.0 × 10-3 mol L-1 solutions of the compounds were used. All reactions are monitored by thin layer chromatography, carried out on 0.2 mm silica gel 60 F254 (Merck) plates using UV light (250 and 400 nm) and Fluorescence light (400 and 600 nm) for detection. For fluorescence quenching studies, the required amount of BSA solution (in phosphate buffer) and the required amount of benzo[b][1, 8]naphthyridines solution in dimethylsulphoxide (DMSO) (1.0× 10-4 mol L-1) were taken in a 5 ml volumetric flask. Since the benzo[b][1, 8]naphthyridines are sparingly soluble in water, their stock solutions were prepared in DMSO, which is used as a solvent for interaction studies of serum albumins [76].
Synthesis
Synthesis of 2-Aminobenzo[b][1, 8]Naphthyridine-3-Carbonitrile (3a, b)
A mixture of 2-aminoquinoline-3-carbaldehyde (1a-b) (0.01 mol) & malononitrile 2 (0.01 mol) in ethanol (10 mL) containing catalytic amount of piperidine was refluxed for 1 h. After completion of reaction (TLC checked), reaction mixture was cooled to room temperature. The separated solid product was collected by suction filtration, washed with cold methanol (10 mL), dried under vacuum and recrystallized from Ethanol: DMF (90:10) (v: v).
2-Aminobenzo[b][1, 8]Naphthyridine-3-Carbonitrile (3a)
Yield: 0.184 g (83%), recrystallized from Ethanol: DMF (90:10) to afford yellow solid; M.p. 283–286 °C, IR (KBr): 3,413 m, 3,375 m, 2,911 s, 2,219 s, 1,633 s cm-1. 1 H NMR (300 MHz DMSO-d 6 ) δ: 7.39 (dd, 1 H, J = 8.2 & 8.5 Hz, Ar-H), 7.53 (bs, 2 H, NH), 7.77 (dd, 1 H, J = 8.5 & 8.1 Hz, Ar-H), 7.92 (d, 1 H, J = 8.2 Hz, Ar-H), 8.08 (d, 1 H, J = 8.1 Hz, Ar-H), 8.66 (s, 1 H, Ar-H), 8.78 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 220 [M+] (20), 193 (30), 150 (20), 136 (60), 105 (40), 77 (40). Anal. Calcd. for C13H8N4 (220.23): C, 70.90; H, 3.63; N, 25.45% Found: C, 70.93; H, 3.60; N, 25.46%
7-Methoxy-2-Amino[b][1, 8]Naphthyridine-3-Carbonitrile (3b)
Yield: 0.218 g (87%), recrystalized from Ethanol: DMF (80: 20) to afford yellow needles; M.p. 278–281 °C. IR (KBr): 3,442 m, 3,378 m, 2,914 s, 2,230 s, 1,621 s, 1,019 m cm-1.1 H NMR (300 MHz DMSO-d 6 ) δ: 3.93 (s, 3 H, OCH3), 6.99 (bs, 2 H, NH), 7.43 (d, 1 H, J = 9.0 Hz, Ar-H), 7.51 (s, 1 H, Ar-H), 8.24 (d, 1 H, J = 9.0 Hz, Ar-H), 9.21 (s, 1 H, Ar-H), 9.44 (s, 1 H, Ar-H). 13 C NMR (75 MHz DMSO-d 6 ) δ: 58.32, 98.26, 108.11, 112.44, 122.78, 123.36, 128.21, 132.66, 133.43, 146.53, 148.27, 156.34, 158.74, 159.63. MS (70 eV) m/z (%): 250 [M+] (79), 223 (44), 207 (49), 130 (51), 69 (28), 44 (61), 32 (74). Anal. Calcd. for C14H10N4O (250.26): C, 67.20; H, 4.00; N, 22.40% Found: C, 67.18; H, 3.98; N, 22.38%
Synthesis of 2-Aminobenzo[b][1, 8]Naphthyridine-3-Carboxymide (5a, b)
A mixture of 2-aminoquinoline-3-carbaldehyde (1a-b) (0.01 mol) & cyanoacetamide 4 (0.01 mol) in ethanol (10 mL) containing catalytic amount of piperidine was refluxed for 2 h. After completion of reaction (TLC checked), reaction mixture was cooled to room temperature. The separated solid product was collected by suction filtration, washed with cold methanol (10 mL), dried under vacuum and recrystallized from Ethanol: DMF (70: 30) (v: v).
2-Aminobenzo[b][1, 8]Naphthyridine-3-Carboxymide (5a)
Yield 0.204 g (85%), recrystallised from Ethanol: DMF (70: 30) to afford yellow solid; M.p. 289–292 °C, IR (KBr): 3,440 m, 3,410 m, 3,245 m, 3,197 m, 2,929 m, 1,671 s, 1,613 s cm-1, 1 H NMR (300 MHz DMSO-d 6 ) δ: 7.15 (dd, 1 H, J = 7.9 & 8.2 Hz, Ar-H), 7.46 (bs, 2 H, NH), 7.89 (dd, 1 H, J = 8.2 & 8.6 Hz, Ar-H), 8.04 (d, 1 H, J = 7.9 Hz, Ar-H), 8.17 (d, 1 H, J = 8.6 Hz, Ar-H), 8.40 (bs, 2 H, NH), 8.82 (s, 1 H, Ar-H), 8.96 (s,1 H, Ar-H). MS (70 eV) m/z (%): 238 [M+] (78), 221 (31), 194 (76), 166 (62), 139 (59), 110 (45), 77 (67). Anal. Calcd. for C13H10N4O (238.24): C, 65.54; H, 4.20; N, 23.52% Found: C, 65.55; H, 4.21; N, 23.55%
2-Amino-7-Methoxybenzo[b][1, 8]Naphthyridine-3-Carboxymide (5b)
Yield 0.232 g (86%), recrystallised from Ethanol: DMF (80:20) to afford yellow prism, M.p. 283–285 °C. IR (KBr): 3,448 m, 3,419 m, 3,266 m, 3,207 m, 2,955 s, 1,675 s, 1,612 s, 1,022 m cm-1. 1 H NMR (300 MHz DMSO-d 6 ) δ: 4.01 (s, 3 H, OCH3), 7.10 (d, 1 H, J = 8.7 Hz, Ar- H), 7.21 (s, 1 H, Ar-H), 7.72 (bs, 2 H, NH), 7.98 (d, 1 H, J = 8.7 Hz, Ar-H), 8.34 (bs, 2 H, NH), 8.61 (s, 1 H, Ar-H), 8.65 (s, 1 H, Ar-H). 13 C NMR (75 MHz DMSO-d 6 ) δ: 55.47, 105.04, 114.51, 115.62, 118.23, 120.37, 130.19, 138.19, 139.98, 152.95, 155.91, 159.36, 161.94, 169.00. MS (70 eV) m/z (%): 268 [M+] (77), 251 (41), 225 (73), 196 (29), 181 (33), 44 (49), 32 (71). Anal. Calcd. for C14H12N4O2 (268.27): C, 62.68; H, 4.47; N, 20.89%. Found: C, 62.66; H, 4.48; N, 20.88%.
Synthesis of 1,2-Dihydro-2-Oxobenzo[b][1, 8]Naphthyridine-3-Carbonitrile (7 a-d)
A mixture of 2-aminoquinoline-3-carbaldehyde (1a-b) (0.01 mol) & ethylcyanoacetate (6a) (0.01 mol) in ethanol (10 mL) containing catalytic amount of piperidine was refluxed for 2 h. After completion of reaction (TLC checked), reaction mixture was cooled to room temperature. The separated solid product was collected by suction filtration, washed with cold methanol or pet-ether, dried under suction and recrystallized from Ethanol: DMF (80: 20) (v: v) or Ethanol.
1,2-Dihydro-2-Oxobenzo[b][1, 8]Naphthyridine-3-Carbonitrile (7a)
Yield: 0.179 g (80%), recrystalized from Ethanol: DMF (80: 20) to afford pale yellow crystal; M.p. 261–264 °C. IR (KBr): 3,240 m, 2,912 m, 2,244 s, 1,674 s, 1,601 s cm-1. 1 H NMR (300 MHz DMSO-d 6 ) δ: 7.22 (bs, 1 H, NH), 7.84 (dd, 1 H, J = 8.2 & 8.6 Hz, Ar-H), 7.97 (dd, 1 H, J = 8.6 & 8.0 Hz, Ar-H), 8.09 (d, 1 H, J = 8.2 Hz, Ar-H), 8.39 (d, 1 H, J = 8.0 Hz, Ar-H), 9.02 (s, 1 H, Ar-H), 9.13 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 221 [M+] (85), 193 (96), 178 (87), 150 (61), 127 (67), 96 (54), 77 (42), 44 (64). Anal. Calcd. for C13H7N3O (221.21): C, 70.58; H, 3.16; N, 19.00%. Found: C, 70.56; H, 3.18; N, 18.98%.
1,2-Dihydro-7-Methoxy-2-Oxobenzo[b][1, 8]Naphthyridine-3-Carbonitrile (7b)
Yield: 0.218 g (86%), recrystalized from Ethanol: DMF (70: 30) to afford yellow needles; M.p. 256–258 °C. IR (KBr): 3,256 m, 2,902 m, 2,239 s, 1,669 s, 1,598 s, 1,027 m cm-1.1 H NMR (300 MHz DMSO-d 6 ) δ: 4.03 (s, 3 H, OCH3), 6.92 (bs, 1 H, NH), 7.25 (d, 1 H, J = 8.6 Hz, Ar-H), 7.47 (s, 1 H, Ar-H), 8.12 (d, 1 H, J = 8.6 Hz, Ar-H), 9.31 (s, 1 H, Ar-H), 9.49 (s, 1 H, Ar-H). 13 C NMR (75 MHz DMSO-d 6 ) δ: 58.13, 98.47, 107.46, 109.11, 114.45, 123.65, 124.73, 126.88, 129.40, 135.29, 145.73, 154.32, 158.23, 166.30. MS (70 eV) m/z (%): 251 [M+] (72), 223 (67), 208 (51), 193 (38), 180 (89), 153 (62), 126 (60), 44 (81). Anal. Calcd. for C14H9N3O2 (251.24): C, 66.93; H, 3.58; N, 16.73% Found: C, 66.96; H, 3.60; N, 16.71%
Ethyl-1,2-Dihydro-2-Oxobenzo[b][1, 8]Naphthyridine-3-Carboxylate (7c)
Yield: 0.232 g (86%), recrystalized from ethanol to afford pale yellow solid; M.p. 195–198 °C. IR (KBr): 3,221 m, 2,901 s, 1,738 s, 1,669 s, 1,618 s, 1,022 m cm-1. 1 H NMR (300 MHz CDCl3) δ: 1.77 (t, 3 H, J = 5.3 Hz, CH3), 4.34 (q, 2 H, J = 5.3 Hz, CH2), 7.18 (bs, 1 H, NH), 7.29 (dd, 1 H, J = 7.7 & 8.1 Hz, Ar-H), 7.57 (dd, 1 H, J = 8.1 & 8.4 Hz, Ar-H), 7.92 (d, 1 H, J = 7.7 Hz, Ar-H), 8.32 (d, 1 H, J = 8.4 Hz, Ar-H), 9.12 (s, 1 H, Ar-H), 9.23 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 268 [M+] (79), 223 (66), 195 (76), 166 (59), 122 (64), 77 (48), 45 (34). Anal. Calcd. for C15H12N2O3 (268.27): C, 67.16; H, 4.47; N, 10.44% Found: C, 67.18; H, 4.45; N, 10.42%
Ethyl-1,2-Dihydro-7-Methoxy-2-Oxobenzo[b][1, 8]Naphthyridine-3-Carboxylate (7d)
Yield: 0.260 g (87%), recrystalized from ethanol to afford yellow needles; M.p. 185–188 °C. IR (KBr): 3,249 m, 2,912 s, 1,737 s, 1,674 m, 1,601 s, 1,027 s cm-1.1 H NMR (300 MHz CDCl3) δ: 1.88 (t, 3 H, J = 5.2 Hz, CH3), 3.98 (s, 3 H, OCH3), 4.28 (q, 2 H, J = 5.2 Hz, CH2), 6.28 (bs, 1 H, NH), 7.31 (d, 1 H, J = 8.6 Hz, Ar-H), 7.61 (s, 1 H, Ar-H), 8.29 (d, 1 H, J = 8.6 Hz, Ar-H), 9.20 (s, 1 H, Ar-H), 9.40 (s, 1 H, Ar-H). 13 C NMR (75 MHz DMSO-d 6 ) δ: 19.22, 55.89, 66.72, 104.22, 120.51, 121.20, 121.88, 122.26, 126.47, 132.77, 135.24, 141.02, 152.13, 161.23, 162.88, 167.34. MS (70 eV) m/z (%): 298 [M+] (76), 253 (68), 226 (91), 198 (79), 183 (51), 127 (52), 44 (31). Anal. Calcd. for C16H14N2O4 (298.29): C, 64.42; H, 4.69; N, 9.39% Found: C, 64.43; H, 4.71; N, 9.37%
Synthesis of Ethyl-2-Methylbenzo[b][1, 8]Naphthyridine-3-Carboxylate (9 a-b)
A mixture of 2-aminoquinoline-3-carbaldehyde (1a-b) (0.01 mol) & ethylacetoacetate (8) (0.01 mol) in ethanol (10 mL) containing 2-3 drops of piperidine was refluxed for 1 h. After completion of reaction (TLC checked), reaction mass dumped over ice-crushed water (20 mL) and stirred for the 30 mins., separated solid was filtered by suction, washed with cold n-hexane (20 mL), dried under vacuum and recrystallized from Ethanol or Toluene.
Ethyl-2-Methylbenzo[b][1, 8]Naphthyridine-3-Carboxylate (9a)
Yield: 0.222 g (83%), recrystalized from ethanol to afford yellow crystal; M.p. 264-267 °C. IR (KBr): 2,945 m, 1,738 s, 1,612 s, 1,018 m cm-1. 1 H NMR (300 MHz CDCl3) δ: 1.69 (t, 3 H, J = 5.9 Hz, CH3), 2.79 (s, 3 H, CH3), 4.33 (q, 2 H, J = 5.9 Hz, CH2), 7.34 (dd, 1 H, J = 8.2 & 8.7 Hz, Ar-H), 7.79 (dd, 1 H, J = 8.7 & 8.1 Hz, Ar-H), 8.09 (d, 1 H, J = 8.2 Hz, Ar-H), 8.36 (d, 1 H, J = 8.1 Hz, Ar-H), 8.78 (s, 1 H, Ar-H), 9.19 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 266 [M+] (95), 251 (89), 213 (85), 197 (64), 158 (80), 77 (71), 69 (47), 53 (38). Anal. Calcd. for C16H14N2O2 (266.29): C, 72.18; H, 5.26; N, 10.52% Found: C, 72.15; H, 5.24; N, 10.50%
Ethyl-7-Methoxy-2-Methylbenzo[b][1, 8]Naphthyridine-3-Carboxylate (9b)
Yield: 0.249 g (84%), recrystalized from ethanol to afford yellow needles; M.p. 257-260 °C. IR (KBr): 2,940 m, 1,740, 1,619 s, 1,024 m cm-1.1 H NMR (300 MHz CDCl3) δ: 1.72 (t, 3 H, J = 4.8 Hz, CH3), 2.66 (s, 3 H, CH3), 3.96 (s, 3 H, OCH3), 4.43 (q, 2 H, J = 4.8 Hz, CH2), 7.43 (d, 1 H, J = 8.8 Hz, Ar-H), 7.56 (s, 1 H, Ar-H), 8.24 (d, 1 H, J = 8.8 Hz, Ar-H), 9.21 (s, 1 H, Ar-H), 9.44 (s, 1 H, Ar-H). 13 C NMR (75 MHz CDCl3) δ: 19.24, 26.72, 59.33, 68.45, 110.21, 121.47, 123.57, 126.94, 129.78, 132.43, 137.44, 138.73, 147.87, 154.27, 158.94, 159.64, 169.09. MS (70 eV) m/z (%): 296 [M+] (69), 277 (94), 253 (74), 224 (41), 182 (57), 152 (59), 127 (49), 77 (64), 44 (88). Anal. Calcd. for C17H16N2O3 (296.32): C, 68.91; H, 5.40; N, 9.45%. Found: C, 68.90; H, 5.42; N, 9.47%.
Synthesis of 1-(2-Methylbenzo[b][1, 8]Naphthyridin-3-yl)Ethanone (11 a-d)
A mixture of 2-aminoquinoline-3-carbaldehyde (1a-b) (0.01 mol) & acetyl acetone (10a) (0.01 mol) in ethanol (10 mL) containing 2-3 drops of piperidine was refluxed for 1 h. After completion of reaction (TLC checked), reaction mass dumped over ice-crushed water (20 mL) and stirred for the 30 mins., separated solid was filtered by suction, washed with cold n-hexane (20 mL), dried under vacuum and recrystallized from Ethanol or Toluene.
1-(2-Methylbenzo[b][1, 8]Naphthyridin-3-yl)Ethanone (11a)
Yield: 0.201 g (85%), recrystalized from ethanol to afford faint yellow solid; M.p. 204-206 °C. IR (KBr): 2,945 s, 1,705 s, 1,632 s cm-1. 1 H NMR (300 MHz CDCl3) δ: 2.55 (s, 3 H, CH3), 2.89 (s, 3 H, CH3), 7.46 (dd, 1 H, J = 7.8 & 8.4 Hz, Ar-H), 7.83 (dd, 1 H, J = 8.4 & 8.3 Hz, Ar-H), 8.17 (d, 1 H, J = 7.8 Hz, Ar-H), 8.29 (d, 1 H, J = 8.3 Hz, Ar-H), 8.78 (s, 1 H, Ar-H), 9.19 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 236 [M+] (79), 221 (74), 205 (67), 193 (47), 190 (69), 152 (39), 121 (49), 77 (64), 44 (81), 31 (64). Anal. Calcd. for C15H12N2O (236.27): C, 76.27; H, 5.08; N, 11.86% Found: C, 76.28; H, 5.10; N, 11.88%
1-(7-Methoxy-2-Methylbenzo[b][1, 8]Naphthyridin-3-yl)Ethanone (11b)
Yield: 0.230 g (86%), recrystalized from ethanol to afford pale yellow needles; M.p. 214-217 °C. IR (KBr): 2,959 m, 1,712 s, 1,620 s, 1,024 s cm-1.1 H NMR (300 MHz CDCl3) δ: 2.44 (s, 3 H, CH3), 2.72 (s, 3 H, CH3), 4.09 (s, 3 H, OCH3), 7.31 (d, 1 H, J = 8.8 Hz, Ar-H), 7.46 (s, 1 H, Ar-H), 8.18 (d, 1 H, J = 8.8 Hz, Ar-H), 9.11 (s, 1 H, Ar-H), 9.39 (s, 1 H, Ar-H). 13 C NMR (75 MHz CDCl3) δ: 18.24, 28.76, 59.84, 109.44, 124.31, 125.74, 129.16, 133.43, 135.24, 136.37, 138.47, 147.89, 156.74, 159.21, 161.47, 187.20. MS (70 eV) m/z (%): 266 [M+] (100), 251 (94), 223 (32), 182 (95), 139 (46), 44 (51). Anal. Calcd. for C16H14N2O2 (266.29): C, 72.18; H, 5.26; N, 10.52%. Found: C, 72.19; H, 5.29; N, 10.50%.
2-Methylbenzo[b][1, 8]Naphthyridine (11c)
Yield: 0.155 g (79%), recrystalized from toluene to afford faint yellow solid; M.p. 90-93 °C. IR (KBr): 2,978 s, 1,626 s cm-1. 1 H NMR (300 MHz CDCl3) δ: 2.92 (s, 3 H, CH3), 7.22 (dd, 1 H, J = 7.9 & 8.7 Hz, Ar-H), 7.37 (d, 1 H, J = 8.5 Hz, Ar-H), 7.67 (dd, 1 H, J = 8.7 & 8.3 Hz, Ar-H), 8.14 (d, 1 H, J = 7.9 Hz, Ar-H), 8.25 (d, 1 H, J = 8.3 Hz, Ar-H), 8.48 (d, 1 H, J = 8.5 Hz, Ar-H), 9.25 (s, 1 H, Ar-H). 13 C NMR (75 MHz CDCl3) δ: 24.11, 121.55, 123.47, 126.74, 127.41, 127.94, 128.56, 129.47, 135.67, 138.66, 148.72, 153.48, 157.49. Anal. Calcd. for C13H10N2 (194.23): C, 80.41; H, 5.15; N, 14.43% Found: C, 80.43; H, 5.17; N, 14.49%
7-Methoxy-2-Methylbenzo[b][1, 8]Naphthyridine (11d)
Yield: 0.187 g (83%), recrystalized from toulene to afford green needles; M.p. 84-86 °C. IR (KBr): 2,968 s, 1,618 s, 1,025 m cm-1.1 H NMR (300 MHz CDCl3) δ: 3.12 (s, 3 H, CH3), 4.02 (s, 3 H, OCH3), 7.29 (d, 1 H, J = 8.2 Hz, Ar-H), 7.48 (d, 1 H, J = 9.0 Hz, Ar-H), 7.56 (s, 1 H, Ar-H), 8.31 (d, 1 H, J = 9.0 Hz, Ar-H), 8.57 (d, 1 H, J = 8.2 Hz, Ar-H), 9.37 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 224 [M+] (82), 201 (77), 181 (64), 152 (47), 77 (87), 51 (78). Anal. Calcd. for C14H12N2O (224.26): C, 75.00; H, 5.35; N, 12.50% Found: C, 75.02; H, 5.37; N, 12.48%
Syntesis of 2-(4-Bromophenyl)Benzo[b][1, 8]Naphthyridine (13 a-n)
A solution of 1a-b (0.001 mol) and p-bromoacetophenone (12a) (0.001 mol) in ethanol (10 mL) containing catalytic amount of piperidine was refluxed for 2 h. Completion of the reaction was monitored by thin layer chromatography (TLC). The mixture was then cooled to room temperature; the separated solid product was collected by suction filtration, washed with pet-ether, dried and recrystallized from ethanol.
2-(4-Bromophenyl)Benzo[b][1, 8]Naphthyridine (13a)
Yield: 0.301 g (90%), recrystalized from ethanol to afford faint yellow solid; M.p. 95-98 °C. IR (KBr): 3,018 m, 1,640 s cm-1. 1 H NMR (300 MHz CDCl3) δ: 7.46 (dd, 1 H, J = 8.2 & 8.6 Hz, Ar-H), 7.52 (d, 2 H, J = 8.3 Hz, Ar-H), 7.77 (dd, 1 H, J = 8.6 & 8.1 Hz, Ar-H), 7.92 (d, 1 H, J = 8.2 Hz, Ar-H), 8.02 (d, 1 H, J = 8.1 Hz, Ar H), 8.12 (d, 1 H, J = 7.8 Hz, Ar-H), 8.22 (d, 2 H, J = 8.3 Hz, Ar-H), 8.42 (d, 1 H, J = 7.8 Hz, Ar-H), 9.23 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 334 [M+] (84), 336 [M + 2] (80), 255 (89), 212 (68), 207 (59), 179 (63), 77 (78). Anal. Calcd. for C18H11N2Br (335.20): C, 64.67; H, 3.29; N, 8.38% Found: C, 64.65; H, 3.30; N, 8.39%
2-(4-Chlorophenyl)Benzo[b][1, 8]Naphthyridine (13b)
Yield: 0.233 g (80%), recrystalized from ethanol to afford faint brown solid; M.p. 120-123 °C. IR (KBr): 3,030 m, 1,646 s cm-1. 1 H NMR (300 MHz CDCl3) δ: 7.29 (dd, 1 H, J = 8.1 & 8.4 Hz, Ar-H), 7.42 (d, 2 H, J = 8.3 Hz, Ar-H), 7.57 (dd, 1 H, J = 8.4 & 8.5 Hz, Ar-H), 7.79 (d, 1 H, J = 8.1 Hz, Ar-H), 8.10 (d, 1 H, J = 8.5 Hz, Ar H), 8.22 (d, 1 H, J = 7.8 Hz, Ar-H), 8.36 (d, 2 H, J = 8.3 Hz, Ar-H), 8.51 (d, 1 H, J = 7.8 Hz, Ar-H), 9.03 (s, 1 H, Ar-H). Anal. Calcd. for C18H11N2Cl (290.75): C, 74.48; H, 3.79; N, 9.65% Found: C, 74.52; H, 3.77; N, 9.68%
2-(3,5-Bis(trifluoromethyl)Phenyl)Benzo[b][1, 8]Naphthyridine (13c)
Yield: 0.344 g (87%), recrystalized from ethanol to afford yellow solid; M.p. 102-105 °C. IR (KBr): 3,028 m, 1,649 s cm-1. 1 H NMR (300 MHz CDCl3) δ: 7.38 (dd, 1 H, J = 8.3 & 8.7 Hz, Ar-H), 7.60 (dd, 1 H, J = 8.7 & 8.5 Hz, Ar-H), 7.84 (d, 1 H, J = 8.3 Hz, Ar-H), 7.93 (d, 1 H, J = 7.9 Hz, Ar-H), 8.18 (d, 1 H, J = 8.5 Hz, Ar-H), 8.34 (d, 1 H, J = 7.9 Hz, Ar-H), 8.42 (s, 1 H, Ar-H), 9.24 (s, 2 H, Ar-H), 9.47 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 392 [M+] (59), 351 (78), 323 (80), 254 (66), 254 (56), 213 (47), 179 (79). Anal. Calcd. for C20H10N2F6 (392.30): C, 61.22; H, 2.55; N, 7.14% Found: C, 61.23; H, 2.56; N, 7.12%
2-(4-Methoxyphenyl)Benzo[b][1, 8]Naphthyridine (13d)
Yield: 0.252 g (88%), recrystalized from ethanol to afford pale yellow needles; M.p. 114-117 °C. IR (KBr): 3,031 m, 1,649 s, 1,027 m cm-1. 1 H NMR (300 MHz CDCl3) δ: 3.98 (s, 3 H, OCH3), 7.10 (d, 2 H, J = 9.2 Hz, Ar-H), 7.46 (dd, 1 H, J = 8.0 & 8.4 Hz, Ar-H), 7.67 (dd, 1 H, J = 8.4 & 8.3 Hz, Ar-H), 7.88 (d, 1 H, J = 8.0 Hz, Ar-H), 7.94 (d, 2 H, J = 9.2 Hz, Ar-H), 8.02 (d, 1 H, J = 7.7 Hz, Ar-H), 8.19 (d, 1 H, J = 8.3 Hz, Ar-H), 8.28 (d, 1 H, J = 7.7 Hz, Ar-H), 9.25 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 286 [M+] (100), 271 (68), 255 (35), 242 (42), 121 (29), 63 (32), 39 (22). Anal. Calcd. for C19H14N2O (286.33): C, 79.72; H, 4.89; N, 9.79% Found: C, 79.73; H, 4.90; N, 9.77%
2-(2,3-Dimethoxyphenyl)Benzo[b][1, 8]Naphthyridine (13e)
Yield: 0.275 g (87%), recrystalized from ethanol to afford yellow crystal; M.p. 119-122 °C. IR (KBr): 3,029 m, 1,646 s, 1,022 m cm-1. 1 H NMR (300 MHz CDCl3) δ: 3.60 (s, 6 H, 2 × OCH3), 7.08 (d, 1 H, J = 8.7 Hz, Ar-H), 7.26 (dd, 1 H, J = 2.5 & 8.7 Hz, Ar-H), 7.38 (d, 1 H, J = 2.5 Hz, Ar-H), 7.49 (dd, 1 H, J = 8.1 & 8.8 Hz, Ar-H), 7.83 (dd, 1 H, J = 8.8 & 7.9 Hz, Ar-H), 7.96 (d, 1 H, J = 8.1 Hz, Ar-H), 8.16 (d, 1 H, J = 7.8 Hz, Ar-H), 8.20 (d, 1 H, J = 7.9 Hz, Ar-H), 8.29 (d, 1 H, J = 7.8 Hz, Ar-H), 9.12 (s, 1 H, Ar-H). 13 C NMR (75 MHz CDCl3) δ: 57.43, 56.79, 115.20, 117.47, 120.12, 121.47, 125.33, 127.12, 127.49, 128.32, 128.78, 129.28, 129.82, 135.43, 137.77, 145.64, 149.74, 152.64, 156.57, 159.71. Anal. Calcd. for C20H16N2O2 (316.35): C, 75.94; H, 5.06; N, 8.86% Found: C, 75.92; H, 5.08; N, 8.88%
2-p-Tolylbenzo[b][1, 8]Naphthyridine (13f)
Yield: 0.237 g (87%), recrystalized from ethanol to afford yellow solid; M.p. 92-95 °C. IR (KBr): 3,004 m, 1,640 s cm-1. 1 H NMR (300 MHz CDCl3) δ: 2.48 (s, 3 H, CH3), 7.44 (d, 2 H, J = 8.7 Hz, Ar-H), 7.60 (dd, 1 H, J = 8.2 & 8.5 Hz, Ar-H), 7.98 (dd, 1 H, J = 8.5 & 8.1 Hz, Ar-H), 8.07 (d, 1 H, J = 8.2 Hz, Ar-H), 8.29 (d, 2 H, J = 8.7 Hz, Ar-H), 8.42 (d, 1 H, J = 7.9 Hz, Ar-H), 8.59 (d, 1 H, J = 8.1 Hz, Ar-H), 8.68 (d, 1 H, J = 7.9 Hz, Ar-H), 8.97 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 270 [M+] (81), 255 (62), 241 (32), 152 (29), 134 (61), 89 (32). Anal. Calcd. for C19H14N2 (270.33): C, 84.44; H, 5.18; N, 10.37% Found: C, 84.45; H, 5.17; N, 10.35%
2-(4-Nitrophenyl)Benzo[b][1, 8]Naphthyridine (13 g)
Yield: 0.239 g (79%), recrystalized from ethanol to afford brown solid; M.p. 115-118 °C. IR (KBr): 3,033 m, 1,540 m, 1,372 m cm-1. 1 H NMR (300 MHz CDCl3) δ: 7.45 (dd, 1 H, J = 7.9 & 7.8 Hz, Ar-H), 7.54 (d, 2 H, J = 8.8 Hz, Ar-H), 7.68 (dd, 1 H, J = 7.8 & 8.0 Hz, Ar-H), 8.02 (d, 1 H, J = 7.9 Hz, Ar-H), 8.22 (d, 1 H, J = 8.0 Hz, Ar-H), 8.36 (d, 1 H, J = 8.9 Hz, Ar-H), 8.43 (d, 1 H, J = 8.9 Hz, Ar-H), 8.56 (d, 2 H, J = 8.8 Hz, Ar-H), 9.18 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 301 [M+] (88), 255 (82), 179 (55), 77 (68). Anal. Calcd. for C18H11N3O2 (301.30): C, 71.76; H, 3.65; N, 13.95% Found: C, 71.77; H, 3.66; N, 13.97%
2-(4-Bromophenyl)-7-Methoxybenzo[b][1, 8]Naphthyridine (13 h)
Yield: 0.312 g (85%), recrystalized from ethanol to afford yellow solid; M.p. 248-249 °C. IR (KBr): 3,010 m, 1,642 s, 1,040 m cm-1. 1 H NMR (300 MHz CDCl3) δ: 4.07 (s, 3 H, OCH3), 7.34 (d, 1 H, J = 9.3 Hz, Ar-H), 7.46 (s, 1 H, Ar-H), 7.89 (d, 2 H, J = 8.1 Hz, Ar- H), 8.04 (d, 1 H, J = 7.8 Hz, Ar-H), 8.19 (d, 2 H, J = 8.1 Hz, Ar-H), 8.35 (d, 1 H, J = 9.3 Hz, Ar-H), 9.05 (d, 1 H, J = 7.8 Hz, Ar-H), 9.46 (s, 1 H, Ar-H). 13 C NMR (75 MHz CDCl3) δ: 57.21, 109.42, 122.74, 123.24, 123.66, 126.47, 127.89, 129.30 (2 C’s), 131.51, 133.46 (2 C’s), 135.66, 136.94, 138.40, 145.55, 153.26, 156.19, 158.74. MS (70 eV) m/z (%): 364 [M+] (89), 366 [M + 2] (88), 285 (45), 242 (57), 142 (32), 121 (51). Anal. Calcd. for C19H13N2BrO (365.23): C, 62.63; H, 3.57; N, 7.69% Found: C, 62.64; H, 3.56; N, 7.70%
2-(4-Chlorophenyl)-7-Methoxybenzo[b][1, 8]Naphthyridine (13i)
Yield: 0.267 g (83%), recrystalized from ethanol to afford yellow crystals; M.p. 254-257 °C. IR (KBr): 3,026 m, 1,635 s, 1,038 m cm-1. 1 H NMR (300 MHz CDCl3) δ: 4.02 (s, 3 H, OCH3), 7.18 (d, 1 H, J = 9.1 Hz, Ar-H), 7.33 (s, 1 H, Ar-H), 7.74 (d, 2 H, J = 8.3 Hz, Ar- H), 7.93 (d, 1 H, J = 7.5 Hz, Ar-H), 8.12 (d, 2 H, J = 8.3 Hz, Ar-H), 8.43 (d, 1 H, J = 9.1 Hz, Ar-H), 9.17 (d, 1 H, J = 7.5 Hz, Ar-H), 9.33 (s, 1 H, Ar-H). Anal. Calcd. for C19H13N2ClO (320.77): C, 71.25; H, 4.06; N, 8.75% Found: C, 71.22; H, 4.09; N, 8.77%
2-(3,5-Bis(Trifluoromethyl)Phenyl)-7-Methoxybenzo[b][1, 8]Naphthyridine (13j)
Yield: 0.359 g (85%), recrystalized from ethanol to afford faint green solid; M.p. 199-202 °C. IR (KBr): 3,024 m, 1,642 s, 1,032 m cm-1. 1 H NMR (300 MHz CDCl3) δ: 4.05 (s, 3 H, OCH3), 7.39 (d, 1 H, J = 9.1 Hz, Ar-H), 7.57 (s, 1 H, Ar-H), 8.08 (d, 1 H, J = 7.9 Hz, Ar-H), 8.27 (d, 1 H, J = 9.1 Hz, Ar-H), 8.43 (s, 1 H, Ar-H), 8.78 (s, 2 H, Ar-H), 8.91 (d, 1 H, J = 7.9 Hz, Ar-H), 9.52 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 423 [M + 1] (100), 380 (69), 354 (74), 310 (18), 285 (64). Anal. Calcd. for C21H12N2F6O (422.32): C, 59.71; H, 2.84; N, 6.63% Found: C, 59.70; H, 2.85; N, 6.64%
7-Methoxy-2-(4-Methoxyphenyl)Benzo[b][1, 8]Naphthyridine (13k)
Yield: 0.272 g (86%), recrystalized from ethanol to afford yellow solid; M.p. 229-232 °C. IR (KBr): 3,021 m, 1,639 s, 1,036 m cm-1. 1 H NMR (300 MHz DMSO-d 6 ) δ: 3.89 (s, 3 H, OCH3), 4.02 (s, 3 H, OCH3), 7.21 (d, 2 H, J = 8.5 Hz, Ar-H), 7.39 (d, 1 H, J = 8.2 Hz, Ar-H), 7.50 (s, 1 H, Ar-H), 7.64 (d, 2 H, J = 8.5 Hz, Ar-H), 8.12 (d, 1 H, J = 8.1 Hz, Ar-H), 8.22 (d, 1 H, J = 8.2 Hz, Ar-H), 8.84 (d, 1 H, J = 8.1 Hz, Ar-H), 9.38 (s, 1 H, Ar-H). 13 C NMR (75 MHz CDCl3) δ: 55.39, 55.62, 105.80, 114.13 (2 C’s), 117.76, 118.57, 121.45, 122.95, 129.05, 129.68 (2 C’s), 131.20, 136.62, 137.75, 153.01, 155.26, 161.18, 161.70, 162.10. MS (70 eV) m/z (%): 316 [M+] (100), 301 (32), 230 (19), 158 (15), 115 (12). Anal. Calcd. for C20H16N2O2 (316.35): C, 75.94; H, 5.06; N, 8.86% Found: C, 75.95; H, 5.08; N, 8.87%
7-Methoxy-2-(2,3-Dimethoxyphenyl)Benzo[b][1, 8]Naphthyridine (13 l)
Yield: 0.307 g (88%), recrystalized from ethanol to afford yellow crystals; M.p. 238-241 °C. IR (KBr): 3,026 m, 1,635 s, 1,038 m cm-1. 1 H NMR (300 MHz DMSO-d 6 ) δ: 3.80 (s, 6 H, 2 × OCH3), 4.04 (s, 3 H, OCH3), 7.10 (d, 1 H, J = 9.2 Hz, Ar-H), 7.18 (dd, 1 H, J = 2.4 & 9.2 Hz, Ar-H), 7.29 (d, 1 H, J = 2.4 Hz, Ar-H), 7.41 (d, 1 H, J = 8.6 Hz, Ar-H), 7.52 (s, 1 H, Ar-H), 7.97 (d, 1 H, J = 8.2 Hz, Ar-H), 8.25 (d, 1 H, J = 8.6 Hz, Ar-H), 8.95 (d, 1 H, J = 8.2 Hz, Ar-H), 9.32 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 345 [M-1] (100), 331 (49), 315 (42), 300 (41), 286 (19), 151 (19), 108 (12). Anal. Calcd. for C21H18N2O3 (346.38): C, 72.83; H, 5.20; N, 8.09% Found: C, 72.85; H, 5.21; N, 8.10%
7-Methoxy-2-p-Tolylbenzo[b][1, 8]Naphthyridine (13 m)
Yield: 0.261 g (87%), recrystalized from ethanol to afford yellow prism; M.p. 208-211 °C. IR (KBr): 3,035 m, 1,625 s, 1,026 m cm-1. 1 H NMR (300 MHz CDCl3) δ: 2.47 (s, 3 H, CH3), 3.98 (s, 3 H, OCH3), 7.35 (d, 1 H, J = 8.7 Hz, Ar-H), 7.49 (d, 2 H, J = 8.5 Hz, Ar-H), 7.59 (s, 1 H, Ar- H), 7.95 (d, 2 H, J = 8.5 Hz, Ar-H), 8.12 (d, 1 H, J = 7.9 Hz, Ar-H), 8.25 (d, 1 H, J = 8.7 Hz, Ar-H), 8.49 (d, 1 H, J = 7.9 Hz, Ar-H), 8.83 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 300 [M+] (97), 285 (92), 209 (77), 77 (89). Anal. Calcd. for C20H16N2O (300.35): C, 80.00; H, 5.33; N, 9.33% Found: C, 79.98; H, 5.32; N, 9.35%
7-Methoxy-2-(4-Nitrophenyl)Benzo[b][1, 8]Naphthyridine (13n)
Yield: 0.265 g (80%), recrystalized from ethanol to afford yellow solid; M.p. 191-194 °C, IR (KBr): 3,020 m, 1,642 s, 1,559 m, 1,367 m, 1,045 m cm-1. 1 H NMR (300 MHz DMSO-d 6 ) δ: 4.03 (s, 3 H, OCH3), 7.32 (d, 2 H, J = 8.3 Hz, Ar-H), 7.48 (d, 1 H, J = 8.5 Hz, Ar-H), 7.52 (s, 1 H, Ar-H), 8.01 (d, 1 H, J = 7.7 Hz, Ar-H), 8.19 (d, 1 H, J = 8.5 Hz, Ar-H), 8.30 (d, 2 H, J = 8.3 Hz, Ar-H), 8.98 (d, 1 H, J = 7.7 Hz, Ar-H), 9.37 (s, 1 H, Ar-H). Anal. Calcd. for C19H13N3O3 (331.33): C, 68.88; H, 3.92; N, 12.68% Found: C, 68.89; H, 3.94; N, 12.70%
Synthesis of 9,10-Dimethoxy-7H-Benzo[b]Indeno[1,2-g][1, 8]Naphthyridine (15 a-d)
The mixture of 2-aminoquinoline-3-carbaldehyde (1a-b) (0.01 mol) & indanone (14a-b) (0.01 mol) in ethanolic potassium hydroxide solution (10 mL, 2%) was refluxed for 1 h. Completion of the reaction was monitored by Thin Layer Chromatography (TLC). The mixture was then dumped over ice-crushed water (20 mL) and stirred for the 30 mins. The separated solid product was collected by suction filtration, washed with pet-ether, dried and recrystallized from Methanol.
9,10-Dimethoxy-7H-Benzo[b]Indeno[1,2-g][1, 8]Naphthyridine (15a)
Yield: 0.281 g (85%), recrystalized from Methanol to afford yellow solid; M.p. 269-272 °C. IR (KBr): 2,997 m, 2,968 m, 1,618 s, 1,024 m cm-1. 1 H NMR (300 MHz CDCl3) δ: 3.89 (s, 2 H, CH2), 3.95 (s, 3 H, OCH3), 4.01 (s, 3 H, OCH3), 6.78 (s, 1 H, Ar-H), 7.34 (dd, 1 H, J = 7.8 & 8.7 Hz, Ar-H), 7.55 (s, 1 H, Ar-H), 7.79 (dd, 1 H, J = 8.7 & 8.1 Hz, Ar-H), 8.09 (d, 1 H, J = 7.8 Hz, Ar-H), 8.36 (d, 1 H, J = 8.1 Hz, Ar-H), 8.78 (s, 1 H, Ar-H), 9.19 (s, 1 H, Ar-H). Anal. Calcd. for C21H16N2O2 (328.36): C, 76.82; H, 4.87; N, 8.53% Found: C, 76.84; H, 4.88; N, 8.55%
2,9,10-Trimethoxy-7H-Benzo[b]Indeno[1,2-g][1, 8]Naphthyridine (15b)
Yield: 0.319 g (89%), recrystalized from Methanol to afford yellow needles; M.p. 231-233 °C. IR (KBr): 3,012 s, 2,977 m, 1,607 s, 1,011 m cm-1.1 H NMR (300 MHz CDCl3) δ: 3.75 (s, 2 H, CH2), 3.88 (s, 3 H, OCH3), 3.96 (s, 3 H, OCH3), 4.05 (s, 3 H, OCH3), 6.87 (s, 1 H, Ar-H), 7.43 (d, 1 H, J = 8.8 Hz, Ar-H), 7.51 (s, 1 H, Ar-H), 7.67 (s, 1 H, Ar-H), 8.94 (d, 1 H, J = 8.8 Hz, Ar-H), 9.21 (s, 1 H, Ar-H), 9.44 (s, 1 H, Ar-H). 13 C NMR (75 MHz CDCl3) δ: 33.47, 55.55, 56.16, 56.38, 104.87, 105.77, 107.41, 113.81, 118.60, 120.77, 122.48, 128.86, 130.57, 132.14, 134.45, 136.43, 149.77, 151.94, 152.73, 155.69, 161.68, 166.94. MS (70 eV) m/z (%): 358 [M+] (58), 327 (51), 288 (56), 207 (57), 189 (50), 175 (62), 164 (82), 150 (87), 131 (74), 118 (70), 91 (68), 63 (42). Anal. Calcd. for C22H18N2O3 (358.39): C, 73.74; H, 5.02; N, 7.82%. Found: C, 73.75; H, 5.04; N, 7.84%.
7H-Benzo[b]Indeno[1,2-g][1, 8]Naphthyridine (15c)
Yield: 0.217 g (80%), recrystalized from Methanol to afford yellow solid; M.p. 277-280 °C. IR (KBr): 3,014 m, 2,968 m, 1,618 s cm-1. 1 H NMR (300 MHz CDCl3) δ: 3.94 (s, 2 H, CH2), 7.24-7.32 (m, 4 H, Ar-H), 7.42 (dd, 1 H, J = 8.2 & 8.4 Hz, Ar-H), 7.79 (dd, 1 H, J = 8.4 & 8.1 Hz, Ar-H), 8.09 (d, 1 H, J = 8.2 Hz, Ar-H), 8.36 (d, 1 H, J = 8.1 Hz, Ar-H), 8.78 (s, 1 H, Ar-H), 9.19 (s, 1 H, Ar-H). Anal. Calcd. for C19H12N2 (268.31): C, 85.07; H, 4.47; N, 10.44%. Found: C, 85.10; H, 4.48; N, 10.45%.
2-Methoxy-7H-Benzo[b]indeno[1,2-g][1, 8]Naphthyridine (15d)
Yield: 0.259 g (86%), recrystalized from Methanol to afford yellow needles; M.p. 252-255 °C. IR (KBr): 3,012 m, 2,968 m, 1,611 s, 1,011 m cm-1.1 H NMR (300 MHz CDCl3) δ: 3.82 (s, 2 H, CH2), 4.05 (s, 3 H, OCH3), 7.09-7.38 (m, 4 H, Ar-H), 7.43 (d, 1 H, J = 8.6 Hz, Ar-H), 7.51 (s, 1 H, Ar-H), 8.24 (d, 1 H, J = 8.6 Hz, Ar-H), 9.21 (s, 1 H, Ar-H), 9.44 (s, 1 H, Ar-H). MS (70 eV) m/z (%): 298 [M+] (100), 277 (32), 255 (64), 227 (32), 149 (38), 128 (45), 114 (18), 77 (13). Anal. Calcd. for C20H14N2O (298.34): C, 80.53; H, 4.69; N, 9.39%. Found: C, 80.55; H, 4.70; N, 9.40%.
References
Meijere A de (1998) In topics in current chemistry, carbon-rich compounds, I, (Ed.) Springer, Berlin, Germany, vol 196
Meijere A de (1999) In topics in current chemistry, carbon-rich compounds, II, (Ed.) Springer, Berlin, Germany, vol 201
Diederich F, Stang PJ, Tykwinski RR (2005) In acetylene chemistry: chemistry, biology and material science, (Eds.) Wiley-VCH, Weinheim, Germany
Haley MM, Tykwinski RR (2006) In carbon-rich compounds: from molecules to materials, (Eds.) Wiely-VCH, Weinheim, Germany
Műllen K, Scherf U (2006) In organic light emitting devices: synthesis properties and applications (Eds.): Wiely-VCH, Weinheim, Germany
Chen J, Reed MA, Dirk SM, Price DW, Rawlett AM, Tour JM, Grubisha DS, Bennett DW (2003) In NATO science series II, mathematics, physics, chemistry (Molecular Electronics: Bio-Sensors and Bio-Computers) (Eds.): Plenum, New York, Vol. 96: pp 59-195
Domerco B, Hreha RD, Zhang YD, Haldi A, Barlow S, Marder SR, Kippelen B (2003) Organic light-emitting diodes with multiple photocrosslinkable hole-transport layers. J Polym Sci Part B: Polym Phys 41(21):2726–2732
Shirota Y (2000) Organic materials for electronic and optoelectronic devices. J Mater Chem 10:1–25
Schwab PFH, Levin MD, Michl J (1999) Molecular rods. 1. Simple axial rods. Chem Rev 99:1863–1933
Műllen K, Wehner G (1998) In electronic materials: the oligomer approach, (Eds.) Wiely-VCH, Weinheim, Germany
Nalwa HS, Miyata S (1997) In nonlinear optics of organic molecules and polymers (Eds.) CRC Press, Boca Raton, FL
Kang H, Evrenenko G, Dutta P, Clays K, Song K, Marks TJ (2006) X-shaped electro-optic chromophore with remarkably blue-shifted optical absorption. synthesis, characterization, linear/nonlinear optical properties, self-assembly, and thin film microstructural characteristics. J Am Chem Soc 128:6194–6205
Knox JE, Halls MD, Hratchian HP, Schlegel HB (2006) Chemical failure modes of Alq3-based OLEDs: Alq3 hydrolysis. Phys Chem Chem Phys 8:1371–1377
Shukla VK, Kumar S, Deva D (2006) Light induced effects on the morphology and optical properties of tris-(8-hydroxyquinoline) aluminium (Alq3) small molecular thin film. Synth Met 156:387–391
Seminario JM (2005) Molecular electronics: approaching reality. Nat Mater 4:111–113
Hughes G, Bryce MR (2005) Electron-transporting materials for organic electroluminescent and electrophosphoresc-ent devices. J Mater Chem 15:94–107
Van der Auweraer M, De Schryver FC (2004) Organic electronics: supra solutions. Nat Mater 3:507–508
Special Issue on Organic Electronics (2004) Chem Mater 16:4381–4846
Simpson CD, Wu J, Watson MD, Műllen K (2004) From graphite molecules to columnar superstructures-an excercise in nanoscience. J Mater Chem 14:494–504
Kapturkiewicz A, Herbich J, Nowacki J (1997) Highly efficient electrochemical generation of fluorescent intramolecular charge-transfer states. Chem Phys Lett 275:355
Herbich J, Kapturkiewicz A (1997) Electronic and molecular structure of charge transfer singlet states: 4-(9-anthryl)julolidine and 4-(9-acridyl)julolidine. Chem Phys Lett 273:8
Herbich J, Kapturkiewicz A, Nowacki J (1996) Phosphorescent intramolecular charge transfer triplet states. Chem Phys Lett 262:633
Rechthaler K, Schamschule R, Parusel ABJ, Rotkiewicz K, Piorun D, Kőhler G (1999) Fluorescence properties of an electron acceptor substituted bis-pyrazolo-pyridine derivative: NO2-DMPP. Acta Phys Polon A 95:321
Miyasaka H, Itaya A, Rotkiewicz K, Rechthaler K (1999) Picosecond laser photolysis studies of DMA–DMPP in solution. Chem Phys Lett 307:121
Piorun D, Parusel ABJ, Rechthaler K, Rotkiewicz K, Kőhler G (1999) Acid–base properties of bis-pyrazolopyridine derivatives in nonaqueous solutions. J Photochem Photobiol A:Chem 129:33
Parusel ABJ, Rechthaler K, Piorun D, Danel A, Khatchatryan K, Rotkiewicz K, Kőhler G (1998) Fluorescence properties of donor–acceptor-substituted pyrazoloquinolines. J Fluoresc 8:375
Khatchatryan K, Rotkiewicz K, Kőhler G, Danel A, Tomasik P, Khatchatryan K (1997) Emissive properties and intramolecular charge transfer of pyrazoloquinoline derivatives. J Fluoresc 7:301
Rotkiewicz K, Rechthaler K, Puchala A, Rasala D, Styrcz S, Kőhler G (1996) Dual fluorescence and intramolecular charge transfer in a bulky electron donor-acceptor system. N, N-Dimethylanilino-bis-pyrazolopyridine. J Photochem Photobiol A: Chem 98:15–19
Parusel ABJ, Schamschule R, Kőhler G (1998) Theoretical description of solvent effects on fluorescence spectra of bulky charge transfer compound DMA-DMPP. J Comput Chem 19:1584
Parusel ABJ, Schamschule R, Kőhler G (1997) A semiempirical study of the fluorescence properties of large charge-transfer compounds. N, N-dimethylanilino-bis-pyrazolopyridine. Ber Bunsenges Phys Chem 101:1836–1843
Parusel ABJ, Schamschule R, Piorun D, Rechthaler K, Puchala A, Rasala D, Rotkiewicz K, Kőhler G (1997) Semiempirical characterization of substituted bis-pyrazolopyridines as new bulky electron donor-acceptor systems in their electronic ground state. J Mol Struct (Theochem) 419:63–76
Singh AK, Kanvah S (2000) Effect of micro heterogeneous media on fluorescence and fluorescence probe properties of diarylpolyenes. New J Chem 24:639–646
Singh AK, Manjula D, Kanvah S (2000) α, ω-diphenylpolyenes cabable of exhibiting twisted intramolecular charge transfer fluorescence: a fluorescence and fluorescence probe study of nitro- and nitrocyano-substituted 1, 4-diphenyl butadienes. J Phys Chem A 104:464–471
Singh AK, Krishna TSR (1997) Photophysical and optical probe properties of 1-(p-N, N-Dimethylaminophenyl)-4-Phenyl-2-Methyl-1E, 3E-Butadiene. J Photosci 4:1–5
Singh AK, Darshi M (2004) A fluorescence study of (4-{(1E, 3E)-4-[4-(dimethyl-amino)phenyl]- buta-1, 3-dienyl}phenyl)methanol and its bioconjugates with bovine and human serum albumins. New J Chem 28:120–126
Caluwe P (1980) Heteroannelations with o-aminoaldehydes. Tetrahedron 36:2359
Fehnel EA (1966) Friedländer syntheses with o-aminoaryl ketones. I. Acid-catalyzed condensations of o-aminobenzophenone with ketones. J Org Chem 31:2899
Boekelheide V, Nottke JE (1969) Novel cyclization reaction of acetylene derivatives. J Org Chem 34(12):4134–4136
Liao TK, Nyberg WH, Cheng CC (1971) Total synthesis of camptotheein. I. Synthesis of ethyl 8-(α-chlorobutyryloxymethyl)-7,9-dioxo-7,8,9,11-tetrahydro indolizino [1,2-a]quinoline-8-carboxylate and related tetracyclic compounds. J Heterocyclic Chem 8:373
Zalkow LH, Nabors JB, French K, Bisarya SC (1971) Studies in the synthesis of Camptothecin. An efficient synthesis of 2,3-dihydro-1H-pyrazolo[3,4-b]quinoline. J Chem Soc (C):3551-3554.
Borch RF, Grudzinskas CV, Peterson DA, Weber LD (1972) New synthesis of substituted 2(1 H)-pyridones. Synthesis of a potential camptothecin intermediate. J Org Chem 37(8):1141–1145
Croisy A, Jacqquignon P, Fravolini A (1974) Sur quelques analogues fluores des [1] benzothiopyrano[4, 3-b]indoles et des 6 H[1]benzothiopyrano[4, 3-b]quinoleines. J Heterocyclic Chem 11:113
Cliff GR, Jones G, Woollard J McK (1974) Intramolecular nitrene insertions into aromatic and heteroaromatic systems. Part II. Insertions into thiophen rings. J Chem Soc Perkin I:2072–2076
Sugasawa T, Toyoda T, Sasakura K (1974) Experiments on the synthesis of dl-camptothecin. III. Total synthesis of dl-camptothecin. Chem Pharm Bull 22:771–781
Tang CSF, Morrow CJ, Rapoport H (1975) Total synthesis of dl-camptothecin. J Am Chem Soc 97:159
Da SA, Primofiore G, Livo O, Ferrarini PL, Spinelli S (1979) Synthesis of some 3-substituted quino[3, 2-c][1, 8]naphtyridines. A new heterocyclic ring system. J Heterocyclic Chem 16:169
Hawes EM, Wibberley DG (1966) 1,8-Naphthyridines. J Chem Soc:315-321
Majewicz TG, Caluwe P (1975) Chemistry of o-aminoaldehydes. Reactions of 2-aminonicotinaldehyde and cyclohexanediones. J Org Chem 40(23):3407–3410
Hawes EM, Wibberley DG (1967) 1,8-Naphthyridines. Part II. Preparation and some reactions of 2-substituted derivatives. J Chem Soc (C):1564-1568.
Hawes EM, Gorecki DKJ, Gedir RG (1977) 2, 3-Disubstituted 1, 8-naphthyridines as potential diuretic agents. 2. 5, 7-Dimethyl derivatives. J Med Chem 20(6):838–841
Haufel J, Breitmaier E (1974) Synthesis of pyrazolo heteroaromatic compounds by means of 5-amino-3-methyl-1-phenylpyrazole-4-carbaldehyde. Angew Chem Internat Edit 13(9):604
Simay A, Takacs K, Toth L (1982) Aminopyrazoles, II. Synthesis of pyrazolo[3, 4-b] pyridines via Vilsmeier-Haack reaction of 5-acetaminopyrazoles. Acta Chim Acad Sci Hung 109:175–187
Ahluwalia VK, Dahiya A (1996) Synthesis of pyrazolo[3’, 4’: 5, 6]pyrido[2, 3-d] pyrimidines. Indian J Chemistry 35B:1208–1210
Ahluwalia VK, Dahiya A, Garg VK (1997) Reaction of 5- amino-4-formyl-3-methyl (or phenyl)-1-phenyl-1 H-prazoles with compounds containing active methylene group: synthesis of fused heterocyclic rings. Indian J Chemistry 36B:88–90
Godard A, Queguiner G (1980) Sur les orthoamino formyl quinoleines, nouveaux synthons heterocycliques. J Heterocyclic Chem 17:465
Godard A, Queguiner G (1982) Synthesis of Benzonaphthyridines. J Heterocyclic Chem 19:1279
Jachak MN, Avhale AB, Tantak CD, Toche RB (2005) Friedländer condensation of 5-Aminopyrazole-4-carbaldehydes with reactive α-methylene ketones: synthesis of pyrazolo[3, 4-b]pyridines. J Heterocyclic Chem 42:1311–1319
Jachak MN, Avhale AB, Tantak CD, Toche RB (2006) A convenient route for the synthesis of pyrazolo[3, 4-d]pyrimidine, pyrazolo[3, 4-b][1, 6]naphthyridine and pyrazolo[3, 4-b]quinoline derivatives. J Heterocyclic Chem 43:1169–1175
Jachak MN, Avhale AB, Toche RB, Sabnis RW (2007) Synthesis of pyrazolo-annelated heterocyclic ring compounds such as pyrazolo[3, 4-b]pyridines and pyrazolo[4′, 3′:5, 6]-pyrido[2, 3-d]pyrimidines. J Heterocyclic Chem 44:343–347
Jachak MN, Bagul SM, Kazi MA, Toche RB (2009) Facile synthesis of novel pyrazolo[3, 4-h][1, 6]naphthyridines derivatives from new 4-amino-pyrazolo[3, 4-b] pyridine-5-carbaldehyde. J Heterocyclic Chem 46:343
Toche RB, Bhavsar DC, Kazi MA, Bagul SM, Jachak MN (2010) Synthesis of pyrazolopyridine 3-carboxylates by Friedlander condensation. J Heterocyclic Chem 47:287–291
Shelar DP, Birari DR, Rote RV, Patil SR, Toche RB, Jachak MN (2010) Novel Synthesis of 2-aminoquinoline-3-carbaldehyde, benzo[b][1, 8] naphthyridines and study of their fluorescence behavior. J Phys Org Chem. doi:10.1002/poc.1727
Peters T (1985) Serum albumin. Jr Advan Prot Chem 37:161–245
Zollinger H (2003) Color Chemistry, 3rd ed., Switzerland, Page No.479
Stewart JJP (1990) J Comput-Aided Mol Des 4:1
Stewart JJP. QCPE Bull. (1989), 9, 10. QCPE program no. 455
Perov AN (1980) Energy of intermediate pair interactions as a characteristics of their nature. Theory of the solvate (Fluoro) Chromism of three-component solutions. Opt Spectrosc 49:371–374
Neporent BS, Bakhshiev NG (1960) On the role of universal and specific intermolecular interactions in the influence of the solvent on the electronic spectra of molecules. Opt Spectrosc 8:408–413
Dey JK, Warner IM (1998) Charge-transfer effects on the fluorescence spectra of 9-aminocamptothecin steady-state and time-resolved fluorescence studies. J Photochem Photobiol A: Chem 116:27
Biswas A, Dey JK (2001) Ground and excited state ionization behavior of 9-aminocamptothecin: an absorption and fluorescence study. Indian J Chem 40A:1143–1148
Lakowicz JR (1999) In principals of fluorescence spectroscopy, 2nd ed., New York
Fletecher AN (1969) Quinine sulfate as a fluorescence quantum yield standard. Phot Chem Photo Biol 9(5):439–444
Eastman JW (1967) Quantitative spectrofluorimetry-the fluorescence quantum yield of quinine sulfate. Photo Chem Photo Biol 6(1):55–72
Adams MJ, Highfield JG, Kirkbright GF (1977) Determination of absolute fluorescence quantum efficiency of quinine bisulfate in aqueous medium by optoacoustic spectrometry. Anal Chem 49(12):1850–1852
Meech SR, Phillips D (1983) Photophysics of some common fluorescence standards. J Photochem 23:193–217
Papadopoulou A, Green RJ, Frazier A (2005) Interaction of flavonoids with bovine serum albumin: a fluorescence quenching study. J Agric Food Chem 53:158–163
Acknowledgement
The authors thank to CSIR, New Delhi, India, for financial support for this research project. We thank Professor D. D. Dhavale, Department of Chemistry, University of Pune, Pune, India, for his valuable cooperation for the measurement of 1 H NMR, 13 C NMR, Mass and Elemental Analysis. Authors also thanks to Dr. V. B. Gaikwad, Principal. K. R. T. Arts, B. H. Commerce and A. M. Science College, Nashik-02, MS, India, for valuable cooperation for the measurement of IR, UV and Fluorescence spectra.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Shelar, D.P., Patil, S.R., Rote, R.V. et al. Synthesis and Fluorescence Investigation of Differently Substituted Benzo[b][1,8]Naphthyridines: Interaction with Different Solvents and Bovine Serum Albumin (BSA). J Fluoresc 21, 1033–1047 (2011). https://doi.org/10.1007/s10895-010-0783-1
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10895-010-0783-1