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Synthesis and characterization of hybrid chloroquinoline_xanthene derivatives

A novel series of chloroquinoline-xanthene hybrids were prepared by one-pot multicomponent cyclo-condensation reaction of 2,7-dihydroxynaphthalene, aromatic aldehydes, and cyclic 1,3-dicarbonyl compounds followed by condensation reaction with 4,7-dichloroquinoline. The synthesized compounds were characterized by various spectroscopic techniques and single crystal X-ray analysis. Subjects: Chemical Spectroscopy; Medicinal & Pharmaceutical Chemistry; Organic Chemistry


PUBLIC INTEREST STATEMENT
In the present study, the synthesis of a library of novel chloroquinoline containing xanthenes i.e. xanthene-chloroquinoline conjugates, via hybridizing the xanthene sub-structure and the chloroquinoline sub-structure, which is a wellknown antimalarial pharmacophore has been described. A novel series of chloroquinolinexanthene hybrids were prepared by one-pot multicomponent cyclo-condensation reaction of 2,7-dihydroxynaphthalene, aromatic aldehydes, and cyclic 1,3-dicarbonyl compounds followed by condensation reaction with 4,7-dichloroquinoline.

IR spectral data of compound 2a
In the IR spectrum of compound 2a (Figure 2), the observed peak at 1,651 cm −1 is characteristic for carbonyl (C=O) stretching frequencies of α, β-unsaturated ketone. Similarly, the C=C stretching frequency associated with α, β-unsaturated ketone was observed at 1,598 cm −1 . The bands observed in the region 1,417-1,517 cm −1 correspond to C=N and aromatic C=C stretching vibrations. The C-H stretching vibration bands were observed in the region of 2,869-2,995 cm −1 . The weak aromatic C-H band appeared at 3,074 cm −1 . Furthermore, the IR spectrum of 1a showed a band near 3,600 cm −1 for O-H stretching which was absent in the IR spectrum of its chloroquinoline analog (2a), and contains a very strong band at 1,221 (aryl conjugated) and 1,374 cm −1 for C-O-C stretching frequencies.

1 H NMR spectral data of compound 2a
In the 1 H NMR spectrum of compound 2a (Figure 3), all aromatic protons were resonating in the range of δ 6.29-8.27. The proton corresponding to the CH (methine) of xanthene ring appeared as a singlet at Scheme 2. Synthesis of 12-aryl-2-(7-chloroquinolin-4-yloxy)-8,9,10,12 tetrahydrobenzo[a] xanthen-11-ones. . The six protons of two methyl groups revealed two different singlets at δ 1.12 ppm and δ 0.97 ppm, respectively. Furthermore, the 1 H NMR spectrum of 1a exhibited a broad singlet at δ 11.00 ppm corresponding to the exchangeable OH proton, which was absent in b, which confirms the oxo linkage between xanthene nucleus and chloroquinoline.

13 C NMR spectral data of compound 2a
In 13 C NMR spectrum of compound 2a, (Figure 4) the observed signal at δ 196.72 accounted for the carbonyl carbon, while the two methylene carbons i.e. CH 2 CMe 2 and CH 2 C=O were observed at δ 50.77 ppm and δ 41.32 ppm, respectively. A signal for methine carbon of xanthene ring was observed at δ 34.37 ppm,

Mass spectral data of compound 2a
ESI-MS of 2a ( Figure 6) displayed m/z at 566 (M + + H) i.e. molecular ion peak (M) with addition of hydrogen corresponds to its molecular formula C 34 H 25 Cl 2 NO 3 and peaks at m/z 568 and 670 corresponding M + 2 and M + 4 peaks due to the presence of the two atoms of isotope ( 17 Cl 37 ) and further the peak intensities were found in accordance with the presence of isotopic atoms.

General
All the chemicals used were purchased from Sigma-Aldrich and used as received. Silica gel 60 F 254 (Precoated aluminum plates) from Merck were used to monitor the reaction progress. Melting points were recorded on a Tropical Labequip apparatus and were uncorrected. IR (KBr) spectra were recorded on Perkin-Elmer FTIR-1710 instrument and the values are expressed as ν max cm −1 . NMR spectra were recorded on Bruker Avance Spectrospin 300 MHz and on Jeol JNM ECX-400P at 400 MHz using TMS as the internal standard. Mass spectra were recorded on JEOL-AccuTOF JMS-T100 mass spectrometer having a DART source and on KC-455-TOF mass spectrometer (Micromass, Manchester, UK). The   chemical shift values are recorded on δ scale (ppm) and coupling constants (J) are in Hertz. X-ray intensity data were collected on Oxford Diffraction Xcalibur CCD diffractometer with graphite monochromated Mo Kα radiation (λ = 0.71073 Å) at temperature 298 K.