MRC letters
Received: 15 July 2013
Revised: 1 November 2013
Accepted: 5 November 2013
Published online in Wiley Online Library: 10 December 2013
(wileyonlinelibrary.com) DOI 10.1002/mrc.4034
NMR study of O and N, O-substituted
8-quinolinol derivatives
Sobia Mastoor,a Shaheen Faizi,b* Rubeena Saleema,c**
and Bina Shaheen Siddiquib
The 1H and 13C NMR spectral study of several biologically active derivatives of 8-quinolinol have been made through extensive
NMR studies including homodecoupling and 2D-NMR experiments such as COSY-45°, NOESY, and HeteroCOSY. Electron
donating resonance and electron withdrawing inductive effect of several groups showed marked changes in chemical shifts
of nuclei at the seventh positions of O-substituted quinolinols (2–15). Although in N-alkyl, 8-alkoxyquinolinium halides
(16–21), ring A rightly showed low frequency chemical shift values. Copyright © 2013 John Wiley & Sons, Ltd.
Keywords: 8-quinolinol; NMR; 1H; 13C; COSY-45°; NOESY; HeteroCOSY; O-substituted quinolinol and N; O-dialkyl derivatives
following parameters: for 300/75 and 400/100 MHz HeteroCOSY
Introduction
(AM-300 and AM-400), J (13C, 1H)= 140 Hz, data matrix 1 K × 2 K
The 8-quinolinol (1), also known as oxine, is a powerful reagent. It
is frequently used in synthesis of a variety of compounds,
which are useful for chemical, biological, and industrial pur-
poses. Oxine derivatives have been reported as a corrosion
inhibitor,[1] in manufacturing dyes[2] and to detect metals.[3]
Its 8-hydroxyquinolinato-bis-salicylato yttrium (III) complexes
inhibits growth of Schizosaccharomyces pombe,[4] whereas
lanthanide (III) complexes of 8-quinolinol Schiff bases are
antioxidant and have the ability to bind DNA.[5] An aqueous
solution of 8-quinolinol helps in quick germination of Eriobotrya
japonica (loquat).[6] Recently, antimicrobial activity of oxine
glucosaminides[7] and anti-inflammatory activity of 8-quinolinol
Mannich bases[8] have been reported. Current work involves the
NMR spectral study of various 8-quinolinol derivatives (2–21)
possessing antimicrobial[9] and antiplatelet aggregating activities.[10]
This is the first report of NMR data for compounds 6, 17–21
according to the Science Finder research engine (Fig. 1).[11]
(256 experiments to 1 K zero filling in F1, 2 K in F2), 128 transients
in each experiment. In NOESY, the mixing time is 0.9 s, the spectral
width ranges from 1470 to 2551 Hz for F2 and 735 to 1275 Hz for F1
in both DMSO-d6 and CDCl3. Data matrix 1 K × 2 K (256 experiments
to 1 K zero filling in F1, 2 K in F2), 64 transients in CDCl3 and 16 in
DMSO-d6. The delta values were referenced to DMSO-d5 (2.50
1
and 39.7ppm for H and 13C, respectively), and CHCl3 (7.24 and
1
77.3ppm for H and 13C, respectively) solvents. Exact assignment
was made through 2D spectroscopy and literature values.[13,14]
Preparation of O-alkyl (2–6) and N, O-dialkyl
(16–20) derivatives
In each experiment, 8-quinolinol (1, 2 g) and alkyl halide (2 ml)
were added to a freshly prepared (15 ml) solution of sodium
ethoxide and refluxed with stirring. The reaction mixture was
monitored through TLC. Compounds 2 and 16 were formed
after 2 hours while formation of 3–6 and 17–20 were
completed after 2 days of reflux. The reaction mixture was
poured into cold water and shaked with ethyl acetate. The
ethyl acetate phase yielded monoalkyl derivatives, 8-methoxy
Experimental
The 1H and 13C NMR spectra were recorded in CDCl3 and DMSO-d6
at 21–22 °C with Bruker Aspect AM-300 and AM-400 spec-
trometers (Switzerland) working at 300 and 400 MHz for 1H NMR
and 75 and 100 MHz for 13C NMR, respectively. For 1D (DEPT)
and COSY-45° experiments, standard Bruker software was applied.
In 1D measurements on AM-300 and AM-400 for 1H and 13C 32 K,
data points were used for free induction decays. The digital reso-
lutions were 0.122 and 0.164 Hz per point (1H), 1.130 and 1.453 Hz
per point (13C) on AM-300 and AM-400, respectively. The spectral
widths (in both CDCl3 and DMSO-d6) at 300 and 400 MHz were 4
*
Correspondence to: Shaheen Faizi, International Center for Chemical and Bio-
logical Sciences, University of Karachi, Karachi-76250, Pakistan. E-mail:
** Correspondence to: Rubeena Saleem, Dr HMI Institute of Pharmacology &
Herbal Sciences, Hamdard University, Karachi, 74600, Pakistan, Pharmaceutical
Chemistry, Faculty of Pharmacy, Hamdard University, Karachi, 74600, Pakistan.
E-mail: rs127pk@yahoo.com
1
and 5 KHz for H NMR and 18 and 23 KHz for 13C NMR at 75 and
a Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Hamdard
100 MHz, respectively. The COSY-45° F1 acquisition ranges between
377 and 4000 and that for F2 recorded between 950 and 4000 Hz.
Other COSY-45° parameters include 512 data points and 512
increments (both zero-filled to 1024), 1.5–2.0s relaxation delay
and 32 transients per increment. For 2D experiment, Bruker
software library was used for the pulse program,[12] with the
University, Karachi, 74600, Pakistan
b International Center for Chemical and Biological Sciences, University of
Karachi, Karachi, 76250, Pakistan
c
Dr HMI Institute of Pharmacology & Herbal Sciences, Hamdard University,
Karachi, 74600, Pakistan
Magn. Reson. Chem. 2014, 52, 115–121
Copyright © 2013 John Wiley & Sons, Ltd.
Mastoor, Sobia
