MAGNETIC RESONANCE IN CHEMISTRY
Magn. Reson. Chem. 2006; 44: 102–105
Spectral Assignments and Reference Data
to DMSO-d6: υH D 2.50 ppm, υC D 39.6 ppm.15 Resonance multiplic-
1H and 13C chemical shifts for 2-aryl and
2-N-arylamino benzothiazole derivatives
ities for 13C signals were established via the acquisition of DEPT
spectra. For two-dimensional experiments, Bru¨ker microprograms
using gradient selection (gs) were applied. The gs-COSY spectra16
were obtained with an F2 spectral width of 10 ppm and 2 K data
points and an F1 spectral width of 256 t1 increments with sine-
bell windows in both dimensions. The gs-HMQC spectra17 resulted
from a 256 ð 1024 data matrix size with 2–16 scans per t1 depend-
ing on the sample concentration, an interpulse delay of 3.2 ms and a
5 : 3 : 4 gradient combination. The gs-HMBC spectra18 were measured
using a pulse sequence optimized for 10 Hz (interpulse delay for the
evolution of long-range couplings, 50 ms) and the same gradient
ratios.
S. Billeau, F. Chatel, M. Robin,∗ R. Faure and J.-P. Galy
Laboratoire de Valorisation de la Chimie Fine, UMR CNRS 6178 Symbio,
Faculte´ des Sciences et Techniques de Saint-Je´ roˆ me, Universite´ Paul
Ce´ zanne, Av. Escadrille Normandie-Niemen, 13397 Marseille Cedex 20,
France
Received 25 May 2005; accepted 25 July 2005
The 1H and 13C NMR resonances for forty-three 2-
aryl and 2-N-arylamino benzothiazole derivatives were
completely assigned using a concerted application of one-
and two-dimensional experiments (DEPT, gs-COSY, gs-
HMQC and gs-HMBC). Copyright 2005 John Wiley &
Sons, Ltd.
RESULTS AND DISCUSSION
In Schemes 1–3, the structures and numbering of substituted
benzothiazoles 1–43 are presented. Their 1H and 13C NMR chemical
shifts are given in Tables 1 and 2 respectively. Routine 13C NMR are
insufficient to obtain unambiguous determination of chemical shifts
since strict additivity using SCS values of all substituents19 does
not apply for polysubstituted aromatic compounds.20–22 Therefore,
we employed a sequence of NMR techniques as follows: (i) DEPT
experiments to determine the multiplicities of the 13C signals; (ii)
gs-COSY diagrams to determine the connectivity of protons; (iii)
HMQC spectra to determine the 13C resonances of the protonated
carbons; (iv) gs-HMBC sequences to assign the signals of quaternary
and protonated carbons via two- and three-bond interactions.
KEYWORDS: NMR; 1H NMR; 13C NMR; COSY; HMQC; HMBC;
2-aryl benzothiazoles; 2-N-arylamino benzothiazoles
INTRODUCTION
During the last decade, a large number of 2-aryl benzothiazoles
(Scheme 1) and 2-N-arylamino benzothiazoles (Scheme 3) have
been prepared because of their wide pharmacological potency.
In fact, this important class of compounds has interesting anti-
inflammatory,1 antimicrobial,2–4 antitumor5,6 and neuroprotective
properties.7 Recently, these compounds were also used as precursors
for in vivo imaging of ˇ-amyloid plaques,8 and for nonlinear optical
application.9 As a part of our program aimed at developing new
heterocyclics bearing a thiazole ring,10–13 we report in this paper
the complete 1H and 13C NMR chemical shift assignments using
one- and two-dimensional NMR techniques, including DEPT, gs-
COSY, gs-HMQC and gs-HMBC, for 2-N-arylamino benzothiazole
and 2-aryl benzothiazole derivatives.
EXPERIMENTAL
Materials:
General procedures for benzothiazoles formation
For 2-aryl benzothiazoles (1–26),14 typically, the corresponding
substituted benzoic acid (10 mmol), 2-amino thiophenol (11 mmol)
°
and PPA (10 g) were heated at 140 C for 24 h. The resulting mixture
was poured into water. The precipitate was collected by filtration,
dried and recrystallized from CH2Cl2 (yield 80–90%).
For 2-N(-aryl)-6-nitro benzothiazoles (27, 29–32, 34, 36, 38–40,
42),3 a mixture of 2-chloro-6-nitrobenzothiazole (10 mmol) and
°
phenol (3 g) was heated at 100 C under nitrogen. When the chloro
compound was dissolved in phenol, the corresponding substituted
anilines (11 mmol) were introduced into the reaction mixture. The
°
mixture was stirred at 80 C for 4 h, cooled to room temperature
and poured into water. The precipitate was then filtered and
recrystallized from ethanol (yield 50–70%).
2-N(-aryl)-6-aminobenzothiazoles (28, 33, 35, 37, 41, 43) were
prepared and purified as described previously (yield 50–70%),3
using catalytic hydrogenation with H2, Pd/C, and an ethanol system.
NMR techniques
NMR spectra were recorded in DMSO-d6 solutions at 300 K using
a Bru¨ker Avance DRX 500 spectrometer equipped with a Bru¨ker
CryoPlatform and a 5 mm cryo TXI probe. The temperature of the
probe and preamplifier was 30 K. Chemical shifts were referenced
ŁCorrespondence to: M. Robin, Laboratoire de Valorisation de la Chimie Fine,
Universite´ Paul Ce´zanne, Av. Escadrille Normandie-Niemen, 13397 Marseille
Cedex 20, France. E-mail: maxime.robin@univ.3-mrs.fr
Scheme 1. Structures of 2-aryl-benzothiazoles derivatives 1–22 (the
numbering of the atoms is arbitrary).
Copyright 2005 John Wiley & Sons, Ltd.
Billeau
