2300
L. Chang et al. / Bioorg. Med. Chem. Lett. 21 (2011) 2297–2301
Figure 2. Relative activities of TNAP determined at 37 °C and pH 10.4 as function of
concentration of levamisole and selected thiopheno-imidazo[2,1-b]thiazole
derivatives.
Figure 3. Relative activities of TNAP determined at 37 °C and pH 7.8 as function of
concentration of levamisole and selected thiopheno-imidazo[2,1-b]thiazole
derivatives.
strategy, the condensation of 3 with the 2-aminothiazoline gave
the intermediate 7 which was converted into the tetramisole
derivative 9 with a global yield of 19% (Scheme 1).
The 2-substituted thiophene analogues were prepared in a sim-
ilar synthetic pathway, 2,3-dehydrotetramisole and tetramisole
analogues 13 and 16 respectively prepared in global yield of 35%
and 23% (Scheme 2).
to design a possible drug therapy to cure pathological calcification
but also to characterize distinct aspects of mineralization
mechanisms.
A large range of IC50 (from 42 13 lM to more than 800 lM) is
obtained with a single chemical modification on the same chemical
motif, thiopheno-imidazo[2,1-b]thiazole. The racemic thiophenyl
analogue of levamisole (6ÁHCl) with apparent IC50 = 42 13
(n = 3, pH 10.4) is twice more potent than enantiomeric levamisole
1 (IC50 = 93 23 M) (as determined with porcine kidney TNAP),
lM
The imidazo[2,1-b]thiazole 17 and its corresponding 2,3-dehy-
dro- derivative 18 were prepared from 3-(2-bromoacetyl)-thio-
phene with 2-aminothiazole and 2-aminothiazoline, respectively,
through intermediates 4 and 7 (Scheme 3). Treatment in acidic
medium allowed the intramolecular condensation and aromatiza-
tion of the ring formed. Other derivative of 2,3-dehydrotetramisole
19 was obtained from 3-(2-bromoacetyl)thiophene 3 upon treat-
ment with 2-imidazolidinethione.
l
indicating some potential to synthesize and optimize enantiomeric
thiophenyl derivatives for therapeutic applications to treat patho-
logical calcifications. Most of the inhibitors were not very soluble
in water medium. Enlarging chemical and physical properties of
inhibitors to obtain the best pharmacokinetic parameters as well
as to increase the selectivity into extra cellular medium, synthesis
of water-soluble inhibitors are a necessary step toward generation
of a series of inhibitors.
The inhibition of TNAP activity has been tested for a series of
thiophenyl tetramisole derivatives at pH 10.4. Best compound 6
as a racemic mixture, inhibited TNAP at lower concentration
(IC50 = 42 13
(IC50 = 93 23
(IC50 = 408 168
l
l
M) than the
M) (Table 1). Other derivatives such as
M) and 13 (IC50 = 331 168
erately TNAP as compared with levamisole. Other compounds such
as 16–19 did not inhibit significantly (IC50 >800 M) (Table 1,
S
enantiomer of levamisole
1
9
Acknowledgment
l
lM) inhibited mod-
The authors deeply acknowledge Professor David Magne
(ICBMS-Université de Lyon) for fruitful discussion.
l
Fig. 2). Values determined at pH 7.8 (Fig. 3) are less indicative since
the assay is based on the detection of nitrophenolate (pKa = 7) but
pointed out that inhibitors kept their properties at neutral pH. At
Supplementary data
pH 7.8, the apparent IC50 of racemic compound 6 (IC50 = 84
is similar to that of levamisole 1 (IC50 = 78 17 M) (Table 1). The
thiophene inhibitors obtained here are less potent than pyrazole
9 lM)
Supplementary data associated with this article can be found, in
l
16,17
derivatives having lower IC50
.
IC50 determined by our team
References and notes
are overestimated as compared with those reported16,17due to dis-
1. Anderson, H. C. Curr. Opin. Orthop. 2007, 18, 428.
tinct origin of TNAP and biological assay. Ki of levamisole also
2. Kalya, S.; Rosenthal, A. K. Curr. Opin. Rheumatol. 2005, 17, 325.
3. Steinbach, L. S.; Resnick, D. Curr. Probl. Diagn. Radiol. 2000, 29, 209.
4. McCarthy, G. M.; Cheung, H. S. Curr. Rheumatol. Rep. 2009, 11, 141.
5. Ea, H. K.; Lioté, F. Curr. Opin. Rheumatol. 2009, 21, 150.
6. Fuerst, M.; Bertrand, J.; Lammers, L.; Dreier, R.; Echtermeyer, F.; Nitschke, Y.;
Rutsch, F.; Schäfer, F. K. W.; Niggemeyer, O.; Steinhagen, J.; Lohmann, C. H.;
Pap, T.; Rüther, W. Arthritis Rheum. 2009, 60, 2694.
7. Ehrlich, J. E.; Rumberger, J. A. Dialysis Transplant. 2004, 33, 306.
8. Van der Heijde, D.; Dijkmans, B.; Geusens, P.; Sieper, J.; DeWoody, K.;
Williamson, P.; Braun, J. Arthritis Rheum. 2005, 52, 582.
9. Antoni, C.; Krueger, G. G.; de Vlam, K.; Birbara, C.; Beutler, A.; Guzzo, C.; Zhou,
B.; Dooley, L. T.; Kavanaugh, A. Ann. Rheum. Dis. 2005, 64, 1150.
amounted to 93
4
l
M,14 while it was 16
l
M for the reported va-
lue.16 TNAP (final TNAP concentration was 6.93–11.4
l
g mLÀ1) was
from porcine origin in our UV–vis assays, while TNAP was from re-
combinant origin in the luminescent assays.16,17
There is an urgent need to obtain other TNAP inhibitors since
there are very few.16,24 One of the problem encountered with
inhibitors is their specificity. For example, levamisole not only
inhibited TNAP but affected indirectly Ca2+ or Pi transport.24 There-
fore, the synthesis of other TNAP inhibitors is a necessity not only