Table
1
IC50 concentrations of caulibugulones for inhibition of
Acknowledgements
recombinant human protein phosphatases. All values are M and are the
mean ± SEM of 3 independent determinations
This work was supported by the National Institutes of Health
CA 78039) and the Fiske Drug Discovery Fund. P. W. and B. J.
also thank Merck & Co. for financial support.
(
Caulibugulone
Cdc25B
VHR
PTP1B
A (1)
B (2)
C (3)
D (4)
E (5)
6.7 ± 1.3
2.7 ± 0.5
5.4 ± 0.7
19.1 ± 0.3
32.5 ± 3.6
>500
>1000
Notes and references
130 ± 23
175 ± 2
>1000
>1000
183 ± 24
322 ± 32
>1000
1 D. J. Milanowski, K. R. Gustafson, J. A. Kelly and J. B. McMahon, J.
Nat. Prod., 2004, 67, 70.
2 (a) J. S. Lazo, D. C. Aslan, E. C. Southwick, K. A. Cooley, B. Joo,
A. P. Ducruet, A. Vogt and P. Wipf, J. Med. Chem., 2001, 44, 4042;
>1000
(
b) J. S. Lazo, K. Nemoto, K. E. Pestell, K. Cooley, E. C. Southwick,
D. A. Mitchell, W. Furey, R. Gussio, D. W. Zaharevitz, B. Joo and
P. Wipf, Mol. Pharmacol., 2002, 61, 720; (c) Y. Han, H. Shen, B. I. Carr,
P. Wipf, J. S. Lazo and S.-S. Pan, J. Pharm. Exp. Ther., 2004, 309, 64;
(
d) J. S. Lazo and P. Wipf, Oncol. Res., 2003, 13, 347; (e) M. A. Lyon,
A. P. Ducruet, P. Wipf and J. S. Lazo, Nature Rev. Drug Discovery,
002, 1, 961.
R. Barret and M. Daudon, Tetrahedron Lett., 1990, 31, 4871.
For the use of CeCl in the addition of amines to isoquinoline diones,
2
3
4
3
see: C. Brahic, F. Darro, M. Belloir, J. Bastide, R. Kiss and E. Delfourne,
Bioorg. Med. Chem., 2002, 10, 2845.
1
5
6
Regioisomeric ratio was determined by H NMR.
Scheme 3 Synthesis of caulibugulone E.
1
Each fraction was checked by H NMR because TLC analysis could not
1
13
differentiate between the two isomers. H NMR and C NMR spectra
matched well with the reported spectra.
As illustrated in Table 1, all five caulibugulones inhibited full-
length human Cdc25B in vitro with IC50 values ranging from 2.7
to 32.5 M, with caulibugulones B and E being the most and
7
8
The regiochemistry of caulibugulone E was confirmed by analysis of the
HMBC spectrum.
6 2
Epitope-tagged (His ) full length human Cdc25B was expressed in
8
least potent, respectively. Moreover, all caulibugulones exhibited
2
E. coli and purified as previously described. Human recombinant
VHR and PTP1B were purchased from BIOMOL (Plymouth
Meeting, PA). Activities of all phosphatases were measured using
the substrate O-methyl fluorescein phosphate (Sigma, St. Louis,
a minimum 30-fold preference as inhibitors against the dual
specificity phosphatase Cdc25B compared to the dual specificity
phosphatase VHR or the protein tyrosine phosphatase PTP1B. In
addition, we have observed cell growth inhibitory activity with
m
MO) at concentrations varying with the K of each enzyme in a 96-
well microtiter plate assay (25 L final volume) based on previously
9
human tumor cells consistent with Cdc25 inhibition.
2
described methods. Fluorescence emission from the product was mea-
In conclusion, the first total synthesis of the naturally occuring
cytotoxic caulibugulones proceeded efficiently in high overall
yields from readily available isoquinolin-5-ol via hypervalent
sured after a 20 or 60 min incubation period at ambient temperature
with a multiwell plate reader (PerSeptive Biosystems Cytofluor II;
Framingham, MA; excitation filter, 485 nm/bandwidth 20 nm; emis-
sion filter, 530 nm/bandwidth 30 nm).
M. Brisson, J. S. Lazo, B. Joo, T. Nguyen, P. Wipf, manuscript in
preparation.
1
0
iodine oxidation, regioselective halogenations, and amination
reactions. Biological assays established this class of natural
products as new phosphatase inhibitors with considerable selectivity
against the Cdc25 family of DSPases. Since this is a potentially
clinically relevant biological mechanism of action, studies continue
to determine the antitumor activity of caulibugulones.
9
1
0 (a) Y. Tamura, T. Yakura, J. Haruta and Y. Kita, J. Org. Chem., 1987,
2, 3927; (b) P. Wipf, Y. Kim and H. Jahn, Synthesis, 1995, 1549;
5
(c) D. Magdziak, S. J. Meek and T. R. R. Pettus, Chem. Rev., 2004, 104,
1383.
2
1 7 4
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 1 7 3 – 2 1 7 4