Thus, it is our goal to undertake a synthetic and biological
strategy to provide insight into the mechanism of action of
thalidomide and related analogues. We propose the synthetic
aspect of the strategy to include the synthesis of an azido
analogue of thalidomide, which will then be examined
biologically for its potential use as a photoaffinity label. The
use of photoaffinity analogues to assist in elucidating
Scheme 2. Synthesis of Azido Photoaffinity Analogue
1
1
mechanisms of action has been reported in the literature.
To our knowledge, there is only one other example of a
1
2
thalidomide photoaffinity label reported in the literature,
but the present analogue more closely resembles the actual
structure of thalidomide.
The synthesis of the azido analogue is broken down into
two parts. The first involves the synthesis of the right half
of the compound, or the glutarimide moiety (Scheme 1).
Scheme 1. Synthesis of the Glutarimide Moiety
Reduction of the nitro group with 10% Pd/C and H
2
(g)
proceeded smoothly to yield the 4-amino-substituted ana-
15
logue 6 in 80% yield. Diazotization of 6, by treatment with
sodium nitrite in aqueous HCl at 0 °C, followed by the slow
addition of sodium azide, afforded the 4-azido-substituted
thalidomide analogue 7 in 35% yield. It is important to note
that the reaction conditions are not yet optimized for this
series of transformations; thus, it is believed that the moderate
yields obtained for some of the steps can be improved upon.
As shown in Table 1, the azido-labeled analogue possesses
greater potency than thalidomide in inhibiting human mi-
The synthesis of 3 begins by utilizing the method of Muller
et al.13 in the treatment of the commercially available NR-
(tert-butoxycarbonyl)-L-glutamine 1 with 1,1′-carbonyldi-
imidazole (CDI) and 4-dimethylamino pyridine in refluxing
THF to afford 2, in which racemization of the product
occurs.14 The resultant N-Boc glutarimide ring 2 is subse-
quently deprotected by TFA at room temperature to afford
to the glutarimide moiety 3 as the TFA salt. Attempts to
isolate the free amine resulted in rapid decomposition,
possibly by hydrolysis of the glutarimide ring. Once in hand,
intermediate 3 was condensed with 4-nitrophthalic anhydride
Table 1. Inhibition of HMEC Proliferation by Analogue 7
HMEC IC50 (µM)a
compound
(+) VEGF
(-) VEGF
thalidomide
>300
>300
7
259 ( 31.2
239 ( 55.8
a
IC50 values reported are averages of triplicate experiments.
4
by refluxing in glacial acetic acid over 2-3 h, affording
15
the 4-nitro-substituted thalidomide derivative 5 in 58% yield
crovessel endothelial cell (HMEC) proliferation, both in the
presence and absence of vascular endothelial growth factor
(
Scheme 2).
1
6
(
9) (a) Eriksson, T.; Bjorkman, S.; Roth, B.; Fyge, A. Hoglund, P.
Chirality 1996, 7, 44. (b) Wintersk, W.; Frankus, E. Lancet 1992, 339,
65.
10) (a) Wnendt, S.; Finkam, M.; Winter, W.; Ossing, J.; Rabbe, G.;
(VEGF). Additionally, the endothelial cell proliferation
effect exhibited by 7 proves that the addition of the azido
group to thalidomide is not detrimental to the compound’s
ability to interact with the thalidomide binding site(s).
Herein, we have described a facile synthesis of a novel
azido photoaffinity thalidomide analogue. The teratogenic
effects of the parent thalidomide are well-known throughout
the chemical and biological community, although the mech-
anism by which the drug elicits these effects remains
unknown. The fact that the (S)-enantiomer of thalidomide
exhibits the strongest antiangiogenic and teratogenic activity17
shows that there is a clear enantioselective preference, and
3
(
Zwingenberger, K. Chirality 1996, 8, 390. (b) Knoche, B.; Blaschke, G. J.
Chromatogr. 1994, 2, 183.
(11) For examples utilizing taxol photoaffinity analogues, see: (a)
Dasgupta, D.; Park, H.; Harriman, G. C. B.; Georg, G. I.; Himes, R. H. J.
Med. Chem. 1994, 37, 2976. (b) Swindell, C. S.; Heerding, J. M.; Krauss,
N. E. J. Med. Chem. 1994, 37, 1446.
(
12) Turk, B. E.; Jiang, H.; Liu, J. O. Proc. Natl. Acad. Sci. U.S.A. 1996,
3, 7552.
13) (a) Muller, G. W.; Konnecke, W. E.; Smith, A. M.; Khetani, V. D.
Org. Process Res. DeV. 1999, 3, 139.
14) For 1: [R]D -10.4 (c 0.1, CH3OH). For 2: [R]D 0.0 (c 0.1, CH3-
OH).
9
(
(
(15) Muller, G. W.; Chen, R.; Huang, S.-Y.; Corral, L. G.; Wong, L.
M.; Patterson, R. T.; Chen, Y.; Kaplan, G.; Stirling, D. I. Bio. Med. Chem.
Lett. 1999, 9, 1625.
(16) VEGF is a known stimulator of endothelial cell proliferation.
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Org. Lett., Vol. 5, No. 16, 2003