Synthesis of chiral 2-(4-phenoxyphenylsulfonylmethyl)thiiranes as selective gelatinase inhibitors

Article abstract of DOI:10.1021/ol0517269

(Chemical Equation Presented) Compound 1, 2-(4-phenoxyphenylsulfonylmethyl) thiirane, is a selective inhibitor of gelatinases, which is showing high promise in studies of animal models for cancer metastasis and stroke. The (R)-1 and (S)-1 enantiomers of c

Full text of DOI:10.1021/ol0517269

ORGANIC
LETTERS
2005
Vol. 7, No. 20
4463-4465
Synthesis of Chiral
2-(4-Phenoxyphenylsulfonylmethyl)thiiranes
as Selective Gelatinase Inhibitors
Mijoon Lee,† M. Margarida Bernardo,‡ Samy O. Meroueh,† Stephen Brown,†
Rafael Fridman,‡ and Shahriar Mobashery*,†
Department of Chemistry and Biochemistry and the Walther Cancer Research Center,
UniVersity of Notre Dame, Notre Dame, Indiana 46556, and Department of Pathology,
School of of Medicine and Proteases and Cancer Program,
Karmanos Cancer Institute, Wayne State UniVersity, Detroit, Michigan 48201
mobashery@nd.edu
Received July 21, 2005
ABSTRACT
Compound 1, 2-(4-phenoxyphenylsulfonylmethyl)thiirane, is a selective inhibitor of gelatinases, which is showing high promise in studies of
animal models for cancer metastasis and stroke. The (R)-1 and (S)-1 enantiomers of compound 1 were each synthesized in this study and
were shown to be equally active in inhibition of gelatinases.
Restructuring of the extracellular matrix is an important
biological event for both physiological and pathologial
processes. These events are highly regulated in physiological
settings. However, when the regulation of these events goes
awry, a number of pathological events ensue, including
cancer growth, tumor metastasis and angiogenesis, arthritis,
connective tissue diseases, inflammation, and cardiovascular,
neurological, and autoimmune diseases.1-8
and -9) have been implicated in a number of diseases, and
inhibitors for these are highly sought. Unfortunately, virtually
all of the known inhibitors for gelatinases are broad-
spectrum.9-14 There are a mere handful known to exhibit
selectivity toward subsets of MMP members.15
We recently reported the design and in vitro evaluation
of racemic 2-(4-phenoxyphenylsulfonylmethyl)thiirane (com-
pound 1).16 This compound is a potent and selective inhibitor
for human gelatinases. The gelatinase inhibitor is highly
active in in vivo models for cancer metastasis and for brain
damage after stroke in mice, both of which are processes
known to be mediated by the activity of gelatinases.17,18
Matrix metalloproteinases (MMPs) constitute a family of
26 closely related zinc-dependent endopeptidases involved
in these processes. Of these enzymes, gelatinases (MMP-2
† University of Notre Dame.
‡ Wayne State University.
(9) Lee, M.; Fridman, R.; Mobashery, S. Chem. Soc. ReV. 2004, 33, 401-
409.
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10.1021/ol0517269 CCC: $30.25
© 2005 American Chemical Society
Published on Web 09/03/2005

The biphenyl moiety fits in the deep hydrophobic pocket
in the active sites of gelatinases, and the inhibitor interacts
with the active-site zinc ion through the thiirane moiety. This
interaction activates the thiirane for nucleophilic attack by
the active site glutamate in these enzymes, resulting in
irreversible inhibition (Scheme 1). The mechanism of action
of this inhibitor is unique among those reported for MMPs.
which indicates that the nucleophilic attack of the thiolate
occurred exclusively at the C-3 of epichlorohydrin and the
stereocenter was not scrambeld during this step. We cannot
rule out the possibility of nucleophilic attack at C-1, and
the released Cl- subsequently attacked at C-3 epoxide
opening, though C-3 attack is the most likely route. The
enantiomeric excess was determined by chiral HPLC (Sup-
porting Information).
We also explored alternative routes to the chiral thiiranes,
starting with the same starting material 2 (Scheme 3). After
Scheme 1
Scheme 3
Whereas we have used a racemic mixture of inhibitor 1
in all previous investigations (including animal studies), we
have been curious if one or both of the enantiomers would
exhibit the biological activity. In the field of enzyme
inhibition, it is widely assumed that one enantiomer is active
while the other is not. To provide the answer to this question,
we report herein the facile syntheses of optically active (R)-
and (S)-enantiomers of compound 1, starting from com-
mercially available (R)- and (S)-epichlorohydrin, respectively
(Figure 1). We also report on the enzyme inhibitory
the thiolate was generated by the reaction of 2 with n-BuLi
and sulfur, we allowed it to react with acetyl chloride,
yielding the thioacetate 6. Compound 6 directly gives (S)-4
by treatment with epichlorohydrin. Another approach is by
the reaction of the thiolate with allyl bromide to give the
allyl sulfide 7, which could further be elaborated to the
corresponding chiral diol, (S)-8, by the Sharpless dihydroxy-
lation reaction.19 The resulting diol could be converted to
the epoxide under Mitsunobu condition.20 After careful
consideration of the yields, the need for purification, and
the issue of enantioselectivity, we opted for the original route
outlined in Scheme 2.
Figure 1. Selective gelatinase inhibitor.
The remainder of the synthetic route was similar to that
of a published method,21 which involves the formation of
the epoxide ring, sulfide oxidation, and thiirane ring forma-
tion. Throughout the synthesis, the stereocenter was intact.
The last step, conversion of the oxirane to the thiirane ring,
involves inversion of stereochemistry.22,23 This was per-
formed in the presence of thiourea to give the desired
product, which was recrystallized from 1-butanol.
properties of the enantiomers and provide answers on
interactions of these molecules within the active site of
MMP-2.
Synthesis commences with lithiation of 4-phenoxyphe-
nylbromide (2), which was then treated with sulfur to
The optical purity was determined by NMR in the presence
of the chiral shift reagent europium tris[3-(heptafluoropro-
Scheme 2
(16) Brown, S.; Bernardo, M. M.; Li, Z. H.; Kotra, L. P.; Tanaka, Y.;
Fridman, R.; Mobashery, S. J. Am. Chem. Soc. 2000, 122, 6799-6800.
(17) Gu, Z.; Cui, J.; Brown, S.; Fridman, R.; Mobashery, S.; Strongin
Alex, Y.; Lipton Stuart, A. J. Neurosci. 2005, 25, 6401-6408.
(18) Kruger, A.; Arlt, M. J. E.; Gerg, M.; Kopitz, C.; Bernardo, M. M.;
Chang, M.; Mobashery, S.; Fridman, R. Cancer Res. 2005, 65, 3523-3526.
(19) Corey, E. J.; Guzman-Perez, A.; Noe, M. C. J. Am. Chem. Soc.
1995, 117, 10805-10816.
(20) Takano, S.; Seya, K.; Goto, E.; Hirama, M.; Ogasawara, K. Synthesis
1983, 116-117.
(21) Lim, I. T.; Brown, S.; Mobashery, S. J. Org. Chem. 2004, 69, 3572-
3573.
generate the corresponding thiolate. The thiolate was allowed
to react with (R)-epichlorohydrin (97% ee) (Scheme 2).
Optical purity of the resultant compound ((R)-3) was 97%,
(22) Sanders, M. Chem. ReV. 1966, 66, 297-339.
(23) Hauptman, E.; Fagan, P. J.; Marshall, W. Organometallics 1999,
18, 2061-2073.
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Org. Lett., Vol. 7, No. 20, 2005

pylhydroxymethylene)-(+)-camphorate], Eu(hfc)3. The NMR
sample was prepared by adding 5 mg of (R)-1 and 1 mg of
Eu(hfc)3 in 0.2 mL of CDCl3. In this condition the other
enantiomer ((S)-1) was not detected in NMR. Thus, we can
say that the enantiomeric excess of (R)-1 is >90%.
figurations of (2S,3R) and (2R,3S) are equally efficient
inhibitors of carboxypeptidase A as evidenced by their
kinetics and by the X-ray crystal structures of the inhibited
enzymes.24
The computational study is supportive of the experimental
findings that both enantiomers of inhibitor 1 are able to bind
to the active site of MMP-2 (Figure 2). In both cases, the
Synthesis of (S)-1 was performed according to the same
procedure, with the sole substitution of (S)-epichlorohydrin
as the reagent of choice. The optical purity was comparable
to the case of the other enantiomer.
The racemic form of inhibitor 1 binds the active site of
gelatinases with high selectivity.16 The compound has a
complicated profile for its inhibition of these two enzymes.
There is an onset of noncovalent slow-binding inhibition
(rapid kon), resulting in a complex that cannot readily reverse
itself (slow koff). The ratio of kon/koff furnishes the dissociation
constant (Ki) for the inhibitor, a measure of the propensity
for the formation of the complex between the inhibitor and
the enzyme. The Ki values are in the nanomolar range for
gelatinases. The noncovalent complex leads to covalent
inhibition of the enzyme. The side-by-side analyses were
performed for the racemate, and for the (R)-1 and (S)-1
enantiomers (Table 1). For approach to the kinetic method-
ologies, consult Brown et al.16
Table 1. Kinetic Parameters for Inhibition of Gelatinases by
the Synthetic Inhibitors
Figure 2. Stereoview of the energy-minimized complexes of (A)
(R)-1 and of (B) (S)-1 bound to the active site of MMP-2. A
Connolly solvent-accessible surface is constructed in the active site
(shown in green), while the loop that constitutes the S1′ subsite of
the enzyme is drawn as a purple tube. The compounds, along with
the active-site Glu-404 (at 11 o’clock) and the three histidines shown
in capped-sticks representation, are colored according to atom types
(yellow, red, blue, and white for S, O, N, and C, respectively).
The zinc ion is shown as an orange sphere.
10-4kon (M-1 s-1
)
104koff (s-1
)
Ki (nM)
MMP-2
(R)-1
(S)-1
(()-1
MMP-9
(R)-1
2.2 ( 0.5
1.7 ( 0.4
2.0 ( 0.5
5.3 ( 0.5
4.0 ( 0.3
5.7 ( 0.3
24 ( 6
23 ( 6
28 ( 7
0.22 ( 0.05
0.28 ( 0.05
0.28 ( 0.09
11.0 ( 0.2
8.8 ( 1.4
12.4 ( 0.2
500 ( 10
310 ( 70
400 ( 150
(S)-1
(()-1
requisite thiirane carbon for the nucleophilic attack by Glu-
404 is presented properly for the reaction with coordination
of the thiirane sulfur to the zinc ion.
In an unexpected outcome to these analyses, both the (R)-1
and (S)-1 enantiomers were equally active.
Acknowledgment. This work was supported by Grant
No. NCI-CA100475 from the National Institutes of Health
to R.F.
While it is unusual for the enantiomers of a racemic
mixture to function equivalently as inhibitors, it is not without
precedence.24,25 For example, Ryu et al. reported that both
enantiomers of 2-benzyl-3-epoxybutanoic acid having con-
Supporting Information Available: Experimental pro-
cedures and chromatographic and spectroscopic data for
compounds 1, 3, 4, and 5. This material is available free of
charge via the Internet at http://pubs.acs.org.
(24) Ryu, S. E.; Choi, H. J.; Kim, D. H. J. Am. Chem. Soc. 1997, 119,
38-41.
(25) Lai, M. T.; Liu, H. W. J. Am. Chem. Soc. 1990, 112, 4034-4035.
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