290
B. Bachand et al. / Bioorg. Med. Chem. Lett. 11 (2001) 287±290
thrombosis model system, doubling and even tripling
the mean occlusion time in some cases.
Acknowledgements
The authors would like to acknowledge Ms. Celine
Locas and Ms. Brigitte Grouix for providing binding
constants, Ms. Annie St-Pierre for performing the in
vivo experiments and Dr. Mirek Cygler of the Bio-
technology Research Institute of Montreal for the X-
ray structure. Finally, we would like to thank Dr.
Alan Cameron for reading the manuscript and Ms.
Lyne Marcil for her help in the preparation of this
manuscript.
Figure 2.
and 1930, respectively) with compounds 2c (Tryp/Thr:
812) or even more dramatically when one compares
analogue 2j with 2k (Tryp/Thr: 7000 and 150, respec-
tively). All these data taken together suggest that the
cyclohexylamine moiety is obviously essential to obtain
a good level of selectivity and moreover that this selec-
tivity could 0be substantially varied by having a polar
group on P1 .
References and Notes
1. St-Denis, Y.; Augelli-Szafran, C. E.; Bachand, B.; Berry-
man, K. A.; DiMaio, J.; Doherty, A. M.; Edmunds, J. J.;
Leblond, L.; Levesque, S.; Narasimhan, L. S.; Penvose-Yi,
J. R.; Rubin, J. R.; Tarazi, M.; Winocour, P. D.; Siddiqui,
M. A. Bioorg. Med. Chem. Lett. 1998, 8, 3193.
2. (a) Brady, S. F.; Lewis, S. D.; Colton, C. D.; Stauer, K. J.;
Sisko, J. T.; Ng, A. S.; Homnick, C. F.; Bogusky, M. J.; Sha-
fer, J. A.; Veber, D. F.; Nutt, R. F. Pept.: Chem., Struct. Biol.,
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Lewis, S. D.; Shafer, J. A.; Feng, D.-M.; Nutt, R.-F.; Brady,
S. F. WO9425051, 1994; Chem. Abstr. 1994, 122, 17839.
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Mulichak, A. M.; Ng, A. S.; Naylor-Olsen, A. M.; Sanders,
W. M. Bioorg. Med. Chem. Lett. 1997, 7, 67.
Most of the compounds with the exception of 2c and 2d
displayed a substantial increase (2- to 3-fold) in anti-
thrombotic activity in the rat arterial thrombosis model
as measured by the MOT. Unfortunately, when these
compounds were given orally to rats, low levels of
bioavailability were observed for all the compounds listed
in Table 1.
4. Ban®, A.; Benedini, F.; Sala, A.; Russo, G. Synth. Com-
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Figure 2 shows the X-ray structure8 of inhibitor 2g with
thrombin. The mode of interaction is very similar to the
structure already reported by us on a compound having
a regular arginine at P1.1 Brie¯y, the benzylsulfonamide
group penetrates deeply in the S3 pocket, while the
amino group of trans-cyclohexylamine makes a salt
bridge interaction with the Asp 189 at the bottom of the
S1 pocket. Since thrombin has a more lipophilic S1
pocket (Ala 190) than trypsin (Ser 190), this dierence
might explain why the more lipophilic P1 side chains are
preferred in thrombin compared to trypsin. This sug-
gests why all the analogues prepared in this paper
showed remarkably good selectivity. Finally, the acti-
vated carbonyl group makes a strong covalent bond
with the Ser 195 forming a tetrahedral intermediate
providing additional binding anity.
7. Compound 14, Ki (thrombin) 0.23 nM, Ki (trypsin) 0.23
nM; Siddiqui, M. A., Unpublished results
.
Conclusion
We have demonstrated that incorporation of a cyclo-
hexylamine unit in the P1 site bearing an electrophilic
carbonyl aords very potent thrombin inhibitors in the
low nanomolar range. These compounds, moreover,
displayed good antithrombotic activity in the rat arterial
8. The authors have deposited X-ray crystallographic data
with the Brookhaven Protein Data Bank. Deposition code
1G37.