Carbacyclic peptide mimetics as VCAM-VLA-4 antagonists

Article abstract of DOI:10.1016/S0960-894X(00)00173-6

Substitution of carbon for sulfur in a potent 13-membered cyclic disulfide containing peptide was accomplished via an intramolecular Wittig reaction and resulted in a series of 'carba' analogues. Potency in the VCAM-VLA-4 assay was sensitive to ring size and lower than that of the parent disulfide. (C) 2000 Elsevier Science Ltd. All rights reserved.

Full text of DOI:10.1016/S0960-894X(00)00173-6

Bioorganic & Medicinal Chemistry Letters 10 (2000) 1163±1165
Carbacyclic Peptide Mimetics as VCAM±VLA-4 Antagonists
Je€erson Tilley,* Gerry Kaplan, Nader Fotouhi, Barry Wolitzky and Karen Rowan
Roche Research Center, Ho€mann-La Roche Inc, Nutley, NJ 07110, USA
Received 17 November 1999; accepted 9 March 2000
AbstractÐSubstitution of carbon for sulfur in a potent 13-membered cyclic disul®de containing peptide was accomplished via an
intramolecular Wittig reaction and resulted in a series of `carba' analogues. Potency in the VCAM±VLA-4 assay was sensitive to
ring size and lower than that of the parent disul®de. # 2000 Elsevier Science Ltd. All rights reserved.
Vascular cell adhesion molecule-1 (VCAM-l), a member
of the immunoglobulin (Ig) supergene family, is expres-
sed on activated, but not resting, endothelium. The
principal receptor for VCAM-1, the integrin very late
antigen 4 (VLA-4, a4b1), is expressed on many lympho-
cytes including circulating eosinophils, basophils, and
monocytes, but not neutrophils. Antibodies to either
protein are e€ective at inhibiting leukocyte in®ltration
and preventing tissue damage in several animal models
of in¯ammation.1 Peptides derived from the connecting
segment 1 (CS1) sequence of ®bronectin have also been
shown to block VCAM±VLA-4 interactions and to
block allergen induced airway responses in a sheep
model of asthma.2,3 Thus we are interested in discover-
ing orally active VCAM±VLA-4 antagonists which
might be useful for the treatment of asthma or rheuma-
toid arthritis.
We were also concerned that the disul®de moiety might
constitute a stability liability. Previous work on soma-
tostatin7 and atrial natriuretic factor8 indicated that
carbon may be substituted for the sulfur atoms in cyclic
disul®des without loss of agonist activity. Our molecular
modeling e€orts suggested that the impact of carbon
substitution on the orientation of the N- and C-terminal
vectors and the relative position of the ®ve-membered
ring of 2 was minor. Thus, we were encouraged to pre-
pare the carbacyclic analogues 2, to determine the e€ect
of this replacement on VCAM±VLA-4 binding activity.
In the accompanying paper,4 we described the develop-
ment of a class of spirocyclic disul®des derived from
tetrapeptides, typi®ed by 1, which are potent inhibitors
of the VCAM±VLA-4 interaction. Since these com-
pounds are of relatively simple structure with MW
<600, we chose to investigate whether further manipu-
lation might lead to orally active VCAM±VLA-4
antagonists. We hypothesized that the carboxyl group
could be masked as a prodrug ester and one or both
ring amide bonds might be modi®ed by N-alkylation
without loss of conformational control. Furthermore,
the previous experience of the Tanabe5 and Genentech6
groups suggested that exploration of potentially more
drug like replacements for the N-terminal tyrosine
should be fruitful.
Results and Discussion
Target compounds were prepared by a Wittig strategy
involving as the key step, an intramolecular cyclization
between an aldehyde and a phosphonoglycine deriva-
tive. The starting materials were prepared as shown in
Scheme 1, beginning with preparation of the pentenyl-
and hexenyl-glycine derivatives 5a and 5b via alkylation of
*Corresponding author. Tel.: +1-973-235-4660; fax: +1-973-235-
7122; e-mail: je€erson.tilley@roche.com
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00173-6

1164
J. Tilley et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1163±1165
Scheme 1.
Scheme 2.
the sulfonimide 4 according to Oppoizer's general proce-
dure.9 This material was coupled with azido acid 64 under
standard conditions, the sulfonimide was cleaved by treat-
ment with LiOH and the carboxyl group was esteri®ed to
give the azide 7 in good yield. This azide was reduced to the
corresponding amine with trimethylphosphine in THF
followed by a water quench and the product was used
immediately. Coupling with the unstable acid 9 proceeded
well when mediated by DCC in the absence of base to
give the key ole®n 10 (Scheme 2).
ole®n isomer predominated, which we presume to be the
trans-isomer. Hydrogenation a€orded in each case, a
mixture of isomers, which could be separated by RP-
HPLC to give 14 and 15, which are isomeric at the newly
formed chiral center (Scheme 3). Both isomers gave
NMR and MS data consistent with the assigned struc-
tures although we were unable to assign their absolute
stereochemistry.
Compounds were assayed for VLA-4 antagonist activity
using a solid-phase, dual antibody ELISA in which
VLA-4 derived from Ramos cells was allowed to com-
pete for bound recombinant human VCAM in the pre-
sence of serial dilutions of test compound. VLA-4
bound to VCAM-1 was detected by a complex of anti-bi
antibody and HRP-conjugated anti-mouse IgG: chro-
mogenic substrate (K-Blue).10 Both isomers in the 13-
membered ring series 14a and 15a were relatively potent
in the VCAM±VLA-4 binding assay (IC50 44 and 89
nM, respectively) and were approximately 10-fold more
potent than the corresponding 14-member ring homo-
logues 14b and 15b. The ole®ns 13a and 13b were in
between with the higher potency again observed with
the 13-member ring compound. In this assay system, the
To complete the synthesis, the Boc group was removed
with methanolic HC1 and the resulting amine was cou-
pled with Boc-Tyr under standard conditions to give 11.
We found that osmium tetraoxide/sodium periodate
gave a cleaner conversion of 11 to the corresponding
aldehyde than treatment with ozone. The reaction was
followed by TLC with veri®cation of the presence of the
aldehyde by NMR. This aldehyde was not isolated, but
treated immediately with DBU in methylene chloride to
give the protected cyclic peptides 12a and 12b in mod-
erate (43±62%) yield for the two steps. Successive
deprotection then a€orded the homologous ole®ns 13a
and 13b. NMR and RP-HPLC data suggest that a single
Scheme 3.

J. Tilley et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1163±1165
1165
prototype disul®de containing 13-member ring com-
pound 1 had an IC50 of 0.5 nM. Thus, while activity and
sensitivity to ring size was retained, the transition from
a cyclic disul®de to a carbacyclic system led to a pro-
nounced decrease in potency.
3. Elices, M. Curr. Opin. Antiin¯ammat. Immunomodulat.
Investigat. Drugs 1999, 1, 14.
4. Fotouhi, N.; Joshi, P.; Fry, D.; Cook, C.; Tilley, J. W.;
Kaplan, G.; Hanglow, A.; Rowan, R.; Schwinge, V.;
Wolitzky, B. Bioog. Med. Chem. Lett. 2000, 10, 1171.
5. Nowlin, D. M.; Goresan, F.; Moscinski, M.; Chiang, S.-L.;
Lobl, T.; Cardarelli, P. M. J. Biol. Chem. 1993, 268, 20352.
6. Jackson, D.; Quan, C.; Artis, D. R.; Rawson, T.; Blackburn,
B.; Struble, M.; Fitzgerald, G.; Chan, K.; Mullins, S.; Burnier,
J. P.; Fairbrother, W. J.; Clark, K.; Berisini, M.; Chui, H.;
Renz, M.; Jones, S.; Fong, S. J. Med. Chem. 1997, 40, 3359.
7. Nutt, R. F.; Veber, D. F.; Saperstin, R. J. Am. Chem. Soc.
1980, 102, 6539.
References and Notes
1. Elices, M. In Cell Adhesion Molecules and Matrix Proteins:
Role in Health and Diseases, Mousa S. A. Ed.; Springer-Ver-
lag: 1998; pp 133±147.
2. Lin, K.-c.; Ateeq, H. S.; Hsiung, S. H.; Chong, L. T.; Zim-
merman, C. N.; Castro, A.; Lee, W-c.; Hammond E.; Kalk-
unte, S.; Chen, L.-L.; Pepinsky, R. B.; Leone, D. R.; Sprague,
A. G.; Abraham, W. M.; Gill, A.; Lobb, R. A.; Adams, S. P.
J. Med. Chem. 1999, 42, 920. Lin, K.-C.; Castro, A. C. Curr.
Opin. Chem. Biol. 1998, 2, 453.
8. DiMaio, J.; Jaramillo, J.; Wernic, D.; Grenier, L.; Welch-
ner, E.; Adams, J. J. Med. Chem. 1990, 33, 661.
9. Oppolzer, W.; Moretti, R.; Zhou, C. Helv. Chimica Acta
1994, 77, 2363.
10. Chen, L.; Guthrie, R. W.; Huang, T.-N.; Hull, K. G.;
Sidduri, A.; Tilley, J. W. WO 9910312, 1999.