Derivatives of tetrahydroisoquinoline: Synthesis and initial evaluation of novel non-peptide antagonists of the αiIbβ3- integrin

Article abstract of DOI:10.1016/j.bmcl.2010.06.051

The novel RGDF mimetics were synthesized with the use of 4-(1,2,3,4-tetrahydroisoquinoline-7-yl)amino-4-oxobutyric or 5-(1,2,3,4-tetrahydroisoquinoline-7-yl)amino-5-oxopentanoic acids as a surrogate of Arg-Gly motif. The synthesized compounds have demonstrated a high potency to inhibit platelet aggregation in vitro and to block FITC-Fg binding to α_IIbβ₃ on washed human platelets.

Full text of DOI:10.1016/j.bmcl.2010.06.051

Bioorganic & Medicinal Chemistry Letters 20 (2010) 4444–4446
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Derivatives of tetrahydroisoquinoline: Synthesis and initial evaluation
of novel non-peptide antagonists of the aIIbb3-integrin
*
Andrei A. Krysko , Olga L. Krysko, Tatyana A. Kabanova, Sergei A. Andronati, Vladimir M. Kabanov
Department of Medicinal Chemistry, A.V. Bogatsky Physico-Chemical Institute of the National Academy of Sciences of Ukraine, 86 Lustdorfskaya Doroga, 65080 Odessa, Ukraine
a r t i c l e i n f o
a b s t r a c t
Article history:
The novel RGDF mimetics were synthesized with the use of 4-(1,2,3,4-tetrahydroisoquinoline-7-yl)a-
mino-4-oxobutyric or 5-(1,2,3,4-tetrahydroisoquinoline-7-yl)amino-5-oxopentanoic acids as a surrogate
of Arg-Gly motif. The synthesized compounds have demonstrated a high potency to inhibit platelet
Received 14 May 2010
Revised 8 June 2010
Accepted 8 June 2010
Available online 15 June 2010
aggregation in vitro and to block FITC-Fg binding to
aIIbb3 on washed human platelets.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Fibrinogen receptor antagonists
aIIbb3
RGD mimetics
1,2,3,4-Tetrahydroisoquinoline
Platelet aggregation
Key events of thrombotic disorders, which result in various car-
diovascular diseases including unstable angina, myocardial infarc-
tion, and arterial re-occlusion following coronary angioplasty
procedures, are theactivationand aggregation ofplatelets.1 The clin-
ical trials of monoclonal antibody c7E3 (ReoProÒ),2 the peptide
IntegrilinÒ,3 and the non-peptides Tirofiban (AggrastatÒ)4 and Lami-
fiban5 have demonstrated the utility of fibrinogen receptor (glyco-
events(Fig. 1). Fragmentswiththeresiduesof p-benzamidine,piper-
idine, p-benzguanidine, etc., and b-alanines with different substitu-
ents in b-position are successfully applied as bioisosteres of arginine
and Asp-Phe moieties, correspondingly, for the design of non-pep-
tide fibrinogen receptor antagonists mimicking RGDF sequence.8,9
Previous reports from our laboratories described the discovery
of the novel series of RGDF mimetics as non-peptide fibrinogen
receptor antagonists.10,11 These compounds represent derivatives
of isoindoline 110or tetrahydroisoquinoline 2 (Fig. 2).11 As an
extension of this work, the synthesis of new tetrahydroisoquino-
protein IIb/IIIa, a3IIbb3) antagonists for the treatment of thrombotic
disorders. Furthermore, RGD mimetic prodrugs Xemilofiban, Orbofi-
ban6 and Sibrafiban7 succeeded in treatment of unstable angina
NH2
O
O
H
H
O
N
O
N
N
O
HN
H
O
HN
N
O
N
H
O
Xemilofiban
NH2
Orbofiban
O
O
O
N
HO
N
N
O
H
H2N
O
Sibrafiban
Figure 1. Structures of Xemilofiban, Orbofiban, and Sibrafiban.
* Corresponding author.
E-mail address: peptides@physchem.od.ua (A.A. Krysko).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.06.051

A. A. Krysko et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4444–4446
4445
O
a
OH
O
N
O
N
( )n
N
NH2
H
O
O
3
O
4a,b
b
O
H
N
OMe
O
N
( )n
N
H
c
O
O
R
O
5a-p
O
H
N
OH
O
N
( )n
N
H
O
6a-p
O
R
O
R
d
O
H
N
OH
HCl*HN
N
H
( )n
O
O
7a-p
Scheme 1. Reagents: (a) succinic or glutaric anhydride, 90–95%; (b) (i) Et3N, HBTU or HATU; (ii) b-amino acid methyl ester, Et3N, 65–70%, two steps; (c) (i) 1 M NaOH, H2O;
(ii) 1 M HCl, H2O, 60–74%, two steps; (d) HCl (gas)/DCM, 95–98%.
line based
a
IIbb3 antagonists and study of their antiaggregative
We used DCC/SuOH method for the preparation of previously
reported RGD mimetics 7a (n = 1, R = H) and 7b (n = 1, R = C6H5).
This method was employed at the stage when acid 4a (n = 1) was
coupled with sodium salts of appropriate b-alanines.11a The target
properties were carried out. With the aim to improve an antiplate-
let activity, b-aryl substituted b-alanines were proposed for imita-
tion of Asp-Phe moiety.
O
O
H
H
HN
HN
N
OH
N
OH
N
N
H
H
O
O
O
O
1a
1b
IC50, nM (PRP): 160.0
IC50, nM (PRP)a: 860.0
IC50, nM (FITC-Fg/αIIbβ3)b: 8.3
IC50, nM (FITC-Fg/αIIbβ3): 2.6
O
O
H
O
HN
H
HN
N
OH
N
OH
N
N
H
O
O
H
O
O
O
1d
IC50, nM (PRP): 890.0
IC50, nM (FITC-Fg/αIIbβ3): 9.0
1c
IC50, nM (PRP): 105.0
O
O
IC50, nM (FITC-Fg/αIIbβ3): 6.0
O
H
HN
O
O
O
N
OH
N
HN
H
N
N
OH
O
O
H
H
1e
IC50, nM (PRP): 31.0
IC50, nM (FITC-Fg/αIIbβ3): 0.22
2a
O
IC50, nM (PRP): 25.0
IC50, nM (FITC-Fg/αIIbβ3): 1.0
O
O
O
O
O
O
O
O
O
O
HN
HN
N
N
OH
N
N
OH
H
H
H
H
2b
2c
IC50, nM (PRP): 11.6
IC50, nM (FITC-Fg/αIIbβ3): 0.7
IC50, nM (PRP): 17.0
IC50, nM (FITC-Fg/αIIbβ3): 0.8
Figure 2. Structures and in vitro activities of
a
IIbb3 antagonists of series 1 and 2. aConcentration required to reduce ADP-induced human platelet aggregation response by 50%.
IIbb3 on the suspension of washed human platelets by 50%.
bConcentration required to reduce binding of FITC-Fg to
a

4446
A. A. Krysko et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4444–4446
Table 1
pronounced increase both in antiaggregative activity and affin-
ity.11b 3,4-Methylenedioxyphenyl derivative 7l had the highest
affinity among the compounds 7 and quite a good antiaggregative
properties, while analogous modification for the derivative 1e
resulted in greater growth of antiaggregative activity and affinity
related to the 1a.10b Replacement of succinyl linker with glutaryl
one generally had a negative impact on PRP activity and affinity,
with the exception of mimetic 7p, which had IC50 values for PRP
activity and affinity comparable to the values for 7l. Decrease of
antiaggregative activity relative to the 7b was observed for ana-
logue 7m containing the residue of b-(naphthalen-1-yl)-b-alanine.
In summary, we have investigated modification of b-phenyl
substituted b-alanines for non-peptide fibrinogen receptor antago-
nists based on 7-amino-1,2,3,4-tetrahydroisoquinoline. Introduc-
tion of fluorine group to para position afforded the potent
analogue, while incorporation of this into meta and ortho positions,
as well as replacement of fluorine with chlorine atom, resulted in
less active compounds. The trend towards lower activity was also
seen with methyl and methoxy substituents in para position, and
at the replacement of succinyl linker by glutaryl one. The use of
b-(3,4-methylenedioxyphenyl)-b-alanines leads to the obtaining
of fibrinogen receptor antagonists with high affinity and good anti-
aggregative activity.
Biological properties of RGDF mimetics 7 with tetrahydroisoquinoline fragment
Compd
n
R
IC50a, nM (PRP)
IC50b, nM
(FITC-Fg/aIIbb3)
1.211a
1.011a
1.0
1100.0
5.0
65.0
0.90
3.5
—
0.63
7a
7b
7c
7d
7e
7f
7g
7h
7i
1
1
1
1
1
1
1
1
1
1
H
C6H5
p-C6H4–F
m-C6H4–F
o-C6H4–F
p-C6H4–Cl
p-C6H4–CH3
p-C6H4–OCH3
p-C6H4-OCH(CH3)2
m,p-C6H3–(OCH3)2
30.011a
13.011a
8.9
10000.0
570.0
2000.0
96.0
310.0
87.0
64.0
7j
O
O
7k
7l
1
1
510.0
90.0
—
O
O
0.4
7m
1
5200.0
—
7n
7o
2
2
p-C6H4–OCH3
m,p-C6H3–(OCH3)2
4200.0
127.0
18.0
5.0
O
O
7p
2
53.0
0.78
References and notes
RGDS
31000.0
13000.0
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b
Concentration required to reduce ADP-induced human platelet aggregation
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compounds 7 described in this Letter were synthesized from the
acids 4 and various b-alanines esters using HBTU or HATU as a cou-
pling reagents (Scheme 1). Esters 5 cleavage followed by deprotec-
tion gave the desired products 7. In our study, we have prepared all
mimetics only as racemic mixtures in order to reveal potent com-
pounds and to determinate general characteristics of structure–
activity relationship.
Biological activity was assessed in vitro by measuring the ability
of compounds to inhibit the binding of fluoresceinisothiocyanate-
labeled fibrinogen (FITC-Fg)12 to
aIIbb3 (in a suspension of human
washed platelets).13 Functional activity was subsequently deter-
mined by measuring the inhibition of ADP induced platelet aggre-
gation in human platelet-rich plasma (PRP) by Born’s method.14
Experimental data (Table 1) evidently show high affinities of the
compounds 7 for aIIbb3.
Analogue 7c, which contains a fluorine atom at para position of
b-phenyl-b-alanine residue, was equipotent with the compound 7b
by affinity and 1.4-fold more active in PRP. Substantial decrease of
antiaggregative activity and affinity compared to the lead 7b was
observed for the meta-fluorine containing derivative 7d. For
ortho-fluorine containing mimetic 7e, activity in both assays less
dramatically decreased related to 7b. Replacement of the fluorine
with chlorine 7f generally resulted in a diminution of inhibitory
properties. Incorporation of a methyl group 7g negatively impacted
antiaggregative activity, while binding affinity was practically
unaffected. Introduction of alkoxy substituents to b-phenyl-b-ala-
nine fragment decreased the activity in PRP. It should be men-
tioned that similar modification for the series 2 afforded more
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