Preparation of novel HIV-protease inhibitors

Article abstract of DOI:10.1039/a805489d

The synthesis and biological properties of new HIV-1-protease inhibitors involving amino acids or dipeptides attached to binaphthol, biphenol or embonic acid are described.

Full text of DOI:10.1039/a805489d

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Preparation of novel HIV-protease inhibitors
Manfred T. Reetz,*† Claudia Merk and Gerlinde Mehler
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim/Ruhr, Germany
The synthesis and biological properties of new HIV-
1-protease inhibitors involving amino acids or dipeptides
attached to binaphthol, biphenol or embonic acid are
described.
synthesis, the hydroxy functions of 1 were first protected by
benzyl groups (Scheme 1). The diastereomeric mixture of 2b
was separated by HPLC to provide analytically pure (R,S,S)-2b
and (S,S,S)-2b. In the case of the dipeptide 5b with two
vinylogous amino acid residues, only direct coupling was
carried out (Scheme 2).
Inspite of recent progress in the development of therapeutics for
the treatment of AIDS, a number of problems persist.1 A well-
known approach concerns the design and synthesis of HIV-
protease inhibitors. The HIV-protease is a well characterized
viral enzyme consisting of two units, each composed of 99
amino acids, which join together to form the C2-symmetric
active homo-dimer. Consequently, one strategy has been to
prepare C2-symmetric inhibitors in the form of peptide
mimetics, one family of active compounds being C2-symmetric
1,2-diols flanked by short peptide units.2 The hydroxy moities
have been shown to participate in the interaction with the HIV-
protease via H-bonding, the configuration at the two stereogenic
centers of the diol playing an important role with respect to the
degree of binding. We speculated that similar compounds based
on chiral binaphthol or biphenol units in place of the traditional
diols could constitute a new class of HIV-1-protease inhibitors,
specifically because the enhanced acidity of such moieties
would be expected to lead to stronger H-bonding. Here we
present the initial results of this strategy.
O
N
H
CO2R
CO2R
i,ii
OH
OH
1
H
N
O
5a R = Et (17%)
b R = H (65%)
Scheme 2
L
Reagents:
i,
NaOH,
NHS,
DCC;
NEt3,
-HCl·H2NCHPriCH§CHCO2Et; ii, LiOH, H2O
Although there is a limited degree of rotational freedom with
respect to the axis going through the two naphthyl units, the
C2-symmetric dipeptides 2b and 5b are in fact fairly rigid. In
order to introduce more conformational flexibility, we prepared
dipeptide 7b based on embonic acid 6 (Scheme 3). Although the
We first envisioned peptides of the type 2b and 5b based on
racemic 2,2A-dihydroxy-1,1A-binaphthyl-3,3A-dicarboxylic acid
1. Direct coupling with valine methyl ester resulted in a 14%
yield of the desired diastereomeric dipeptide esters 2a, which
were hydrolyzed to the acids 2b. In order to improve the
O
CO2H
N
H
CO2R
CO2R
O
CO2H
OH
OH
OH
OH
N
H
CO2R
CO2R
CH2
CH2
i,ii
i,ii
OH
OH
OH
OH
H
N
H
N
CO2H
CO2H
O
O
6
7a R = Me (27%)
b R = H (80%)
1
2a R = Me (14%)
b R = H (66%)
iii
iii
O
O
CO2R
N
H
CO2Me
v
CO2R
N
H
CO2R
v
OR′
OR′
OBn
CH2
iv
iv
CH2
OR′
OR′
OR′
OR′
7a (82%)
2a (93%)
OBn
H
N
H
N
CO2Me
CO2R
CO2R
CO2R
O
O
8a R = R′ = Bn (85%)
b R = H, R′ = Bn (91%)
9 (74%)
3a R = R′ = Bn (82%)
b R = H, R′ = Bn (81%)
4 R = Me, R′ = Bn (81%)
Scheme 1 Reagents: i, NaOH, N-hydroxysuccinimide (NHS), DCC,
L
Scheme 3 Reagents: i, NaOH, NHS, DCC, L
-H2NCHPriCO2Me; ii, LiOH,
H2O; iii, BnBr, K2CO3, KOH, H2O; iv, NHS, DCC,
Pd(OH)2, cyclohexene
-H2NCHPriCO2Me; ii, LiOH, H2O; iii, BnBr, K2CO3; iv, NHS, DCC,
-H2NCHPriCO2Me; v, Pd(OH)2, cyclohexene
L
-H2NCHPriCO2Me; v,
L
Chem. Commun., 1998
2075

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Table 1 Properties of synthesized compounds
latter is achiral, conformational enantiomers (or diastereomers
in the case of 7b) are likely, especially upon binding to the
C2-symmetric HIV-protease. The dipeptide 10b incorporating
vinylogous valine was synthesized analogously.
In order to test the biological effect of extending the peptidic
side-arms, the tetrapeptide 11b was prepared in a direct manner
Compound
Solubility/m
M
IC50/mM
(R,S,S)-2b
(S,S,S)-2b
(R,S,S)-5b
(S,S,S)-5b
7b
> 65
> 65
> 50
> 50
> 100
~ 30
47
48
46
13
40
8
2.8
24
240
by NHS–DCC-mediated coupling of 6 with
L
-valinyl- -valine
L
ethyl ester. Here, as in all previous cases, the compounds were
purified by HPLC and characterized by standard spectroscopic
and analytical means.
10b
11b
13b
14
> 10
> 100
> 100
O
N
H
CO2R
CO2R
OH
OH
units (i.e. prevention of homo-dimer formation). In order to
shed some light on these aspects, kinetic studies using the model
of Zhang were carried out on select compounds, i.e. dissociative
inhibition constants (Ki) and competitive inhibition constants
(Kc) were measured.5 Accordingly, in the case of the most
active compound 11b, the Ki and Kc values turned out to be 6.9
CH2
H
N
O
and 2.0 m , respectively. This means that active site (com-
M
petitive) inhibition dominates, although dissociative inhibition
plays some role. Mixed inhibition also pertains to the related
10a R = Me (32%)
b R = H (80%)
dipeptide 7b (Ki = 15.8 m
M
; Kc = 6.2 m ). In contrast, the
M
mechanism of action of the tyrosin derivative 13b appears to be
O
based primarily on the inhibition of dimerization of the
H
N
CO2R
monomeric HIV-protease units (Ki = 6.8 m
M
; Kc = 229 m ).
M
N
H
This still needs to be studied more closely, e.g. using light
scattering. However, preliminary molecular modelling is in line
with these conclusions.
O
OH
OH
CH2
In summary, we have designed and prepared new HIV-
1-protease inhibitors based on naphtholic and phenolic units to
which amino acids or dipeptides are attached. Although the
respective activities are lower than those of the most potent
drugs currently known,1,2 the discovery of these new lead
structures allows for the (combinatorial) synthesis of analogs
which may show improved performance.
We thank H.-J. Schramm, J. Büttner and T. Wenger (group of
R. Huber at Max-Planck-Institut für Biochemie, Martinsried)
for help in the determination of IC50 values and kinetic data and
for stimulating discussions.
O
H
N
N
H
CO2R
O
11a R = Et (46%)
b R = H (16%)
Finally, the biphenol derivative 13 was prepared by oxidative
coupling3 of N-benzyloxycarbonyl-
-tyrosine methyl ester 12.
Deprotection delivered the dipeptide 14 (Scheme 4).
L
HO OH
OH
HO OH
Notes and References
† E-mail: reetz@mpi-muelheim.mpg.de
i,ii
iii
1 Reviews: G. Moyle and B. Gazzard, Drugs, 1996, 51, 701; J. W.
Erickson, Nat. Struct. Biol., 1995, 2, 523; E. K. Wilson, Chem. Eng.
News, July 29, 1996, p. 42; C. Perez, M. Pastor, A. R. Ortiz and F. Gago,
J. Med. Chem., 1998, 41, 836.
CO2Me
H N
CO2H
2
ZNH
CO2R
NH2
CO2H
ZNH
CO2R
ZNH
12
2 See for example: M. V. Hosur, T. N. Bhat, D. J. Kempf, E. T. Baldwin,
B. Lui, S. Gulnik, N. E. Wideburg, D. W. Norbeck, K. Appelt and J. W.
Erickson, J. Am. Chem. Soc., 1994, 116, 847; G. T. Wang, S. Li, N.
Wideburg, G. A. Krafft and D. J. Kempf, J. Med. Chem., 1995, 38, 2995;
T. N. Bhat, E. T. Baldwin, B. Liu, Y.-S. E. Cheng and J. W. Erickson,
Struct. Biol., 1994, 1, 552; C. N. Hodge, P. Y. S. Lam, C. J. Eyermann,
P. K. Jadhav, Y. Ru, C. H. Fernandez, G. V. De Lucca, C.-H. Chang,
R. F. Kaltenbach III, E. R. Holler, F. Woerner, W. F. Danecker, G.
Emmett, J. C. Calabrese and P. E. Aldrich, J. Am. Chem. Soc., 1998, 120,
4570; W. W. Wilkerson, S. Dax and W. W. Cheatham, J. Med. Chem.,
1997, 40, 4079; P. K. Jadhav, P. Ala, F. J. Woerner, C. H. Chang, S. S.
Garber, E. D. Anton and L. T. Bacheler, J. Med. Chem., 1997, 40, 181.
3 A. G. Brown and P. D. Edwards, Tetrahedron Lett., 1990, 31, 6581; S. M.
Kupchan, O. P. Dhingra and C.-K. Kim, J. Org. Chem., 1978, 43,
4076.
13a R = Me (52%)
b R = H (94%)
14 (90%)
(Z = benzyloxycarbonyl)
Scheme 4 Reagents: i, VOF3; ii, LiOH, H2O; iii, H2, Pd-C
In order to screen the ability of the compounds to inhibit the
HIV-1-protease, the IC50 values were measured using standard
procedures.4 Table 1 shows that several compounds have
activities similar to a number of other HIV-protease inhibitors
which have been reported in recent years.2 It is interesting to
note that in the case of 5b (but not 2b) the absolute
configuration of the binaphthol backbone plays a significant
role in the degree of HIV-protease inhibition. Specifically, the
(R,S,S)-compound is considerably more active than the (S,S,S)-
diastereomer. However, the conformationally more flexible
compounds based on embonic acid 6 are more active, especially
the tetrapeptide 11b.
4 H.-J. Schramm, J. Boetzel, J. Büttner, E. Fritsche, W. Göhring, E. Jaeger,
S. König, O. Thumfart, T. Wenger, N. E. Nagel and W. Schramm,
Antiviral Res., 1996, 30, 155.
5 Z.-Y. Zhang, R. A. Poorman, L. L. Maggioria, R. L. Heinrikson and F. J.
Kézdy, J. Biol. Chem., 1991, 266, 15 591.
Theoretically, the mode of action of the above compounds
can either be due to active-site inhibition of the HIV-protease or
to a possible inhibition of dimerization of the two 99-amino acid
Received in Cambridge, UK, 15th July 1998; 8/05489D
2076
Chem. Commun., 1998