Design and synthesis of highly potent HIV protease inhibitors with activity against resistant virus

Article abstract of DOI:10.1016/S0960-894X(03)00262-2

A series of highly potent HIV protease inhibitors have been designed and synthesized. These compounds are active against various clinical viral isolates as well as wild-type virus. The synthesis and biological activity of these HIV protease inhibitors are discussed.

Full text of DOI:10.1016/S0960-894X(03)00262-2

Bioorganic & Medicinal ChemistryLetters 13 (2003) 1821–1824
Design and Synthesis of Highly Potent HIV Protease
Inhibitors with Activity Against Resistant Virus
Zhijian Lu,a,* Subharekha Raghavan,a Joann Bohn,a Mark Charest,a
b
Mark W. Stahlhut,b Carrie A. Rutkowski,b AmyL. Simcoe, David B. Olsen,b
b
William A. Schleif,b AnthonyCarella, Lori Gabryelski,b Lixia Jin,c Jiunn H. Lin,c
Emilio Emini,b Kevin Chapmana and James R. Tataa
aDepartment of Medicinal Chemistry, Merck Research Laboratories, Rahway, NJ 07065, USA
bDepartment of Antiviral Research, Merck Research Laboratories, West Point, PA 19486, USA
cDepartment of Drug Metabolism, Merck Research Laboratories, West Point, PA 19486, USA
Received 10 October 2002; accepted 19 December 2002
Abstract—A series of highlypotent HIV protease inhibitors have been designed and synthesized. These compounds are active
against various clinical viral isolates as well as wild-type virus. The synthesis and biological activity of these HIV protease inhibitors
are discussed.
# 2003 Elsevier Science Ltd. All rights reserved.
The AIDS epidemic has spread around the world at an
alarming rate. Although the first generation of HIV
protease inhibitors,1 including indinavir, nelfinavir,
saquinavir and ritonavir, were initiallyeffective against
HIV infection, the fast emerging resistance to above
agents has been a substantial and persistent problem in
the treatment of AIDS.2 Attempts to address the resis-
tance issue with ‘salvage therapy’ consisting of high
doses of multiple protease inhibitors have onlybeen
moderatelysuccessful due to the high level of cross
resistance and toxicities associated with the protease
inhibitors. Accordingly, there remains a need for new
protease inhibitors having improved effectiveness
against the resistant viral variants.
In an effort to search for a new structure-type of HIV
protease inhibitors, we took advantage of the C2 sym-
metryof the protease bypreparing hbyrid inhibitors
combining the P3P2P1 ligand of the a-hydroxy amide
based inhibitor JE-21473 with the P10P30 portion of
indinavir (Fig. 1).
*Corresponding author. Tel.: +1-732-594-4392; fax: +1-732-594-
9473; e-mail: zhijian_lu@merck.com
Figure 1. Design of a hybrid between indinavir and JE-2147.
0960-894X/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0960-894X(03)00262-2

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Z. Lu et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1821–1824
In order to explore the scope of the proposed hybrid
series, several compounds were initiallysnythesized.
Surprisinglythis combination resulted in HIV protease
inhibitors (PI) that exhibited high potencyin both the
protease enzyme inhibition assay (IC50) and the spread
assay(inhibition of the spread of viral infection in MT4
human T-lymphoid cells, CIC95).4 Theywere also tested
against highlyPI-resistant viral constructs that were
engineered from clinic viral isolates of patients infected
lysis, gave acids which were coupled with 4-amino-3-
chromanol7 (13) leading to compound 14. Deprotection
of the TBS group with 1 M tetrabutylammonium fluo-
ride solution provided final products 15 in 95% yield.
The amines that were used in this studyare listed in
Table 2. The synthesis of 3,5-dimethylisothiazole-4-
methyl amine (17) is outlined in Scheme 2, and is
representative of how all the amines were prepared.
5
with multiplyPI-resistant HIV. As shown in Table 1,
the results show that all compounds but 2 are more
potent than indinavir; the a-hydroxy amide 1 is 10-fold
more potent than the hydroxy ethylene amine moiety 2.
Commercially available ethyl 5-amino-3-methyl-iso-
thiazole-4-carboxylate 18 was treated with isoamyl
nitrite and iodine in chloroform under refluxing condi-
Aminochromanol7 moietyis twice as effective as the
aminoindanol (3 vs 5); o-disubstituted-benzyl amide 3 is
twice as potent as o-mono-substituted-benzyl amide 1.
The stereochemistry of the hydroxyl group also plays an
important role for activity. An analogue of S configur-
ation 3 is 3–14-fold more potent than that of the R iso-
mer 4. On the basis of the initial studies, we decided to
investigate the SARs of the lead 3 and the results are
discussed below.
Synthesis of this series of compounds is generalized in
Scheme 1. Commerciallyavailable acid 6 was protected
with Boc anhydride under basic conditions in 42%
yield. Treatment of resulting acid 7 with allyl bromide
and triethyl amine in DMF afforded compound 8
(80%). Deprotection of the Boc group, followed by
Py.Brop (bromo-tris-pyrrolidino-phosphonium hexa-
fluorophosphate) coupling of acid 9,6 gave amide 10 in
47% overall yield. Catalytic removal of the allyl group
with tetrakis(triphenylphosphine) palladium afforded
acid 11 (85%). EDC coupling with various amines 16
(see Table 2) or 17 provided amides 12 (40–70%).
Treatment of 12 with 1M aqueous LiOH solution in
dioxane, followed bytreatment of TBSOTf and hydro-
Table 1. Antiviral activities of hybrid series
IC50 (nM)
WT K-60C V-18C WT K-60C V-18C
0.6 61.2 43.6 45 1000 890
CIC95 (nM)
X
Indinavir
O, 1 0.07 0.83 0.4
H,H, 2 0.52 7.90 8.8 250 >1000 1000
19
125
41
OH, S, 3 0.03 0.1
OH, R, 4 0.28 1.9
0.08 15
1.14 47
70
500
15
62
Scheme 1. (a) Boc2O, NaOH/H2O/i-PrOH, 42%; (b) allyl bromide,
Et3N, DMF, rt, 80%; (c) TFA/CH2Cl2, 100%; (d) Py.Brop, HOAT,
DIEA, 9, CH2Cl2, rt, 47%; (e) Pd(PPh3)4, morpholine, THF, rt, 85%;
(f) 16, or 17, EDC, HOAT, DIEA, CH2Cl2, rt, 40–70%; (g) LiOH/
H2O/dioxane, rt; (h) TBSOTf/EtOAc, DIEA, rt; H2O/THF; (i) 13, O-
benzotriazole-N,N,N0,N0-tetramethyl-uronium hexafluorophosphate
(HBTU), DIEA, 1-hydroxy-7-azabenzotrizole (HOAT) (cat), DMF, rt
(j) Bu4NF, THF, rt, 95%.
5
0.04 0.062 0.062 31
125
31

Z. Lu et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1821–1824
1823
Table 2. A list of amines used
Scheme 2. (a) Isoamyl nitrite, I2, CHCl3, reflux, 50%; (b) (CH3)4Sn,
PdCl2(PPh3)2, toluene, reflux, 83%; (c) LiAlH4, THF, 0 ꢀC!rt, 57%;
(d) CBr4, Ph3P, NaN3, DMF, rt, 83%; (e) Ph3P, THF/H2O, rt, 84%.
tions to give 19 in 50% yield. The Castro–Stevens reac-
tion8 afforded compound 20 (83%). LiAlH4 reduction
of 20 provided alcohol 21 (57%) which was then con-
verted to azide 22 in good yield. Reduction of 22 gave
the desired amine 17 in 84% yield.
potent protease inhibitor 23, with slight loss of the
spread activity. Dichloro substituted analogue 2410
appears to be one of the most potent compounds in this
series in the spread assay. However, difluoro substituted
analogue 25 apparentlyis less potent than methyl or
chloro-substituted analogues due to smaller size. On the
other hand, methyl substituted pyridyl methyl amides
are less active than the substituted phenyl analogues.
The 2-pyridyl analogue is more active than the 3-pyridyl
analogue (26 vs 27). The substituted 5-membered het-
erocycles were also investigated. Compounds 28 and 29
are two most potent analogues. Especially, compound
2911 is comparable to the most potent substituted
phenyl analogue 24. Indinavir is much less active
against the resistant virus in the study.
SAR studyof the lead 3 was carried out and the influ-
ence of different substituents on in vitro potencyagainst
mutant variants9 is summarized in Table 3. Searching
for other types of substituents on the phenyl ring and
exploring heterocycles have been the focus of this study.
Replacement of one of the methyl groups with a chlor-
ine atom on the phenyl ring results in another highly
Table 3. Influence of substituents on antiviral activities
In summary, we have designed and synthesized a new
series of highlyactive HIV protease inhibitors against
various clinic isolates. The successful incorporation of
substituted 5-membered heterocycles provides us with
another option to studythe antiviral activityof this
class of compounds.
Compd
R
IC50 (nM)
CIC95 (nM)
WT K-60C V-18C WT K-60C V-18C
Indinavir
3
0.6
61.2
0.1
43.6
0.08
45
15
1000
70
890
15
0.03
23
24
25
26
27
28
29
0.03
0.04
0.24
0.13
0.16
0.07
0.05
0.11
0.23
2.0
0.08
0.12
1.48
0.26
0.72
0.9
31
<8
23
46
23
16
250
250
187
250
250
250
References and Notes
62
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39
46
2.37
0.21
0.24
187
156
16
125
62
0.11
31

1824
Z. Lu et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1821–1824
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1
10. Data for compound 24: H NMR (CDCl3, 500 MHz): 1:1
mixture of rotamers: 6.80–7.70 (m, 12H), 6.00 (m, 2H), 5.18
(m, 1H), 4.85 (m, 3H), 4.70 (s, 1/2H), 4.61 (m, 1H), 4.40 (s, 1/
2H), 4.38 (m, 1H), 4.05 (m, 3H), 3.78 (m, 1H), 2.80–3.10 (m,
4H), 2.20 (m, 1H), 1.61 (m, 1H), 1.60 (s, 3/2H), 1.57 (s, 3/2H),
1.40 (s, 3/2H), 1.39 (s, 3/2H). LC–MS (ES) 686.1 (M+1).
1
11. Data for compound 29: H NMR (CDCl3, 500 MHz): 1:1
mixture of rotamers: 6.80–7.40 (m, 9H), 5.88 (br.S, 1H), 5.10
(m, 1H), 4.90 (m, 1H), 4.65 (s, 1/2H), 4.40 (3/2H), 4.29 (m, 1H),
4.05 (m, 2H), 3.72 (m, 1H), 2.88 (m, 4H), 2.53 (s, 3/2H), 2.50 (s,
3/2H), 2.40 (s, 3H), 2.08 (m, 1H), 1.59 (s, 3/2H), 1.56 (s, 3/2H),
1.42 (s, 3/2H), 1.36 (s, 3/2H). LC–MS (ES) 653.1 (M+1).
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Guare, J. P.; Darke, P. L.; Zugay, J. A.; Emini, E. A.; Schleif,