Synthesis and evaluation of efavirenz (Sustiva) analogues as HIV-1 reverse transcriptase inhibitors: Replacement of the cyclopropylacetylene side chain

Article abstract of DOI:10.1016/S0960-894X(01)00192-5

Two series of efavirenz analogues have been developed: one in which the cyclopropane ring has been replaced by small heterocycles and another in which the entire acetylenic side chain has been replaced by alkyloxy groups. Several members of both series show equivalent potency to efavirenz against both wild-type virus and the key K103N mutant.

Full text of DOI:10.1016/S0960-894X(01)00192-5

Bioorganic & Medicinal Chemistry Letters 11 (2001) 1177–1179
Synthesis and Evaluation of Efavirenz (SustivaTM) Analogues as
HIV-1 Reverse Transcriptase Inhibitors: Replacement of the
Cyclopropylacetylene Side Chain
Anthony J. Cocuzza,* Dennis R. Chidester, Beverly C. Cordova, Susan Jeffrey,
Rodney L. Parsons, Lee T. Bacheler, Susan Erickson-Viitanen,
George L. Trainor and Soo S. Ko
DuPont Pharmaceuticals Company, Experimental Station, E336/141, PO Box 80336, Wilmington, DE 19880-0336, USA
Received 16 January 2001; accepted 5 March 2001
Abstract—Two series of efavirenz analogues have been developed: one in which the cyclopropane ring has been replaced by small
heterocycles and another in which the entire acetylenic side chain has been replaced by alkyloxy groups. Several members of both
series show equivalent potency to efavirenz against both wild-type virus and the key K103N mutant. # 2001 DuPont Pharmaceuticals
Company. Published by Elsevier Science Ltd. All rights reserved.
Effective therapy for the treatment of HIV-1 infection
and AIDS requires a combination of antiviral drugs.
Currently, the standard of care for antiretroviral naıve
patients is efavirenz or an HIV protease inhibitor and
two nucleoside reverse transcriptase inhibitors. Efavir-
enz,1 a non-nucleoside reverse transcriptase inhibitor
(NNRTI), has demonstrated clinical activity in both
antiretroviral naıve and experienced patients and may
also provide an option of a protease-sparing regimen
when used with two nucleoside reverse transcriptase
(RT) inhibitors.2
generation drug with improved activity against K103N
and other resistant mutants, an SAR investigation was
launched. While earlier reports from our laboratory4,5
described the effect of varying the aromatic substitution
pattern of efavirenz, herein we describe the effect of
modifying and replacing the acetylenic side chain.
We first examined the preparation of analogues of efa-
virenz in which the cyclopropane ring was replaced with
a five- or six-membered heterocycle. The synthesis of
these compounds was greatly facilitated by the avail-
ability of 4-chlorobenzoxazinones (2–4) which are pre-
pared in high yield by treatment of 2-amino-
trifluoroacetophenones 14 with phosgene in toluene
solution at 110 ꢀC (Scheme 1).6 These stable crystalline
intermediates react with a variety of nucleophiles
through an elimination–addition pathway. For exam-
ple, reaction of 2 with 2 equiv of the lithium salt of 2-
pyridylacetylene in THF at 0 ꢀC afforded 7. In most
Although HIV infection is generally well controlled by
efavirenz-containing regimens, a number of patients
develop resistence to the drug. In these patients, the
K103N mutation is present in over 90% of the RT
sequences examined.3 In an effort to develop a second-
*Corresponding author. Fax: +1-302-695-6670; e-mail: anthony.j.
cocuzza@dupontpharma.com
Scheme 1.
0960-894X/01/$ - see front matter # 2001 DuPont Pharmaceuticals Company. Published by Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00192-5

1178
A. J. Cocuzza et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1177–1179
cases, the heterocyclic acetylenes are not commercially
available, however the corresponding carboxaldehydes 5
are (Scheme 2). Using the Weinreb7 modification of the
Corey–Fuchs8 procedure, treatment of 5 with carbon
tetrabromide/triphenylphosphine/triethylamine yielded
the dibromo-olefins 6 which form the corresponding
lithium acetylides in situ when treated with 2 equiv of n-
butyllithium. Reaction of the acetylides with 4-chloro-
benzoxazinones 2–4 afforded the target compounds.9 In
addition to the 6-chlorobenzoxazinones 7–13, we also
chose to prepare the 6-fluoro- (14–19) and 5,6-difluoro-
(20–25) analogues, since these aromatic ring substituents
proved optimal in earlier SAR studies.4
contrast to other ketals, 26–50 are very stable to acidic
conditions. The presence of the trifluoromethyl group
markedly destabilizes the developing positive charge at
C-4 which would necessarily arise during acid hydro-
lysis. In fact when 4-(butyloxy)benzoxazinone 28 was
treated with 1 N aq HCl at room temperature, no reaction
could be detected by HPLC or NMR even after 48 h. Thus,
4-alkyloxy-4-(trifluoromethyl)benzoxazinones would be
expected to survive the acidic conditions present in the
GI tract and consequently may exhibit oral bioavail-
ability. Since any alcohol that forms a stable sodium
salt can be introduced into the 4-position of a 4-(tri-
fluoromethyl)-benzoxazinone, a much greater variety of
side chains could be examined than in previous SAR
investigations.
Scheme 2.
Scheme 3.
Table 1 summarizes the antiviral activity of 7–25 against
both wild-type and K103N mutant viruses.10 It can be
seen that, with the exception of 4-pyridyl, all the het-
erocycles employed can effectively replace the cyclopro-
pane ring of efavirenz to give analogues that retain
potent activity against wild-type HIV-1. Selected com-
pounds were also tested against the K103N virus. While
a number of these exhibited activity comparable to efa-
virenz against this key mutant, none displayed the sig-
nificant increase in potency we sought.
Inspection of the first eight entries of Table 2 reveals
that optimal side-chain length is four or five and that
larger substituents result in decreased potency. Inclu-
sion of a terminal cyclopropyl group (30 and 31) as is
present in efavirenz does not improve activity against
wild-type virus. However, introduction of unsaturation,
either a double or triple bond (e.g., 34–38, 45, and 48)
provides the most active compounds, while incorpora-
tion of electronegative groups (Cl, F, CN, OMe) (40–44)
results in a marked reduction in potency. The optimal
side chain is dimethallyloxy, and the three compounds
(37, 45, and 48) which incorporate this side chain in this
series are the most potent against both wild-type and
K103N virus.
Simple room temperature treatment of 4-chlorobenzox-
azinones 2–4 with sodium alkoxides in THF afforded 4-
alkoxybenzoxazinones 26–50, compounds that would
otherwise be very difficult to obtain (Scheme 3). In
Table 1. Antiviral activity of heterocyclic analogues of efavirenz
Compound
X
Het
Wild-type IC90 (nM)a
K103N IC90 (nM)
Efavirenzb
7
8
9
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-F
6-F
6-F
6-F
6-F
6-F
5,6-diF
5,6-diF
5,6-diF
5,6-diF
5,6-diF
5,6-diF
Cyclopropyl
2-Pyridyl
3-Pyridyl
4-Pyridyl
2-Furanyl
3-Furanyl
3-Thienyl
5-Thiazolyl
2-Pyridyl
3-Pyridyl
2-Furanyl
3-Furanyl
2-Thienyl
3-Thienyl
2-Pyridyl
3-Pyridyl
2-Furanyl
3-Furanyl
2-Thienyl
3-Thienyl
1.70
5.39
3.97
102.10
3.80
3.80
4.47
6.69
12.19
2.56
2.58
2.52
2.93
2.55
6.78
2.23
3.79
3.21
2.23
2.34
64.0
1105.8
144.6
—
152.2
321.9
106.2
—
—
329.3
—
369.0
—
193.0
—
59.3
—
279.7
155.9
139.2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
aAll compounds were assayed for whole cell antiviral activity according to the protocol described in ref 10.
bThe data presented for efavirenz reflect values determined for a single enantiomer, whereas the data shown for all other compounds are for racemic
mixtures. The biological evaluation of efavirenz and other benzoxazinones had determined that only one enantiomer was active.

A. J. Cocuzza et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1177–1179
Table 2. Antiviral activity of 4-alkyloxybenzoxazinonesa
1179
Compound
X
R
Wild-Type IC90 (nM)
K103N IC90 (nM)
64.0
Efavirenz
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
1.70
18.26
5.81
10.19
10.07
7.70
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-Cl
6-F
CH2CH3
CH2CH2CH3
CH2CH2CH2CH3
CH2CH2CH(CH3)2
CH2cycPr
CH2CH2cycPr
CH2Ph
CH2CH2Ph
989
286
8.04
17.89
166.80
3.90
4.35
5.60
2.68
3.13
13.68
9.50
61.41
>1500
75.27
650.60
2.98
CH2CH¼CH2
CH2CH¼CHCH3 (cis)
CH2CH¼CHCH3 (trans)
CH2CH¼C(CH3)2
CH2CꢂCCH3
237
404
83
310
CH2CH2CH¼CH2
CH2CH¼CCl2
CH2CH2OCH3
CH2CH2CN
242
CH2(3-pyridyl)
CH2CF2CF3
CH2CH¼C(CH3)2
CH2CH¼CHCH3 (trans)
CH2CH¼CCl2
CH2CH¼C(CH3)2
CH2CH¼CH2
107
1148
6-F
6-F
5,6-diF
5,6-diF
5,6-diF
8.85
11.94
1.54
6.47
65
1617
183
50
CH2CH¼CCl2
6.35
aSee notes to Table 1.
In summary, we have demonstrated that the potent
activity of efavirenz against wild-type HIV-1 can be
retained despite significant modification of its side
chain. The cyclopropane ring can be replaced with a
variety of small heterocyclic rings, and the entire cyclo-
propylacetylene group can be replaced by an alkoxy side
chain containing either a double or triple bond. While a
number of these analogues displayed potency equivalent
to efavirenz against K103N virus, no compound
demonstrated the increased activity required for devel-
opment of a second-generation compound.
Abstract, presented at the 38th Interscience Conference on
Antimicrobial Agents and Chemotherapy, San Diego, CA, 24–
27 September 1998.
4. Patel, M.; Ko, S. S.; McHugh, R. J.; Markwalder, J. A.;
Srivastava, A. S.; Cordova, B. C.; Klabe, R. M.; Erickson-
Viitanen, S.; Trainor, G. L.; Seitz, S. P. Bioorg. Med. Chem.
Lett. 1999, 9, 2805.
5. Patel, M.; McHugh, R. J.; Cordova, B. C.; Klabe, R. M.;
Erickson-Viitanen, S.; Trainor, G. L.; Ko, S. S. Bioorg. Med.
Chem. Lett. 1999, 9, 3221.
6. For a complete description of the synthesis and reactions of
2, see: Parsons, R. L.; Fortunak, J. M. Tetrahedron Lett. sub-
mitted for publication.
7. McIntosh, M. C.; Weinreb, S. M. J. Org. Chem. 1993, 58,
4823.
8. Corey, E. J.; Fuchs, P. L. Tetrahedron Lett. 1972, 36, 3769.
9. The following is a representative synthetic procedure: To a
ꢁ20 ꢀC solution of 1,1-dibromo-2-(2-furanyl)ethylene (6,
4.0 mmol) in THF (20 mL) was added dropwise n-butyllithium
(8.0 mmol) in THF (5 mL). This solution was allowed to warm
to 0 ꢀC over 30 min and then cooled to ꢁ50 ꢀC. After 2
(1.5 mmol) was added in a single portion, the reaction mixture
was stirred at ꢁ50 to ꢁ35 ꢀC for 30 min and then the reaction
was quenched by the addition of aqueous ammonium chlo-
ride. Extraction of the aqueous layer with ethyl acetate fol-
lowed by flash chromatography on silica gel (hexane/ethyl
acetate 3:1) afforded 10 (mp 170–171 ꢀC) in 53% yield.
10. Bacheler, L. T.; Paul, M.; Jadhav, P. K.; Otto, M.; Miller,
J. Antiviral. Chem. Chemother. 1994, 5, 111.
References and Notes
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Lumma, W. C.; Lyle, T. A.; Huff, J. R.; Anderson, P. S.;
Olsen, D. B.; Carroll, S. S.; Pettibone, D. J.; O’Brien, J. A.;
Ball, R. G.; Balani, S. K.; Lin, J. H.; Chen, I-W.; Scheif, W. A.;
Sardana, V. V.; Long, W. J.; Brynes, V. W.; Emini, E. A.
Antimicrob. Agents Chemother. 1995, 39, 2602.
2. Panel on Clinical Practices for the Treatment of HIV
Infection. Guidelines for the Use of Antiretroviral Agents in
HIV-Infected Adults and Adolescents. 28 January 2000; http://
www.hivatis.org
3. Bacheler, L.; Weislow, O.; Snyder, S.; Hanna, G.;
D’Aquila, R.; the SUSTIVA Resistance Study Team.