Inhibitors of HIV-1 attachment. Part 3: A preliminary survey of the effect of structural variation of the benzamide moiety on antiviral activity

Article abstract of DOI:10.1016/j.bmcl.2009.07.027

1-(4-Benzoylpiperazin-1-yl)-2-(1H-indol-3-yl)ethane-1,2-dione (1a) has been characterized as an inhibitor of HIV-1 attachment that interferes with the interaction of viral gp120 with the host cell receptor CD4. In previous studies, the effect of indole su

Full text of DOI:10.1016/j.bmcl.2009.07.027

Bioorganic & Medicinal Chemistry Letters 19 (2009) 5136–5139
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Inhibitors of HIV-1 attachment. Part 3: A preliminary survey of the effect
of structural variation of the benzamide moiety on antiviral activity q
a
a
a
a
Nicholas A. Meanwell a, , Owen B. Wallace , Henry Wang , Milind Deshpande , Bradley C. Pearce ,
Ashok Trehan a, Kap-Sun Yeung a, Zhilei Qiu a, J. J. Kim Wright a, Brett A. Robinson b, Yi-Fei Gong b,
Hwei-Gene Heidi Wang b, Wade S. Blair b, Pei-Yong Shi b, Pin-fang Lin b
*
a Department of Chemistry, Bristol-Myers Squibb Research and Development, 5 Research Parkway, Wallingford, CT 06492, United States
b Department of Virology, Bristol-Myers Squibb Research and Development, 5 Research Parkway, Wallingford, CT 06492, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
1-(4-Benzoylpiperazin-1-yl)-2-(1H-indol-3-yl)ethane-1,2-dione (1a) has been characterized as an inhib-
itor of HIV-1 attachment that interferes with the interaction of viral gp120 with the host cell receptor
CD4. In previous studies, the effect of indole substitution pattern on antiviral activity was probed. In this
Letter, the effect of structural variation of the benzamide moiety is described, a study that reveals the
potential or the phenyl moiety to be replaced by five-membered heterocyclic rings and a restricted tol-
erance for the introduction of substituents to the phenyl ring.
Received 15 May 2009
Revised 23 June 2009
Accepted 2 July 2009
Available online 10 July 2009
Keywords:
HIV attachment inhibitor
Antiviral
Ó 2009 Elsevier Ltd. All rights reserved.
Indole glyoxamide
HIV inhibitor
We have recently described the preliminary structure–activity
relationships associated with a series of HIV-1 inhibitors derived
optimal antiviral activity in a novel pharmacophore. Whilst the
substrate selected for the initial phase of this work was the sim-
ple unsubstituted indole moiety found in 1a, the discovery that
the 4-fluoro derivative 1an exhibited over 50-fold improved po-
tency led to the inclusion of this indole moiety into the latter
stages of the study.
from the indole glyoxamide 1a,
a compound discovered by
screening the Bristol-Myers Squibb compound collection using a
pseudotype virus assay.1–6 Mechanistic studies suggest that these
compounds act by stabilizing a conformation of the HIV-1 glyco-
protein gp120 that is poorly recognized by the host cell receptor
CD4, thereby interfering with a specific cell attachment event, one
of the initial steps in virus entry.6–8 However, under different
experimental conditions, these compounds appear to be capable
of forming a ternary complex with gp120 and CD4 in a fashion
that blocks CD4-mediated exposure of the gp41 fusion apparatus,
providing an additional mechanistic facet.9,10 In previous articles,
we have described fundamental aspects of the structure–activity
relationships (SAR) associated with the introduction of relatively
simple substituents to the indole ring, a survey that established
the patterns conferring optimal antiviral activity.2 In this Letter,
we describe the results of a complementary survey conducted
after discovering 1a in which the effect of structural variation
of the benzamide moiety on HIV-1 inhibitory activity was probed.
The objective of this exercise was straightforward and focused
simply on defining the basic structural parameters required for
O
O
N
Ph
R
N
O
N
H
1a: R = H
1an: R = F
The target compounds were synthesized by the straightforward
process depicted in Scheme 1. Coupling of 2-(1H-indol-3-yl)-2-
oxoacetyl chloride or the 4-F derivative (3) with tert-butyl-1-pip-
erazinecarboxylate in CH2Cl2 or THF using iPr2NEt or Et3N as the
base afforded the piperazinamide 4.4,11 The Boc protecting element
was removed from 4 by stirring with 20% CF3CO2H in CH2Cl2 and
the resulting amine 5 coupled with a carboxylic acid using either
1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) or the
polymer-supported version of this reagent as the dehydrating
agent in DMF to afford compounds 1a–1aag, compiled in Table 1.
q
See Refs. 1 and 2 for Parts 1 and 2 of this series.
* Corresponding author. Tel.: +1 203 677 6679.
E-mail address: Nicholas.Meanwell@bms.com (N.A. Meanwell).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.07.027

N. A. Meanwell et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5136–5139
5137
O
Boc
R1
O
NH
O
O
O
N
N
R
R
R
R
N
Cl
N
N
a
b
c
O
O
O
O
N
H
N
H
N
H
N
H
1
3
4
5
R = H, F
Scheme 1. Reagents and conditions: (a) tert-butyl-1-piperazinecarboxylate/iPr2NEt or Et3N in CH2Cl2 or THF; (b) 20% CF3CO2H/CH2Cl2; (c) R1CO2H/1-(3-dimethylamino-
propyl)-3-ethylcarbodiimide (EDC) or polymer-supported 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (P-EDC)/DMF.
The antiviral properties of target compounds were assessed in a
pseudotype virus infection system using an engineered virus. A
proviral clone of LAI virus with the env gene replaced by the firefly
luciferase gene1–5 was co-transfected into HEK-293 cells with a
plasmid expressing the envelope of the JRFL virus, a CCR5-specific
virus. After 48 h, supernatant containing the recombinant pseudo-
parent 1ai may be a function, in part, of the intrinsically more po-
tent background provided by the substituted indole analogue or
the increased lipophilicity. A smaller furan ring is well tolerated,
with the 2-furanyl derivative 1as fourfold more potent than the
3-isomer 1aw, and potent antiviral activity is preserved with the
introduction of small substituents in the 2-substituted series
(1at–1av). The 2- and 3-thienyl analogues 1ax and 1aab are also
potent HIV-1 attachment inhibitors but activity in the former ser-
ies is abrogated by 4-, 17- and 24-fold when Br (1aaa), Cl (1az) or
CH3 (1ay) substituents, respectively, are introduced at C-3. Within
the series of azoles examined in the context of 1aac–1aag, the 4-
thiazole 1aaf is optimal, with the more basic imidazolyl derivative
1aae proving to be the weakest representative of this subset of
compounds.
virus, designated as JRFL-LucDEnv, was harvested and the titer
determined by performing serial dilutions in HeLa67 cells, which
express the primary HIV-1 receptor CD4 and the coreceptor
CCR5. Virus growth was quantified by measuring luciferase activity
(Luciferase Gene Reporter Assay Kit by Roche) three days post-
infection. For the analysis of the antiviral activity of test com-
pounds, fourfold serial dilutions of compounds were added to
JRFL-LucDEnv-infected HeLa67 cells at the time of infection. After
three days, the extent of luciferase activity was compared to con-
trols where no compound was added and used to calculate the
EC50 values for individual compounds. The cytotoxicity of test com-
pounds was determined in parallel on HeLa67 cells and an XTT as-
say performed three days after compound addition. The results are
presented in Table 1 where individual results are provided as a
measure of assay variability when the data reported are the aver-
age of only two experiments.
The data presented in Table 1 provide essential insights into the
structural requirements of the benzamide phenyl element in this
series of HIV-1 attachment inhibitors. In the context of the simple
indole 1a, substitution of the benzamide phenyl ring with halo-
gens, alkyl, alkoxy or dialkylamino moieties, examined in the con-
text of compounds 1b–1u, invariably resulted in reduced antiviral
potency. Only the 2-F derivative 1b maintained an EC50 of less than
Collectively, these results define the scope of substitution toler-
ated by the benzamide element as somewhat limited, with the
most effective structural modifications restricted to isosteric
replacement of the phenyl ring by either pyridyl or select five-
membered ring heterocycles.12 Based on resistance mapping
experiments, this series of HIV-1 attachment inhibitor is thought
to bind to a conserved, recessed pocket within gp120 that recog-
nizes Phe43 of CD4.5–10,13,14 The sensitivity of the benzamide moi-
ety to modification reflects the notion that this element of the
pharmacophore may bind to a hydrophobic cavity of defined
dimensions.13,14 These structure–activity findings are similar to
that reported for a related series of HIV-1 attachment inhibitors
based on an indole-3-sulfonamide scaffold that appears to be
inherently less potent and for which benzamide replacements
were examined in a less systematic fashion.15 Although we were
unable to identify benzamide derivatives or replacements that of-
fered markedly enhanced potency compared to the prototype 1a,
these results provided a clear definition of the optimal amide moi-
eties. Consequently, the simple benzamide was included in BMS-
377806 (6), an inhibitor of HIV-1 attachment that has been shown
to protect macaques from vaginal SHIV challenge,1,16 and BMS-
488043 (7), a related compound that has demonstrated antiviral
activity in early clinical trials conducted in HIV-1-infected sub-
jects.17–21 These studies have established the viability for this
mechanistic class of HIV-1 inhibitor to function effectively in a pre-
clinical model of prophylaxis and as a therapeutic agent in HIV-1
infected subjects.
1 lM in the pseudotype assay, with larger substituents generally
providing compounds 20–200-fold weaker than the parent, irre-
spective of the site of deployment on the phenyl ring. This result
is interpreted as a limited tolerance for sterically demanding sub-
stituents in this element of the pharmacophore, an aspect con-
firmed with the series of polysubstituted analogs 1v–1af that
focused specifically on assessing patterns of fluorine and chlorine
substitution. Fusion of an additional ring (1ah) or homologation
to the phenylacetic acid derivatives 1ag and 1ao provided inactive
compounds whilst saturation of the phenyl ring (1al) resulted in a
22-fold reduction in antiviral potency that was further eroded by
homologation, as probed with compound 1am.
With these results in hand, attention was focused on exploring
the effect of ring systems that would more subtly alter the silhou-
ette cast by the phenyl ring. Within the pyridyl series captured by
compounds 1ai, 1aj, 1ap–1ar, a 2-pyridyl moiety is superior to the
more exposed 3- and 4-isomers, best exemplified in the context of
indole 4-fluoro-substitution where 1ap exhibits potency approach-
ing that of the prototype 1an. That the potency of the 2-pyridyl
derivative is largely retained in the context of the 4-fluoroindole
series 1ap but leads to a 10-fold reduction in the unsubstituted
O
O
O
N
Ph
O
N
Ph
OCH3
OCH3
OCH3
N
N
N
O
O
CH3
N
N
H
N
H
7
6

5138
N. A. Meanwell et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5136–5139
Table 1
Structure, HIV pseudotype virus inhibitory activity and cytotoxicity associated with indole glyoxamide derivatives 1a–1aag.
O
R1
N
O
R
N
O
N
H
R1
EC50
(lM)
CC50 (lM)
a
Compound #
R
1a
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
1m
1n
1o
1p
1q
1r
1s
1t
1u
1v
1w
1x
1y
1z
1aa
1ab
1ac
1ad
1ae
1af
1ag
1ah
1ai
1aj
1ak
1al
1am
1an
1ao
1ap
1aq
1ar
1as
1at
1au
1av
1aw
1ax
1ay
1az
1aaa
1aab
1aac
1aad
1aae
1aaf
1aag
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
F
C6H5
2-F–C6H4
2-Cl–C6H4
2-Br–C6H4
2-CH3O–C6H4
2-HO–C6H4
2-(CH3)2N–C6H4
3-F–C6H4
3-Cl–C6H4
3-Br–C6H4
3-CH3O–C6H4
3-(CH3)2N–C6H4
4-F–C6H4
4-Cl–C6H4
4-Br–C6H4
4-CH3O–C6H4
4-HO–C6H4
4-(CH3)2N–C6H4
4-CH3–C6H4
4-nPr–C6H4
0.153 0.119 (n = 21)
0.391 0.025 (n = 3)
35 (n = 1)
10.5 (n = 1)
>10 (n = 3)
3.65 (n = 1)
>0.50 (n = 2)
2.76 0.08 (n = 4)
17.5 (n = 1)
6.70 3.61 (n = 3)
> 56.0 (n = 3)
338.8 50.7 (n = 21)
101 (n = 1)
>300 (n = 1)
>300 (n = 1)
>300 (n = 1)
194 (n = 1)
89.0 (82.4, 95.7)
200 (n = 1)
117 (n = 1)
76 (n = 1)
>300 (n = 1)
230 (199.1, 260.9)
280 (n = 1)
92 (n = 1)
>240 (n = 1)
129 (n = 1)
136.1 46.1 (n = 3)
>300 (n = 1)
>99 (n = 3)
48 (n = 1)
31 (n = 1)
>300 (n = 1)
>300 (n = 1)
>300 (n = 1)
>300 (n = 1)
>300 (n = 1)
>300 (n = 1)
>300 (n = 1)
235 (n = 1)
>0.50 (n = 2)
8.91 5.63 (n = 3)
65.80 18.31 (n = 3)
30 (n = 1)
30.18 (31.75, 28.60)
2.49 1.94 (n = 3)
>100 (n = 1)
8.38 4.3 (n = 3)
82 (n = 1)
9 (n = 1)
6 (n = 1)
8.3 (n = 1)
6.7 (n = 1)
36.5 (n = 1)
55 (n = 1)
>54 (n = 1)
>100 (n = 1)
18 (n = 1)
37 (n = 1)
14.5 (n = 1)
3.5 (n = 1)
>100 (n = 1)
>100 (n = 1)
1.55 (n = 1)
4.2 (n = 1)
86.5 (n = 1)
3.5 (n = 1)
>100 (n = 1)
0.0026 0.0025 (n = 17)
>50 (n = 1)
0.0045 (0.0042, 0.0049)
0.154 0.071 (n = 3)
0.0237 0.006 (n = 3)
0.0054 0.0016 (n = 3)
0.0031 0.0017 (n = 4)
0.0014 0.0007 (n = 4)
0.007 (0.008, 0.005)
0.0204 0.0116 (n = 4)
0.0007 0.0005 (n = 3)
0.0173 0.0016 (n = 4)
0.0119 0.001 (n = 4)
0.0032 (0.0040, 0.0025)
0.0004 0.0003 (n = 4)
0.1558 0.032 (n = 3)
0.0718 0.027 (n = 3)
1.23 (1.50, 0.97)
0.0087 0.0034 (n = 3)
0.0228 0.0124 (n = 4)
4-tBu–C6H4
2,4-Di-F–C6H3
3,4-Di-F–C6H3
2,6-Di-F–C6H3
2,4,5-Tri-F–C6H2
3,4,5-Tri-F–C6H2
2,4,6-Tri-F–C6H2
2,3,4,5-Tetra-F–C6H
2,3-Di-Cl–C6H3
2,4-Di-Cl–C6H3
3,4-Di-Cl–C6H3
2-F,3-Cl–C6H3
C6H5CH2
1-Naphthyl
2-Pyridyl
3-Pyridyl
4-CH3-3-Pyridyl
C6H11
C6H11CH2
C6H5
C6H5CH2
2-Pyridyl
3-Pyridyl
4-Pyridyl
2-Furanyl
3-Cl-2-Furanyl
3-Br-2-Furanyl
3-CN-2-Furanyl
3-Furanyl
111 (n = 1)
123 (n = 1)
>300 (n = 1)
>300 (n = 1)
>300 (n = 1)
>300 (n = 1)
>300 (n = 1)
>300 (n = 1)
>300 (n = 1)
158 (n = 1)
>300 (n = 7)
>300 (n = 1)
>300 (n = 2)
>300 (n = 3)
>205 (n = 1)
>300 (n = 3)
250.2 (250.3, 250.2)
236.4 (198.2, 274.6)
187.3 (257.3, 117.4)
>300 (n = 4)
>300 (n = 1)
260 (n = 1)
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
2-Thienyl
3-CH3-2-Thienyl
3-Cl-2-Thienyl
3-Br-2-Thienyl
3-Thienyl
5-Isoxazolyl
3-Pyrazolyl
4-Imidazolyl
4-Thiazolyl
2-CH3-4-thiazolyl
50.5 (43.4, 57.6)
69.7 (47.6, 91.8)
>300 (n = 2)
>300 (n = 3)
>300 (n = 3)
>300 (n = 2)
>250 (n = 1)
>300 (n = 2)
F
F
F
a
Data are the means of two or more experiments, except where noted, with individual data provided for those experiments conducted twice.

N. A. Meanwell et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5136–5139
5139
9. Si, Z.; Madani, N.; Cox, J. M.; Chruma, J. J.; Klein, J. C.; Schön, A.; Phan, N.; Wang,
L.; Biorn, A. C.; Cocklin, S.; Chaiken, I.; Freire, E.; Smith, A. B., III; Sodroski, J. G.
Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 5036.
10. Madani, N.; Perdigoto, A. L.; Srinivasan, K.; Cox, J. M.; Chruma, J. J.; LaLonde, J.;
Head, M.; Smith, A. B., III; Sodroski, J. G. J. Virol. 2004, 78, 3742.
11. Lingens, F.; Lange, J. Justus Liebigs Ann. Chem. 1970, 738, 46.
12. Patani, G. A.; LaVoie, E. J. Chem. Rev. 1996, 96, 3147.
13. Kong, R.; Tan, J. J.; Ma, X. H.; Chen, W. Z.; Wang, C. X. Biochim. Biophys. Acta
2006, 1764, 766.
14. Teixeira, C.; Serradji, N.; Maurel, F.; Barbault, F. Eur. J. Med. Chem. 2009.
doi:10.1016/j.ejmech.2009.03.028.
15. Lu, R.-J.; Tucker, J. A.; Zinevitch, T.; Kirichenko, O.; Konoplev, V.; Kuznetsova, S.;
Sviridov, S.; Pickens, J.; Tandel, T.; Brahmachary, E.; Yang, Y.; Wang, J.; Freel, S.;
Fisher, S.; Sullivan, A.; Zhou, J.; Stanfield-Oakley, S.; Greenberg, M.; Bolognesi,
D.; Bray, B.; Koszalka, B.; Jeffs, P.; Khasanov, A.; Ma, Y.-A.; Jeffries, C.; Liu, C.;
Proskurina, T.; Zhu, T.; Chucholowski, A.; Li, R.; Sexton, C. J. Med. Chem. 2007,
50, 6535.
16. Veazey, R. S.; Klasse, P. J.; Schadr, S. M.; Hu, Q.; Ketas, T. J.; Lu, M.; Marx, P. A.;
Dufour, J.; Colonno, R. J.; Shattock, R. J.; Springer, M. S.; Moore, J. P. Nature 2005,
438, 99.
17. Hanna, G.; Lalezari, J.; Hellinger, J.; Wohl, D.; Masterson, T.; Fiske, W.; Kadow,
J.; Lin, P.-F.; Giordano, M.; Colonno, R.; Grasela D. In 11th Conf. Retroviruses
Opportunistic Infections, San Francisco, February 8–11, 2004, Abstract 141.
18. Doms, R. W.; Trono, D. Genes Dev. 2000, 14, 2677.
19. Biscone, M. J.; Pierson, T. C.; Doms, R. W. Curr. Opin. Pharmacol. 2002, 2, 529.
20. Kadow, J.; Wang, H.-G. H.; Lin, P.-F. Curr. Opin. Invest. Drugs 2006, 7, 721.
21. Strizki, J. Adv. Pharmacol. 2008, 56, 93.
References and notes
1. For Part 1 of this series see: Wang, T.; Zhang, Z.; Wallace, O. B.; Deshpande, M.;
Fang, H.; Yang, Z.; Zadjura, L. M.; Tweedie, D. L.; Huang, S.; Zhao, F.; Ranadive,
S.; Robinson, B.; Gong, Y.-F.; Riccardi, K.; Spicer, T. P.; Deminie, C.; Rose, R.;
Wang, H.-W. H.; Blair, W. S.; Shi, P.-Y.; Lin, P.-F.; Colonno, R. J.; Meanwell, N. A.
J. Med. Chem. 2003, 46, 4236.
2. For Part 2 of this series see: Meanwell, N. A.; Wallace, O. B.; Fang, H.; Wang, H.;
Deshpande, M.; Wang, T.; Yin, Z.; Zhang, Z.; Pearce, B. C.; James, J.; Yeung, K.-S.;
Qiu, Z.; Wright, J. J. K.; Yang, Z.; Zadjura, L.; Tweedie, D. L.; Yeola, S.; Zhao, F.;
Ranadive, S.; Robinson, B. A.; Gong, Y.-F.; Wang, H.-G. H.; Blair, W. S.; Shi, P.-Y.;
Colono, R. J.; Lin, P.-F. Bioorg. Med. Chem. Lett. 2009, 19, 1977.
3. Blair, W., Spicer, T. P. World Patent Application, WO-2001/96610, December 20,
2001.
4. Blair, W. S.; Deshpande, M.; Fang, H.; Lin, P.-F.; Spicer, T. P.; Wallace, O. B.;
Wang, H.; Wang, T.; Zhang, Z.; Yeung, K.-S. World Patent Application, WO2000/
76521, December 21, 2000.
5. Lin, P.-F.; Blair, W.; Wang, T.; Spicer, T.; Guo, Q.; Zhou, N.; Gong, Y.-F.; Wang,
H.-W. H.; Rose, R.; Yamanaka, G.; Robinson, B.; Li, C.-B.; Fridell, R.; Deminie, C.;
Demers, G.; Yang, Z.; Zadjura, L.; Meanwell, N.; Colonno, R. Proc. Natl. Acad. Sci.
U.S.A. 2003, 100, 11013.
6. Wang, H.-W. H.; Williams, R. E.; Lin, P.-F. Curr. Pharm. Des. 2004, 10, 1785.
7. Guo, Q.; Ho, H.-T.; Dicker, I.; Fan, L.; Zhou, N.; Friborg, J.; Wang, T.; McAuliffe, B.
V.; Wang, H.-W. H.; Rose, R. E.; Fang, H.; Scarnati, H. T.; Langley, D. R.;
Meanwell, N. A.; Abraham, R.; Colonno, R. J.; Lin, P.-f. J. Virol. 2003, 77, 10528.
8. Ho, H.-T.; Nowicka-Sans, B.; McAuliffe, B.; Li, C.-B.; Yamanaka, G.; Zhou, N.;
Fang, H.; Dicker, I.; Dalterio, R.; Gong, Y.-F.; Wang, T.; Yin, Z.; Ueda, Y.;
Matiskella, J.; Kadow, J.; Clapham, P.; Robinson, J.; Colonno, R.; Lin, P.-F. J. Virol.
2006, 80, 4017.