S. E. Metobo et al. / Bioorg. Med. Chem. Lett. 16 (2006) 3985–3988
3987
laid together.12 Indeed, this C3 position could be used
as a point through which these ‘reverse’ inhibitors may
be constructed. The implication of this new series
remains to be seen but could have effects ranging from
intrinsic potency to resistance mutations.
Table 1. Integration strand transfer inhibition, anti-HIV proliferation
and cytotoxicity assay results for compounds 1, 6, 8, 9, 10, 14, and 1710
Compound
Strand
transfer
Anti-HIV
in MT4
Cytotoxicity
in MT4
IC50 (lM)
EC50 (lM)
CC50 (lM)
1
6
0.05
0.21
0.089
3.55
5.1
87
In summary, based on the compounds we have studied,
we have shown that the pyridine ring is optimal in our
novel tricyclic-based scaffold. Indeed, observations
made from our SAR indicate that an aromatic nitrogen
is important for biological activity. Also, substitutions
at the 3-position of the quinoline ring are well tolerated.
This position is an attractive site for future structural–
activity studies to modulate both chemical and pharma-
cokinetic properties of the tricyclic analogs. Additional-
ly, further work is also underway to explore 2- and 4-
substitutions of the quinoline in this scaffold.
8
24
>10
25
9
0.033
0.255
0.093
0.0072
0.54
2.7
1.4
2.1
33.3
10
14
17
0.007
0.07
1.54
The aromatic nitrogen lone pair is a Lewis base in the
pyridine ring. Thus, when non-aromatic heterocycles
are present as in the piperazinyl-based 7, poor antiviral
activity is noted (EC50 > 10 lM and IC50 0.85 lM).
Acknowledgments
Inspired by use of five-membered heterocycles as car-
boxylate isosteres in 2 and 3, we synthesized and tested
the imidazole analog 8. This analog completely lost inhi-
bition activity toward the enzyme along with its antiviral
potency. However, it is unclear whether the benzyl
group on the benzimidazole in 8 was detrimental.
The authors are wholly indebted to Fang Yu and Gregg
Jones of the biology group for determination of biolog-
ical activity and Martin McDermott and the protein
Chemistry/HTS group. The authors also wish to
acknowledge Will Watkins, Randall Halcomb, Maria
Fardis, and Michael Mish for useful discussions in the
preparation of the manuscript.
We believe that both the shape of heterocycles and
electronic properties of nitrogen in the ring play an
important role in formation of an optimal tricyclic inte-
grase inhibitor. Introduction of small five-membered
heterocycles proved to be deleterious to both intrinsic
potency and the cell-based EC50.
Supplementary data
Supplementary data associated with this article can be
Since the pyridine was confirmed as the optimal moiety
for our tricyclic scaffold, and in light of recently
disclosed observations,12 we decided to further evaluate
the effect of substitution. Our attention initially was
focused to the 3-quinoline position (C3) position of
the pyridine moiety of 1. The preliminary examination
of the tolerance to C3 substitution of the pyridine
revealed intriguing results. Methoxy substitution at C3
in 14 largely preserved the enzymatic activity while
improving anti-HIV potency in the cell assay when
compared to 1. Furthermore, replacement of hydrogen
by fluorine at C3 in 17 resulted in significant enhance-
ment of enzymatic activity but at the same time, signif-
icant loss of anti-HIV activity in the cell assay.
Correlation between activity at the enzyme and activity
in the cell culture has not been particularly strong.
Generally, this trend was true for most series. This
disconnect may be due to inherently poor solubility of
the inhibitors. This may contribute to poor permeation
through cell membranes. Additionally, the pKas of the
pyridine nitrogen and phenol which comprise the
binding motif is altered in analogs 14 and 17 and this
may also play a role in the observed changes of activity.
References and notes
1. Billich, A.; Schauer, M.; Frank, S.; Rosenwirth, B.;
Billich, S. Antiviral Chem. Chemother. 1992, 3, 113.
2. Pommier, Y.; Johnson, A. A.; Marchand, C. Nature 2005,
9, 236.
3. Clavel, F.; Hance, A. J. N. Eng. J. Med. 2004, 10, 350,
1023.
4. Jin, H.; Cai, R. Z.; Schacherer, L.; Jabri, S.; Tsiang, M.;
Jones, G.; Fardis, M.; Chen. J.; Kim, C.U. Bioorg. Med.
Chem. Lett. accepted for publication.
5. Santo, R. Di.; Costi, R.; Artico, M.; Ragno, R.; Greco,
G.; Novellino, E.; Marchand, C.; Pommier, Y. Farmaco
2005, 60, 409.
6. Zhuang, L.; Wai, J. S.; Embrey, M. W.; Fisher, T. E.;
Egbertson, M. S.; Payne, L. S.; Guare, J. P., Jr.; Vacca, J.
P.; Hazuda, D. J.; Ferlock, P. J.; Wolfe, A. L.; Stillmock,
K. A.; Witmer, M. V.; Moyer, G.; Schleif, W. A.;
Gabryelski, L. J.; Leonard, Y. M.; Lynch, J. J., Jr.;
Michelson, S. R.; Young, S. D. J. Med. Chem. 2003, 46,
453.
7. Clercq, E. D. Expert Opin. Emerging Drugs 2005, 10, 24.
8. Fardis, M., Jin, H., Jabri, S., Cai, R. Z., Mish, M., Kim,
C. U., Bioorg. Med. Chem. Lett. accepted for publication.
9. LeBas, M.-D.; Gueret, C.; Perrio, C.; Lasne, M.-C.; Barre,
L. Synthesis 2001, 2495.
Nevertheless, the discovery that an electron-donating
group such as methoxy at C3 is well tolerated implies
the opportunity for further expansion and optimization
at this position. It has been shown that inhibitors can
bind to IN in a ‘forward’ or ‘reverse’ direction if over-
10. (a) Strand transfer assay modified from a previous report.
(Hazuda et al., Nucleic Acids Res. 1994, 22, 1121).