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4-nitro substitution was also explored with 9i and 10f,
which also afforded potent binding. The sulfonamide 11
(Scheme 1) was less active than 3f (IC50=300 vs 40 nM).
The more potent compounds were also tested in a
PBMC cell-based assay using the R5 HIV-1 viral isolate
YU-2.14 Since considerable variation in results was
obtained in this assay with only moderately potent
inhibitors, 1b was usually included as a standard during
this assay period.9 Disappointingly, the enhanced CCR5
binding seen for 3j, 3s–t, and amide 10c did not trans-
late into improved antiviral efficacy compared to 1b
(IC95=13–25 mM vs 25 mM, respectively), although the
ureas 9d and 9e did offer some improvement (IC95=3
and 6 mM). Interestingly, while the CCR5 binding assay
results were essentially the same, the allyl derivatives 3v
and 4v finally showed significantly better antiviral
activity compared to 3t (IC95=both 800 nM vs 25 mM).
Introduction of the polar 4-nitro and carboxamide
groups of 4aa and 5dd also afforded enhanced antiviral
activity in the PBMC assay (IC95=100–400 nM). The
combination of both the allyl and 4-nitro moieties in the
carbamates 3bb and 5bb (IC95=200 nM), urea 9i
(IC95=250 nM), and especially amide 10f (IC95=50
nM) afforded the best efficacy in the PBMC assay with
IC95’s now in the lower nanomolar range.
Figure 1. Four possible conformations of carbamate derivatives.
while the former series adopts conformation D in which
the larger alkyl group is away from the piperidine and
the smaller methoxy occupies the more restricted posi-
tion. The better activity of the benzyloxy series then
implies a superior interaction of the carbonyl of con-
former C with the receptor. The extended conformation
of the benzyl in conformation C was also in agreement
with the good binding, but poor antiviral activity14 (see
below), previously seen with a 4-(3-phenylpropyl)piper-
idine compound (IC50=5 nM, PBMC assay,
IC95=50,000 nM).10
Previously, the chiral, 3-chlorophenyl derivative 1b had
shown 3- to 4-fold improvement over the racemic
unsubstituted compound 1c in both the binding
(IC50=10 vs 35 nM) and antiviral assays. Unfortu-
nately, for unknown reasons, neither the expected affin-
ity enhancement nor any improvement in antiviral
efficacy were realized for the chiral, 3-chlorophenyl
analogues 5r and 5t with these non-spiro carbamate
derivatives.
Thus, with the synthesis of the initial carbamates, the
spiro structure of 1 and 2 was found not to be required
for potent CCR5 binding activity. Optimization of the
two alkyl portions implicated two distinct binding
motifs of which the N-alkyl-N-benzyloxycarbonyl-
amino derivatives were the more potent. Further use of
the N-allyl, substitution on the benzyl, and investigation
of other linking functionality led to significantly
enhanced antiviral activity of the N-allyl-4-nitrobenzyl
compounds with IC95’s of 50–200 nM in the PBMC
assay. Further investigations of these findings in com-
bination with other core structures will be reported in
the near future.
Substitution on the benzyl was also investigated. The
isomeric 2-, 3-, and 4-methyl derivatives 3w–y showed
very little effect on binding, although the larger tri-
fluoromethyl groupof 3z appeared to be detrimental, as
well as 4-phenyl and 1- or 2-naphthyl (data not shown).
However, the polar 4-nitro and 3- and 4-carboxamide
moieties of 3aa, 4aa, 3bb, and 4dd showed equal or more
potent binding which was also maintained in 5bb–dd.
Although not evident from the binding data (IC50=1–2
nM), the 4-nitro and 4-carboxamide groups provided
much improved antiviral activity (see below).
References and Notes
1. For a review of the chemokines and their receptors, see:
Baggiolini, M.; Dewald, B.; Moser, B. Annu. Rev. Immunol.
1997, 15, 675.
2. For a review of the co-receptor search, see: Fauci, A. S.
Nature 1996, 384, 529.
3. Liu, R.; Paxton, W. A.; Choe, S.; Ceradini, D.; Martin,
S. R.; Horuk, R.; MacDonald, M. E.; Stuhlmann, H.; Koup,
R. A.; Landau, N. R. Cell 1996, 86, 367.
4. (a) Blair, W. S.; Lin, P.-F.; Meanwell, N. A.; Wallace, O. B.
Drug Discovery Today 2000, 5, 183. (b) ; Horuk, R.; Ng, H. P.;
Med. Res. Rev. 2000, 2, 155.
5. Shiraishi, M.; Aramaki, Y.; Seto, M.; Imoto, H.; Nishi-
kawa, Y.; Kanzaki, N.; Okamoto, M.; Sawada, H.; Nishi-
mura, O.; Baba, M.; Fujino, M. J. Med. Chem. 2000, 43, 2049.
6. Armour, D. R.; Price, D. A.; Stammen, B. L. C.; Wood, A.;
Perros, M.; Edwards, M. P. EPO Patent 1,013,276 A1, 2000
(Pfizer); Chem. Abstr. 2000, 133, 74,024x.
7. Baroudy, B. M.; Clader, J. W.; Josien, H. B.; McCombie,
S. W.; McKittrick, B. A.; Miller, M. W.; Neustadt, B. R.;
Palani, A.; Smith, E. M.; Steensma, R.; Tagat, J. R.; Vice, S.
Other acyl groups were also investigated with the prep-
aration of amides and ureas. The same SAR was seen
regarding the relative size of the two groups with the
best again being the benzyl related compounds as illus-
trated in the urea series 9a–e. While neither showed
improved activity over 9e, the results of the a-methyl
urea derivatives 9g and 9h showed that a stereochemical
preference exists for the (R) isomer, thus indicating a
preferred directionality for the benzyl moiety in the
binding site. A second alkylation on the terminal nitro-
gen (9f) was always detrimental by at least 10-fold.
Several amide derivatives were also quite potent as seen
with 10a–e; however, the benzamide 10b was a con-
siderably poorer inhibitor than 10c, indicating that the
binding site could not tolerate the extended confirma-
tion of the planar benzamide, in agreement with the
previously proposed binding model.10 The effect of the
Finke, Paul E.
