Library of 1,4-disubstituted 1,2,3-triazole analogs of oxazolidinone RNA-binding agents

Article abstract of DOI:10.1021/cc100029y

The design and synthesis of small molecules that target RNA is immensely important in antibacterial therapy. We had previously reported on the RNA binding of a series of 4,5-disubstituted 2-oxazolidinones that bind to a highly conserved bulge region of bacterial RNA. This biological target T box antitermination system, which is found mainly in Gram-positive bacteria, regulates the expression of several amino acid related genes. In an effort to amplify our library, we have prepared a library of 1,4-disubstituted 1,2,3-triazole analogs that entails an isosteric replacement of the oxazolidinone nucleus. The synthesis of the new analogs was enhanced via copper(I) catalysis of an azide and alkyne cycloaddition reaction. A total of 108 1,4-disubstituted 1,2,3-triazole compounds have been prepared. All compounds were evaluated as RNA binding agents.

Full text of DOI:10.1021/cc100029y

J. Comb. Chem. 2010, 12, 491–496
491
Library of 1,4-Disubstituted 1,2,3-Triazole Analogs of Oxazolidinone
RNA-Binding Agents
George Acquaah-Harrison, Shu Zhou, Jennifer V. Hines, and Stephen C. Bergmeier*
Department of Chemistry and Biochemistry, Ohio UniVersity, Athens, Ohio 45701
ReceiVed February 23, 2010
The design and synthesis of small molecules that target RNA is immensely important in antibacterial therapy.
We had previously reported on the RNA binding of a series of 4,5-disubstituted 2-oxazolidinones that bind
to a highly conserved bulge region of bacterial RNA. This biological target T box antitermination system,
which is found mainly in Gram-positive bacteria, regulates the expression of several amino acid related
genes. In an effort to amplify our library, we have prepared a library of 1,4-disubstituted 1,2,3-triazole
analogs that entails an isosteric replacement of the oxazolidinone nucleus. The synthesis of the new analogs
was enhanced via copper(I) catalysis of an azide and alkyne cycloaddition reaction. A total of 108 1,4-
disubstituted 1,2,3-triazole compounds have been prepared. All compounds were evaluated as RNA binding
agents.
The identification of ligands for RNA that modulate
transcription has significant potential for the development
of new therapeutics. In previous communications, we
reported on a novel class of 4,5-disubstituted oxazolidin-2-
ones with good binding affinity toward the T box antiter-
minator RNA system.1 The T box transcription antitermi-
nation system regulates many genes in Gram-positive
bacteria, including aminoacyl-tRNA synthetase, amino acid
biosynthesis, and amino acid transport genes. Transcription
of these genes requires the interaction of the uncharged
cognate tRNA with the 5′ untranslated mRNA leader region,
which results in the formation and stabilization of an
antiterminator element.2,3 Small ligands that bind to the
antiterminator and disrupt the tRNA-antiterminator interac-
tion have the potential to halt the gene expression.
Given the ready availability of 1,4-disubstituted triazoles
and the fact that the 1,2,3-triazole ring has been reported to
function as an amide bond surrogate,8,9 we wished to
examine an appropriately substituted triazole as a potential
isosteric replacement for the oxazolidinone ring. Such a
bioisosteric replacement would have an advantage in avoid-
ing the stereochemical considerations associated with ANB-
22 and ANB-40, as well as provide RNA ligands with
potentially improved water solubility. In the context of
identifying structurally diverse potential analogs, we desired
a library of 1,4-disubstituted 1,2,3-triazole compounds 1
(Figure 1) that incorporated the diversity elements used in
the 4,5-disubstituted oxazolidinone compound library. Based
on ANB-22 and ANB-40, R1 would be an aliphatic, aryl, or
amide group, while R3 and R4 would be alkyl groups. This
would provide analogs in which key functional groups
The previously reported oxazolidinones bind the targeted
RNA without significant dependence on electrostatic interac-
tions. These compounds also exhibited good binding speci-
ficity and affinity for model RNA AM1A relative to C11U.1
More recently, two oxazolidinones, ANB-22 and ANB-40,
with improved biological activity have been identified.4
These oxazolidinone leads bind to our model RNA at low
micromolar to nanomolar concentrations.4 We were inter-
ested in analogs of the oxazolidinone ring that could provide
enhanced water solubility and eliminate both stereocenters.
Several isosteric analogs to the oxazolidinone ring have been
reported with varying degrees of success.5 These include
isoxazoline (removes the carbonyl and introduces a CdN
double bond),6 benzisoxazolinones (CdC double bond,
replacement of sp3 carbon with an N),7 and pyrroles
(completely flat aromatic ring system).7 Of these bioisosteric
analogs of the oxazolidinone, only the isoxazoline and the
benzisoxazolinone had activity similar to the parent compound.
Figure 1. General structure of the lead oxazolidinone and proposed
1,2,3-triazole compound library.
* To whom correspondence should be addressed. E-mail: bergmeis@
ohio.edu.
10.1021/cc100029y  2010 American Chemical Society
Published on Web 06/17/2010

492 Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 4
Acquaah-Harrison et al.
Scheme 1
Scheme 2
Figure 2. Overlay of triazole analog and oxazolidinone.
The azide components were prepared in two or three steps
by following three related synthetic routes (Schemes 1-3).
In general, the requisite azide was prepared via the opening
of an epoxide with azide. Azidolysis methods have been well
documented and azidohydrins in general have been prepared
from the ring-opening reactions of epoxide with a variety
of azide nucleophiles including sodium azide.19
Figure 3. Retrosynthesis and general structure of 1,2,3-triazole
library and key intermediates.
occupy the same space in both the oxazolidinone and 1,2,3-
triazole analogs.
Modeling of a simple analog of triazole 1 (n ) 1, R1, R2,
R3 ) Me) and a similarly substituted oxazolidinone showed
good overlap of both the basic amine and the ester.10 The
N-acyl oxygen distance in the triazole 1 is 5.847 Å, while
the N-acyl oxygen distance for the oxazolidinone is 5.937
Å. An overlay of the triazole with the oxazolidinone is shown
in Figure 2. One can clearly see the excellent overlap of
both basic nitrogens and the ester functionality.
Glycidol 5 was acylated with three acid chlorides to
provide the glycidyl esters 6 in good to excellent yields
(Scheme 1).20 We were interested in examining methods for
epoxide opening by azide that might be amenable for parallel
synthesis of the requisite azides. Several epoxide-opening
methods, including a Ce(III)-mediated epoxide opening using
NaN3,21 NaN3 on zeolite,22 NaN3/SiO2 neat,23 NaN3, and 4
Å MS, were evaluated.24 These conditions gave either
complex reaction mixtures or provided very low yields of
the expected azidohydrins. Ultimately, the classical protocol,
which entailed the use of sodium azide in the presence of
NH4Cl was employed to afford the first set of azide diversity
elements 3{1-3} in good yield. This provided a series of
azide components that were used to generate analogs of the
lead ANB-22.
The 1,2,3-triazole scaffolds are generally synthesized via
the Huisgen [3 + 2] cycloaddition reaction of an organic
azide and a terminal alkyne.11,12 Though the classic Huisgen
1,3-dipolar cycloaddition reaction provided a regioisomeric
mixture of 1,2,3-triazoles, recent advances utilizing Cu(I)-
catalysis have added great utility to the [3 + 2] cycloaddition
reaction in the synthesis of more complex, diverse, and
biologically relevant compounds.13-18 Thus, this Cu(I)
variant of the Huisgen 1,3-dipolar cycloaddition reaction
enables us to access the desired library of 1,4-disubstituted
1,2,3-triazole compounds in a reliable and efficient manner
with only the 1,4-disubstituted regioisomer being produced.
We also wanted to prepare a set of carbamoyl-substituted
azides to provide analogs of the lead ANB-40. The synthesis
of carbamoyl epoxide 8 from the reaction of glycidol and
an isocyanate gave extremely low yields of the expected
product. A plausible explanation for the low yield could be
attributed to intramolecular ring-opening of the epoxide by
the neighboring carbamate.25
The retrosynthetic analysis and general structure of the
1,4-disubstituted 1,2,3-triazole library (2) and key intermedi-
ates are outlined in Figure 3. The triazole 2, will be obtained
from an azide (3), alkyne (4) cycloaddition reaction. As we
planned to prepare the azide component 3 via ring-opening
reactions of an epoxide, we have an opportunity to introduce
additional substitutions on the target molecule (e.g., R2 and
R3). Such substitution could lead to improved affinity to the
RNA target.
In view of this, an alternative synthetic route starting from
allyl alcohol was developed. Allyl alcohol was treated with
benzyl and butyl isocyanate respectively to give the corre-
sponding allylcarbamates (Scheme 2). Epoxidation of the
olefin using mCPBA afforded the epoxide 8, in excellent
yield. The epoxide ring of 8 was then opened with sodium

Analogs of Oxazolidinone RNA-Binding Agents
Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 4 493
Scheme 3
Figure 5. Alkyne diversity elements (4{1-9}) employed in library
synthesis.
Scheme 4
azide to provide a second set of carbamoyl azide diversity
elements 3{4} and 3{5}.
As outlined in Scheme 3, four commercially available
epoxides 9a-d were also treated with sodium azide to
provide the racemic azidoalcohols 3{6-9} in good to
excellent yields. To again provide analogs related to lead
ANB-22, one azidoalcohol, racemic trans-2-azidocyclohex-
anol (3{9}), was acylated with three different acid chlorides
to afford the final set of trans-2-azidocyclohexyl ester
diversity elements 3{10-12} in good yields. These syntheses
provided structural diversification of three different sets of
azide components for the 1,4-disubstituted 1,2,3-triazole
synthesis (Figure 4).
Scheme 5
The alkyne diversity elements (Figure 5) were readily
accessed in one step via two different N-alkylation reactions
in either THF or methanol.26 As outlined in Scheme 4,
propargyl bromide was alkylated with a series of secondary
amines 11 to provide a set of propargylamine-derived alkyne
diversity elements, 4{1-7}, in good yields. The modification
of Verron et al. was used for the preparation of 4{4}.27 In a
similar manner, N-methyl propargylamine 12 was also
alkylated with 2 different alkyl halides, 13a and 13b, to
provide the remainder of the alkyne diversity elements 4{8}
and 4{9} which were needed for the synthesis of the triazole
library (Scheme 5).
Having the twelve azide components (3{1-12}, Figure
4) and nine propargylamine derived alkynes (4{1-9}, Figure
5) in hand, we initiated the synthesis of the targeted 1,4-
disubstituted 1,2,3-triazole analogs of the oxazolidinone RNA
binding agents.
We planned to initially carry out a few cycloaddition
reactions to ascertain if the general conditions for the
previously reported Cu(I) catalyzed azide/alkyne variant of
the Huisgen’s 1,3-dipolar cycloaddition reaction would be a
suitable method for preparing our targeted library. A trial
cycloaddition reaction was carried out using 3{6} and
phenylacetylene following typical Sharpless conditions.
These reaction conditions afforded the expected triazole in
a yield of 98%. On the basis of this result, a small scouting
library of 16 members was prepared using the azides 3{2},
3{3}, 3{8}, and 3{9} and the alkynes 4{1}, 4{2}, 4{5} and
4{6}. In contrast to the trial cycloaddition reaction in which
phenylacetylene was used as the alkyne component, these
[3 + 2] cycloaddition reactions using catalytic amounts of
CuSO4 afforded very poor yields (∼20%) of the 1,4-
disubstituted 1,2,3-triazole with substantial amount of starting
materials. Increasing the temperature and increasing the
length of reaction time did not significantly alter the yield.
We attributed this decrease in yield to the prescence of a
basic amine on the alkyne. The prescence of a basic amine
Figure 4. Azide diversity elements 3{1-12} employed in the
library synthesis.

494 Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 4
Acquaah-Harrison et al.
Scheme 6
mixture through poly(vinylpyridine). This method was ef-
ficient in cleaning up library members when catalytic amount
of Cu(II) salts were used. As the amount of Cu(II) salts was
increased to a full equivalent, purification using poly(vi-
nylpyridine) as a copper scavenger became inefficient in
removing copper residues from the mixture. This was
apparent from the paramagnetic effect of copper in the proton
NMR. Consequently, an additional aqueous workup was
required to completely remove copper ions. This was time-
consuming especially considering the size of the library.
Adding poly(vinylpyridine) to the reaction mixture and
stirring, followed by filtering through a phase separator,
produced similar results as filtration through the poly(vi-
nylpyridine). The final workup procedure involved adding a
1:1 mixture of NH4OH/H2O to the reaction, then adding
CH2Cl2, and using a phase separator to cleanly obtain the
organic layer. This provided a quick, efficient and simple
workup procedure, which afforded the desired product in high
yields and excellent purity. As a result, this third workup
procedure was adopted for the library.
elements in Cu-catalyzed azide-alkyne cycloadditions ap-
pears to be quite limited.28-32 While many of these reactions
use the catalytic Cu protocols, these methods were unsuc-
cessful in our hands. We had previously observed that 100
mol % of Cu(I) was required for complete consumption of
the starting materials in the cycloaddition when basic amine
groups were present as part of a library synthesis.33 Further
experimental trials using different stoichiometric amounts
of CuSO4 · 5H2O and sodium ascorbate indicated that a full
molar equivalent of both CuSO4 · 5H2O and a 2-fold excess
of sodium ascorbate relative to the alkyne to be the optimal
loading for the [3 + 2] cycloaddition reaction. Thus, the
library synthesis was carried out as outlined in Scheme 6
using 100 mol % of CuSO4 and 200 mol % of sodium
ascorbate.
A typical workup procedure for these reactions entailed
concentrating the reaction mixture, diluting the residue with
CH2Cl2, washing consecutively with a mixture of 1:1
NH4OH/H2O, H2O, brine, drying over MgSO4, filtering, and
concentrating the filtrate. This process seemed challenging
considering the library size. Three different workup proce-
dures were examined in an attempt to discern a relatively
simple and quick workup condition for the library preparation.
All three workup conditions required the reaction mixture
to be concentrated to at least half its initial volume prior to
workup. We first examined a simple filtration of the reaction
With the synthetic method and purification scheme opti-
mized, all 12 azides (Figure 4) and 9 alkynes (Figure 5) were
subjected to the reaction and workup conditions described
previously. As depicted in Table 1, yields in the range of
88-96% were obtained for the synthesis of the targeted
triazoles. The masses of all 1,4-disubstituted 1,2,3-triazole
library members were verified via LC/MS analysis. Purities
of 80-96% were obtained for the compound library members
based on the integration of the major peak in the HPLC trace.
The 1,4-disubstituted 1,2,3-triazole compounds were tested
for their ability to bind to the wildtype antiterminator model
RNA AM1A34 and the reduced function variant C11U by
using a fluorescence resonance energy transfer (FRET)
screening assay.35
Table 1. Yield and Purity of the 1,4-Disubstituted 1,2,3-Triazole Library Membersa
compd
yield
purity
compd
yield
purity
compd
yield
purity
compd
yield
purity
2{1,1}
2{1,2}
2{1,3}
2{1,4}
2{1,5}
2{1,6}
2{1,7}
2{1,8}
2{1,9}
2{2,1}
2{2,2}
2{2,3}
2{2,4}
2{2,5}
2{2,6}
2{2,7}
2{2,8}
2{2,9}
2{3,1}
2{3,2}
2{3,3}
2{3,4}
2{3,5}
2{3,6}
2{3,7}
2{3,8}
2{3,9}
94
92
93
96
94
91
92
93
89
92
91
93
90
94
92
93
95
92
91
94
94
90
97
92
96
94
92
93
81
91
87
100
98
97
95
84
100
83
93
81
84
81
84
82
84
83
100
100
91
90
82
96
84
85
2{4,1}
2{4,2}
2{4,3}
2{4,4}
2{4,5}
2{4,6}
2{4,7}
2{4,8}
2{4,9}
2{5,1}
2{5,2}
2{5,3}
2{5,4}
2{5,5}
2{5,6}
2{5,7}
2{5,8}
2{5,9}
2{6,1}
2{6,2}
2{6,3}
2{6,4}
2{6,5}
2{6,6}
2{6,7}
2{6,8}
2{6,9}
92
94
93
92
92
96
96
90
92
94
91
95
92
94
93
92
90
92
92
96
91
93
93
95
93
93
89
100
98
95
84
100
80
97
84
81
96
99
94
100
100
80
92
85
84
94
84
84
100
89
80
98
94
95
2{7,1}
2{7,2}
2{7,3}
2{7,4}
2{7,5}
2{7,6}
2{7,7}
2{7,8}
2{7,9}
2{8,1}
2{8,2}
2{8,3}
2{8,4}
2{8,5}
2{8,6}
2{8,7}
2{8,8}
2{8,9}
2{9,1}
2{9,2}
2{9,3}
2{9,4}
2{9,5}
2{9,6}
2{9,7}
2{9,8}
2{9,9}
91
91
94
95
93
96
91
93
89
89
95
91
92
95
96
91
93
93
92
92
92
92
94
95
92
92
91
100
86
99
90
90
84
99
98
86
92
81
84
94
98
81
98
98
90
100
89
100
82
84
90
98
81
100
2{10,1}
2{10,2}
2{10,3}
2{10,4}
2{10,5}
2{10,6}
2{10,7}
2{10,8}
2{10,9}
2{11,1}
2{11,2}
2{11,3}
2{11,4}
2{11,5}
2{11,6}
2{11,7}
2{11,8}
2{11,9}
2{12,1}
2{12,2}
2{12,3}
2{12,4}
2{12,5}
2{12,6}
2{12,7}
2{12,8}
2{12,9}
93
91
92
89
90
92
89
95
89
93
91
92
91
94
92
91
93
94
91
95
92
92
91
93
92
93
88
81
100
84
84
100
82
94
83
100
86
96
86
86
98
81
100
95
95
81
97
93
81
98
84
96
84
82
a Purities >80% were obtained for all library members based on HPLC analysis.

Analogs of Oxazolidinone RNA-Binding Agents
Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 4 495
Figure 6. FRET screening of 1,4-disubstituted 1,2,3-triazole binding affinity for model RNAs AM1A and C11U. The relative fluorescence
intensity change ∆F was calculated by ∆F ) [(F - F0)/F0] × 100, where F is the fluorescence intensity with ligand and F0 is without
ligand at 585 nm upon excitation at 467 nm. All of the compounds were tested at a final concentration of 10 µM.
The reduced function variant C11U has been used in other
ligand-antiterminator RNA binding assays as a specificity
control.1,4 The model RNAs were labeled with a fluorescein
(donor) on the 3′ end and a rhodamine (acceptor) on U18 in
the UUCG loop of AM1A as previously described.1,4
Previous studies correlated changes in FRET with ligand
binding affinities.
Prior to examination of the library in the FRET-based
RNA binding assay, all 108 compounds prepared were
examined for both solubility in the assay buffer and inter-
ferring fluorescence. This led to the exclusion of 27
compounds from the RNA binding assay.
Figure 6 shows all compounds that were evaluated in the
FRET assay (including ANB-22 and ANB-40) where the X
and Y coordinates represent ∆FAM1A and ∆FC11U, respec-
tively.36 The lead compounds ANB-22 and ANB-40 in-
creased the fluorescence intensity of FRET-labeled RNA for
both AM1A and C11U significantly. The 11% difference
between the signal change of AM1A (8.53%) and C11U
(19.53%) nicely correlates with the previous finding that
ANB-22 has high binding specificity for these two antiter-
minator models.4 Gratifyingly a number of compounds are
clustered near ANB-22 and ANB-40. Clearly the triazole
analogs prepared have retained the RNA affinity of the lead
oxazolidinones. As might be expected, compounds with
similar side chain substitution as oxazolidinones ANB-22
and ANB-40 (e.g., 2{4,5}, 2{4,6}, 2{12,5}, and 2{12,6})
showed similar fluorescence values as the parent oxazolidi-
nones. A total of forty-nine 1,4-disubstituted 1,2,3-triazole
compounds enhanced the AM1A fluorescence intensity more
than 8.53%. Furthermore, 2{4,5}, 2{7,4}, 2{8,4}, and 2{5,1}
showed larger differences of ∆F between AM1A and C11U
compared to ANB-22, which indicated higher specificities.
Interestingly, 2{10,9}, 2{3,8}, and 2{1,2} caused a decrease
of the fluorescence intensity. One explanation for the
decreased fluorescence intensity of 2{10,9}, 2{3,8}, and
2{1,2} could be that these compounds bind to the antiter-
minator in a unique manner that induced an RNA confor-
mational change different from the others.
We have developed useful conditions for the synthesis of
amine-substituted 1,2,3-triazoles by using stoichiometric
quantities of Cu(I). We have also shown that the 1,2,3-
triazole ring can be an effective bioisosteric replacement for
an oxazolidinone ring. The 1,4-disubstituted 1,2,3-triazole
prepared represents a considerable simplification in both
topography and synthesis relative to the oxazolidinone.
Further work to determine the structure activity relationships
of this class of RNA binding agent and understand the mode
of interaction with the RNA target is ongoing and will be
reported in due course.
Acknowledgment. We thank the National Institutes of
Health (GM073188) for support of this work. We also thank
Ohio University for support of the BioMolecular Innovation
and Technology project.
Supporting Information Available. General synthesis of
all compounds, HPLC and LCMS data, spectroscopic data,
1
and H NMR and 13C NMR characterizations, as well as a
listing of the fluorescence data for Figure 6. This information
is available free via the Internet at http://pubs.acs.org.
References and Notes
(1) Means, J.; Katz, S. J.; Anupam, R.; Nayek, A.; Hines, J. V.;
Bergmeier, S. C. Bioorg. Med. Chem. Lett. 2006, 16, 3600–
3604.

496 Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 4
Acquaah-Harrison et al.
(2) Grundy, F. J.; Rollins, S. M.; Henkin, T. M. J. Bacteriol. 1994,
176, 4518–4526.
(17) Kolb, H. C.; Sharpless, K. B. Drug DiscoVery Today 2003,
8, 1128–1137.
(18) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem.,
Int. Ed. 2001, 40, 2004–2021.
(19) Scriven, E.; Turnbull, K. Chem. ReV. 1988, 88, 297–398.
(20) Stamatov, S. D.; Stawinski, J. Tetrahedron 2005, 61, 3659–
3669.
(3) Gutierrez-Preciado, A.; Henkin, T. M.; Grundy, F. J.; Yanof-
sky, C.; Merino, E. Microbiol. Mol. Biol. ReV. 2009, 36–61.
(4) Anupam, R.; Nayek, A.; Green, N. J.; Grundy, F. J.; Henkin,
T. M.; Means, J. A.; Bergmeier, S. C.; Hines, J. V. Bioorg.
Med. Chem. Lett. 2008, 18, 3541–3544.
(5) Hutchinson, D. K. Curr. Top. Med. Chem. 2003, 3, 1021–
1042.
(21) Sabitha, G.; Babu, R. S.; Rajkumar, M.; Yadav, J. S. Org.
Lett. 2002, 4, 343–345.
(22) Onaka, M.; Sugita, K.; Izumi, Y. J. Org. Chem. 1989, 54,
1116–1123.
(23) Kiasat, A. R.; Kazemi, F. Phosphorus, Sulfur Silicon Relat.
Elem. 2003, 178, 2387–2392.
(24) Boruwa, J.; Borah, J. C.; Kalita, B.; Barua, N. C. Tetrahedron
Lett. 2004, 45, 7355–7358.
(25) Langlois, N.; Moro, A. Eur. J. Org. Chem. 1999, 3483–3488.
(26) Lambert, S. J.; Kabalka, G. W.; Knapp, F. F., Jr.; Srivastava,
P. C. J. Org. Chem. 1991, 56, 3707–3711.
(27) Verron, J.; Malherbe, P.; Prinssen, E.; Thomas, A. W.; Nock,
N.; Masciadri, R. Tetrahedron Lett. 2007, 48, 377–380.
(28) Chittaboina, S.; Xie, F.; Wang, Q. Tetrahedron Lett. 2005,
46, 2331–2336.
(29) Yan, Z.-Y.; Zhao, Y.-B.; Fan, M.-J.; Liu, W.-M.; Liang, Y.-
M. Tetrahedron 2005, 61, 9331–9337.
(30) Kaval, N.; Ermolat’ev, D.; Appukkuttan, R.; Dehaen, W.;
Kappe, C. O.; Van der Eycken, E. J. Comb. Chem. 2005, 7,
490–502.
(6) Snyder, L. B.; Meng, Z.; R., M.; D’Andrea, S. V.; Marinier,
A.; Quesnelle, C. A.; Gill, P.; DenBleyker, K. L.; Fung-Tomc,
J. C.; Frosco, M.; Martel, A.; Barrett, J. F.; Bronson, J. J.
Bioorg. Med. Chem. Lett. 2004, 14, 4735–4739.
(7) Barbachyn, M. R.; Cleek, G. J.; Dolak, L. A.; Garmon, S. A.;
Morris, J.; Seest, E. P.; Thomas, R. C.; Toops, D. S.; Watt,
W.; Wishka, D. G.; Ford, C. W.; Zurenko, G. E.; Hamel, J. C.;
Schaadt, R. D.; Stapert, D.; Yagi, B. H.; Adams, W. J.; Friis,
J. M.; Slatter, J. G.; Sams, J. P.; Oien, N. L.; Zaya, M. J.;
Wienkers, L. C.; Wynalda, M. A. J. Med. Chem. 2003, 46,
284–302.
(8) Tron, G. C.; Pirali, T.; Billington, R. A.; Canonico, P. L.;
Sorba, G.; Genazzani, A. A. Med. Res. ReV. 2008, 28, 278–
308.
(9) Brik, A.; Alexandratos, J.; Lin, Y.-C.; Elder, J. H.; Olson,
A. J.; Wlodawer, A.; Goodsell, D. S.; Wong, C.-H. Chem-
BioChem 2005, 6, 1167–1169.
(10) Molecular modeling was performed with Spartan’08 for
Macintosh, Wavefunction Inc., Irvine, CA. The lowest energy
conformer for each compound was obtained using molecular
mechanics MMFF base set.
(11) Huisgen, R. In 1,3-Dipolar Cycloaddition Chemistry; Padwa,
A., Ed.; Wiley: New York, 1984; p 1-176.
(12) Huisgen, R.; Knorr, R.; Moebius, L.; Szeimies, G. Chem. Ber.
1965, 98, 4014–4021.
(31) Collin, M.-P.; Hobbie, S. N.; Bottger, E. C.; Vasella, A. HelV.
Chim. Acta 2008, 91, 1838–1848.
(32) Smith, N. M.; Greaves, M. J.; Jewell, R.; Perry, M. W. D.;
Stocks, M. J.; Stonehouse, J. P. Synlett 2009, 1391–1394.
(33) Luesse, S. B.; Wells, G.; Nayek, A.; Smith, A. E.; Kusche,
B. R.; Bergmeier, S. C.; McMills, M. C.; Priestley, N. D.;
Wright, D. L. Bioorg. Med. Chem. Lett. 2008, 18, 3946–3949.
(34) Gerdeman, M. S.; Henkin, T. M.; Hines, J. V. Nucleic Acids
Res. 2002, 30, 1065–1072.
(35) Means, J. A.; Hines, J. V. Bioorg. Med. Chem. Lett. 2005,
15, 2169–2172.
(36) A tabular listing of the fluoresence data used to generate Figure
6 can be found in the Supporting Information.
(13) Tornøe, C. W.; Christensen, C.; Meldal, M. J. Org. Chem.
2002, 67, 3057–3064.
(14) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B.
Angew. Chem., Int. Ed. 2002, 41, 2596–2599.
(15) Moses, J. E.; Moorhouse, A. D. Chem. Soc. ReV. 2007, 36,
1249–1262.
(16) Bock, V. D.; Hiemstra, H.; van Maarseveen, J. H. Eur. J. Org.
Chem. 2006, 51–68.
CC100029Y