Synthesis of deuterated 1,2,3-triazoles

Article abstract of DOI:10.1021/jo301146j

The copper-catalyzed azide-alkyne cycloaddition (CuAAC) is a highly effective method for the selective incorporation of deuterium atom into the C-5 position of the 1,2,3-triazole structure. Reactions of alkynes and azides can be conveniently carried out in a biphasic medium of CH₂Cl ₂/D₂O, using the CuSO₄/Na ascorbate system. The mildness of the method renders it applicable to substrates of relatively high complexity, such as nucleosides. Good yields and high levels of deuterium incorporation were observed. A reaction conducted in equimolar H₂O and D₂O showed 2.7 times greater incorporation of hydrogen atom as compared to deuterium. This is consistent with the H⁺ and D ⁺ ion concentrations in H₂O and D₂O, respectively. With appropriately deuterated precursors, partially to fully deuterated triazoles were assembled where the final deuterium atom was incorporated in the triazole-forming step.

Full text of DOI:10.1021/jo301146j

Article
pubs.acs.org/joc
Synthesis of Deuterated 1,2,3-Triazoles
Hari K. Akula and Mahesh K. Lakshman*
Department of Chemistry, The City College and The City University of New York, 160 Convent Avenue, New York, New York
10031-9198, United States
S
* Supporting Information
ABSTRACT: The copper-catalyzed azide−alkyne cycloaddi-
tion (CuAAC) is a highly effective method for the selective
incorporation of deuterium atom into the C-5 position of the
1,2,3-triazole structure. Reactions of alkynes and azides can be
conveniently carried out in a biphasic medium of CH2Cl2/
D2O, using the CuSO4/Na ascorbate system. The mildness of
the method renders it applicable to substrates of relatively high
complexity, such as nucleosides. Good yields and high levels of
deuterium incorporation were observed. A reaction conducted
in equimolar H2O and D2O showed 2.7 times greater
incorporation of hydrogen atom as compared to deuterium.
This is consistent with the H+ and D+ ion concentrations in
H2O and D2O, respectively. With appropriately deuterated precursors, partially to fully deuterated triazoles were assembled
where the final deuterium atom was incorporated in the triazole-forming step.
A review of the literature indicated that although deuteration
of 1,2,3-triazoles has been accomplished, procedures for C-5
deuteration are not particularly simple as compared to the
CuAAC approach. For instance, C-5 deuterated triazoles can be
obtained from alkynyl aluminum10 or copper11 intermediates or
via lithiation of the triazole (Scheme 1).12 Notably, the isolated
alkynyl copper intermediate in Scheme 1 did not undergo
ligation with azide in the absence of MeCO2H(D).11 In a
INTRODUCTION
■
The Huisgen ligation of azides and alkynes is an exceptionally
atom-economical reaction leading to the formation of 1,2,3-
triazoles.1 However, the thermal process is not regioselective,
resulting in the formation of 1,4- and 1,5-disubstituted 1,2,3-
triazoles. The copper-catalyzed azide−alkyne cycloaddition
(CuAAC) has emerged as an outstanding procedure for access
to 1,4-disubstituted 1,2,3-triazoles, in a regioselective man-
ner.2−4
Scheme 1. Known Syntheses of Deuterated Triazoles
The mechanism of the copper-catalyzed reaction of azides
and terminal alkynes has been actively investigated5−8 and
several notable factors have emerged. Under catalytic
conditions, the reaction is second order in CuI, either due to
the involvement of one Cu each with the azide and the
alkyne,6,7 or due to the involvement of two Cu centers with the
alkyne.5 There has also been a question of the involvement of
alkyne with π-coordinated copper versus a copper acetylide.6−8
In this regard, the experimental evidence suggests intermediacy
of Cu-acetylides from terminal alkynes. This is because the
CuAAC reaction of PhCC−D with PhCH2N3 in t-BuOH/
H2O gave only the C-5 protio triazole,8 consistent with a prior
observation.6 Therefore, CuAAC reactions of alkynes with a
terminal deuterium atom are unlikely to lead to C-5 deuterated
triazoles under aqueous conditions. However, aqueous
conditions produce faster reactions.7 To our knowledge, use
of alkynes with a terminal deuterium atom in azide−alkyne
cycloadditions is rare, and their use would be limited to
processes where the deuterium will not be lost. In one example,
an alkyne with a terminal deuterium atom has been employed
in a thermal intramolecular reaction so as to control the
cycloaddition regiochemistry and to ensure retention of the
heavier isotope.9
Received: June 3, 2012
© XXXX American Chemical Society
A
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a
Table 1. Conditions Tested for the One-pot Triazole Formation and Deuteration
bc
,
entry
solvent, catalytic system, reaction time
product: result
de
,
1
1:1 CH2Cl2/D2O, 2 equiv alkyne, 5 mol % CuSO4, 10 mol % Na ascorbate, 12 h
1-D: 60% yield, 80% D incorporation, reaction was
f
incomplete
gh
,
2
1:1 CH2Cl2/D2O, 2 equiv alkyne, 7 mol % CuSO4, 15 mol % Na ascorbate, 12 h
1:1 CH2Cl2/D2O, 2 equiv alkyne, 10 mol % CuSO4, 20 mol % Na ascorbate, 12 h
1-D: 65% yield, 95% D incorporation, reaction was
i
incomplete
gh
,
3
4
1-D: 75% yield, 96% D incorporation
gh
,
1:1 CH2Cl2/D2O, 2 equiv alkyne, 10 mol % CuSO4, 20 mol % Na ascorbate (dried from D2O), 1-D: 74% yield, 96% D incorporation
12 h
gh
,
j
5
6
1:1 CH2Cl2/D2O, 1 equiv alkyne, 10 mol % CuSO4, 20 mol % Na ascorbate (dried from D2O), 1-D: reaction was incomplete (ca. 80% azide consumed)
12 h
gh
,
j
1:1 CH3CN/D2O, 2 equiv alkyne, 10 mol % CuSO4, 20 mol % Na ascorbate (dried from D2O), 1-D: reaction was incomplete (<5% conversion)
24 h
j
7
8
1:1 CH3CN/H2O, 2 equiv alkyne, 10 mol % CuSO4, 20 mol % Na ascorbate, 5 d
1:1 CH2Cl2/H2O, 2 equiv alkyne, 20 mol % CuCl, 48 h
1-H: reaction was incomplete (<5% conversion)
k
1-H: reaction was incomplete
a
b
Reactions were conducted at room temperature with 0.2 M azide in anhydrous CH2Cl2 or in CH3CN. Where reported, yield is of isolated and
c
purified product. %D incorporation was assessed from the residual H-5 resonance in the 1H NMR spectra. Deuterium resonances are referenced to
d
e
the 2H resonance of CDCl3 (δ = 7.24 ppm). D2O contained 98% D (not a freshly opened sample). CuSO4·5H2O was heated with a heat gun until
f
g
h
the color changed from blue to gray. Phenyl azide (10%) was recovered. D2O contained 99.8% D. CuSO4·5H2O was heated at 120 °C, under
vacuum, until the color changed from blue to gray. Phenyl azide (8%) was recovered. Assessed by H NMR. Assessed by TLC.
i
j
k
1
complementary reaction, a magnesiated alkyne yielded the C-4
deuterated triazole.13 Dideuterotriazoles can be made from
acetylene gas generated in situ from CaC2, in the presence of
Et3N/D2O.14
acetylide.7 These mechanistic considerations supported our
one-pot triazole-forming, deuteration strategy.
In recent work20 with the CuAAC reactions of 6-azido purine
nucleosides we had encountered a significant problem that is
not typical in the reactions of simpler azides. That is, the azido
group underwent competing reduction in the presence of
aqueous CuSO4/Na ascorbate.20 To remedy this, we resorted
to a biphasic reaction medium, which suppressed the undesired
azide reduction and gave good to excellent product recoveries.
This led us to reason that use of biphasic reaction conditions
with cheap, commercially available D2O as one phase, should
allow for capture of a deuterium atom by the C-4 cuprated
intermediates formed in the CuAAC while suppressing other
undesired processes.
Despite the widespread application of the CuAAC reaction
and its possible use for the deuteration of triazoles, we were
surprised to find the absence of a general method for this
purpose.15 In the broader context, the importance of isotopic
labeling is well-recognized, for example, in mechanistic and
biosynthetic considerations, mass spectrometry applications,
and in metabolism studies, to name a few. The 1,2,3-triazolyl
moiety is also prominent in medicinal chemistry, where it has
been likened to an amide linkage, with the N-3 atom serving as
a hydrogen-bond acceptor and the C-4 atom the hydrogen-
bond donor.16−18 However, in contrast to amides, the triazole
ring is chemically and biologically robust. These considerations
have led to the design of bioactive entities containing a 1,2,3-
triazolyl ring.16,17 Additionally, “heavy drugs”, namely pharma-
ceuticals that contain one or more deuterium atom(s) in place
of hydrogen(s), have received increased attention due to the
positive attributes gained upon deuteration.19 On the basis of
these overall considerations, a method to deuterated triazoles is
likely to be of broad relevance. Herein we report a simple, mild,
and general route to deuterated 1,2,3-triazoles wherein
introduction of the deuterium atom at the C-4 position occurs
in the triazole-forming step.
With these considerations we conducted a series of initial
optimization reactions (Table 1). We opted to desiccate
CuSO4·5H2O in order to increase the extent of deuterium
incorporation by eliminating as much water as possible. Entry 1
in Table 1 indicates proof of principle. Here, simply drying the
CuSO4·5H2O with a heat gun, use of D2O with 98% D, and use
of low catalyst load, gave a respectable product yield and %D
incorporation, but the reaction was incomplete. Use of better
conditions (more rigorously dried CuSO4 and D2O with 99.8%
D), gave excellent D incorporation, but again the reaction
remained incomplete (entry 2). Complete reaction, with 96% D
incorporation was achieved by increasing the amounts of
CuSO4 and Na ascorbate (entry 3). In this case %D
incorporation was evaluated in two ways. Use of CH2Cl2 as
an internal NMR standard indicated 96% D whereas assess-
ment by comparison of the residual H-5 to other product
resonances indicated 94% D. In an attempt to further improve
the extent of D incorporation, a reaction was carried out under
conditions of entry 3, except that Na ascorbate was evaporated
from D2O under vacuum prior to its use in the reaction. Under
these conditions (entry 4), practically no further improvement
in %D incorporation was observed and product yield remained
essentially unchanged. Next, the amount of alkyne was lowered
RESULTS AND DISCUSSION
■
Of importance to the success of the approach would be the
formation of Cu-acetylides as intermediates in CuAAC
reactions. It has been proposed that π-coordination of CuI
increases the acidity of the alkynyl proton, rendering the
formation of Cu-acetylides feasible in aqueous media.7 This
implies that terminal alkynes can be directly utilized since the
alkynyl proton would be lost early in the process. Azide
coordination to the Cu center occurs after formation of the Cu-
B
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a e
−
so as to reduce the amount of a proton source, but here
incomplete reaction was observed (entry 5).
Table 2. Generality of the Triazole Deuteration Protocol
Attempts were then made to evaluate whether a water-
miscible solvent offered any advantage. Use of CH3CN led to
less than 5% product formation in 24 h (entry 6). Surprised by
this result, we conducted a reaction with H2O rather than with
D2O, over an extended period. Again, less than 5% product
formation was observed in 5 days (entry 7, a repeat of this
experiment gave a comparable result). A prior report
documents the failure of azide−alkyne ligation reactions with
CuSO4·5H2O/Na ascorbate in CH3CN/H2O, DMSO/H2O,
EtOH/H2O, t-BuOH/H2O, and other solvent combinations.21
In that study, the superiority of the CH2Cl2/H2O system led
the authors to propose a rate-enhancing influence of this
solvent combination on the CuAAC reactions.21 Finally, in
comparison to the CuSO4/Na ascorbate system (entries 3 and
4), CuCl was inferior at catalyzing this reaction (entry 8).
Having completed these initial studies, we next focused on
evaluating the generality of this regioselective deuteration.
Product structures, yields, and %D incorporation are shown in
Table 2.
As can be seen from Table 2, generally good-excellent
product yields were obtained, with excellent D incorporation
(92−98%). From a medicinal chemistry perspective, com-
pounds 1-D to 7-D are structurally very similar to resveratrol
analogues that have shown more potent cytotoxic and
antiproliferative activity than resveratrol.22 Compound 9-D is
a deuterated version of a highly active nicotinic acetylcholine
receptor modulator.23 Although a 54% yield of the protio
analogue 9-H is reported in the literature,23 under our
conditions both 9-H and 9-D were obtained in 70% yield.
Even the more complex nucleoside substrates gave high yields
and showed excellent D incorporation. The 96% yield of 10-D
compares very favorably to the microwave-mediated CuAAC
reactions of AZT.24 Protio triazolyl nucleoside analogues such
as 10-D, derived from AZT, have proven to be excellent
substrates for thymidine kinase of the pathogen Ureaplasma
parvum.24 We have previously shown that the C-6 azido purine
nucleoside precursor to 11-D exhibits significant azide-tetrazole
equilibrium and is prone to facile reduction under CuAAC
conditions.20 However, as seen here, this substrate reacted
smoothly. These results clearly indicate that the reaction
conditions are generally very effective for a broad range of
substrates.
a
Reactions were conducted at room temperature with 0.2 M azide and
b
c
2 mol equiv of alkyne. Yields are of isolated and purified products. %
D incorporation was assessed from the residual H-5 resonance in the
1H NMR spectra. Deuterium resonances are referenced to the 2H
d
resonance of CDCl3 (δ = 7.24 ppm). Syntheses of compounds 2-D to
In comparing protonation to deuteration, the former should
be a more facile reaction due to the difference in the O−H and
O−D bond energies.25 To assess the relative difference in
protonation versus deuteration when both processes compete
in the triazole-forming-deuteration reactions, two reactions of
phenyl azide with 4-ethynyltoluene were conducted in parallel.
One reaction was with D2O (99.8%) only and the other was
with equimolar H2O/D2O (99.8%). By 1H NMR analysis, using
CH2Cl2 as an internal standard, the amount of 1-H formed in
the reaction with only D2O was estimated to be 4%, whereas in
the H2O/D2O reaction 1-H was formed to an extent of 73%
(77% observed − 4% formed in the control experiment). The
isolated product yields from the two reactions were
comparable, 75% for the D2O reaction and 76% in the H2O/
D2O reaction. The ratio of 1-H/1-D formed in the latter
experiment was 2.7. It is therefore plausible that the greater
proportion of 1-H as compared to 1-D results from a more
rapid protonation of the cuprated triazole. This could be a
contributing factor toward the amounts of the protio products
10-D were performed using 10 mol % CuSO4 (0.048 M in 99.8%
D2O) and 20 mol % Na ascorbate (0.096 M in 99.8% D2O).
e
Synthesis of 11-D was performed using 5 mol % CuSO4 (0.048 M in
99.8% D2O) and 10 mol % Na ascorbate (0.096 M in 99.8% D2O).
formed in these reactions, which exceed what would be
predicted based solely upon the deuterium content of the D2O
used.
Although monodeuteration reactions proceeded efficiently,
we were curious to assess the ability to build poly- and fully
deuterated molecules by this general methodology, where final
deuteration of the triazole occurred in the CuAAC step.
Therefore, using the optimized conditions, the synthesis of
three compounds was undertaken (Scheme 2). For this, phenyl
26−28
29−32
azide-D5
and ethynylbenzene-D5
were synthesized
from bromobenzene-D5 (99% D).
Reaction of phenyl azide-D5 with 4-ethynyltoluene yielded
12-D6, whereas reaction of TBDMS-protected AZT with
C
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MHz in CDCl3 and are referenced to the solvent resonance. 2H NMR
spectra were recorded at 77 MHz using CDCl3 as an internal standard.
For this, first the H NMR spectrum of CDCl3 was recorded at 500
Scheme 2. Synthesis of Poly- and Fully-deuterated 1,2,3-
Triazoles
1
MHz and the residual protonated solvent resonance was set to δ 7.26
ppm. Next, the 2H NMR spectrum of the same sample was recorded at
77 MHz, and this showed a resonance at δ 7.24 ppm. From this
analysis, CDCl3 was referenced to δ 7.24 ppm for all 2H NMR
experiments. The 19F NMR spectrum was recorded at 282 MHz using
CFCl3 as an internal standard. Chemical shifts (δ) are reported in parts
per million (ppm) and coupling constants (J) are in hertz (Hz).
HRMS analyses were performed using a TOF analyzer, the ionization
methods are provided in the compound characterization.
Synthesis of 3-Ethynylpyridine. Step 1. Synthesis of 3-
((Triisopropylsilyl)ethynyl)pyridine. Following a literature proce-
dure,31 in a clean, dry, round-bottom flask equipped with a stirring
bar, 3-bromopyridine (122 μL, 1.26 mmol) was dissolved in iPr2NH
(5 mL). TIPS-acetylene (336 μL, 1.512 mmol), PdCl2(Ph3P)2 (44.0
mg, 0.063 mmol) and CuI (12.0 mg, 0.063 mmol) were added, and the
reaction mixture was stirred and heated at 100 °C under a reflux
condenser for 1 h, in a nitrogen atmosphere. The reaction mixture was
diluted with EtOAc (20 mL) and filtered through Celite. The filtrate
was washed with deionized H2O (3 × 20 mL) and brine (15 mL). The
organic layer was separated, dried over anhydrous Na2SO4, and
concentrated under reduced pressure. Purification of the crude
material, by passing it through a short silica gel plug with initial
elution using hexanes followed by 5% EtOAc in hexanes, gave 294 mg
(90% yield) of TIPS-protected ethynylpyridine as a pale-yellow,
ethynylbenzene-D5 gave 13-D6, a more extensively deuterated
analogue of 10-D. Finally, reaction of phenyl azide-D5 with
ethynylbenzene-D5 gave 14-D11, which is a fully deuterated
version of 2-D. %D incorporation in 12-D6 and 13-D6 was
assessed from the residual H-5 triazolyl resonances in the H
NMR spectra. In the case of 14-D11, this assessment was done
1
1
viscous liquid. Rf (SiO2/10% EtOAc in hexanes) = 0.40. H NMR
with CH2Cl2 as an internal standard.
(500 MHz, CDCl3): δ 8.69 (s, 1H, H-2), 8.51 (d, 1H, H-6, J = 4.1
Hz), 7.73 (dt, 1H, H-4, J = 1.9, 7.8 Hz), 7.22 (dd, 1H, H-5, J = 4.9, 7.8
Hz), 1.13 (s, 21H, Si(iPr)3). 13C NMR (125 MHz, CDCl3): δ 153.0,
148.8, 139.0, 123.0, 120.9, 103.8, 95.1, 18.7, 11.6. HRMS (ESI)
calculated for C16H26NSi [M + H]+ 260.1829, found 260.1835.
Step 2. Synthesis of 3-Ethynylpyridine.33 Following a literature
procedure,34 in a clean, dry, round-bottom flask equipped with a
stirring bar, TIPS-protected ethynylpyridine (286 mg, 1.102 mmol)
was dissolved in dry MeOH (15 mL). Powdered KOH (433 mg, 7.72
mmol) was added and the reaction mixture was stirred at 45 °C for 24
h. To the reaction mixture was added a saturated aqueous NH4Cl
solution and the mixture was extracted with Et2O (3 × 15 mL). The
organic layer was separated, washed with brine (10 mL), dried over
anhydrous Na2SO4, and carefully evaporated. Purification of the crude
material on a short silica gel column using 10% Et2O in hexanes
yielded 51.0 mg (45% yield) of 3-ethynylpyridine as a white solid. Rf
(SiO2/20% Et2O in hexanes) = 0.39. 1H NMR (500 MHz, CDCl3): δ
8.73 (s, 1H, H-2), 8.57 (d, 1H, H-6, J = 4.6 Hz), 7.77 (d, 1H, H-4, J =
7.8 Hz), 7.37 (t, 1H, H-5, J = 6.4 Hz), 3.22 (s, 1H, CH).
CONCLUSIONS
■
In summary, a straightforward and mild procedure for
regioselective C-5 deuteration of 1,2,3-triazoles has been
developed via the CuAAC protocol, utilizing desiccated
CuSO4 and Na ascorbate. Cuprated triazoles formed in these
reactions capture deuterium from cheap and readily available
D2O. Use of biphasic CH2Cl2/D2O for these reactions
eliminates certain problems, such as azide reduction encoun-
tered during the CuAAC reactions of azido nucleosides, and
this combination is superior to CH3CN/D2O. Mono to fully
deuterated compounds can be readily assembled via this
methodology. It is foreseeable that this deuteration process can
be coupled with the incorporation of other atomic isotopes,
such as 13C and/or 15N, to yield multiply labeled compounds.
All these factors contribute to the importance of the described
chemistry. This simple deuteration method circumvents
chemical manipulations of the triazole that may not be easily
accomplished with molecules of increased complexity, and this
is also likely to be of value in medicinal chemistry applications.
Synthesis of Ethynylbenzene-D5. Step 1. Synthesis of
Triisopropyl(phenylethynyl)silane-D5. Following a literature proce-
EXPERIMENTAL SECTION
■
General Experimental Considerations. Thin layer chromatog-
raphy was performed on aluminum foil-backed TLC plates of 200 μm
thickness and column chromatographic purifications were performed
on 200−300 mesh silica gel. CH2Cl2 and MeCN were distilled over
CaH2, Et2O was distilled over LiAlH4 and then over Na. All other
reagents were obtained from commercial sources and were used
without further purification. Glassware used for reactions was dried at
150 °C in an oven and cooled in a desiccator. Melting points reported
dure,31 in a clean, dry, round-bottom flask equipped with a stirring bar,
bromobenzene-D5 (500 mg, 3.085 mmol) was dissolved in iPr2NH
(12.5 mL). TIPS-acetylene (823 μL, 3.702 mmol), PdCl2(Ph3P)2
(108.3 mg, 0.154 mmol) and CuI (29.4 mg, 0.154 mmol) were added,
and the reaction mixture was stirred and heated under a reflux
condenser at 100 °C for 1.5 h, in a nitrogen atmosphere. The reaction
mixture was diluted with EtOAc (20 mL) and filtered through Celite.
The filtrate was washed with deionized H2O (3 × 20 mL) and brine
(15 mL). The organic layer was separated, dried over anhydrous
1
are of chromatographically purified materials and are uncorrected. H
NMR spectra were recorded at 500 MHz and are referenced to the
residual solvent resonance. 13C NMR spectra were recorded at 125
D
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Na2SO4, and concentrated under reduced pressure. Purification of the
crude material, by passing it through a short silica gel plug using
hexanes as the eluting solvent gave 500 mg (61% yield) of TIPS-
protected ethynylbenzene as a colorless, viscous liquid. Rf (hexanes/
SiO2) = 0.70. 1H NMR (500 MHz, CDCl3): δ 1.16 (s, 21H, Si(iPr)3).
13C NMR (125 MHz, CDCl3): δ 131.8 (t, J = 24.8 Hz), 128.0 (t, J =
Phenyl azide-D5.27
Following a literature procedure,28 in a clean, dry, round-bottom flask
equipped with a stirring bar, bromobenzene-D5 (400 mg, 2.468 mmol)
was dissolved in 7:3 EtOH/H2O (4.8 mL). N,N′-Dimethylethylenedi-
amine (40 μL, 0.37 mmol), NaN3 (321 mg, 4.936 mmol), Na
ascorbate (24.4 mg, 0.123 mmol), and CuI (47 mg, 0.247 mmol) were
added, and the mixture was stirred and heated at 100 °C under a reflux
condenser for 2 h, in an argon atmosphere. The mixture was cooled to
room temperature, and diluted with Et2O (20 mL) and deionized H2O
(10 mL). The aqueous layer was separated and extracted with Et2O (3
× 20 mL). The organic layers were combined and washed with brine
(10 mL), dried over anhydrous Na2SO4 and concentrated under
reduced pressure. Chromatography of the crude material on a short
silica gel column using hexanes yielded 261 mg (85% yield) of the title
compound as a yellow liquid. Rf (SiO2/hexanes) = 0.50. 13C NMR
(125 MHz, CDCl3): δ 139.8, 129.2 (t, J = 24.2 Hz), 124.3 (t, J = 24.2
Hz), 118.6 (t, J = 24.2 Hz). 2H NMR (77 MHz, CHCl3): δ 7.29, 7.08,
6.98. Phenyl azide-D5 has previously been synthesized by diazotization
of aniline-D5.27
2
24.0 Hz), 127.8 (t, J = 24.5 Hz), 123.6, 107.3, 90.6, 18.9, 11.6. H
NMR (77 MHz, CHCl3): δ 7.51, 7.33, 7.20. HRMS (ESI) calculated
for C17H21D5Si [M]+ 263.2112, found 263.2101.
Step 2. Synthesis of Ethynylbenzene-D5.30 By modifying a
literature procedure,32 in a clean, dry, 25 mL round-bottom flask
equipped with a stirring bar, TIPS-protected ethynylbenzene-D5 (700
mg, 2.656 mmol) was dissolved in dry Et2O (11 mL) with stirring. A 1
M solution of n-Bu4N+F− in THF (3.2 mL, 3.2 mmol) was added and
the mixture was stirred for 5 min. The mixture was concentrated under
a stream of nitrogen gas and loaded onto a short silica gel column.
Elution with hexanes, followed by careful rotary evaporation of the
fractions containing the product using a water bath at ≤65 °C, gave
171 mg (61% yield) of ethynylbenzene-D5 as a pale-yellow liquid. Rf
1
(SiO2/hexanes) = 0.42. H NMR (500 MHz, CDCl3): δ 3.08 (s, 1H,
2
CH). H NMR (77 MHz, CHCl3): δ 7.52, 7.38, 7.35.
Synthesis of Azides. The C-6 azido purine ribonucleoside
precursor20 and 3′-azido-3′-deoxy-5′-O-(t-butyldimethylsilyl)-
thymidine35 were synthesized as described in the literature. Unless
mentioned otherwise, all other azides were synthesized from the
corresponding boronic acids.36
General Procedure for the Synthesis of Deuterated
Triazoles (1-D to 14-D11). In a clean, oven-dried, 10 mL round-
bottom flask equipped with a stirring bar, was placed the appropriate
azide (0.335 mmol) in 1.6 mL of dry CH2Cl2. To this stirring mixture
the appropriate alkyne (0.67 mmol) was added. In a separate vial
CuSO4·5H2O (8.4 mg, 0.0335 mmol, 10 mol %) was heated at 120 °C
under vacuum until the color changed from blue to gray. Using this
desiccated CuSO4, a 0.048 M solution was prepared in a glovebag by
the addition of D2O (99.8% D, 0.7 mL), and this solution was
transferred to the reaction mixture. To the reaction mixture a 0.096 M
solution of Na ascorbate (13.3 mg in 0.7 mL of 99.8% D2O, 20 mol %)
was added. The reaction mixture was sealed and stirred in a nitrogen
atmosphere at room temperature until TLC showed consumption of
azide. The organic layer of the reaction mixture was separated and the
aqueous layer was back extracted with EtOAc (3 × 5 mL). The
combined organic layer was washed with brine (5 mL), dried over
anhydrous Na2SO4, and concentrated under reduced pressure. The
crude material was purified by chromatography on a silica gel column.
See compound headings below for details.
4-(t-Butyl)phenyl azide.37
In a clean 10 mL round-bottom flask equipped with a stirring bar, 4-(t-
butyl)phenylboronic acid (356 mg, 2 mmol) was dissolved in MeOH
(6 mL). NaN3 (156 mg, 2.4 mmol) and CuSO4·5H2O (50 mg, 0.2
mmol) were added to the reaction mixture, and the mixture was stirred
in an open flask at room temperature for 16 h. The solvent was
evaporated under reduced pressure and EtOAc (10 mL) was added.
The mixture was extracted with H2O (10 mL) and the aqueous layer
was back extracted with EtOAc (3 × 10 mL). The combined organic
layers were dried over Na2SO4 and concentrated under reduced
pressure. Chromatography of the crude material on a short silica gel
plug using hexanes yielded 311.5 mg (89% yield) of the title
compound as an orange-red liquid. Rf (SiO2/hexanes) = 0.60. 1H
NMR (500 MHz, CDCl3): δ 7.38 (d, 2H, Ar−H, J = 8.6 Hz), 6.98 (d,
2H, Ar−H, J = 8.6 Hz), 1.32 (s, 9H, t-Bu). 4-(t-Butyl)phenyl azide has
previously been synthesized by diazotization of 4-t-butylaniline.37
m-Azidobenzonitrile.38
5-Deutero-1-phenyl-4-(p-tolyl)-1H-1,2,3-triazole (1-D).12a
Chromatography using hexanes followed by 20% EtOAc in hexanes
gave 59.5 mg (75% yield) of 1-D as an off-white solid. Mp = 156−158
°C. Rf (SiO2/25% EtOAc in hexanes) = 0.34. H NMR (500 MHz,
1
CDCl3): δ 7.82−7.79 (m, 4H, Ar−H), 7.55 (t, 2H, Ar−H, J = 7.4 Hz),
7.46 (t, 1H, Ar−H, J = 7.3 Hz), 7.28 (d, 2H, Ar−H, J = 7.4 Hz), 2.41
(s, 3H, CH3). 13C NMR (125 MHz, CDCl3): δ 148.7, 138.5, 137.5,
129.9, 129.8, 128.8, 127.8, 126.1, 120.7, 117.2 (t, J = 30.4 Hz), 21.4.
2H NMR (77 MHz, CHCl3): δ 8.19. HRMS (ESI) calculated for
C15H13DN3 [M + H]+ 237.1245, found 237.1248.
Assessment of %D Incorporation Using an External Standard.
CH2Cl2 (16 μL, 0.25 mmol) was added to a solution of the product
(11.8 mg, 0.05 mmol) in CDCl3 (0.5 mL). The 1H NMR spectrum of
this solution was acquired and the resonances were integrated. The
signal at δ 5.30 ppm (CH2Cl2) was set to 10 whereby the signal at δ
8.16 ppm (residual triazolyl C5−H) integrated to 0.04. Thus, the %D
incorporation in the reaction was estimated to be 4%.
Following a literature procedure,39 in a clean, dry, round-bottom flask
equipped with a stirring bar, 3-aminobenzonitrile (200 mg, 1.69
mmol) was dissolved in dry MeCN (4 mL) and cooled to 0 °C. To the
stirring solution, t-butyl nitrite (300 μL, 2.54 mmol) was added
dropwise, followed by dropwise addition of Me3SiN3 (270 μL, 2.03
mmol). The mixture was warmed to room temperature and stirred for
2 h. This reaction mixture was diluted with EtOAc (15 mL) and
washed with deionized H2O (3 × 15 mL), and brine (10 mL). The
organic layer was separated, dried over anhydrous Na2SO4, and
concentrated under reduced pressure. Chromatography of the crude
material on a silica gel column using 5% EtOAc in hexanes yielded 190
mg (78% yield) of the title compound as a brown solid. Rf (SiO2/10%
EtOAc in hexanes) = 0.30. 1H NMR (500 MHz, CDCl3): δ 7.49−7.42
(m, 2H), 7.29−7.26 (m, 2H). m-Azidobenzonitrile has previously been
synthesized by diazotization of m-cyanoaniline.38
5-Deutero-1,4-diphenyl-1H-1,2,3-triazole (2-D).
E
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2
Chromatography using hexanes followed by 20% EtOAc in hexanes
gave 53.5 mg (72% yield) of 2-D as a white solid. Mp = 183−185 °C.
Rf (SiO2/25% EtOAc in hexanes) = 0.34. 1H NMR (500 MHz,
CDCl3): δ 7.92 (d, 2H, Ar−H, J = 8.1 Hz), 7.80 (d, 2H, Ar−H, J = 7.8
Hz), 7.55 (t, 2H, Ar−H, J = 7.8 Hz), 7.48−7.45 (m, 3H, Ar−H), 7.37
(t, 1H, Ar−H, J = 7.4 Hz). 13C NMR (125 MHz, CDCl3): δ 148.6,
137.4, 130.6, 130.0, 129.1, 128.9, 128.6, 126.2, 120.8, 117.6 (s, J = 28.1
Hz). 2H NMR (77 MHz, CHCl3): δ 8.22. HRMS (ESI) calculated for
C14H11DN3 [M + H]+ 223.1089, found 223.1086.
126.0, 120.4, 117.8 (t, J = 28.9 Hz), 35.0, 31.5. H NMR (77 MHz,
CHCl3): δ 8.20. HRMS (ESI) calculated for C18H19DN3 [M + H]+
279.1715, found 279.1709.
5-Deutero-1-(naphthalen-1-yl)-4-phenyl-1H-1,2,3-triazole
(7-D).
5-Deutero-1-(4-methoxyphenyl)-4-(p-tolyl)-1H-1,2,3-triazole
(3-D).
Chromatography using hexanes followed by 20% EtOAc in hexanes
gave 80.0 mg (72% yield) of 7-D as a brown solid. Mp = 86−88 °C. Rf
1
(SiO2/25% EtOAc in hexanes) = 0.34. H NMR (500 MHz, CDCl3):
δ 8.00−7.92 (m, 4H, Ar−H), 7.69 (d, 1H, Ar−H, J = 8.3 Hz), 7.59−
7.49 (m, 4H, Ar−H), 7.46 (t, 2H, Ar−H, J = 7.7 Hz), 7.04 (dt, 1H,
Ar−H, J = 1.0, 7.4 Hz). 13C NMR (125 MHz, CDCl3): δ 147.9, 134.5,
134.0, 130.6, 130.5, 129.1, 128.9, 128.6, 128.5, 128.1, 127.3, 126.1,
125.2, 123.7, 122.6, 122.2 (t, J = 28.6 Hz). 2H NMR (77 MHz,
CHCl3): δ 8.17. HRMS (ESI) calculated for C18H13DN3 [M + H]+
273.1245, found 273.1247.
Chromatography using hexanes followed by 20% EtOAc in hexanes
gave 89.0 mg (87% yield) of 3-D as a white solid. Mp = 174−176 °C.
Rf (SiO2/25% EtOAc in hexanes) = 0.26. 1H NMR (500 MHz,
CDCl3): δ 7.80 (d, 2H, Ar−H, J = 7.6 Hz), 7.67 (d, 2H, Ar−H, J = 8.6
Hz), 7.26 (d, 2H, Ar−H, J = 7.6 Hz), 7.02 (d, 2H, Ar−H, J = 8.6 Hz),
3.87 (s, 3H, OCH3), 2.40 (s, 3H, CH3). 13C NMR (125 MHz,
CDCl3): δ 159.9, 148.3, 138.4, 130.7, 129.7, 127.7, 125.9, 122.3, 117.5
(t, J = 28.9 Hz), 114.9, 55.8, 21.5. 2H NMR (77 MHz, CHCl3): δ 8.10.
HRMS (ESI) calculated for C16H15DN3O [M + H]+ 267.1351, found
267.1356.
5-Deutero-1-(4-methoxyphenyl)-4-(N-phthalimidomethyl)-
1H-1,2,3-triazole (8-D).
5-Deutero-4-(4-fluorophenyl)-1-(4-methoxyphenyl)-1H-
1,2,3-triazole (4-D).
Chromatography using hexanes followed by 40% EtOAc in hexanes
gave 80.0 mg (71% yield) of 8-D as an off-white solid. Mp = 181−183
1
°C. Rf (SiO2/50% EtOAc in hexanes) = 0.40. H NMR (500 MHz,
CDCl3): δ 7.85 (dd, 2H, Ar−H, J = 3.1, 5.3 Hz), 7.72 (dd, 2H, Ar−H,
J = 3.1, 5.3 Hz), 7.57 (d, 2H, Ar−H, J = 8.9 Hz), 6.97 (d, 2H, Ar−H, J
= 8.9 Hz), 5.06 (s, 2H, CH2), 3.83 (s, 3H, OCH3). 13C NMR (125
MHz, CDCl3): δ 167.8, 159.9, 143.3, 134.3, 132.2, 130.5, 123.6, 122.4,
121.1 (t, J = 28.8 Hz), 114.8, 55.8, 33.2. 2H NMR (77 MHz, CHCl3):
δ 7.97. HRMS (ESI) calculated for C18H14DN4O3 [M + H]+ 336.1201,
found 336.1204.
Chromatography using hexanes followed by 20% EtOAc in hexanes
gave 90.5 mg (70% yield) of 4-D as an off-white solid. Mp = 184−186
1
°C. Rf (SiO2/25% EtOAc in hexanes) = 0.22. H NMR (500 MHz,
CDCl3): δ 7.89−7.86 (m, 2H, Ar−H), 7.67 (d, 2H, Ar−H, J = 8.9 Hz),
7.14 (t, 2H, Ar−H, J = 8.6 Hz), 7.04 (d, 2H, Ar−H, J = 8.9 Hz), 3.88
(s, 3H, OCH3). 13C NMR (125 MHz, CDCl3): δ 163.1 (d, J = 247.7
Hz), 160.3, 147.5, 130.8, 127.8 (d, J = 8.1 Hz), 127.0 (d, J = 3.2 Hz),
2
1-(3-Cyanophenyl)-4-(pyridin-3-yl)-1H-1,2,3-triazole (9-H).23
122.4, 117.6 (t, J = 28.9 Hz), 116.1 (d, J = 21.8 Hz), 115.1, 55.9. H
NMR (77 MHz, CHCl3): δ 8.09. 19F NMR (282 MHz, CDCl3): δ
−113.8 (relative to CFCl3). HRMS (ESI) calculated for
C15H12DFN3O [M + H]+ 271.1100, found 271.1105.
5-Deutero-1-(4-methoxyphenyl)-4-phenyl-1H-1,2,3-triazole
(5-D).
In a clean, oven-dried, 10 mL round-bottom flask equipped with a
stirring bar, m-azidobenzonitrile (57 mg, 0.335 mmol) was dissolved in
CH2Cl2 (1.6 mL). 3-Ethynylpyridine (69 mg, 0.67 mmol) was added
to the flask, followed by CuSO4·5H2O (8.4 mg, 0.0335 mmol), Na
ascorbate (13.3 mg, 0.067 mmol), and H2O (1.4 mL). The mixture
was stirred at room temperature for 48 h and then diluted with
CH2Cl2 (5 mL). The aqueous layer was separated and back extracted
with CH2Cl2 (3 × 5 mL). The combined organic layers were washed
with brine (5 mL), dried over anhydrous Na2SO4, and concentrated
under reduced pressure. Chromatography of the crude material on a
short silica gel plug by sequential elution with 10% EtOAc in hexanes
followed by EtOAc, gave 58.0 mg (70% yield) of 9-H as an off-white
solid. Mp = 215−217 °C (lit. 214−216 °C23). Rf (SiO2/EtOAc) =
0.34. 1H NMR (500 MHz, CDCl3): δ 9.13 (br s, 1H, Ar−H), 8.68 (br
s, 1H, Ar−H), 8.33 (s, 1H, Ar−H), 8.31 (d, 1H, Ar−H, J = 7.7 Hz),
8.15 (t, 1H, Ar−H, J = 1.5 Hz), 8.11 (ddd, 1H, Ar−H, J = 1.1, 2.1, 8.1
Hz), 7.79 (dt, 1H, Ar−H, J = 1.2, 7.8 Hz), 7.73 (t, 1H, Ar−H, J = 7.9
Hz), 7.47 (br s, 1H, Ar−H). 13C NMR (125 MHz, CD3OD, 55 °C): δ
150.2, 147.8, 146.8, 139.1, 135.2, 133.7, 132.5, 128.4, 126.1, 125.7,
125.1, 121.4, 118.7, 115.4.
Chromatography using hexanes followed by 20% EtOAc in hexanes
gave 77.0 mg (91% yield) of 5-D as a white solid. Mp = 166−169 °C.
Rf (SiO2/25% EtOAc in hexanes) = 0.23. 1H NMR (500 MHz,
CDCl3): δ 7.90 (d, 2H, Ar−H, J = 7.8 Hz), 7.69 (d, 2H, Ar−H, J = 8.9
Hz), 7.46 (t, 2H, Ar−H, J = 7.6 Hz), 7.37 (t, 1H, Ar−H, J = 7.4 Hz),
7.04 (d, 2H, Ar−H, J = 8.9 Hz), 3.88 (s, 3H, OCH3). 13C NMR (125
MHz, CDCl3): δ 160.2, 148.4, 130.9, 130.8, 129.1, 128.5, 126.1, 122.4,
2
117.8 (t, J = 28.3 Hz), 115.1, 55.9. H NMR (77 MHz, CHCl3): δ
8.16. HRMS (ESI) calculated for C15H13DN3O [M + H]+ 253.1194,
found 253.1199.
1-(4-(t-Butyl)phenyl)-5-deutero-4-phenyl-1H-1,2,3-triazole
(6-D).
1-(3-Cyanophenyl)-5-deutero-4-(pyridin-3-yl)-1H-1,2,3-tria-
zole (9-D).
Chromatography using hexanes followed by 20% EtOAc in hexanes
gave 93.3 mg (85% yield) of 6-D as an off-white solid. Mp = 153−156
1
°C. Rf (SiO2/25% EtOAc in hexanes) = 0.46. H NMR (500 MHz,
CDCl3): δ 7.92 (d, 2H, Ar−H, J = 8.1 Hz), 7.70 (d, 2H, Ar−H, J = 8.5
Hz), 7.53 (d, 2H, Ar−H, J = 8.5 Hz), 7.44 (t, 2H, Ar−H, J = 7.6 Hz),
7.35 (dt, 1H, Ar−H, J = 1.0, 7.4 Hz), 1.38 (s, 9H, t-Bu). 13C NMR
(125 MHz, CDCl3): δ 152.3, 148.3, 134.8, 130.5, 129.1, 128.5, 126.8,
Chromatography using 10% EtOAc in hexanes followed by EtOAc
gave 52.8 mg (70% yield) of 9-D as an off-white solid. Mp = 218−220
F
dx.doi.org/10.1021/jo301146j | J. Org. Chem. XXXX, XXX, XXX−XXX

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°C. Rf (SiO2/EtOAc) = 0.34. 1H NMR (500 MHz, CDCl3): δ 9.17 (br
s, 1H, Ar−H), 8.73 (br s, 1H, Ar−H), 8.31 (d, 1H, Ar−H, J = 7.9 Hz),
8.15 (t, 1H, Ar−H, J = 1.6 Hz), 8.11 (ddd, 1H, Ar−H, J = 1.1, 2.2, 8.1
Hz), 7.79 (dt, 1H, Ar−H, J = 1.3, 7.7 Hz), 7.74 (t, 1H, Ar−H, J = 7.9
Hz), 7.47 (br s, 1H, Ar−H). 13C NMR (125 MHz, CD3OD, 55 °C): δ
150.2, 147.8, 146.8, 139.1, 135.2, 133.7, 132.5, 128.4, 126.1, 125.7,
125.1, 121.2 (t, J = 29.6 Hz), 118.7, 115.4. 2H NMR (77 MHz,
CHCl3): δ 8.38. HRMS (ESI) calculated for C14H9DN5 [M + H]+
249.0993, found 249.0997.
−4.7, −5.1. 2H NMR (77 MHz, CHCl3): δ 9.35. HRMS (ESI)
calculated for C37H60DN7O4Si3Na [M + Na]+ 775.4048, found
775.4046.
5-Deutero-1-phenyl-D5-4-(p-tolyl)-1H-1,2,3-triazole (12-D6).
Chromatography using hexanes followed by 20% EtOAc in hexanes
5′-O-(t-Butyldimethylsilyl)-3′-deoxy-3′-(5-deutero-4-(p-
tolyl)-1H-1,2,3-triazol-1-yl)thymidine (10-D).
gave 60.5 mg (75% yield) of 12-D6 as an off-white solid. Mp = 153−
1
155 °C. Rf (SiO2/50% EtOAc in hexanes) = 0.60. H NMR (500
MHz, CDCl3): δ 7.83 (d, 2H, Ar−H, J = 7.8 Hz), 7.29 (d, 2H, Ar−H, J
= 7.8 Hz), 2.42 (s, 3H, −CH3). 13C NMR (125 MHz, CDCl3): δ
148.6, 138.5, 137.2, 129.8, 129.5 (t, J = 25.0 Hz), 128.4 (t, J = 25.0
Hz), 127.6, 126, 120.3 (t, J = 24.9 Hz), 117.2 (t, J = 29.4 Hz), 21.5. 2H
NMR (77 MHz, CHCl3): δ 8.19, 7.82, 7.58, 7.49. HRMS (ESI)
calculated for C15H8D6N3 [M + H]+ 242.1559, found 242.1553.
5′-O-(t-Butyldimethylsilyl)-3′-deoxy-3′-(5-deutero-4-(phe-
nyl-D5)-1H-1,2,3-triazol-1-yl)thymidine (13-D6).
For this reaction 0.131 mmol of azide, 0.262 mmol of alkyne, 10 mol
% of anhydrous CuSO4 in 273 μL of D2O, 20 mol % of Na ascorbate
in 273 μL of D2O, and 0.65 mL of dry CH2Cl2 were used.
Chromatography using hexanes followed by 45% EtOAc in hexanes
gave 63.0 mg (96% yield) of 10-D as a white solid. Mp = 176−178 °C.
Rf (SiO2/75% EtOAc in hexanes) = 0.48. 1H NMR (500 MHz,
CDCl3): δ 9.41 (br s, 1H, NH), 7.70 (d, 2H, Ar−H, J = 7.9 Hz), 7.49
(s, 1H, Ar−H), 7.22 (d, 2H, Ar−H, J = 7.9 Hz), 6.44 (t, 1H, H-1′, J =
6.5 Hz), 5.33 (app dt, 1H, H-3′, Japp = 4.6, 9.1 Hz), 4.49−4.47 (m, 1H,
H-4′), 4.02 (dd, 1H, H-5′, J = 2.4, 11.6 Hz), 3.88 (dd, 1H, H-5′, J =
2.4, 11.6 Hz), 3.00 (app dt, 1H, H-2′, Japp = 5.9, 13.1 Hz), 2.63 (ddd,
1H, H-2′, J = 6.8, 8.5, 14.6 Hz), 2.37 (s, 3H, CH3), 1.94, (s, 3H, CH3),
0.93 (s, 9H, t-Bu), 0.13 and 0.12 (2s, 6H, SiCH3). 13C NMR (125
MHz, CDCl3): δ 163.8, 150.5, 148.6, 138.5, 135.5, 129.8, 127.7, 125.9,
118.5 (t, J = 28.7 Hz), 111.3, 85.8, 85.0, 62.9, 59.8, 38.8, 26.1, 21.4,
For this reaction 0.131 mmol of azide, 0.262 mmol of alkyne, 10 mol
% of anhydrous CuSO4 in 0.273 mL of D2O, 20 mol % of Na ascorbate
in 0.273 mL of D2O, and 0.65 mL of dry CH2Cl2 were used.
Chromatography using hexanes followed by 50% EtOAc in hexanes
gave 61.0 mg (95% yield) of 13-D6 as a white solid. Mp = 96−98 °C.
Rf (SiO2/50% EtOAc in hexanes) = 0.21. 1H NMR (500 MHz,
CDCl3): δ 9.20 (br s, 1H, NH), 7.50 (s, 1H, Ar−H), 6.45 (t, 1H, H-1′,
J = 6.5 Hz), 5.34 (app dt, 1H, H-3′, Japp = 4.6, 8.8 Hz), 4.49−4.51 (m,
1H, H-4′), 4.03 (dd, 1H, H-5′, J = 2.1, 11.5 Hz), 3.88 (dd, 1H, H-5′, J
= 1.8, 11.5 Hz), 3.01 (ddd, 1H, H-2′, J = 5.2, 6.3, 14.0 Hz), 2.64 (ddd,
1H, H-2′, J = 6.5, 8.1, 14.3 Hz), 1.95 (s, 3H, CH3), 0.94 (s, 9H, t-Bu),
0.14 and 0.13 (2s, 6H, SiCH3). 13C NMR (125 MHz, CDCl3): δ
163.8, 150.5, 148.4, 135.5, 130.1, 128.6 (t, J = 23.8 Hz), 128.1 (t, J =
23.0 Hz), 125.6 (t, J = 24.1 Hz), 118.7 (t, J = 28.8 Hz), 111.4, 85.6,
85.0, 62.8, 59.8, 38.9, 26.1, 18.6, 12.8, −5.1, −5.2. 2H NMR (77 MHz,
CHCl3): δ 7.87, 7.45. HRMS (ESI) calculated for C24H28D6N5O4Si
[M + H]+ 490.2751, found 490.2766.
2
18.6, 12.7, −5.1, −5.2. H NMR (77 MHz, CHCl3): δ 7.85. HRMS
(ESI) calculated for C25H35DN5O4Si [M + H]+ 499.2594, found
499.2600.
6-[5-Deutero-4-(p-tolyl)-1H-1,2,3-triazol-1-yl]-9-[2,3,5-tri-O-
(t-butyldimethylsilyl)-β-D-ribofuranosyl]purine (11-D).
5-Deutero-1,4-diphenyl-D10-1H-1,2,3-triazole (14-D11).
For this reaction 0.198 mmol of azide, 0.395 mmol of alkyne, 5 mol %
of anhydrous CuSO4 in 0.2 mL of D2O, 10 mol % of Na ascorbate in
0.2 mL of D2O, and 0.95 mL of CH2Cl2 were used. Chromatography
using hexanes followed by 15% EtOAc in hexanes gave 131.0 mg (88%
yield) of 11-D as a pale-yellow solid. Mp = 89−91 °C. Rf (SiO2/20%
Chromatography using hexanes followed by 20% EtOAc in hexanes
gave 58.4 mg (72% yield) of 14-D11 as an off-white solid. Mp = 183−
186 °C. Rf (SiO2/50% EtOAc in hexanes) = 0.60. 13C NMR (125
MHz, CDCl3): δ 148.5, 137.2, 130.3, 129.5 (t, J = 24.3 Hz), 128.6 (t, J
= 23.3 Hz), 128.5(t, J = 23.1 Hz), 128.1 (t, J = 21.8 Hz), 125.7 (t, J =
24.2 Hz), 120.3 (t, J = 25.2 Hz), 117.6 (t, J = 26.9 Hz). 2H NMR (77
MHz, CHCl3): δ 8.23, 7.94, 7.83, 7.58, 7.49. HRMS (ESI) calculated
for C14HD11N3 [M + H]+ 233.1716, found 233.1717.
1
EtOAc in hexanes) = 0.28. H NMR (500 MHz, CDCl3): δ 8.97 (s,
1H, Ar−H), 8.65 (s, 1H, Ar−H), 7.91 (d, 1H, Ar−H, J = 8.0 Hz), 7.29
(d, 2H, Ar−H, J = 8.0 Hz), 6.24 (d, 1H, H-1′, J = 5.1 Hz), 4.68 (t, 1H,
H-2′, J = 4.7 Hz), 4.35 (t, 1H, H-3′, J = 3.9 Hz), 4.20 (app q, 1H, H-4′,
Japp = 3.0 Hz), 4.06 (dd, 1H, H-5′, J = 3.5, 11.4 Hz), 3.85 (dd, 1H, H-
5′, J = 2.4, 11.4 Hz), 2.41 (s, 3H, CH3), 0.99, 0.96, and 0.81 (3s, 27H,
Assessment of %D in 14-D11. CH2Cl2 (16 μL, 0.25 mmol) was
added to the solution of 14-D11 (11.7 mg, 0.05 mmol) in CDCl3 (0.5
1
mL). The H NMR spectrum of this solution was acquired and the
t-Bu), 0.19, 0.18, 0.13, 0.12, −0.02, and −0.21 (6s, 18H, Si-CH3). 13
C
resonances were integrated. The signal at δ 5.30 ppm (CH2Cl2) was
set to 10 whereby the signal at δ 8.19 ppm (residual triazolyl C5−H)
integrated to 0.06. Thus, the %D incorporation in the reaction was
estimated to be 94%.
NMR (125 MHz, CDCl3): δ 154.5, 152.5, 148.5, 145.2, 145.0, 138.8,
129.8, 127.5, 126.4, 123.5, 119.5 (t, J = 26 Hz), 88.9, 86.1, 76.5, 72.3,
62.8, 26.4, 26.1, 25.9, 21.5, 18.8, 18.3, 18.1, −4.1, −4.3, −4.4, −4.6,
G
dx.doi.org/10.1021/jo301146j | J. Org. Chem. XXXX, XXX, XXX−XXX

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Competitive Experiment using H2O and D2O. In a clean, oven-
dried, 10 mL round-bottom flask equipped with a stirring bar, was
placed phenyl azide (40.0 mg, 0.335 mmol) in dry CH2Cl2 (1.6 mL).
To this stirring solution 4-ethynyltoluene (85 μL, 0.67 mmol) was
added. In a separate vial CuSO4·5H2O (8.4 mg, 0.0335 mmol, 10 mol
%) was heated at 120 °C under vacuum until the color changed from
blue to gray. Using this dehydrated CuSO4, a 0.048 M solution was
prepared in a glovebag by the addition of D2O (99.8% D, 0.7 mL) and
this solution was transferred to the reaction mixture. To the reaction
mixture a 0.096 M solution of Na ascorbate (13.3 mg in 0.7 mL of
H2O, 20 mol %) was then added. The reaction mixture was sealed and
stirred under nitrogen gas at room temperature until TLC showed
consumption of azide. The organic layer of the reaction mixture was
separated and the aqueous layer was back extracted with EtOAc (3 × 5
mL). The organic layers were combined and washed with brine (5
mL), dried over anhydrous Na2SO4, and concentrated under reduced
pressure. The crude material was purified by chromatography on a
silica gel column to give 60 mg of an off-white solid. On the basis of
the 1H NMR analysis, this mixture contained 15.6 mg (19.7%) of 1-D
and 44.4 mg (56.3%) of 1-H. Rf (25% EtOAc in hexanes/SiO2) = 0.34.
Assessment of the Amounts of 1-H and 1-D in the Product
Mixture. CH2Cl2 (16 μL, 0.25 mmol) was added to a solution of the
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1
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integrated. The signal at δ 5.30 ppm (CH2Cl2) was set to 10 whereby
the signal at δ 8.16 ppm (residual triazolyl C5−H) integrated to 0.77.
On the basis of these values the amount of 1-H was estimated at 9.058
mg (77%) and that of 1-D was estimated as 2.741 mg (23%).
1237−1240.
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(15) In ref 7, the authors indicate that conducting CuAAC in D2O
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paper). However, no other details are available.
ASSOCIATED CONTENT
* Supporting Information
■
(16) Kolb, H. C.; Sharpless, K. B. Drug Discovery Today 2003, 24,
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1128−1137.
Spectral data for 1-D to 14-D11, 9-H, as well as for other
relevant intermediates. This material is available free of charge
via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Tel. (212) 650-7835; fax (212) 650-6107; e-mail lakshman@
sci.ccny.cuny.edu.
Notes
■
(20) Lakshman, M. K.; Singh, M. K.; Parrish, D.; Balachandran, R.;
Day, B. W. J. Org. Chem. 2010, 75, 2461−2473.
The authors declare the following competing financial
interest(s): A patent application has been filed.
(21) Lee, B.-Y.; Park, S. R.; Jeon, H. B.; Kim, K. S. Tetrahedron Lett.
2006, 47, 5105−5109.
(22) Pagliai, F.; Pirali, T.; Del Grosso, E.; Di Brisco, R.; Tron, G. C.;
Sorba, G.; Genazzani, A. A. J. Med. Chem. 2006, 49, 467−470.
(23) Dahl, B. H.; Olsen, G. M.; Christensen, J. K.; Peters, D. PCT Int.
Appl. 2010026134, 2010.
ACKNOWLEDGMENTS
■
This work was supported by NIH (NIAID) Grant AI094545-
01. Infrastructural support at CCNY was provided by National
Institutes of Health Grants 2G12RR03060-26A1 from the
National Center for Research Resources and by
8G12MD007603-27 from the National Institute on Minority
Health and Health Disparities. We thank Mr. Gerry Guilfoy of
Cambridge Isotope Laboratories, Inc. for a sample of 99.8%
D2O, Ms. Nonka Sevova and Dr. Bill Boggess (University of
Notre Dame Mass Spectrometry and Proteomics Facility) for
some of the HRMS analyses, which were supported by NSF
Grant CHE-0741793.
(24) Lin, J.; Roy, V.; Wang, L.; You, L.; Agrofoglio, L. A.; Deville-
Bonne, D.; McBrayer, T. R.; Coats, S. J.; Schinazi, R. F.; Eriksson, S.
Bioorg. Med. Chem. 2010, 18, 3261−3269.
̈
(25) Olgun, A.; Ozturk, K.; Bayr, S.; Akman, S.; Erbil, M. K. Ann. N.Y.
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Acad. Sci. 2007, 1100, 400−403 (ionization constant of H2O = 1.008 ×
10−14 and that of D2O = 1.95 × 10−15; pH of H2O = 6.998 and pD
D2O = 7.355). Thus, the ratio of H+ to D+ ion concentration of H2O
and D2O = 2.28.
27
(26) Phenyl azide-D5 was synthesized from bromobenzene-D5 as
described for the unlabeled compound in ref 28.
(27) Bencivenni, G.; Cesari, R.; Nanni, D.; El Mkami, H.; Walton, J.
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