Synthesis and photophysical characterization of 1- and 4-(purinyl)triazoles

Article abstract of DOI:10.1016/j.tet.2013.08.023

Fluorescent adenine mimetics are useful tools for studying DNA, RNA and enzyme functions. Herein we describe the synthesis of eight 1-(purinyl)triazoles and two 4-(purinyl)triazoles utilizing the 1,4-regioselective copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction as the key step. The fluorescence properties of five of the synthesized 1-(purinyl)triazoles are also presented. The five measured compounds displayed low quantum yields. The results, when compared to previously published data, suggest a high influence of the substitution pattern of the triazole on the fluorescence properties.

Full text of DOI:10.1016/j.tet.2013.08.023

Tetrahedron 69 (2013) 8857e8864
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and photophysical characterization of 1- and 4-(purinyl)
triazolesq
Itedale Namro Redwan y, David Bliman y, Munefumi Tokugawa, Christopher Lawson,
*
Morten Grøtli
€
Department of Chemistry and Molecular Biology, University of Gothenburg, SE-41296 Goteborg, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history:
Fluorescent adenine mimetics are useful tools for studying DNA, RNA and enzyme functions. Herein
we describe the synthesis of eight 1-(purinyl)triazoles and two 4-(purinyl)triazoles utilizing the
1,4-regioselective copper-catalyzed azideealkyne cycloaddition (CuAAC) reaction as the key step. The
fluorescence properties of five of the synthesized 1-(purinyl)triazoles are also presented. The five
measured compounds displayed low quantum yields. The results, when compared to previously pub-
lished data, suggest a high influence of the substitution pattern of the triazole on the fluorescence
properties.
Received 31 March 2013
Received in revised form 30 July 2013
Accepted 12 August 2013
Available online 15 August 2013
Keywords:
Purinyltriazole
CuAAc
Ó 2013 The Authors. Published by Elsevier Ltd. All rights reserved.
Fluorescent purines
1. Introduction
Adenylate-forming enzymes are involved in a range of different
essential biological processes, such as ribosomal and non-
ribosomal peptide synthesis, fatty acid oxidation, and enzyme
regulation.1
Scheme 1. The two-step adenylation process catalyzed by adenylate-forming en-
zymes, which results in the formation of thioesters, amides, and esters.
In the first step catalyzed by adenylate-forming enzymes, a car-
boxylate reacts with ATP to afford an acyl-adenylate intermediate
(acyl-AMP) with concomitant release of pyrophosphate (PPi)
(Scheme 1, Step 1). In the second step the reactive intermediate
reacts with a nucleophile to form the final product together with
a release of AMP (Scheme 1, Step 2). Some of the adenylate-forming
enzymes have been regarded as potential drug targets, such as
aminoacyl-tRNA synthetases,2 Mycobacterium tuberculosis panto-
thenate synthetase,3,4 and aryl acid adenylating enzymes involved
in siderophore biosynthesis in M. tuberculosis.5,6 Since the acyl-
AMP is assumed to bind tightly to the active site of adenylate-
forming enzymes it is envisaged that non-reactive analogues of
acyl-AMP could potentially serve as inhibitors of the enzymes.
There are several examples in the literature where non-reactive
analogues of acyl-AMP have been synthesized and evaluated as
inhibitors of specific adenylate-forming enzymes.1,2,7e16 One such
example is the use of sulfamoyl-adenylate analogues as inhibitors
of aminoacyl-tRNA synthetases (Fig. 1, A).2,16 We have previously
reported the design and synthesis of several non-hydrolyzable
sulfamoyl analogues of acyl-AMP, which have been used in struc-
tural studies of a number of tRNA synthetases.17e21
Fluorescence is a useful technique to study macromolecules,
such as DNA and RNA. For this purpose artificial base analogues
with intrinsic fluorescence are potentially useful tools.22,23 We
have previously reported the synthesis of 4-(adenosinyl)triazoles
as fluorescent base analogues utilizing the 1,4-regioselective
copper-catalyzed azideealkyne cycloaddition (CuAAC).24,25 The
use of CuAAC facilitates the variation of substituents in the 1- and
4-positions of the 1,2,3-triazole through the use of a variety of a-
zides/acetylenes. Small fluorescent compounds capable of detect-
ing specific enzyme targets have been shown to be useful for
studying enzymatic activation and regulation within the cell. Such
q
This is an open-access article distributed under the terms of the Creative
Commons Attribution-NonCommercial-No Derivative Works License, which per-
mits non-commercial use, distribution, and reproduction in any medium, provided
the original author and source are credited.
* Corresponding author. E-mail address: grotli@chem.gu.se (M. Grøtli).
y
These individuals contributed equally to this work.
0040-4020/$ e see front matter Ó 2013 The Authors. Published by Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.08.023

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I.N. Redwan et al. / Tetrahedron 69 (2013) 8857e8864
Fig. 1. A. Structures of sulfamoyloxy- and purinyltriazole-based (B and C) analogues of
acyl-AMP. Blue dashed lines indicate similarities in the end groups of the compounds
in their extended conformations.
tools have been used in enzyme function studies of kinases,26
ATPase,27 and glutathione transferase.28
We hypothesized that purinyltriazoles (Fig. 1B and C) may fit
into the adenylate-binding site of tRNA synthetases in a manner
similar to the sulfamoyl analogues of acyl-AMP (Fig. 1A). Ex-
changing the ribose unit for a small lipophilic substituent would
eliminate the need for the rather extensive protecting group
strategies required for ribose-containing structures. These com-
pounds could potentially be used as fluorescent probes to study
adenylate-forming enzymes. In this paper we present the synthesis
and photophysical characterization of a small series of 1- and
4-purinyltriazoles.
Scheme 2. Synthesis of imide-based compounds. Reagents and conditions: (a)
Pd(PPh3)2Cl2 (5 mol %), CuI (20 mol %), Amberlite IRA-67 (5 equiv), ethynyl-
triisopropylsilane (3.3 equiv), THF, MW 120 ꢁC, 30 min. (b) PS-fluoride (2.4e3.6 equiv,
2e3 mmol/g loading), THF, rt, N2, 24 h. (c) 1. NaN3 (1.2 equiv), 2-bromoacetamide
(1.1 equiv), DMF, MW 80 ꢁC, 20 min. 2. 3 (1.0 equiv), sodium ascorbate (0.6 equiv),
CuI (0.2 equiv), N,N0-dimethylenediamine (0.3 equiv), MW 80 ꢁC, 2 h. (d) 4a, NaH
(2.0 equiv), R2-amino acid-ONp (1.1 equiv), THF, 0 ꢁC 15 min then at rt, 3e5 h. (e) H2/
Pd/C (10% CatCart, 30ꢂ4 mm, H-cubeÒ, 21 ꢁC, 25 min, MeOH, flow rate: 1 ml/min). (f)
50% TFA in DCM, 1e1.5 h. ¤Unstable compounds.
purified by flash chromatography using an eluent containing
MeOH, since the same side reaction occurred on the column. It was
however not possible to identify a suitable replacement eluent
system for this purification. The Boc-protecting group in 5b was
removed using TFA (50% in DCM), resulting in the isolation of 6b in
63% yield after purification by preparative HPLC. Although, these
compounds degraded within days when stored at ꢀ10 ꢁC.
Due to the instability of 6a and 6b in the presence of nucleo-
philes like MeOH as well as on storage, it was decided to prepare
compounds in which the imide was replaced by the more stable
amide functionality. The existing route to the 4-(purinyl)triazoles
involved a Sonogashira coupling on the 8-bromopurine derivative
and subsequent desilylation followed by CuAAC with different
azides to obtain the purinyltriazoles. Inverting the triazole would
enable the cyclization on a range of more easily accessible alkynes.
Aminoacyl substituted 1-(purinyl)triazoles would be accessible
from a two-step azide formation/cyclization reaction with the
alkynylamide of the amino acid and 8-bromo-9-alkyladenines,
such as 1.29
2. Results and discussion
2.1. Synthesis
The initial strategy to obtain aminoacyl bearing 4-purinyltriazoles
utilized our previously described route to 8-(1H-1,2,3-triazole-4-yl)
adenosine derivatives.24 8-Bromo-9-ethyladenine (1)29 was synthe-
sized in two steps from adenine. A Sonogashira cross-coupling was
performed on 1 to introduce (triisopropylsilyl)acetylene in the
8-position using Pd(PPh3)2Cl2 and CuI as catalysts with Amberlite
IRA-67 as base (Scheme 2). The desired product 2 was obtained in
84% yield. The TIPS protecting group was removed with polymer-
supported fluoride, which enabled work-up by filtration and com-
pound 3 was isolated in 83% yield after purification. Initial attempts
to synthesize 3 using (trimethylsilyl)acetylene resulted in in situ
deprotection and low yields. The 1,2,3-triazole ring was synthesized
using a copper-catalyzed [3þ2]-cycloaddition between the alkyne 3
and an appropriate azide. Compound 4a was isolated by pre-
cipitation from water in 78% yield and was used in the next step
without further purification.
As in the case of the 4-(purinyl)triazoles, the synthesis of
1-(purinyl)triazoles started from 8-bromo-9-ethyladenine (1).29
Initial attempts to prepare imides from 4a using nitrophenyl
activated esters and n-BuLi as base, were unsuccessful.30 Changing
the base to sodium hydride (NaH) resulted in acylation of 4a using
Propargylamides 7aec and b-alkynylamides 7d,e were synthe-
sized by amide coupling of the corresponding Boc-protected amino
acids with propargylamine and 4-butynylamine, respectively
(Table 1). Heating 1 and sodium azide at 90 ꢁC for 22 h in DMF with
the exclusion of light resulted in the formation of 8-azido-9-
ethyladenine (observed by LC/MS). Existing protocols for similar
transformations using DMSO failed to provide satisfactory conver-
sions in our hands.31,32
Without isolation of the formed azide intermediate, copper(I)
iodide (CuI), sodium ascorbate (NaAsc), N,N0-dimethylethylenedi-
amine (DMEDA), and Cbz-valine-propargylamide were added to
the reaction mixture and heated at 90 ꢁC for 24 h. Although 1H NMR
Cbz-L-valine 4-nitrophenyl ester or Boc-L-leucine 4-nitrophenyl
ester affording 5a and 5b in 35% and 47% yield, respectively. The
benzyl carbamate (Cbz) protecting group in 5a was removed using
a continuous-flow catalytic hydrogenation reactor (H-cubeÒ) with
Pd/C (10 wt % catalyst cartridge) and MeOH as solvent, affording 6a
in 22% yield after purification by preparative HPLC. The low isolated
yield of 6a can be partly attributed to the formation of the methyl
ester 4b (identified by NMR and LC/MS) by nucleophilic attack of
MeOH on the imide functionality of 5a. Compound 5a could not be

I.N. Redwan et al. / Tetrahedron 69 (2013) 8857e8864
8859
Table 1
Synthesis of compounds 8beh
Entry
1
Alkyne
Alkyne
Compd
R
Yield, %
7a
7b
8a
__a
40
2
8b
3
4
7c
8c
40
45
7d
8d
5
7e
8e
38
6
7
7f
8f
48
50
7g
8g
8
7h
8h
50
Compounds 8bee were purified by preparative HPLC while compounds 8feh were purified by flash chromatography on silica. (i) NaN3 (1.8 equiv), DMF, 90 ꢁC, 22 h. (ii) Alkyne
(1.4 equiv), sodium ascorbate (0.4 equiv), CuI (20 mol %), DMEDA (0.3 equiv), rt, 24 h, in the dark.
a
No product isolated.
indicated formation of debenzoylated product 8a, the HRMS data
Table 2
did not correspond with the calculated value. Likewise, the corre-
Deprotection of 8bee
sponding cyclization using Cbz-leucine-propargylamide (data not
shown) did not produce the expected product in satisfying yield.
These poor results prompted us to consider an alternative to Cbz-
protected propargylamides. Changing the protecting group to Boc
and running the cyclization step at room temperature overnight
afforded 8bee in 40e66% yield (Table 1). The protecting group of
8bee was subsequently removed with TFA in DCM to afford the
corresponding trifluoroacetate salts 9bee in high yields (Table 2).
To access substrates more comparable with our previously pub-
lished fluorescent purinyltriazoles,24 1 was reacted with alkynes
7feh under the same reaction conditions utilized for 7bee. Tri-
azoles 8feh were isolated in 48e50% yield. When the reaction was
attempted with N,N-dimethylpropargylamine, low conversion was
observed (LCMS) and only trace amounts could be isolated even
after prolonged reaction times (data not shown).
Entry
1
R
Compd
Yield, %
94
8b
9b
R1¼Boc
R1¼H
2
3
8c
9c
99
99
R1¼Boc
R1¼H
The modest yields in these reactions can in part be attributed to
the reduction of the azidopurine to the corresponding amine under
the cyclization conditions. The amine was observed on LC/MS (data
not shown). In situ reduction of azides by excess NaN3 in the
presence of copper has previously been reported.33 Procedures for
8d
9d
R1¼Boc
R1¼H
synthesis of 8-azido purines reported in the literature generally
4
8e
9e
71
31,32,34
R1¼Boc
R1¼H
utilize a large excess of NaN3
and reducing the amount
of NaN3 below 1.8 equiv resulted in lower conversion of 1 to
8-azidopurine in our case.
Reaction conditions: a: TFA/DCM 1:1 (v/v), rt, 1 h.

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I.N. Redwan et al. / Tetrahedron 69 (2013) 8857e8864
2.2. Photophysical characterization
by automated column chromatography on a Biotage SP-4 in-
strument using pre-packed silica columns. Analytical high-
performance liquid chromatography (HPLC) analysis was carried
out on a Waters separation module 2690 connected to a Waters
Molar absorptivities and quantum yields for five of the synthe-
sized compounds were determined in MeOH (Table 3). All de-
rivatives have similar absorption maxima (between 282 nm and
291 nm) and emission maxima (401e409 nm). The absorption
maximum for the derivative with the phenyl group conjugated
with the triazole moiety (8h) is red-shifted (9 nm) compared to the
aliphatic derivatives (9b, 9d, 8f, 8g). Furthermore the quantum
yield is significantly lower for 8h compared to the aliphatic and
benzylic derivatives. This result is in agreement with our previous
study of 8-(1H-1,2,3-triazole-4-yl)-adenosine derivatives.24
photodiode array detector 996 using an AtlantisÒ
5
m
m C18 AQ
(250ꢂ4.6 mm) column. Preparative HPLC was carried out on
a Waters 600 controller connected to a Waters 2487 Dual Ab-
sorbance detector using an AtlantisÒ Prep T3
C-18
l
5
mm
(250ꢂ19 mm) column, unless otherwise stated. 1H and 13C NMR
spectra were obtained at 400 and 100 MHz, respectively, using
a Varian 400/54 spectrometer. IR absorption was measured on
a Biotools ChiralIR-2X instrument, optical rotations were measured
on a PerkineElmer 341LC Polarimeter, and melting points were
recorded with a Mettler FP82 heater connected to a Mettler FP80
processor.
Table 3
Photophysical characterization of absorption and fluorescence properties of com-
pounds 9b, d, f, g, h in MeOH
4.2. Photophysical measurements
Compound
Absmax (nm)
Em
(nm)
F [%]
max
9b
9d
8f
8h
8g
283
284
282
408
409
401
401
404
0.55
0.64
0.60
0.21
0.57
All photophysical measurements were performed in MQ-water
or MeOH. Absorption spectra were measured with a Varian Cary
4000 spectrophotometer. Solutions of samples containing adenine
analogues in MeOH, which gave absorption of approximately 0.06
at the excitation wavelength (290 nm) were used in all experi-
ments. Steady-state fluorescent measurements were performed
with a Spex Fluorolog 3 spectrofluorimeter (JY Horiba). The quan-
tum yields of the adenine analogues were determined relative to
282, 291
283
However the aliphatic and benzylic 1-(purinyl)triazole de-
rivatives (9b, 9d, 8f, 8g) have significantly lower quantum yields
(below 1%) compared to previously published 4-(adenosinyl)tri-
azole derivatives (49e64%).24 Most notably 8f and 8g have the
same substituent on the triazole as the 4-(adenosinyl)triazoles,
which showed some of the highest quantum yields (62 and 64%,
respectively) in our previous study.24 These results indicate that the
position of the nitrogen atoms in the triazole has a significant in-
fluence on the quantum yields of these types of compounds. Pu-
rines substituted with a triazole in the 2-postion35 were recently
reported to have fluorescent properties with quantum yields of up
to 53%, which indicates that the position of the triazole on the
purine is also important for the fluorescent properties. As discussed
above, the 4-(purinyl)triazoles 6a and 6b were not stable in MeOH
and their fluorescent properties were therefore not measured.
2-aminopyridine (
F
¼0.60)36 in 0.05 M H2SO4 at 25 ꢁC with the
excitation wavelength of 290 nm.
4.3. Synthesis
4.3.1. 6-Amino-8-bromo-9-ethyl-9H-purine (1). Following a modi-
fied literature procedure,37 6-amino-9-ethyl-9H-purine was syn-
thesized by the addition of ethyl iodide (3.6 ml, 45 mmol) to a white
suspension of adenine (5.00 g, 37.0 mmol) and cesium carbonate
(14.5 g, 44.4 mmol) in dry DMF (60 ml) under nitrogen. The sus-
pension was heated at 60 ꢁC for 7 h. A white solid was filtered off,
the yellow solution was quenched with water (5 ml) and the sol-
vents were removed under reduced pressure. The yellow solid was
partially dissolved in CHCl3 and MeOH and the insoluble material
was removed by filtration. Removal of the solvents under reduced
pressure resulted in a crude yellow solid that was purified by flash
column chromatography (gradient, 2e10% v/v MeOH in CHCl3).
6-Amino-9-ethyl-9H-purine was isolated as a white solid (3.97 g,
24.3 mmol, 66%). Mp 191e194 ꢁC (lit. 192e193 ꢁC,38 185e187 ꢁC39).
3. Conclusion
We have synthesized two 4-(purinyl)triazoles and eight
1-(purinyl)triazoles. The key step in the synthesis is the copper-
catalyzed azideealkyne cycloaddition (CuAAC) reaction. The pre-
sented synthesis provides access to the desired products in a two-
step reaction from 8-bromopurine and terminal alkynes. The
photophysical properties of five of the 1-(purinyl)triazoles were
investigated. The compounds display fluorescence properties, al-
beit with significantly lower quantum yields than previously re-
ported for 4-(adenosinyl)triazoles. A deeper understanding of the
results will require further studies and such are currently being
undertaken in our laboratory.
The 1H NMR data were consistent with that in the literature.39 1
H
NMR (DMSO-d6): 8.14 (s, 1H), 8.13 (s, 1H), 7.16 (br s, 2H), 4.16 (q, J
7.3 Hz, 2H),1.39 (t, J 7.3 Hz, 3H); 13C NMR (DMSO-d6,1): 155.9,152.3,
149.3, 140.4, 118.8, 38.0, 15.3; nmax (DMSO) 3250, 2250, 2120,
1640 cmꢀ1; HRMS m/z [MþH]þ calculated for C7H9N5: 164.0936.
Found: 164.0935. The regioisomer (6-amino-7-ethyl-7H-purine)
was also isolated as a white solid (0.60 g, 3.68 mmol, 10%).
Following a modified literature procedure,37 bromine (15 ml)
was slowly added to an ice-cold solution of 6-amino-9-ethyl-9H-
purine (5.86 g, 35.9 mmol) in a HOAc buffer (pHw4, 20 ml), THF
(20 ml), and MeOH (20 ml). The reaction mixture was stirred at
room temperature for 24 h, then cooled on ice, and quenched with
an aqueous sodium metabisulfite and sodium thiosulfate solution
(10 wt %). The mixture was neutralized with an aqueous NaOH
solution (3 M), which resulted in the precipitation of a solid. The
solid was filtered off, washed with water, and dried overnight
yielding a pale yellow solid, which was purified by column chro-
matography (gradient, 0e10% MeOH in CHCl3), which gave 1 as an
off-white solid (5.39 g, 62%). Mp 221e225 ꢁC (lit. 218e220 ꢁC39).
4. Experimental section
4.1. General
All commercial chemicals were used without prior purification.
DCM was distilled from calcium hydride. THF was distilled from
sodium/benzophenone. All reactions were monitored by TLC
(Merck silica gel 60F254) and analyzed under UV (254 nm). Micro-
wave reactions were performed in a Biotage Initiator reactor with
fixed hold time. Column chromatography was performed by man-
ual flash chromatography (wet-packed silica, 0.04e0.063 mm) or
The 1H NMR data were consistent with that in the literature.39 1
NMR (DMSO-d6): 8.13 (s, 1H), 7.36 (br s, 2H), 4.15 (q, J 7.2 Hz, 2H),
H

I.N. Redwan et al. / Tetrahedron 69 (2013) 8857e8864
8861
1.31 (t, J 7.2 Hz, 3H); 13C NMR (DMSO-d6): 154.7, 152.8, 150.4, 125.9,
119.1, 38.9, 14.6; nmax (DMSO) 3400, 3250, 3000, 2900, 2250, 2120,
1710 cmꢀ1; HRMS m/z [MþH]þ calculated for C7H8N5Br: 242.0041.
Found: 242.0042.
15 min, then allowed to reach room temperature and stirred for
45 min. Cbz- -valine 4-nitrophenyl ester (71.3 mg, 0.19 mmol) was
L
dissolved in THF (1.5 ml) and added dropwise to the bright yellow
reaction mixture at 0 ꢁC under nitrogen, the mixture was stirred at
that temperature for 15 min and then at room temperature for 5 h.
The reaction was quenched by the addition of 1 M HCl (1 ml), the
layers were separated and the aqueous layer was extracted with
EtOAc (2ꢂ5 ml). The combined organic layers were washed with
aqueous saturated NaHCO3 (5 ml), dried over MgSO4 and the sol-
vent was removed under reduced pressure. The crude product was
purified using automated flash chromatography (gradient, 2e20%
MeOH in CHCl3) and preparative HPLC (H2O/AcCN (0.1% TFA) 100:0
to 0:100 for 36 min, then at 0:100 for 15 min, with a flow of 14 ml/
min). The desired compound 5a was obtained as a white crystalline
material (32.0 mg, 0.06 mmol, 35%). However, 5a was unstable and
13C NMR could not be obtained. 1H NMR (CDCl3/MeOH-d4): 8.46 (s,
1H), 8.26 (s, 1H), 7.30e7.15 (m, 5H), 5.72 (s, 2H), 5.03 (s, 2H),
4.97e4.72 (m, 2H), 4.30e3.71 (m, 3H), 2.53e1.72 (m, 1H), 1.45 (t, J
6.6 Hz, 3H), 1.01e0.81 (m, 6H).
4.3.2. 6-Amino-9-ethyl-8-(2-triisopropylsilylethynyl)-9H-purine
(2). Compound 1 (100 mg, 0.41 mmol), Pd(PPh3)2Cl2 (14.7 mg,
0.0209 mmol), CuI (15.7 mg, 0.0824 mmol) were added to a mi-
crowave vial followed by THF (2 ml) and Amberlite IRA-67 (362 mg,
2.03 mmol). The vial was capped and nitrogen was bubbled through
the reaction mixture. (Triisopropylsilyl)acetylene (300
ml,
1.34 mmol) was added and the reaction mixture was heated in
a microwave reactor (120 ꢁC, 30 min). The reaction mixture was
filtered through a short plug of silica, eluted with 10% MeOH in
CHCl3 and the solvents were removed to produce a pale pink solid,
which was purified by automated flash column chromatography
(gradient, 2e10% MeOH in CHCl3). Compound 2 was isolated as
a white solid (119 mg, 0.35 mmol, 84%). Mp 167 ꢁC; 1H NMR
(CDCl3): 8.34 (s, 1H), 6.17 (br s, 2H), 4.34 (q, J 7.2 Hz, 2H), 1.46 (t, J
7.2 Hz, 3H), 1.27e1.05 (m, 21H); 13C NMR (CDCl3): 155.5, 153.9,
149.5, 134.5, 119.4, 100.2, 94.7, 38.8, 18.7, 15.3, 11.3; nmax(DMSO)
3250, 3000, 2250, 2120 cmꢀ1; HRMS m/z [MþH]þ calculated for
C18H29N5Si: 344.2271. Found: 344.2273.
4.3.6. N-(2-(4-(6-Amino-9-ethyl-9H-purine-8-yl)-1H-1,2,3-triazol-
1-yl)acetyl)-2-tert-butoxycarbonylamino-4-methylpentanamide
(5b). NaH (14.5 mg, 0.35 mmol) was added to 4a (50 mg,
0.17 mmol), which was suspended in THF (5 ml) at 0 ꢁC under ni-
trogen. The reaction mixture was stirred at 0 ꢁC for 15 min then
allowed to reach room temperature and stirred for another 45 min.
4.3.3. 6-Amino-9-ethyl-8-ethynyl-9H-purine
(3). Polymer-sup-
ported fluoride (2.0 g, 2e3 mmol/g loading) was added to a solution
of 2 (0.580 g, 1.69 mmol) in THF (10 ml). The reaction mixture was
stirred at room temperature for 24 h, after which a white pre-
cipitate had formed. The reaction mixture was diluted in MeOH
(the precipitate dissolved), and the polymer was filtered off and
washed with MeOH. Removal of the solvents yielded a yellow solid
that was purified by automated flash column chromatography
(gradient, 2e10% MeOH in CHCl3). Compound 3 was isolated as
a white solid (261 mg, 1.39 mmol, 83%). The 1H NMR data were
consistent with published data for this compound.40 Mp de-
composes at 210 ꢁC (lit.>200 ꢁC ignition40); 1H NMR (DMSO-d6):
8.18 (s, 1H), 7.46 (br s, 2H), 4.92 (s, 1H), 4.22 (q, J 7.2 Hz, 2H), 1.35 (t, J
7.2 Hz, 3H); 13C NMR (DMSO-d6): 155.9, 153.8, 148.9, 132.0, 118.5,
Boc-L-leucine 4-nitrophenyl ester (67.5 mg, 0.19 mmol) was dis-
solved in THF (1.5 ml) and added dropwise to the bright yellow
reaction mixture at 0 ꢁC under nitrogen, and stirred at that tem-
perature for 15 min and then at room temperature for 3 h. The
reaction was quenched by the addition of 1 M HCl (1 ml), the phases
were separated and the aqueous layer was extracted with EtOAc
(2ꢂ5 ml). The combined organic phases were washed with an
aqueous saturated NaHCO3 (5 ml), dried over MgSO4 and the sol-
vent was removed under reduced pressure. The crude product was
purified using automated flash chromatography (gradient, 2e20%
MeOH in CHCl3) and preparative HPLC (H2O/AcCN (0.1%TFA) 100:0
to 0:100 for 36 min, then at 0:100 for 15 min, with a flow of 14 ml/
min). The desired compound 5b was obtained as a white crystalline
material (41.0 mg, 0.08 mmol, 47%). However, 5b was unstable and
13C NMR could not be obtained. 1H NMR (CDCl3/MeOH-d4): 8.37 (s,
1H), 8.15 (s,1H), 5.62 (s, 2H), 4.71 (q, J 7.1 Hz, 2H), 4.15e4.06 (m,1H),
1.62e1.53 (m, 1H), 1.41e1.38 (m, 2H), 1.35 (t, J 7.1 Hz, 3H), 1.28 (s,
9H), 0.80 (t, J 6.5 Hz, 6H).
86.4, 73.0, 38.1, 14.9; nmax (DMSO) 3250, 3000, 2250, 2120 cmꢀ1
.
HRMS m/z [MþH]þ calculated for C9H9N5: 188.0936. Found:
188.0930.
4.3.4. 2-(4-(6-Amino-9-ethyl-9H-purine-8-yl)-1H-1,2,3-triazol-1-yl)
acetamide (4a). NaN3 (49 mg, 0.75 mmol), DMF (4 ml), and 2-
bromoacetamide (97 mg, 0.70 mmol) were added to a microwave
vial that was flushed with nitrogen and the reaction mixture was
heated in a microwave reactor (80 ꢁC, 20 min). Compound 3
(120 mg, 0.64 mmol), sodium ascorbate (52 mg, 0.41 mmol), and
CuI (24 mg, 0.13 mmol) were added followed by N,N0-dimethyle-
4.3.7. 2-Amino-N-(2-(4-(6-amino-9-ethyl-9H-purine-8-yl)-1H-
1,2,3-triazol-1-yl)acetyl)-3-methylbutanamide (6a). Compound 5a
(47 mg, 0.09 mmol) was dissolved in MeOH (5 ml) and catalytic
hydrogenation was carried out in a continuous-flow hydrogenation
reactor (H-cubeÒ) (flow rate: 1 ml/min; temperature: 21 ꢁC; cata-
lyst: 10% Pd/C CatCart, 30ꢂ4 mm; time: 25 min). The solvent was
removed under reduced pressure and the desired product was
purified by preparative HPLC (H2O/AcCN (0.1%TFA) 100:0 to 0:100
for 36 min, then at 0:100 for 15 min, with a flow of 14 ml/min).
Compound 6a was obtained as a white crystalline material (8.0 mg,
0.02 mmol, 22%). However, 6a was unstable and 13C NMR could not
be obtained. 1H NMR (MeOH-d4): 8.66 (s, 1H), 8.39 (br s, 2H),
5.98d5.80 (m, 6H), 5.09 (br s,1H), 4.66e4.55 (m, 2H),1.90e1.80 (m,
1H), 1.50 (d, J 7.2 Hz, 3H), 0.92 (d, J 7.6 Hz, 3H), 0.66 (d, J 6.5 Hz, 3H).
nediamine (18 ml, 0.17 mmol). The reaction mixture was heated in
a microwave reactor (80 ꢁC, 2 h) and allowed to reach room tem-
perature before being poured into water (10 ml). The product
precipitated and was filtered off, washed thoroughly with ice-cold
water, and dried under vacuum to yield 4a as an off-white solid
(143 mg, 0.50 mmol, 78%). Mp 299e300 ꢁC; 1H NMR (DMSO-d6):
8.61 (s, 1H), 8.19 (br s, 1H), 7.82 (s, 1H), 7.49 (s, 1H), 7.29 (br s, 2H),
5.24 (s, 2H), 4.63 (q, J 6.9 Hz, 2H), 1.38 (t, J 7.0 Hz, 3H); 13C NMR
(DMSO-d6): 167.0, 155.6, 152.6, 150.5, 140.9, 138.8, 127.2, 118.7, 51.7,
38.5, 15.3; nmax (DMSO) 3250, 3000, 2910, 2250, 2120 cmꢀ1; HRMS
m/z [MþH]þ calculated for C11H13N9O: 288.1321. Found: 288.1317.
4.3.8. 2-Amino-N-(2-(4-(6-amino-9-ethyl-9H-purine-8-yl)-1H-
1,2,3-triazol-1-yl)acetyl)-4-methylpentanamide (6b). Compound 5b
(30.0 mg, 0.06 mmol) was dissolved in DCM (1 ml) and TFA (1 ml)
was added dropwise. The reaction mixture was stirred for 1 h at
room temperature. TFA was removed using a stream of nitrogen,
and the solvent was removed under reduced pressure. The crude
4.3.5. N-(2-(4-(6-Amino-9-ethyl-9H-purine-8-yl)-1H-1,2,3-triazol-
1-yl)acetyl)-2-benzyloxycarbonylamino-3-methylbutanamide
(5a). NaH (14.5 mg, 0.35 mmol, 60% mineral dispersion) was added
to 4a (50.0 mg, 0.17 mmol), which was suspended in THF (6 ml) at
0
ꢁC under nitrogen. The reaction mixture was stirred at 0 ꢁC for

8862
I.N. Redwan et al. / Tetrahedron 69 (2013) 8857e8864
product was purified by preparative HPLC (H2O/AcCN (0.1%TFA) at
100:0 to 0:100 for 36 min, then at 0:100 for 15 min, with a flow of
14 ml/min). The desired compound 6b was obtained as a white
crystalline material (15.0 mg, 0.04 mmol, 63%). However, 6b was
unstable and 13C NMR could not be obtained. 1H NMR (DMSO-d6):
8.40 (s, 1H), 8.38 (br s, 2H), 8.07 (s, 1H), 5.92 (s, 2H), 4.71e4.61 (m,
2H), 3.72e3.62 (m, 1H), 1.67e1.62 (m, 1H), 1.56e1.50 (m, 3H),
1.45e1.35 (m, 2H), 0.91e0.88 (m, 6H).
(0.16 ml, 2.0 mmol) and N-Boc-
substrates in DMF (6 ml). N-tert-Butoxycarbonyl-
nylamide (7d) was isolated as a white solid (0.24 g, 0.85 mmol,
L
-leucine (300 mg, 1.3 mmol) as
L-leucinylbuty-
20
66%). Mp 106 ꢁC; [
a
]
D
ꢀ43.0 (c 0.1, DMSO); 1H NMR (CDCl3):
6.85 (br s, 1H), 5.16 (br s, 1H), 4.11 (br s, 1H), 3.47e3.25 (m, 2H), 2.35
(br s, 2H), 1.95 (br s, 1H), 1.73e1.31 (m, 12H), 0.89 (t, J 5.7 Hz, 6H);
13C NMR (CDCl3): 173.0, 155.8, 81.4, 80.0, 70.0, 53.1, 41.5, 38.1,
28.4, 24.8, 23.0, 22.1, 19.4; nmax (DMSO) 3370, 2940, 2820 cmꢀ1
;
HRMS m/z [MþH]þ calculated for C15H26N2O3: 283.2021. Found:
4 . 3 . 9 . N - B e n z y l o x y c a r b o n y l -
L
- v a l y l p r o p a r g y l a m i d e
-valine
283.2016.
(7a).41 Propargylamine (0.14 ml, 2.19 mmol), N-Cbz-
L
(509 mg, 2.03 mmol), HOBt (489 mg, 3.19 mmol), EDC$HCl
(588 mg, 3.07 mmol), and Et3N (0.6 ml, 4.30 mmol) were added to
DMF (8.5 ml) and the reaction mixture was stirred under nitrogen
at room temperature for 3 days. The reaction mixture was par-
titioned between water (50 ml) and EtOAc (50 ml). The aqueous
phase was extracted with EtOAc (2ꢂ50 ml), and the organic
phases were collected and washed with 1 M HCl (2ꢂ10 ml), water
(10 ml), aqueous saturated NaHCO3 (2ꢂ10 ml), and brine. The
solution was dried over Na2SO4 and the solvents were removed to
yield an off-white solid (515 mg, 1.79 mmol, 89%), which was
recrystallized from MeOH to yield the expected product as white,
4.3.14. N-tert-Butoxycarbonyl-
(7e). Following general procedure
(0.15 ml, 1.8 mmol) and N-Boc- -homoleucine (300 mg, 1.2 mmol)
as substrates in DMF (6 ml). N-tert-Butoxycarbonyl- -homo-
L
-homoleucinylbutynylamide
A
using 3-butynylamine
L
L
leucinylbutynylamide (7e) was isolated as a white solid (0.24 g,
20
0.81 mmol, 66%). Mp 121 ꢁC; [
a
]
D
ꢀ80.0 (c 0.1, DMSO); 1H NMR
(CDCl3): 6.69 (br s, 1H), 5.22 (br s, 1H) 3.96e3.83 (m, 1H),3,38e3.28
(m, 2H), 2.41e2.29 (m, 4H), 1.95 (t, J 2.5 Hz, 1H), 1.67e1.33 (m, 11H),
1.29e1.17 (m, 1H), 0.89 (dd, J 6.6, 1.7 Hz, 6H); 13C NMR (CDCl3):
171.5, 155.9, 81.6, 79.3, 70.0, 46.4, 43.9, 42.1, 38.2, 28.4, 25.0, 23.0,
22.1, 19.4; nmax (DMSO) 3260, 2360, 1650, 1560, 1510 cmꢀ1; HRMS
m/z [MþH]þ calculated for C16H28N2O3: 297.2178. Found: 297.2174.
needle-shaped crystals (321 mg, 1.11 mmol, 55%). Mp 171e174 ꢁC
20
(lit. ref. not found); [
a
]
ꢀ9.6 (c 0.4, CHCl3) 1H NMR (CDCl3):
D
7.42e7.28 (m, 5H), 6.39 (br s, 1H), 5.40 (br d, 1H), 5.13 (d, J
12.4 Hz, 1H), 5.10 (d, J 12.3 Hz, 1H), 4.15e3.94 (m, 3H), 2.21 (t, 1H),
2.14 (app. h, J 6.7 Hz, 1H), 0.97 (d, J 6.8 Hz, 3H), 0.93 (d, J 6.8 Hz,
3H); 13C NMR (CDCl3): 171.2, 156.6, 136.2, 128.7, 128.4, 128.2, 79.3,
71.9, 67.3, 60.5, 31.2, 29.3, 19.3, 18.0. nmax (CHCl3) 3435, 3252,
4.3.15. General procedure B 1-(Purinyl)triazoles (8beh). NaN3
(1.8e2.0 equiv) was added to 1 (1 equiv) in DMF in a microwave
vial. The vial was capped, flushed with nitrogen and the reaction
mixture was stirred for 22 h at 90 ꢁC with exclusion of light. The
reaction mixture was allowed to reach room temperature and
opened. Compounds 7beh (1.2e1.4 equiv) in DMF, CuI (20 mol %),
sodium ascorbate (0.4 equiv), and N,N0-dimethylenediamine
(0.3 equiv) were added. The microwave vial was recapped, flushed
with nitrogen, and stirred at room temperature for 22e24 h with
exclusion of light. The reaction mixture was then poured into water
(20 ml) and extracted with EtOAc (3ꢂ30 ml) (Caution! Should be
kept slightly basic to avoid hydrazoic acid formation from excess
NaN3). The organic phases were collected and dried over Na2SO4
before the solvents were removed and the crude product was pu-
rified by preparative HPLC (isocratic H2O/AcCN 50:50, 0.1% TFA)
unless otherwise mentioned.
3070, 2999, 2912, 2251, 2124, 1996, 1832, 1767, 1677, 1620 cmꢀ1
.
HRMS m/z [MþH]þ calculated for C16H21N2O3: 289.1547 Found:
289.1551.
4.3.10. N-tert-Butoxycarbonyl-L -leucinylpropargylamide
(7b).42 Compound 7b was synthesized according to a literature
procedure and analytical data were in agreement with the
literature.
4.3.11. General procedure A for N-tert-butoxycarbonyl-leucinyl and
homoleucinyl alkyne derivatives (7cee). Alkynylamine (1.5 equiv)
was added to N-Boc-L-leucine or N-Boc-L-b-homoleucine (1 equiv)
and HATU (1.1 equiv) in DMF at room temperature under nitrogen.
The solutions were cooled on ice and Et3N (3 equiv) was added,
the reaction mixture was then allowed to reach room temperature
and stirred for 22 h. The reaction mixture was diluted with
EtOAc (30 ml), washed with 0.1 M HCl (2ꢂ10 ml), saturated NaHCO3
(10 ml), brine (20 ml), dried over Na2SO4 and the solvents
were removed. The crude product was purified by automated
flash chromatography (gradient, 0e100% EtOAc in heptane).
4.3.16. N-(1(1-(6-Amino-9-ethyl-9H-purine-8-yl)-1H-1,2,3-triazol-
4-yl)methyl)-2-tert-butoxycarbonylamino-4-methynylpentanamide
(8b). Following general procedure B, using NaN3 (20 mg,
0.31 mmol), 1 (50 mg, 0.21 mmol), and 7b (70 mg, 0.25 mmol) as
substrates in DMF (3 ml). Compound 8b was isolated as a white
20
solid (31 mg, 40%). Mp 97e102 ꢁC; [
a]
ꢀ22.1 (c 0.03, DMSO); 1H
D
NMR (CDCl3): 8.40 (s, 1H), 8.33 (s, 1H), 7.96 (br s, 1H), 7.61 (br s, 1H),
5.10 (d, J 8.0 Hz, 1H), 4.89 (dd, 1H), 4.71 (q, J 7.1 Hz, 2H), 4.46 (d, 1H),
4.27 (m,1H),1.79e1.51 (m, 3H),1.48 (t, J 7.1 Hz, 3H),1.36 (s, 9H), 0.96
(d, 3H), 0.93 (d, 3H); 13C NMR (CDCl3): 173.6, 156.4, 151.7, 149.7,
145.0, 141.7, 123.1, 116.9, 80.8, 77.4, 53.5, 41.5, 35.3, 28.4, 24.9, 23.1,
21.9, 15.2; nmax (DMSO) 3431, 3262, 3001, 2959, 2914, 1695, 1606,
4.3.12. N-tert-Butoxycarbonyl-
(7c). Following general procedure A using propargylamine (40
0.62 mmol) and N-Boc- -homoleucine (100 mg, 0.62 mmol) as
substrates in DMF (4 ml). N-tert-Butoxycarbonyl- -homo-
L
-homoleucinylpropargylamide
ml,
L
L
1541 cmꢀ1
;
HRMS m/z [MþH]þ calculated for C21H32N10O3:
leucinylpropargylamide (7c) was isolated as a white solid (102 mg,
473.2737. Found: 473.2737.
20
0.36 mmol, 88%). Mp 114e116 ꢁC; [
a]
ꢀ47.7 (c 0.03, DMSO); 1H
D
NMR (CDCl3): 6.92 (br s, 1H), 5.19 (br d, J 9.2 Hz, 1H), 3.96 (dd, J 5.3,
2.6 Hz, 2H), 3.93e3.84 (m, 1H), 2.46e2.28 (m, 2H), 2.16 (t, J 2.5 Hz,
1H), 1.68e1.51 (m, 1H), 1.37 (s, 9H), 1.29e1.17 (m, 1H), 0.85 (dd, J 6.6,
2.6 Hz, 6H). 13C NMR (CDCl3): 171.1, 155.9, 79.7, 79.3, 71.3, 46.3, 43.9,
41.8, 29.1, 28.4, 24.9, 23.0, 22.1; nmax (DMSO) 3261, 2957, 1703, 1668,
4.3.17. N-(2(1-(6-Amino-9-ethyl-9H-purine-8-yl)-1H-1,2,3-triazol-
4-yl)methyl)-tert-butoxycarbonylamino-5-methylhexanamide
(8c). Following general procedure
B using NaN3 (28 mg,
0.43 mmol), 1 (70 mg, 0.29 mmol), and 7c (90 mg, 0.32 mmol) as
substrates in DMF (3 ml). Compound 8c was isolated as a white
20
1535 cmꢀ1
;
HRMS m/z [MþH]þ calculated for C15H26N2O3:
solid (56 mg, 0.12 mmol, 40%). Mp 206e207 ꢁC; [
a
]
ꢀ21.0 (c 0.1,
D
283.2021. Found: 283.2013.
DMSO); 1H NMR (CDCl3): 8.41 (s,1H), 8.39 (s, 1H), 7.02 (br s, 1H),
6.03 (br s, 2H), 5.14 (d, J 8.8 Hz, 1H), 4.69e4.56 (m, 4H), 4.01e3.87
(m, 1H), 2.57e2.38 (m, 2H), 1.64 (sept, J 6.8 Hz, 1H), 1.52e1.20 (m,
14H), 0.89 (d, J 6.6 Hz, 6H); 13C NMR (CDCl3): 171.7, 156.1, 155.2,
4.3.13. N-tert-Butoxycarbonyl-
(7d). Following general procedure
L
-leucinylbutynylamide
using 3-butynylamine
A

I.N. Redwan et al. / Tetrahedron 69 (2013) 8857e8864
8863
153.2, 150.7, 145.3, 140.1, 123.5, 117.4, 79.7, 46.5, 44.1, 42.4, 40.2,
35.0, 28.5, 25.0, 23.1, 22.1, 15.3; nmax (DMSO) 3447, 3275, 1701, 1654,
1604, 1533 cmꢀ1; HRMS m/z [MþH]þ calculated for C22H34N10O3:
487.2893. Found: 487.2877.
0.32 mmol) as substrates in DMF (3 ml). Compound 8h was isolated
as a white solid (44 mg, 0.14 mmol, 50%) after purification by au-
tomated flash chromatography (gradient, 0e10% MeOH in CHCl3).
Mp 178 ꢁC; 1H NMR (DMSO-d6): 9.28 (br s,1H), 8.31 (s,1H), 8.02 (d, J
7.3 Hz, 2H), 7.61 (br s, 1H), 7.51 (t, J 7.6 Hz, 2H), 7.43 (t, J 7.4 Hz, 1H),
4.32 (q, J 7.2 Hz, 2H), 1.36 (t, J 7.1 Hz, 3H); 13C NMR (DMSO-d6):
155.8, 155.7, 153.5, 149.9, 146.7, 139.0, 129.3, 129.1, 128.7, 122.7,
169.5, 38.9, 14.9; nmax (DMSO) 3250, 2250, 2120, 2000, 1770, 1710,
1620 cmꢀ1; HRMS m/z [MþH]þ calculated for C15H14N8: 307.1336.
Found: 307.1407.
4.3.18. N-(1(1-(6-Amino-9-ethyl-9H-purine-8-yl)-1H-1,2,3-triazol-
4-yl)ethyl)-2-tert-butoxycarbonylamino-4-methylpentanamide
(8d). Following general procedure
B using NaN3 (27 mg,
0.41 mmol), 1 (50 mg, 0.21 mmol), and 7d (70 mg, 0.25 mmol) as
substrates in DMF (3 ml). Compound 8d was isolated as a white
solid (45 mg, 0.10 mmol, 45%). Mp 128 ꢁC; [
a
]
20 ꢀ27.0 (c 0.1, DMSO);
D
1H NMR (CDCl3): 10.84 (br s, 1H), 8.31 (s, 1H), 8.21 (s, 1H), 7.82 (br s,
1H), 7.41 (br s, 1H), 5.24 (br s, 1H) 4.77e4.61 (m, 2H), 4.08e3.99 (m,
1H), 3.88e3.70 (m, 1H), 3.54e3.39 (m, 1H), 3.07 (t, J 5.9 Hz, 2H),
1.68e1.26 (m, 15H), 0.89 (dd, J 15.9, 6.3 Hz, 6H); 13C (CDCl3): 174.0,
156.3, 151.2, 149.4, 146.0, 144.4, 122.9, 116.7, 80.5, 53.3, 41.7, 41.6,
38.8, 28.4, 25.6, 24.8, 23.0, 21.8,15.4; nmax (DMSO) 3370, 2940, 2820,
4.3.23. General procedure C for Boc deprotection of 8bee. To a sus-
pension of 8bee in DCM (1 ml), TFA (1 ml) was added. The solutions
were stirred at room temperature for 1 h. The solvents and TFA
were then removed and the product was freezedried ꢂ3 from
MQ-water to yield the trifluoroacetate salt of 9bee.
1700 cmꢀ1
487.2810. Found: 487.2878.
;
HRMS m/z [MþH]þ calculated for C22H34N10O3:
4.3.24. 2-Amino-N-((1-(6-amino-9-ethyl-9H-purine-8-yl)-1H-1,2,3-
triazol-4-yl)methyl)-4-methylpentanamide (9b). Following pro-
cedure C with 8b (14.4 mg, 0.031 mmol) 9b was obtained as a white
20
4.3.19. N-(2(1-(6-Amino-9-ethyl-9H-purine-8-yl)-1H-1,2,3-triazol-
4-yl)ethyl)-3-tert-butoxycarbonylamino-5-methylhexanamide
solid (14.0 mg, 0.029 mmol, 94%). Mp 123 ꢁC; [
a
]
ꢀ18.8 (c 0.03,
D
DMSO); 1H NMR (CD3CN): 8.42 (s, 1H), 8.34 (s, 1H), 8.25 (br t, J
5.7 Hz, 1H),7.82 (br s, 4H), 4.64 (dd, J 6.1, 15.5 Hz, 1H), 4.49 (q, J
7.1 Hz, 2H), 4.43 (dd, J 5.3, 15.6 Hz, 1H), 4.09 (t, J 7.0 Hz, 1H),
1.78e1.63 (m, 3H), 1.39 (t, J 7.2 Hz, 3H), 0.93 (d, J 2.8 Hz, 3H), 0.91 (d,
J 2.8 Hz, 3H); 13C NMR (CD3CN): 170.5, 154.2, 151.0, 149.2, 146.3,
142.1, 124.7, 53.2, 41.3, 41.2, 35.8, 25.1, 22.8, 22.2, 15.2; nmax (DMSO)
3447, 3263, 1693, 1653, 1558, 1541 cmꢀ1; HRMS m/z [MþH]þ cal-
culated for C16H24N10O: 373.2213. Found: 373.2188.
(8e). Following general procedure
B using NaN3 (27 mg,
0.41 mmol), 1 (51 mg, 0.21 mmol), and 7e (75 mg, 0.25 mmol) as
substrates in DMF (3 ml). Compound 8e was isolated as a white
solid (40 mg, 0.10 mmol, 38%). Mp 143 ꢁC; [
a]
20 ꢀ30.0 (c 0.1, DMSO);
D
1H NMR (CDCl3): 8.40 (s, 1H), 8.24 (s, 1H), 6.57 (br s, 1H), 5.80
(br s, 2H), 5.18 (br s, 1H), 4.63 (q, J 14.0, 7.0 Hz, 2H) 3.94e3.83
(m, 1H), 3.73e3.59 (m, 2H), 3.04 (t, J 6.5 Hz, 1H), 2.50e2.33
(m, 2H), 1.67e1.53 (m, 1H), 1.52e1.19 (m, 14H), 0.86 (d, J 6.4 Hz, 6H);
13C NMR (CDCl3): 171.4, 156.0, 155.4, 153.8, 150.8, 145.7, 140.2, 122.5,
117.4, 79.5, 46.6, 44.0, 42.2, 40.2, 38.4, 28.5, 25.8, 25.1, 23.1, 22.2,
15.3; nmax (DMSO) 3370, 2940, 2820,1700 cmꢀ1; HRMS m/z [MþH]þ
calculated for C23H36N10O3: 501.3050. Found: 501.3036.
4.3.25. 3-Amino-N-(2-(1-(6-amino-9-ethyl-9H-purine-8-yl)-1H-
1,2,3-triazol-4-yl)methyl)-5-methylhexanamide
(9c). Following
procedure C with 8c (17 mg, 0.035 mmol), 9c was obtained as white
20
solid (18 mg, 0.035 mmol, 99%). Mp 96 ꢁC; [
a
]
ꢀ62.8 (c 0.03,
D
DMSO); 1H NMR (CD3CN): 8.42 (s, 1H), 8.35 (s, 1H), 7.90e7.62 (m,
4H), 4.62e4.45 (m, 4H), 3.65e3.55 (m, 1H), 2.68 (dd, J 16.4, 3.7 Hz,
1H), 2.59 (dd, J 16.4, 8.8 Hz, 1H), 1.69 (sept, J 6.7 Hz, 1H), 1.62e1.44
(m, 2H),1.40 (t, J 7.2 Hz, 3H), 0.90 (t, J 6.4 Hz, 6H); 13C NMR (CD3CN):
172.6, 162.5, 153.7, 150.9, 148.4, 146.4, 142.4, 124.7, 49.0, 42.2, 41.4,
36.6, 35.3, 24.9, 22.7, 22.2, 15.2. nmax (DMSO) 3449, 3298, 1696,
4.3.20. 9-Ethyl-8-(4-butyl-1H-1,2,3-triazol-1-yl)-9H-purin-6-amine
(8f). Following general procedure
0.43 mmol), 1 (70 mg, 0.29 mmol), and 1-hexyne (36
B
using NaN3 (28 mg,
l, 26 mg,
m
0.32 mmol) as substrates in DMF (3 ml). Compound 8f was isolated
as a white solid (40 mg, 0.14 mmol, 48%) after purification by au-
tomated flash chromatography (gradient, 0e10% MeOH in CHCl3).
Mp 112 ꢁC; 1H NMR (CDCl3): 8.39 (s, 1H), 8.10 (t, J 0.8 Hz, 1H), 6.21
(br s, 2H), 4.63 (q, J 7.1 Hz, 2H), 2.80 (t, J 7.7 Hz, 2H), 1.76e1.67 (m,
2H), 1.48e1.35 (m, 5H), 0.93 (t, J 7.3 Hz, 3H); 13C NMR (CDCl3):
155.2, 153.2, 150.8, 148.7, 140.6, 121.4, 117.4, 40.3, 31.2, 25.2, 22.4,
15.3, 13.9; nmax (DMSO) 3450, 3250, 3070, 3000, 2250, 2120, 2000,
1830, 1770, 1620 cmꢀ1; HRMS m/z [MþH]þ calculated for C13H18N8:
287.1649. Found: 287.1719.
1653, 1558, 1541 cmꢀ1
;
HRMS m/z [MþH]þ calculated for
C17H26N10O: 387.2369. Found: 387.2374.
4.3.26. 2-Amino-N-(2-(1-(6-amino-9-ethyl-9H-purine-8-yl)-1H-
1,2,3-triazol-4-yl)ethyl)-4-methylpentanamide (9d). Following pro-
cedure C with 8d (40 mg, 0.08 mmol), 9d was obtained as white
20
solid (38 mg, 0.08 mmol, 99%). Mp 173 ꢁC; [
a
]
ꢀ23.0 (c 0.1,
D
DMSO); 1H NMR (CD3CN): 8.40 (s, 1H), 8.36 (s, 1H), 7.89 (br s, 3H),
4.52 (q, J 7.1 Hz, 2H), 3.93 (br s, 1H), 3.67e3.49 (m, 2H), 3.00 (t, J
6.4 Hz, 2H), 1.71e1.54 (m, 3H), 1.41 (t, J 7.1 Hz, 3H), 0.87 (d, J 3.6 Hz,
6H); 13C NMR (CDCl3): 170.4, 152.7, 150.7, 146.6, 146.4, 142.9, 124.5,
117.7, 53.2, 41.6, 41.1, 39.6, 25.9, 25.1, 22.7, 22.2, 15.2; nmax (DMSO)
3360, 2940, 2820, 2510, 1870, 1830, 1770, 1690, 1650, 1610, 1540,
4.3.21. 9-Ethyl-8-(4-benzyl-1H-1,2,3-triazol-1-yl)-9H-purin-6-
amine (8g). Following general procedure B using NaN3 (28 mg,
0.44 mmol),1 (70 mg, 0.29 mmol), and 3-phenyl-1-propyne (37 mg,
0.32 mmol) as substrates in DMF (3 ml). Compound 8g was isolated
as a white solid (46 mg, 0.14 mmol, 50%) after purification by au-
tomated flash chromatography (gradient, 0e10% MeOH in CHCl3).
Mp 193 ꢁC; 1H NMR (CDCl3): 8.39 (br s, 1H), 8.01 (br s, 1H),
7.32e7.23.61 (m, 5H), 6.16 (s, 2H), 4.63 (q, J 7.1 Hz, 2H), 4.18 (br
s, 2H) 1.46 (t, J 7.1 Hz, 3H); 13C NMR (CDCl3): 155.2, 153.1, 150.7,
148.1, 140.3, 138.1, 128.9, 128.9, 127.0, 122.3, 117.3, 40.3, 32.1, 25.6,
1510 cmꢀ1
;
HRMS m/z [MþH]þ calculated for C17H26N10O:
387.2286. Found: 387.2377.
4.3.27. 3-Amino-N-(2-(1-(6-amino-9-ethyl-9H-purine-8-yl)-1H-
1,2,3-triazol-4-yl)ethyl)-5-methylhexanamide (9e). Following pro-
cedure C with 8e (35 mg, 0.07 mmol), 9e was obtained as white
15.3; nmax (DMSO) 3250, 2250, 2120, 2000, 1770, 1710, 1620 cmꢀ1
;
solid (34 mg, 0.05 mmol, 71%). Mp 183 ꢁC; [
a
]
ꢀ50.0 (c 0.1,
20
D
HRMS m/z [MþH]þ calculated for C16H16N8: 321.1492. Found:
DMSO); 1H NMR (CD3CN): 8.36 (s, 2H), 7.82 (s, 1H), 7.82 (br s, 1H),
7.74 (s, 1H), 7.30 (br s, 1H) 4.51 (q, J 7.0 Hz, 2H), 3.63e3.39 (m, 3H),
3.00 (br s, 2H), 2.59e2.29 (m, 2H), 1.71e1.46 (m 3H), 1.41 (t, J 7.1 Hz,
3H), 0.87 (t, J 6.6 Hz, 6H); 13C NMR (CDCl3): 153.3, 150.8, 147.4,
146.6,142.7,138.9,126.2,124.4, 49.0, 42.0, 41.4, 39.2, 36.7, 26.0, 24.9,
22.7, 22.2, 15.2; nmax (DMSO) 3390, 3000, 2930, 2820, 1770, 1690,
321.1560.
4.3.22. 9-Ethyl-8-(4-phenyl-1H-1,2,3-triazol-1-yl)-9H-purin-6-
amine (8h). Following general procedure B using NaN3 (28 mg,
0.44 mmol), 1 (70 mg, 0.29 mmol), and phenylacetylene (32 mg,

8864
I.N. Redwan et al. / Tetrahedron 69 (2013) 8857e8864
1670, 1510 cmꢀ1; HRMS m/z [MþH]þ calculated for C18H28N10O:
16. Belrhali, H.; Yaremchuk, A.; Tukalo, M.; Larsen, K.; Berthetcolominas, C.; Leb-
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Acknowledgements
We are thankful to the Department of Chemistry and Molecular
Biology, University of Gothenburg, the Swedish Academy of Phar-
maceutical Sciences and the Swedish Research Council (project #
62120083533) for their financial support.
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Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2013.08.023.
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