An efficient convergent synthesis of adenosine-5′-N-alkyluronamides

Article abstract of DOI:10.1016/j.tet.2007.11.100

Herein we report an efficient synthesis of adenosine-5′-N-alkyluronamides in which an enzyme-mediated deacetylation reaction is a key to the selective modification of the 5′-N-position, prior to coupling the ribose and purine components via a microwave-as

Full text of DOI:10.1016/j.tet.2007.11.100

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 1772e1777
www.elsevier.com/locate/tet
An efficient convergent synthesis of adenosine-50-N-alkyluronamides
*
Shane M. Devine, Peter J. Scammells
Department of Medicinal Chemistry, Victorian College of Pharmacy, Monash University, 381 Royal Parade, Parkville, VIC 3052, Australia
Received 25 September 2007; received in revised form 5 November 2007; accepted 29 November 2007
Available online 3 December 2007
Abstract
Herein we report an efficient synthesis of adenosine-50-N-alkyluronamides in which an enzyme-mediated deacetylation reaction is a key to
the selective modification of the 50-N-position, prior to coupling the ribose and purine components via a microwave-assisted Vorbruggen cou-
¨
pling. This approach provides access to highly functionalised adenosines with 2- and N6-substitutents, which can be incorporated before or after
the ribose-coupling step. In all cases the microwave-assisted Vorbruggen coupling conditions afforded anomerically pure purine ribosides in
¨
good to excellent yields.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
applications.1,6 Furthermore, the prototypical A3AR agonist,
Cl-IB-MECA (3), is an adenosine analogue with a 50-methyl
carboxamido group and a 3-chlorobenzyl substituent in the
N6-position.7 This compound has been shown to have cardio-
protective effects against myocardial ischemia/reperfusion in-
jury as well as potential therapeutic applications in the
treatment of liver cancer.8,9
In general, the preparation of functionalised adenosine-50-
N-uronamides has involved relatively lengthy syntheses in
which modifications are made to a nucleoside precursor such
as inosine in a linear fashion. Alternatively, convergent ap-
proaches where the appropriately functionalised purines and
sugars are coupled together have also been employed. The lat-
ter are generally more efficient for the synthesis of highly
functionalised adenosine-50-N-uronamides. Glycosylation con-
Adenosine is an endogenous purine nucleoside, which regu-
lates a number of physiological processes in the cardiac, ner-
vous and immune systems.1 Adenosine’s effects are mediated
by four receptor subtypes, namely A1, A2A, A2B and A3, which
are members of the G-protein coupled receptor superfamily.
Agonists with high adenosine receptor subtype selectivity
have therapeutic potential in a range of areas, including the
treatment of cardiovascular disease, pain, wound healing, rheu-
matoid arthritis and colorectal cancer.2 One modification which
has proven beneficial in the development of selective agonists
for the A1, A2A and A3 adenosine receptors (ARs) is the instal-
lation of a 50-N-alkyluronamide moiety. Selodenoson (1) is an
N6-substituted adenosine-50-N-ethyl uronamide, which acts as
a potent and selective agonist at the A1AR.3 A controlled release
formulation of this compound has been patented for the treat-
ment of atrial flutter and atrial fibrillation.4 A range of adeno-
sine-50-N-ethyl uronamides with additional C2 substitution
have proven to be potent and selective agonists of the A2AAR.
For example, apadenoson (ATL-146e, 2)5 is a 2-alkynyl deriva-
tive of N-ethylcarboxamidoadenosine, which acts as an anti-in-
flammatory agent and has a range of potential therapeutic
ditions developed by Vorbruggen generally afford the desired
¨
b-anomer in reasonable to good yield.10 This coupling ap-
proach requires the presence of an anomeric acyloxy moiety
and ester protection of the 20-hydroxy as the reaction proceeds
via a cyclic 1,2-acyloxonium intermediate upon treatment with
a Lewis acid. These structural features are incompatible with
the typical reaction conditions required for the introduction
of the carboxamido group in the 50-position, which generally
necessitates the use of a convoluted protecting group strategy.
For example, the original synthesis of 2-chloro-N6-(3-iodoben-
zyl)adenosine-50-N-methyl uronamide (Cl-IB-MECA, 3)11
was achieved in a 10-step sequence in which the modified
* Corresponding author. Tel.: þ61 3 9903 9542; fax: þ61 3 9903 9582.
E-mail address: peter.scammells@vcp.monash.edu.au (P.J. Scammells).
0040-4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.11.100

S.M. Devine, P.J. Scammells / Tetrahedron 64 (2008) 1772e1777
1773
Cl
HN
N
NH2
HN
N
O
N
N
N
N
N
N
N
N
N
H
N
H
N
H
N
OCH3
O
O
O
O
O
O
N
Cl
H3C
OH
OH
OH
HO
HO
HO
Selodenoson
(RG14202, 1)
Apadenoson
(ATL-146e, 2)
Cl-IB-MECA (3)
sugar, N-methyl-1-O-acetyl-2,3-dibenzoyl-D-ribofuranurona-
mide, was prepared in 8 steps and coupled to the appropriate
substituted purine prior to deprotection. The coupling step
the lipase, Candida rugosa (CRL Type VII, Sigma 1754),
under the conditions that were reported by Fernandez-Lorente
et al.12 and subsequently optimised by Chien and Chern.13 Se-
lective deprotection of primary acetyl esters of carbohydrates
and nucleosides has also been achieved with iodine and meth-
anol.14 In our case, these reaction conditions failed to produce
any detectable amounts of the desired deacetylated product.
Oxidation of the alcohol 5 with TEMPO and BAIB in a 1:1
mixture of MeCN/H2O15 afforded the corresponding 5-carboxy-
lic acid 6 in good yield. This acid was treated without purifica-
tion with EDCI and DMAP in methanol to give methyl 1,2,3-
tri-O-acetyl-b-D-ribofuronate (7). The overall yield of this
strategy from the tetraacetyl ribose was 43%, which is an im-
provement over previous methods.
was performed using the conditions developed by Vorbruggen
¨
and proceeded in quite modest yield (33%). Moreover, the
overall yield of this approach was 1.7%, highlighting the
need for a more efficient synthetic route. The same research
team subsequently developed an improved approach in which
methyl 1,2,3-tri-O-acetyl-b-D-ribofuronate was prepared from
D-ribose in four steps (17% yield) and coupled with the purine
base prior to 50-carboxamide formation and deprotection.11
This coupling reaction afforded a mixture of isomers, which
necessitated the use of chromatography to isolate the desired
b-anomer in 52% yield. Overall, this six-step sequence pro-
vided Cl-IB-MECA in 5.6% yield.
We now report an improved synthetic approach to adeno-
sine-50-N-alkyluronamides in which an enzyme-mediated de-
protection provides selective access to the 50-position of the
ribose and a microwave-assisted coupling affords the desired
nucleosides in good to excellent yield.
Methyl 1,2,3-tri-O-acetyl-b-D-ribofuronate (7) was subse-
quently coupled with a range of purine bases using the general
reaction conditions developed by Vorbruggen. The purines
¨
8ae8g were heated under reflux in HMDS with a catalytic
amount of (NH4)2SO4 and the excess HMDS was evaporated
at reduced pressure (Scheme 1). The silylated purines were
then coupled to the triacetylated ribofuronate 7 in DCE with
TMSOTf in a Biotage microwave reactor for 20 min at
90 ꢀC. After the reaction a pale yellow solution is formed,
which was then carefully treated with saturated NaHCO3
and extracted into CH2Cl2 to give the coupled products
9ae9g. Adenine coupled with 7 to form the corresponding aden-
osine analogue 9a in good yield (71%) (entry 1, Table 1). N6-
Substituted adenosines could also be efficiently prepared using
2. Results and discussion
In our approach the desired 5-modified sugar, methyl 1,2,3-
tri-O-acetyl-b-D-ribofuronate (7), was prepared in three steps
from the commercially available starting material, 1,2,3,5-
tetra-O-acetyl-b-D-ribofuranoside (4) (Scheme 1). This ini-
tially involved selective deacylation at the 5-position using
AcO
HO
HO
O
O
H3CO
O
O
OAc
OAc
OAc
OAc
(i)
(ii)
(iii)
O
O
AcO OAc
AcO OAc
AcO OAc
AcO OAc
4
5
6
7
(iv)
X
N
N
X
N
X
N
N
H
N
Y
N
N
N
N
8
H
N
O
O
(v)
H3CO
O
O
N
N
Y
Y
H3C
OH
AcO
OAc
HO
10
9
Scheme 1. Reagents and conditions: (i) Candida rugosa lipase, 9:1 (0.1 M sodium phosphate buffer (ph 7.0)/DMF), 25 ꢀC, 50e80%; (ii) TEMPO, C6H5I(OAc)2,
25 ꢀC; (iii) EDCI, DMAP, MeOH, 25 ꢀC, 63% (over two steps); (iv) (a) 8, HMDS, (NH4)2SO4, 125 ꢀC; (b) 7, TMSOTf, DCE, 90 ꢀC [MW], 63e91%; (v) for
9ae9e: MeNH2, THF, 110 ꢀC [MW], 58e69%.

1774
S.M. Devine, P.J. Scammells / Tetrahedron 64 (2008) 1772e1777
Table 1
Efficiency of microwave-assisted riboseepurine coupling
CH3
Cl
HN
N
N
N
(i)
N
N
Entry
Product (9)
X
Y
Yield %a
N
N
X
H
N
H3CO
O
O
N
X
H3C
1
2
3
4
5
6
7
8
a
9a
9b
9c
9d
9e
9f
NH2
NHBn
NH2
NH2
NHBn
Cl
H
71
75
89
63
71
81
91
89
O
O
H
Cl
AcO OAc
OH
HO
C^CPh
9f-g
11a X = H
11b X = Cl
Cl
H
Cl
I
(ii)
9g
9h
Cl
Cl
NHBn
NHBn
N
Isolated yields following column chromatography.
N
N
N
H
N
this approach, as exemplified by the coupling of N6-benzylade-
nine with 7, which proceeded in 75% yield (entry 2, Table 1).
A substituent in the 2-position was well tolerated as evidenced
by the coupling of 2-chloroadenine and 2-(2-phenylethynyl)-
adenine in 89% and 63% yield, respectively (entries 3 and 4,
Table 1). One example of a 2,N6-disubstituted adenine was
also included (2-chloro-N6-benzyladenine, entry 5, Table 1)
and proceeded in the identical yield to adenine itself (71%).
In all cases there was no sign of the unwanted a-anomer ap-
parent in the 1H NMR spectrum of the crude reaction products.
This reaction was significantly more efficient than closely re-
lated couplings of 2,N6-disubstituted adenines performed with
conventional heating. For example, the coupling of 2-chloro-
N6-(3-iodobenzyl)adenine with 7 was heated at reflux for
48 h and afforded a 52% yield of the desired product along
with 12% of the corresponding a-anomer.11 The improved ef-
ficiency of the microwave-assisted process may have resulted
from more effective generation of the initial acetoxonium ion
intermediate (thereby reducing the formation of the a-anomer)
and/or the shorter reaction time minimising the amount of de-
composition of material relative to an extended period of re-
flux. The halopurines 8fe8h were also converted to the
corresponding purine ribosides in excellent yields ranging
from 81% to 91% (entries 6e8, Table 1).
N
X
O
N
H3CO
O
N
N
X
H3C
O
O
AcO OAc
9e
OH
HO
10e
Scheme 2. Reagents and conditions: (i) MeNH2 (excess), THF, 110 ꢀC [MW],
68% (X¼H), 65% (X¼Cl); (ii) from 9g: (a) NH2Bn (1 equiv), DIPEA, MeOH,
80 ꢀC [MW], 79%; (b) MeNH2 (excess) in THF, 110 ꢀC [MW], 60%.
and 9g with excess methylamine, which simultaneously ef-
fected N6-substitution and N-methylcarboxamide formation at
C50 as well as deprotection of the 20- and 30-hydroxyls to form
the corresponding N6-methyladenosine-50-methyl uronamides
in 68% and 65% yield, respectively (Scheme 2). Alternatively,
the use of 1 molar equiv of amine allowed the N6-substituent
to be installed selectively, followed by 50-carboxamide forma-
tion with concomitant deprotections with a different amine.
The use of 1 equiv of benzylamine followed by a 20-fold excess
of methylamine afforded 2-chloro-N6-benzyladenosine-50-N-
methyl uronamide (10e) in an overall yield of 47% from 9g.
3. Conclusions
An efficient and high yielding synthesis of adenosine-
50-uronamides as well as 2- and/or N6-substituted adenosine-
50-uronamides has been developed. In this work, methyl
1,2,3-tri-O-acetyl-b-D-ribofuronate (7) was prepared in three
steps from commercially available sugar, 1,2,3,5-tetra-O-ace-
tyl-b-D-ribofuranose (4) and then coupled to a range of purine
bases. The coupling reactions were achieved in good to high
During the course of this research a related microwave-as-
sisted glycosylation reaction was reported in the literature.16
In this case the Vorbruggen coupling was adapted to a one-
¨
step microwave-assisted protocol, which proceeded at 130 ꢀC
for 5 min. Although this approach was quite efficient for the
generation of nucleoside libraries, it was generally low yielding
and therefore less useful for preparative applications. For ex-
ample, the coupling of N6-benzyladenine and 1-O-acetyl-2,
3,5-tri-O-benzoyl-b-D-ribofuranose afforded the corresponding
adenosine in 11% yield, along with 9% of the N7-glycosylated
product. Likewise, 6-chloropurine was coupled with the same
sugar to afford 6-chloropurine riboside in 29% yield.
yield (63e91%) using a microwave-assisted Vorbruggen reac-
¨
tion. Subsequent 50-carboxamide formation with concomitant
20,30-deprotection afforded the desired target products. When
2,6-dihalopurine ribofuronates were prepared via this
approach it was also possible to functionalise these positions
post-coupling.
The coupled products 9ae9e were subsequently treated
with methylamine in THF, which introduced the 50-carbox-
amide with concomitant deprotection of 20- and 30-hydroxyls
to afford the desired adenosine-50-N-methyl uronamides
(10ae10e) in good yield (Scheme 1).
4. Experimental
4.1. General
The halogenated purine ribosides 9fe9h are versatile syn-
thetic intermediates, which can be readily functionalised in
the 2-, 50- and/or 6-positions via nucleophilic or organometallic
coupling protocols. This was exemplified by the treatment of 9f
Melting points were determined on an Electrothermal melt-
ing point apparatus and are uncorrected. All microwave reac-
tions took place in a Biotage Initiator Microwave Synthesiser.
All NMR spectra were recorded on a Bruker Avance DPX 300

S.M. Devine, P.J. Scammells / Tetrahedron 64 (2008) 1772e1777
1775
spectrometer and H and 13C NMR spectra were recorded at
300.13 MHz and 75.4 MHz, respectively. Infrared spectra
were recorded with a Scimitar Series Varian 800 FT-IR Spec-
trometer fitted with a PIKE Technologies MIRacle ATR and
samples were run as pure solids. High Resolution Mass Spec-
trometry analyses were collected on a Waters Micromass LCT
Premier XE TOF mass spectrometer fitted with an ESI ion
source. Optical rotations were measured on an Atago polari-
meter. Thin layer chromatography was conducted on 0.2 mm
plates using Merck silica gel 60 F254. Column chromatography
was achieved using Merck silica gel 60 (particle size 0.063e
0.200 mm, 70e230 mesh). Adenine was purchased from the
SigmaeAldrich Chemical company, while 6-chloropurine
and 2,6-dichloropurine were obtained from Advanced Mole-
cular Technologies. The other purines that were used were
prepared by literature methodology.17
4.2. General procedure for the riboseepurine coupling
1
A mixture of purine (8, 1.2 molar equiv), ammonium sulfate
(0.25 molar equiv) and hexamethyldisilazane was heated under
reflux for 16 h under nitrogen. The solution was concentrated to
dryness and dissolved in anhydrous DCE and a solution of
methyl 1,2,3-tri-O-acetyl-b-D-ribofuronate (7) (1 molar equiv)
in anhydrous DCE and TMS triflate (2.0 molar equiv) was
added. In the cases of 9a, 9c and 9d, anhydrous MeCN was
added to solubilise the silylation step. The mixture was then
heated in the microwave (90 ꢀC, 20 min) under nitrogen. A
saturated solution of NaHCO3 was added and the whole was
stirred for 15 min. The aqueous layer was then extracted with
DCM (ꢁ2), washed with brine (ꢁ2), dried over MgSO4, filtered
and concentrated to dryness to afford 9 as a foamy residue,
which was routinely reacted further without purification.
4.1.1. 1,2,3-Tri-O-acetyl-b-D-ribofuranose (5)
4.2.1. Methyl 1-[adenin-9-yl]-2,3-di-O-acetyl-b-D-
ribofuronate (9a)
A solution of 1,2,3,5-tetra-O-acetyl-b-D-ribofuranose (4)
(3.82 g, 12 mmol) in N,N-dimethylformamide (30 mL) was di-
luted with 0.1 M pH 7.0 sodium phosphate buffer (270 mL)
and C. rugosa lipase [5.93 g, lipase/ribose¼1.5:1 (w/w)] was
stirred very slowly at room temperature for 24 h. The mixture
was filtered and the filtrate extracted with EtOAc (3ꢁ500 mL),
washed with brine (2ꢁ500 mL), dried with MgSO4 and evapo-
rated under reduced pressure. The subsequent oil was purified
by silica column chromatography (Et2O, Rf¼0.35) to give 5
as a colourless oil in yields of 50e80%. [a]2D0 ꢂ8.61 (lit.13
ꢂ10.44). 1H NMR (CDCl3): d 2.06 (s, 3H, OAc), 2.09 (s, 3H,
OAc), 2.12 (s, 3H, OAc), 3.61e3.67 (m, 1H, H-5), 3.79e3.84
(m, 1H, H-5), 4.22e4.26 (m, 1H, H-4), 5.32e5.40 (m, 2H,
H-2, H-3), 6.12 (s, 1H, H-1).
Adenine (8a) (30 mg, 0.224 mmol), (NH4)2SO4 (6 mg,
0.047 mmol), anhydrous MeCN (2 mL) in HMDS (2 mL), and
then 7 (57 mg, 0.187 mmol), TMSOTf (68 mL, 0.375 mmol)
in DCE (4 mL) gave 9a (hexane/EtOAc, 1:1, Rf¼0.05) as a col-
1
ourless foam (50 mg, 71%). H NMR (CDCl3): d 2.09 (s, 3H,
OAc), 2.23 (s, 3H, OAc), 3.89 (s, 3H, OMe), 4.80 (s, 1H,
H-40), 5.84e5.89 (m, 2H, H-20, H-30), 6.07 (br s, 2H, NH2),
6.50 (d, J¼6.0 Hz, 1H, H-10), 8.39 (s, 1H), 8.46 (s, 1H).
ESMS calcd for C15H18N5Oþ7 (MþH) 380.1, found 380.4.
4.2.2. Methyl 1-[N6-(benzyl)adenin-9-yl]-2,3-di-O-acetyl-b-
D-ribofuronate (9b)
N6-Benzylaminoadenine (8b) (57 mg, 0.253 mmol),
(NH4)2SO4 (7 mg, 0.053 mmol) in HMDS (2 mL), and then 7
(64 mg, 0.211 mmol), TMSOTf (76 mL, 0.421 mmol) in DCE
(4 mL) gave 9b (hexane/EtOAc, 1:1, Rf¼0.15) as a yellow
4.1.2. Methyl 1,2,3-tri-O-acetyl-b-D-ribofuronate (7)
A solution of 5 (1.68 g, 6.08 mmol), TEMPO (238 mg,
1.52 mmol) and BAIB (4.11 g, 12.77 mmol) in MeCN/H2O
(1:1) was stirred at room temperature for 16 h and reduced in
vacuo to a third of its volume. The residue was then extracted
with DCM (3ꢁ50 mL) and the combined organic fractions
were washed with water, then brine, dried (MgSO4), filtered
and the filtrate was evaporated to dryness. A solution of the re-
sultant oil (1.63 g) in MeOH (50 mL) was treated with EDCI
(2.69 g, 14.05 mmol) and DMAP (172 mg, 1.41 mmol) and
then stirred at room temperature for 2 h. The MeOH was evap-
orated and the residue extracted with DCM (3ꢁ50 mL), washed
with water (50 mL), then brine (2ꢁ50 mL). The organic
extracts were dried over MgSO4, filtered and concentrated to
dryness. The yellow oil was then purified by silica column chro-
matography (hexane/EtOAc, 1:1, Rf¼0.30) to give 7 as a colour-
1
foam (74 mg, 75%). H NMR (CDCl3): d 2.06 (s, 3H, OAc),
2.21 (s, 3H, OAc), 3.87 (s, 3H, OMe), 4.77 (s, 1H, H-40), 4.92
(br s, 2H, CH2), 5.79e5.83 (m, 2H, H-20, H-30), 6.33 (s, 1H,
NH), 6.47 (d, J¼6.3 Hz, 1H, H-10), 7.29e7.42 (m, 5H, ArH),
8.35 (s, 1H), 8.42 (s, 1H). ESMS calcd for C22H24N5O7þ
(MþH) 470.2, found 470.2.
4.2.3. Methyl 1-[2-chloroadenin-9-yl]-2,3-di-O-acetyl-b-D-
ribofuronate (9c)
2-Chloroadenine (8c) (33 mg, 0.197 mmol), (NH4)2SO4
(5 mg, 0.041 mmol), anhydrous MeCN (2 mL) in HMDS
(2 mL), and then 7 (50 mg, 0.164 mmol), TMSOTf (59 mL,
0.329 mmol) in DCE (4 mL) gave 9c (hexane/EtOAc, 1:1,
Rf¼0.05) as a colourless foam (60 mg, 89%). 1H NMR
(CDCl3): d 2.10 (s, 3H, OAc), 2.26 (s, 3H, OAc), 3.92 (s, 3H,
OMe), 4.80 (s, 1H, H-40), 5.77e5.81 (m, 2H, H-20, H-30),
6.31 (br s, 2H, NH2), 6.45 (d, J¼6.6 Hz, 1H, H-10), 8.47
(s, 1H, H-8). ESMS calcd for C15H17ClN5Oþ7 (MþH) 414.1,
416.1, found 413.2.
1
less oil (805 mg, 63%). H NMR (CDCl3): d 2.07 (s, 6H,
2ꢁOAc), 2.11 (s, 3H, OAc), 3.76 (s, 3H, OMe), 4.58
(d, J¼6.3 Hz, 1H), 5.33 (d, J¼4.8 Hz, 1H), 5.61 (dd, J¼6.3,
4.8 Hz, 1H), 6.17 (s, 1H, H-1). 13C NMR (CDCl3): d 20.3,
20.4, 20.8, 52.7, 72.5, 73.8, 79.1, 98.5, 168.9, 169.3, 169.4,
169.7.

1776
S.M. Devine, P.J. Scammells / Tetrahedron 64 (2008) 1772e1777
4.2.4. Methyl 1-[2-(phenylethynyl)adenin-9-yl]-2,3-di-O-
acetyl-b-D-ribofuronate (9d)
1547, 1340, 1201, 729. 1H NMR (CDCl3): d 2.09 (s, 3H,
OAc), 2.26 (s, 3H, OAc), 3.90 (s, 3H, OMe), 4.81 (s, 1H, H-
40), 5.76e5.80 (m, 2H, H-20, H-30), 6.47 (d, J¼6.3 Hz,
1H, H-10), 8.77 (s, 1H, H-8). HRMS (ESI) calcd for
C15H15ClIN4Oþ7 (MþH) 524.9669, found 524.9678.
2-(2-Phenylethynyl)adenine (8d) (60 mg, 0.257 mmol),
(NH4)2SO4 (7 mg, 0.053 mmol), anhydrous MeCN (2 mL) in
HMDS (2 mL), and then 7 (65 mg, 0.214 mmol), TMSOTf
(77 mL, 0.428 mmol) in DCE (4 mL) gave 9d (hexane/EtOAc,
1:1, Rf¼0.05) as a yellow foam (65 mg, 63%). 1H NMR
(CDCl3): d 2.11 (s, 3H, OAc), 2.26 (s, 3H, OAc), 3.92 (s, 3H,
OMe), 4.80 (s, 1H, H-40), 5.68e5.87 (m, 2H, H-20, H-30),
6.00 (br s, 2H, NH2), 6.60 (d, J¼6.6 Hz, 1H, H-10), 7.41e
7.43 (m, 3H, ArH), 7.70e7.72 (m, 2H, ArH), 8.59 (s, 1H,
H-8). ESMS calcd for C23H22N5Oþ7 (MþH) 480.2, found 480.3.
4.3. General procedure for carboxamide formation and
deprotection
4.3.1. Adenosine-50-N-methyl uronamide (10a)
MeNH2 (2.0 M) in THF (1 mL) was added to the foamy
residue (9a) (45 mg, 0.119 mmol) in THF (1 mL) and heated
in a Biotage microwave reactor in a 2e5 mL microwave vial
(110 ꢀC, 20 min). The solution was then evaporated onto
SiO2 and purified by column chromatography to give 10a
(CHCl3/MeOH/Et3N, 89:10:1, Rf¼0.05) as a colourless solid
4.2.5. Methyl 1-[N6-benzyl-2-chloroadenin-9-yl]-2,3-di-O-
acetyl-b-D-ribofuronate (9e)
N6-Benzyl-2-chloroadenine (8e) (53 mg, 0.205 mmol),
(NH4)2SO4 (6 mg, 0.043 mmol) in HMDS (2 mL), and then
7 (52 mg, 0.171 mmol), TMSOTf (62 mL, 0.342 mmol) in
DCE (4 mL) gave 9e (hexane/EtOAc, 1:1, Rf¼0.05) as a yellow
1
(24 mg, 69%). H NMR (CD3OD): d 2.90 (s, 3H, NHCH3),
4.35 (dd, J¼4.8, 1.2 Hz, 1H, H-30), 4.51 (s, 1H, H-40), 4.77
(dd, J¼7.5, 4.8 Hz, 1H, H-20), 6.05 (d, J¼7.5 Hz, 1H, H-10),
8.29 (s, 1H), 8.31 (s, 1H). 13C NMR (CD3OD): d 26.2, 73.6,
75.1, 86.7, 90.7, 120.9, 142.8, 151.7, 154.0, 157.2, 173.0.
ESMS calcd for C11H15N6Oþ4 (MþH) 295.1, found 295.2.
1
foam (65 mg, 71%). H NMR (CDCl3): d 2.11 (s, 3H, OAc),
2.27 (s, 3H, OAc), 3.93 (s, 3H, OMe), 4.79 (s, 1H, H-40),
4.88 (br s, 2H, CH2), 5.76e5.80 (m, 2H, H-20, H-30), 6.24
(s, 1H, NH), 6.48 (d, J¼6.0 Hz, 1H, H-10), 7.36e7.43
(m, 5H, ArH), 8.40 (s, 1H, H-8). ESMS calcd for
C22H23ClN5Oþ7 (MþH) 504.1, 506.1, found 504.2, 506.2.
4.3.2. N6-Benzyladenosine-50-N-methyl uronamide (10b)
Compound 9b (74 mg, 0.158 mmol) in THF (1 mL) and
MeNH2 (2.0 M) in THF (1 mL) gave 10b (CHCl3/MeOH/
Et3N, 89:10:1, Rf¼0.20) as a colourless solid (37 mg, 61%).
1H NMR (CD3OD): d 2.89 (s, 3H, NHCH3), 4.35 (d,
J¼4.8 Hz, 1H, H-30), 4.51 (s, 1H, H-40), 4.77 (dd, J¼7.8,
4.8 Hz, 1H, H-20), 4.85 (br s, 2H, CH2), 6.04 (d, J¼7.8 Hz,
1H, H-10), 7.23e7.41 (m, 5H, ArH), 8.25 (s, 1H), 8.33
(s, 1H). 13C NMR (CD3OD): d 24.7, 43.6, 72.2, 73.6, 85.0,
89.1, 120.2, 126.9, 127.4, 128.4, 135.3, 138.8, 140.7, 152.5,
154.9, 171.3. ESMS calcd for C18H21N6Oþ4 (MþH) 385.2,
found 385.2.
4.2.6. Methyl 1-[6-chloropurin-9-yl]-2,3-di-O-acetyl-b-D-
ribofuronate (9f)
6-Chloropurine (8f) (31 mg, 0.197 mmol), (NH4)2SO4
(5 mg, 0.041 mmol) in HMDS (2 mL), and then 7 (50 mg,
0.164 mmol), TMSOTf (59 mL, 0.329 mmol) in DCE (4 mL)
gave 9f (hexane/EtOAc, 1:1, Rf¼0.15) as a yellow foam
1
(53 mg, 81%). H NMR (CDCl3): d 2.10 (s, 3H, OAc), 2.27
(s, 3H, OAc), 3.93 (s, 3H, OMe), 4.83 (s, 1H, H-40), 5.80e
5.90 (m, 2H, H-20, H-30), 6.56 (d, J¼6.6 Hz, 1H, H-10), 8.81
(s, 1H), 8.86 (s, 1H). ESMS calcd for C15H15N4Oþ7 (MþH)
399.8, found 399.3.
4.3.3. 2-Chloroadenosine-50-N-methyl uronamide (10c)
Compound 9c (50 mg, 0.121 mmol) in THF (1 mL) and
MeNH2 (2.0 M) in THF (1 mL) gave 10c (CHCl3/MeOH/
Et3N, 89:10:1, Rf¼0.05) as a colourless solid (26 mg, 65%).
1H NMR (CD3OD): d 2.96 (s, 3H, NHCH3), 4.34 (d,
J¼4.8 Hz, 1H, H-30), 4.50 (s, 1H, H-40), 4.71 (dd, J¼7.8,
4.8 Hz, 1H, H-20), 5.98 (d, J¼7.8 Hz, 1H, H-10), 8.25 (s, 1H,
H-8). 13C NMR (CD3OD): d 25.1, 71.8, 73.4, 85.0, 89.2,
120.2, 141.5, 149.9, 153.8, 157.0, 171.0. ESMS calcd for
C11H14ClN6Oþ4 (MþH) 329.1, 331.1, found 329.0, 330.9.
4.2.7. Methyl 1-[2,6-dichloropurin-9-yl]-2,3-di-O-acetyl-b-
D-ribofuronate (9g)
2,6-Dichloropurine (8g) (45 mg, 0.237 mmol), (NH4)2SO4
(7 mg, 0.049 mmol) in HMDS (2 mL), and then 7 (60 mg,
0.197 mmol), TMSOTf (71 mL, 0.395 mmol) in DCE (4 mL)
gave 9g (hexane/EtOAc, 1:1, Rf¼0.15) as a yellow foam
1
(78 mg, 91%). H NMR (CDCl3): d 2.09 (s, 3H, OAc), 2.26
(s, 3H, OAc), 3.91 (s, 3H, OMe), 4.83 (s, 1H, H-40), 5.75e
5.81 (m, 2H, H-20, H-30), 6.50 (d, J¼6.3 Hz, 1H, H-10), 8.90
(s, 1H, H-8). ESMS calcd for C15H15Cl2N4Oþ7 (MþH) 433.0,
435.0, found 433.3, 435.2.
4.3.4. 2-(Phenylethynyl)adenosine-50-N-methyl uronamide
(10d)
Compound 9d (55 mg, 0.115 mmol) in THF (1 mL) and
MeNH2 (2.0 M) in THF (1 mL) gave 10d (CHCl3/MeOH/
Et3N, 89:10:1, Rf¼0.20) as a colourless solid (26 mg, 58%).
1H NMR (CD3OD): d 3.00 (s, 3H, NHCH3), 4.36 (d,
J¼4.8 Hz, 1H, H-30), 4.52 (s, 1H, H-40), 4.71 (dd, J¼7.8,
4.8 Hz, 1H, H-20), 6.03 (d, J¼7.8 Hz, 1H, H-10), 7.41e7.47
(m, 3H, ArH), 7.61e7.64 (m, 2H, ArH), 8.32 (s, 1H, H-8).
13C NMR (CD3OD): d 25.9, 72.2, 74.0, 85.3, 85.7, 89.8, 97.6,
4.2.8. Methyl 1-[6-chloro-2-iodopurin-9-yl]-2,3-di-O-
acetyl-b-D-ribofuronate (9h)
2-Iodo-6-chloropurine (8h) (46 mg, 0.167 mmol), (NH4)2SO4
(5 mg, 0.035 mmol) in HMDS (2 mL), and then 7 (42 mg,
0.138 mmol), TMSOTf (50 mL, 0.276 mmol) in DCE (4 mL)
gave 9h as a colourless foam onto SiO2 (hexane/EtOAc, 1:1,
Rf¼0.15) as a yellow foam (64 mg, 89%). IR n 1748, 1583,

S.M. Devine, P.J. Scammells / Tetrahedron 64 (2008) 1772e1777
1777
120.1, 121.8, 129.0, 129.9, 132.2, 142.8, 146.7, 149.4, 156.9,
171.9. ESMS calcd for C19H19N6Oþ4 (MþH) 395.1, found
395.2.
Et3N, 89:10:1, Rf¼0.15) as a colourless solid (26 mg, 65%).
IR n 3361, 3287, 3127, 2857, 1618, 1582, 1352, 1310, 1225,
1046, 869, 621. 1H NMR (CD3OD): d 2.97 (s, 3H, CONHCH3),
3.11 (br s, 3H, NHCH3), 4.33 (d, J¼4.8 Hz, 1H, H-30), 4.49
(s, 1H, H-40), 4.70 (dd, J¼7.8, 4.8 Hz, 1H, H-20), 5.97 (d,
J¼7.8 Hz, 1H, H-10), 8.18 (s, 1H, H-8). 13C NMR (CD3OD): d
25.1, 26.3, 71.8, 73.5, 85.1, 89.2, 119.5, 141.0, 149.9, 153.7,
155.9, 171.4. HRMS (ESI) calcd for C12H15ClN6O4$Naþ
(MþNa) 365.0736, found 365.0741.
4.3.5. N6-Benzyl-2-chloroadenosine-50-N-methyl uronamide
(10e)
Method A. Compound 9e (62 mg, 0.123 mmol) in THF
(1 mL) and MeNH2 (2.0 M) in THF (1 mL) gave 10e (CHCl3/
MeOH/Et3N, 89:10:1, Rf¼0.20) as a pale yellow solid
1
(31 mg, 60%). H NMR (CD3OD): d 2.96 (s, 3H, NHCH3),
4.34 (d, J¼4.8 Hz, 1H, H-30), 4.50 (s, 1H, H-40), 4.71 (dd,
J¼7.5, 4.8 Hz, 1H, H-20), 4.80 (br s, 2H, CH2), 5.96 (d,
J¼7.5 Hz, 1H, H-10), 7.27e7.43 (m, 5H, ArH), 8.20 (s, 1H,
H-8). 13C NMR (CD3OD): d 25.1, 43.8, 71.8, 73.5, 85.1,
89.2, 119.5, 127.0, 127.4, 127.7, 128.2, 138.5, 149.0, 153.8,
155.3, 171.5. HRMS (ESI) calcd for C18H19ClN6O4$Naþ
(MþNa) 441.1049, found 441.1054.
Acknowledgements
The authors wish to thank the ARC Centre of Excellence
for Free Radical Chemistry and Biotechnology for financial
support and Dr. Richard Foitzik for his generous contribution
of 6-chloro-2-iodopurine.
Method B. A solution of 9g (56 mg, 0.130 mmol), BnNH2
(14 mL, 0.130 mmol) and DIPEA (25 mL, 0.143 mmol) in
MeOH (2 mL) was heated in a microwave reactor at 80 ꢀC
for 10 min. The solution was then evaporated onto SiO2 and
purification by column chromatography (hexane/EtOAc, 1:1,
Rf¼0.20) gave 9e as a colourless foam (46 mg, 79%). This
was then dissolved in THF (1 mL) and 2.0 M MeNH2 in THF
(1 mL) was added and heated at 110 ꢀC for 20 min in a micro-
wave reactor. The solution was evaporated onto SiO2 and puri-
fied by column chromatography, which gave 10e (CHCl3/
MeOH/Et3N, 89:10:1, Rf¼0.20) as a pale yellow solid (23 mg,
60%), which had an identical 1H NMR spectrum to the previous
preparation.
References and notes
1. For a recent review see: Jacobson, K. A.; Gao, Z.-G. Nat. Rev. Drug
Discov. 2006, 5, 247e264.
2. Jacobson, M. A. Expert Opin. Ther. Patents 2002, 12, 489e501.
3. Hamilton, H. W.; Patt, W. C. Eur. Pat. Appl. EP222330, 1987; Chem.
Abstr. 1987, 107, 134632.
4. Shrikant, G.; Wheeler, W.; McDonald, S.; O’Dell, S. PCT Int. Appl.
WO2004100964, 2004; Chem. Abstr. 2004, 141, 420439.
5. Rieger, J. M.; Brown, M. L.; Sullivan, G. W.; Linden, J.; MacDonald, T. L.
J. Med. Chem. 2001, 44, 531e539.
6. Cristalli, G.; Cacciari, B.; Dal Ben, D.; Lambertucci, C.; Moro, S.;
Spalluto, G.; Volpini, R. ChemMedChem 2007, 2, 260e281.
7. Kim, H. O.; Ji, X.-D.; Siddiqi, S. M.; Olah, M. E.; Stiles, G. L.; Jacobson,
K. A. J. Med. Chem. 1994, 37, 3614e3621.
8. Ge, Z.-D.; Peart, J. N.; Kreckler, L. M.; Wan, T. C.; Jacobson, M. A.;
Gross, G. J.; Auchampach, J. A. J. Pharmacol. Exp. Ther. 2006, 319,
1200e1210.
4.3.6. N6-Methyladenosine-50-N-methyl uronamide (11a)
Compound 9f (57 mg, 0.143 mmol) in THF (1 mL) and
MeNH2 (2.0 M) in THF (1 mL) gave 11a (CHCl3/MeOH/
Et3N, 89:10:1, Rf¼0.10) as a colourless solid (30 mg, 68%).
IR n 3234, 3095, 2941, 1630, 1580, 1356, 1305, 1223, 1055,
9. Fishman, P.; Bar-Yehuda, S. PCT Int. Appl. WO2007043054, 2007;
Chem. Abstr. 2007, 146, 435182.
10. Vorbruggen, H.; Ruh-Pohlenz, C. Org. React. 2000, 55, 1e630.
¨
11. Kim, H. O.; Hawes, C.; Towers, P.; Jacobson, K. A. J. Labelled Compd.
Radiopharm. 1996, 38, 547e560.
1
865, 633. H NMR (CD3OD): d 2.97 (s, 3H, CONHCH3),
3.11 (br s, 3H, NHCH3), 4.33 (d, J¼4.8 Hz, 1H, H-30), 4.49
(s, 1H, H-40), 4.70 (dd, J¼7.8, 4.8 Hz, 1H, H-20), 5.97
(d, J¼7.8 Hz, 1H, H-10), 8.18 (s, 1H), 8.30 (s, 1H). 13C NMR
(CD3OD): d 24.7, 26.3, 72.1, 73.6, 85.1, 89.1, 120.3, 140.6,
152.5, 155.5, 161.9, 171.4. ESMS calcd for C12H18N6O4þ
(MþH) 309.1, found 309.4.
4.3.7. 2-Chloro-N6-methyladenosine-50-N-methyl uronamide
(11b)
Compound 9g (51 mg, 0.118 mmol) in THF (1 mL) and
MeNH2 (2.0 M) in THF (1 mL) gave 11b (CHCl3/MeOH/
12. Fernandez-Lorente, G.; Palomo, J. M.; Cocca, J.; Mateo, C.; Moro, P.;
Terreni, M.; Fernandez-Lafuente, R.; Guisan, J. M. Tetrahedron 2003,
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Calenbergh, S. Bioorg. Med. Chem. 2006, 14, 1403e1412; (b) Taddei, D.;
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