Synthesis, SAR, and preliminary mechanistic evaluation of novel antiproliferative N6,5′-bis-ureido- and 5′-carbamoyl- N6-ureidoadenosine derivatives

Article abstract of DOI:10.1016/j.bmc.2011.11.043

We have developed efficient methods for the preparation of N ⁶,5′-bis-ureidoadenosine derivatives and their 5′-carbamoyl-N⁶-ureido congeners. Treatment of 5′-azido-5′-deoxy-N⁶-(N-alkyl or -arylurea)adenosine derivatives (6a-d) with H₂/Pd-C or Ph₃P/H₂O, followed by N-methyl-p-nitrophenylcarbamate gave N⁶,5′-bis- ureido products 7a-d in 49-78% yield. Analogous derivatives in the 5′-carbamoyl-N⁶-ureido series were prepared by treatment of 2′,3′-bis-O-TBS-adenosine (11) with N-methyl-p-nitrophenylcarbamate followed by acylation with appropriate isocyanates which gave 13a-d in 45-69% yield. A more versatile route for obtaining potentially vast libraries of compounds from both series was achieved by treatment of 5′-N-methylureido- or 5′-N-methylcarbamoyladenosine derivatives with ethylchlorformate to give N⁶-ethoxycarbonyl derivatives (9 and 14) in 55-63% yields, respectively. Simple heating of 9 or 14 in the presence of primary alkyl- or arylamines gave the corresponding N⁶,5′-bis-ureido- or 5′-carbamoyl-N⁶-ureidoadenosine derivatives in good yields (33-72% and 39-83%; 10a-e and 15a-e, respectively). Significant antiproliferative activities (IC₅₀ ≈ 4-10 μg/mL) were observed for a majority of the N⁶,5′-bis-ureido derivatives, whereas the 5′-carbamoyl-N⁶-ureido derivatives were generally less active (IC₅₀ >100 μg/mL). A 2′,3′-O-desilylated derivative (5′-amino-5′-deoxy-5′-N-methylureido-N⁶-(N- phenylcarbamoyl)adenosine, 16) was shown to inhibit binding of 16 of 441 protein kinases to immobilized ATP-binding site ligands by 30-40% in a competitive binding assay at 10 μM. Compound 16 was also shown to bind to bone morphogenetic protein receptor 1b (BMPR1b) with a Kd = 11.5 ± 0.7 μM.

Full text of DOI:10.1016/j.bmc.2011.11.043

Bioorganic & Medicinal Chemistry 20 (2012) 1008–1019
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis, SAR, and preliminary mechanistic evaluation of novel
antiproliferative N6,50-bis-ureido- and 50-carbamoyl-N6-ureidoadenosine
derivatives
Jadd R. Shelton a, Christopher E. Cutler a, Marcelio Oliveira a, Jan Balzarini b, Matt A. Peterson a,
⇑
a Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602-5700, USA
b Rega Institute for Medical Research, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium
a r t i c l e i n f o
a b s t r a c t
We have developed efficient methods for the preparation of N6,50-bis-ureidoadenosine derivatives and
their 50-carbamoyl-N6-ureido congeners. Treatment of 50-azido-50-deoxy-N6-(N-alkyl or -arylurea)adeno-
sine derivatives (6a–d) with H2/Pd–C or Ph3P/H2O, followed by N-methyl-p-nitrophenylcarbamate gave
N6,50-bis-ureido products 7a–d in 49–78% yield. Analogous derivatives in the 50-carbamoyl-N6-ureido
series were prepared by treatment of 20,30-bis-O-TBS-adenosine (11) with N-methyl-p-nitrophenylcarba-
mate followed by acylation with appropriate isocyanates which gave 13a–d in 45–69% yield. A more ver-
satile route for obtaining potentially vast libraries of compounds from both series was achieved by
treatment of 50-N-methylureido- or 50-N-methylcarbamoyladenosine derivatives with ethylchlorformate
to give N6-ethoxycarbonyl derivatives (9 and 14) in 55–63% yields, respectively. Simple heating of 9 or 14
in the presence of primary alkyl- or arylamines gave the corresponding N6,50-bis-ureido- or 50-carbamoyl-
N6-ureidoadenosine derivatives in good yields (33–72% and 39–83%; 10a–e and 15a–e, respectively). Sig-
Article history:
Received 14 October 2011
Revised 19 November 2011
Accepted 19 November 2011
Available online 2 December 2011
Keywords:
Anticancer nucleosides
N6,50-Bis-ureidoadenosines
Antiproliferative activity
BMPR1b
nificant antiproliferative activities (IC50 ꢀ 4–10
ido derivatives, whereas the 50-carbamoyl-N6-ureido derivatives were generally less active (IC50 >100
mL).
20,30-O-desilylated derivative (50-amino-50-deoxy-50-N-methylureido-N6-(N-phenylcarba-
moyl)adenosine, 16) was shown to inhibit binding of 16 of 441 protein kinases to immobilized ATP-bind-
ing site ligands by 30–40% in a competitive binding assay at 10 M. Compound 16 was also shown to bind
to bone morphogenetic protein receptor 1b (BMPR1b) with a Kd = 11.5 0.7 M.
l
g/mL) were observed for a majority of the N6,50-bis-ure-
g/
l
A
l
l
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
COMPARE algorithm5 available from the NCI Developmental Ther-
apeutics Program,6 pointed to a correlation between protein kinase
expression and antiproliferative activity.3c
Over the past several decades, nucleoside derivatives have at-
tracted significant interest as templates for the development of
anticancer and/or antiviral therapeutics.1,2 Hundreds of such deriv-
atives have been made, and numerous analogs have proven useful
for the treatment of cancer or viral infection. Recently, a new class
of nucleosides, bis-ureidoadenosine derivatives, typified by struc-
tures 1–3 (Fig. 1), were found to possess broad-spectrum antipro-
liferative activities against human cancer cells in vitro.3 The most
potent compound (3) was also found to exhibit selective toxicities
toward human colon cancer and renal cancer cells in vitro.4 A pre-
liminary structure–activity relationship study (SAR) had revealed
that the 20-O-TBS group (TBS = tert-butyldimethylsilyl) was neces-
sary for optimal antiproliferative activity, and neither N6- nor
50-ureido substituents were sufficient to achieve significant (IC50
A competitive binding inhibition assay7 revealed that binding of
11 of 353 protein kinases to ATP-binding site ligands was inhibited
by 30–50% by compound 1 at 10 l
M concentration.3c These data
suggested that protein kinases may be molecular targets for com-
pounds of this class, and prompted our investigation of a series of
derivatives that might reasonably be expected to bind with en-
hanced affinity to protein kinase targets in general. The currently
accepted pharmacophore binding model8 for the ATP-binding site
of protein kinases invokes a phosphate binding region near the
50-position and a hydrophobic binding pocket in close proximity
to N6. In addition, a sugar binding pocket also exists in close prox-
imity to the 20,30-hydroxyls of the ribose ring. With this model as a
guide, we set out to perform an SAR to refine our understanding of
the structural requirements needed for optimal antiproliferative
activity. Herein we report the synthesis and biological evaluation
of a series of derivatives of compound 3 with various substituents
at the N6 and/or 50-positions. These substituents were designed to
interrogate the effect of substitution at these positions as a prelude
<10 l
M) antiproliferative effects in the absence of each other.3b
Analysis of the antiproliferative effects of compound 1 using the
⇑
Corresponding author. Tel.: +1 801 422 6843; fax: +1 801 422 0153.
E-mail address: matt_peterson@byu.edu (M.A. Peterson).
0968-0896/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2011.11.043

J. R. Shelton et al. / Bioorg. Med. Chem. 20 (2012) 1008–1019
1009
O
N
addition, aliphatic C–H/
p
-electron interactions between the recep-
O
N
Ph
Ph
tor and ligand can occur and can be exploited to enhance molecular
HN
N
N
HN
N
N
H
recognition.10 As has been demonstrated in previously studied sys-
H
N
N
N
N
O
O
tems, electron-donating substituents increase the
sity and enhance the Lewis-basicity of phenyl rings, whereas
electron-withdrawing substituents decrease -electron density
leading to increased Lewis-acidity of the phenyl ring.9a Fine-tuning
the -electron density of aromatic moieties is a strategy that has
p-electron den-
CH3
CH3
N
N
H
N
N
H
O
H
O
2
H
p
O
OTBS
O
1
OTBS
p
OEt
N
been applied successfully to enhance binding between ligands
CH3O
CH3
and hydrophobic receptors. Accordingly, we reasoned that deriva-
tives that varied in the p-electron density of the phenyl ring (e.g.,
7a–d) might reasonably be expected to bind with different affini-
ties to the hydrophobic pocket of the assumed primary biomolec-
ular receptor(s). Thus, compounds 6a–d were treated by Method A
to prepare derivatives 7a–d which vary by virtue of their posses-
sion of either electron withdrawing (7a,b) or electron donating
O
O
N
Ph
Ph
HN
N
N
HN
N
H
H
N
N
N
N
N
O
O
CH3
CH3
N
N
N
N
O
O
H
H
O
H
TBSO
OTBS
3
TBSO
4
OTBS
(7c) substituents, or by loss of conjugation with the
p-system of
the phenyl ring and the urea moiety (7d). Yields ranged from
49–78% via this method, in general agreement with the yield ob-
tained for the parent compound (3). Lower yields were observed
for compounds 7a–d than for 3, owing to either the required use
of Staudinger reduction conditions for compounds 7a and 7b (to
avoid reduction of the C–Cl, or NO2 moieties, respectively), and/
or owing to the challenges associated with chromatographic sepa-
ration of the diphenylurea byproducts that invariably accompanied
formation of 7a–d. In order to avoid these complications and to
provide access to a potentially unlimited, easily accessible, com-
pound pool, Method B was also investigated (Scheme 1). In this
method, the azido group is reduced and the 50-N-methylurea group
is introduced before N6 is acylated. Treatment of compound 8 with
ethylchloroformate gave compound 9 which could potentially be
converted to a broad array of N6-aryl- or alkylurea derivatives by
simple heating in the presence of a virtually unlimited number of
primary aryl- or alkylamines, respectively.
In this study, relatively hindered (e.g., cyclohexyl, 10a), unhin-
dered (e.g., propyl, hexyl, 10b and 10c) primary alkyl- and
arylamines (e.g., m-iodoaniline, p-iodoaniline, 10d and 10e) gave
products in moderate to good yields, thus providing proof of
concept that Method B could potentially be exploited for producing
large libraries of derivatives 10. There are relatively few commer-
cially available isocyanates when compared to commercially avail-
able primary amines. Thus, Method B (in contrast to Method A
Figure 1.
to more focused SARs that could be conducted once the biomolec-
ular receptor(s) had been unequivocally identified. A derivative of
the most potent compound (3) lacking 20,30-O-TBS groups was also
evaluated in order to determine possible reasons this substitution
is necessary for optimal antiproliferative activity.
2. Results
2.1. Chemistry
In order to test the effect of varying substitution at N6, two syn-
thetic approaches were examined (Scheme 1). It was reasoned that
varying the
tighter binding in the (assumed) hydrophobic pocket of the biomo-
lecular receptor. Increasing or decreasing the inherent -electron
p
-electron density in the N6-phenyl ring might lead to
p
density of the phenyl ring could enhance binding in the hydropho-
bic pocket by fine-tuning electronic interactions between the li-
gand and amino acid residues in the binding pocket of the
receptor, as has been observed in numerous related instances.9
It has been well established that face-to-face and edge-to-face
bonding interactions can occur between aromatic side chains in
receptors and aromatic moieties found in receptor ligands.9a In
Method A
O
N
O
R
R
NH2
N
HN
N
N
HN
N
N
H
H
CH3
N
N
N
N
N
N
N
3
R = Phenyl (86%)
O
H
7a R = p-Chlorophenyl (78%)
7b R = p-Nitrophenyl (77%)
7c R = p-Methoxyphenyl (57%)
7d R = Benzyl (49%)
N
N
N3
N3
N
H
O
O
O
b (or c), d
a
TBSO OTBS
TBSO OTBS
TBSO OTBS
7a d
6a d
5
(50 81%)
(49 78%)
O
O
O
R
Method B
NH2
NH2
HN
HN
N
N
H
CH3
N
N
N
N
N
CH3
N
CH3
N
N
N
N
N
N
N
H
N
3
R = Phenyl (49%)
O
O
O
H
H
10a R = Cyclohexyl (46%)
10b R = Propyl (72%)
N
N
N
N
N3
N
H
N
N
H
H
O
O
10c R = Hexyl (39%)
10d R = m-Iodophenyl (70%)
10e R = p-Iodophenyl (33%)
O
O
RNH2
b, d
e
TBSO OTBS
TBSO OTBS
TBSO OTBS
TBSO OTBS
8
9
10a e
(3372%)
5
(83%)
(55%)
Scheme 1. Reagents: (a) R–N@C@O; (b) H2, Pd–C; (c) Ph3P, H2O; (d) p-NO2-C6H4O2CNHCH3; (e) ethylchloroformate.

1010
J. R. Shelton et al. / Bioorg. Med. Chem. 20 (2012) 1008–1019
Table 1
which is limited due to the relatively small number of commercially
available isocyanates) opens up a viable path that can be exploited
for straightforward preparation of large arrays of N6-arylurea or
N6-alkylurea derivatives from the large number of commercially
available primary amines, as exemplified by the synthesis of com-
pounds 10a–e.
Inhibitory effects of the test compounds on the proliferation of murine leukemia cells
(L1210), murine mammary carcinoma cells (FM3A), human T-lymphocyte cells (CEM)
and human cervix carcinoma cells (HeLa).
a
Compound
IC50
(
l
g/ml)
L1210
FM3A
CEM
HeLa
In previously reported synthetic approaches to compounds 1–3,
it had become apparent that the overall efficiency of the synthesis
could be enhanced if the 50-N-methylurea moiety were replaced
with the isosteric N-methylcarbamoyl group. Replacement of the
50-urea moiety with a 50-carbamate would reduce the total number
of steps by three (from adenosine), and also eliminate the synthet-
ically challenging introduction of the 50-azido group from a 50-acti-
vated precursor (such as a 50-chloro-, or 50-O-tosyladenosine
derivative).11 For compounds 1 and 2, the latter transformation
(i.e., introduction of the 50-azido group from a 50-activated adeno-
sine derivative without competing cyclonucleoside formation)11
required fairly labor-intensive conditions, and unusual attention
to detail was required to obtain optimum yields.3c Assuming that
the isosteric 50-N-methylcarbamoyl derivatives retained biological
activity, the proposed NH to O substitution would be a favorable
modification. Toward this end, compounds 4 (Fig. 1) and 13a–d
and 15a–e were prepared and evaluated (Scheme 2).
3
4
7a
7b
7c
7d
10a
10b
10c
10d
10e
13a
13b
13c
13d
15a
15b
15c
15d
15e
3.8 0.3
160 56
5.6 1.1
P200
3.8 0.0
4.6 0.9
20 13
3.9 0.3
5.9 1.1
> 200
8.3 2.9
> 200
3.2 0.2
P200
3.4 0.0
>200
2.6 0.8
3.8 2.1
33
2
14
8
>200
>200
5.8 0.4
9.2 0.2
8.4 0.8
4.7 0.5
ND
ND
ND
>200
5.2 1.3
8.3 0.8
5.2 0.3
4.4 1.1
11
3
3.3 0.7
74
8
68
9
74
21
18
9
1
2
38 17
43 15
>200
7.7 1.6
>200
182
8
68 34
>200
>200
1.5 1.0
P200
24
5
15
1
>200
>200
>200
>200
>200
175
101
74
5
0
23
4
8
8
69 51
55 32
88 56
>200
18 11
>200
>200
23
4
59
7
>200
>200
>200
175
>200
P200
>200
143 80
a
Compounds 13a–d and 15a–e were designed to probe SAR fea-
tures analogous to those of 7a–d and 10a–e, respectively. The syn-
theses proceeded smoothly and provided desired products in good
to moderate overall yields from compound 11, which was readily
obtained in excellent yield in only two steps from adenosine.12
50% Inhibitory concentration or compound concentration required to inhibit
tumor cell proliferation by 50%.
pound 3, although comparable activities were exhibited by 7a,
7c, 7d, 10a and 10b. N-Methylcarbamoyl analogs 4, 13a–d and
15a–e, exhibited generally inferior activities, with the exception
of 13b which exhibited cytostatic activities that were markedly
higher than observed for the parent compound 4.
2.2. Biology
2.2.1. Antiproliferative activity
Compounds 3, 4, 7a–d, 10a–e, 13a–d, and 15a–e were exam-
ined for their antiproliferative activity using the following cell
lines: murine leukemia L1210, murine mammary carcinoma
FM3A, human lymphoblastic leukemia CEM, and human cervix car-
cinoma HeLa. The results of these assays are presented in Table 1.
As these data illustrate, none of the derivatives 7a–d or 10a–e
showed significantly improved activities relative to lead com-
2.2.2. Protein kinase binding activity
In order to determine whether compound 3 exerts its antiprolif-
erative effect via inhibition of protein kinases after intracellular
hydrolysis of the TBS groups, the desilylated derivative 16 was
prepared and subjected to the competitive binding inhibition assay
of Fabian et al.7 In this assay, compound 16 was shown to inhibit
Method A
O
R
NH2
N
NH2
N
HN
N
N
H
CH3
N
N
N
N
N
CH3
N
N
N
N
O
O
H
H
N
N
4
R = Phenyl (90%)
HO
O
O
13a R = p-Chlorophenyl (45%)
13b R = p-Nitrophenyl (66%)
13c R = p-Methoxyphenyl (69%)
13d R = Benzyl (47%)
O
O
O
a
b
TBSO OTBS
TBSO OTBS
TBSO OTBS
11
12
13a d
(84%)
(45 69%)
O
O
R
Method B
NH2
HN
O
HN
N
N
H
CH3
N
N
CH3
N
CH3
N
N
N
N
N
N
N
N
4
R = Phenyl (55%)
N
O
O
O
H
H
H
15a R = Cyclohexyl (83%)
15b R = Propyl (65%)
N
N
O
O
O
O
15c R = Hexyl (63%)
15d R = m-Iodophenyl (55%)
15e R = p-Iodophenyl (39%)
O
RNH2
O
c
TBSO OTBS
TBSO OTBS
TBSO OTBS
12
14
15a e
(63%)
(39 83%)
Scheme 2. Reagents: (a) p-NO2-C6H4O2CNHCH3; (b) R–N@C@O; (c) ethylchloroformate.

J. R. Shelton et al. / Bioorg. Med. Chem. 20 (2012) 1008–1019
1011
45
43
41
40
45
40
35
30
25
20
15
10
5
38 38
37 37 37
35
33
33
32
31
30 30
0
Protein Kinases
Figure 2a. Inhibition of binding of protein kinases to immobilized ATP-binding site ligands by compound 16 (10 lM).
47
40
50
45
40
35
30
25
20
15
10
5
38
37
35
34
33
31
31
31
0
Protein Kinases
Figure 2b. Inhibition of binding of protein kinases to immobilized ATP-binding site ligands by compound 1 (10 lM).
0
0
0
0
binding of 16 of 441 protein kinases to ATP-binding site ligands by
30–45% (Fig. 2a). The binding profile for 16 varied significantly
from that of 1 (Fig. 2b),3b but both 16 and 1 inhibited binding to
bone morphogenetic protein receptor 1b (BMPR1b) to a similar
degree (45% and 47%, respectively). In a multi-dose binding assay,
supported by J1 ,2 /J3 ,4 coupling constant data, as well as results
from 1D-NOESY experiments (Tables 2 and 3).
The equilibrium constant (Keq) relating the mole fraction of S
conformer (XS) to the mole fraction of N conformer (XN) was calcu-
lated from the observed J1 ,2 and J3 ,4 according to Eq. 1, and is a
measure of the conformational equilibrium between the syn and
anti conformers. (The C20-endo (S) conformation correlates with a
0
0
0
0
compound 16 was found to bind to BMPR1b with
a
Kd = 11.5 0.7 M, whereas compound 3 did not bind to BMPR1b
l
at concentrations as high as 30
lM (Fig. 3).
predominant syn glycosyl conformation (
the C30-endo (N) conformation correlates with the anti glycosyl
conformation (
= 200–210°).14 Equilibrium constants calculated
v = 10–30°), whereas
2.3. Conformational analysis
v
with Eq. 1 compare very favorably to those obtained by a full
It has been well established that conformations of nucleosides
play a key role in determining their biological activities.13 In a re-
cent communication, we had reported that one possible factor that
could contribute to the difference in antiproliferative activities ob-
served for 3 and 4 might be the difference in the syn/anti conforma-
tional preference for the two compounds (Fig. 4).4 We now report
that 50-ureido derivatives 3, 7a–d, and 10a–e each exhibit similar
conformational preferences for the syn glycosyl conformer, while
the conformational preference for the 50-carbamate derivatives 4,
13a–d, and 15a–e is much less pronounced. Such a conclusion is
pseudorotational analysis.14,15
0
0
0
0
ðKeqÞ ¼ XS=XN ¼ J1 ;2 =J3 ;4
ð1Þ
Intramolecular hydrogen bonding between 50 H-bond donors
and N3 of the adenine heterocycle has been reported for several
adenosine derivatives.16 In such compounds (e.g., NECA), a syn gly-
cosyl conformation was observed in the solid state, and the syn gly-
cosyl conformer was preferred in solution. The 1D-NOESY data we
obtained for the 50-ureido derivatives are consistent with a strong
preference for the syn conformer, which would be consistent with

1012
J. R. Shelton et al. / Bioorg. Med. Chem. 20 (2012) 1008–1019
intramolecular hydrogen bonding between the 50-NH of the urea
moiety and the N3 of the adenine heterocycle (see strong NOE
enhancement of H-10 and H-8 when either one is irradiated,
Table 3).
Absence of a strong NOE when either H-10, H-2, or H-8 are irra-
diated in the 50-carbamates supports the conclusion that these
compounds are much less conformationally rigid, consistent with
the fact that an intramolecular H-bond cannot exist between the
50-O and N3. Interestingly, when H-8 is irradiated in the 50-ureido
derivatives, NOE enhancement is observed for only H-10. When H-8
is irradiated in the 50-carbamates, H-10, H-5000, H-20, H-3’, and H-5’
are enhanced, although to a much weaker extent. When H-2 is irra-
diated in the 5’-carbamates, enhancement is observed for only H-
6’. In contrast, irradiation of H-2 in the 50-ureido compounds gives
enhancement in H-60, H-500, H-5000, and the NCH3 of the 50-urea moi-
ety. These data support the conclusion that the 50-ureas are much
more conformationally constrained, with H-2 being in close prox-
imity to the 50-urea and H-8 being in close proximity to H-10, con-
sistent with the syn glycosyl conformational preference indicated
by the coupling constant data (Table 2). Taken together, the
coupling constant and 1D-NOESY data suggest that conformational
differences between the 50-ureido and 50-carbamate derivatives
may play a role in the observed difference in antiproliferative
activities.
3. Discussion
It is generally accepted that a majority of biologically active
nucleoside analogs are phosphorylated before they exert their ef-
fect biologically.17 This typically requires that the nucleoside pos-
sess either a free 50-OH or a prodrug feature that is easily
hydrolyzed to generate either a free 50-OH or a 50-monophosphate
in vivo.17c,d A common strategy for enhancing membrane perme-
ability has been to increase lipophilicity of the nucleoside deriva-
tive by protecting hydroxyls as benzoyl, acetyl, or isobutyryl
esters that are cleaved once the compound has crossed the cell
membrane.17a,b Lipophilic silyl protecting groups have also been
reported to be required for the biological activity of nucleoside
analogs. For example, TBS groups at the 20 and 50 positions were
found to be required for optimal activity of the tert-butyldimethyl-
silyl-spiroaminooxathioledioxide-thymine (TSAO-T) class of HIV-1
reverse transcriptase (RT) inhibitors.18 A recent crystal structure of
the TSAO–T/RT complex shows that the TBS groups occupy hydro-
phobic pockets in the non-nucleoside RT inhibitor binding pocket,
and play a critical role in defining the dimensions of the binding
pocket as well as determining molecular recognition between the
pocket and the TSAO–T ligand.19
Figure 3. Effect of 3 and 16 on equilibrium competition binding of BMPR1b to
immobilized ATP-binding site ligand.7
O
s
6
H
5
N
N
H
m
7
6'
6
5'''
H
5''
H
N
1
N
2
H
m
8
N
N
w
5'
4
N
N
3
s
H
9
CH3
O
H
H
1'
4'
O
2'
H
H
3'
3
TBSO
Since our initial discovery that the N6,50-bis-ureidoadenosines
require a TBS group for antiproliferative activity, we have been in-
trigued by the question of what role the TBS group might play in
this class of compounds. The observation that the 50-carbamates
are in general substantially less active in the cytostatic assays in
spite of the fact that they possess the 20,30-bis-O-TBS substitution,
implies that the TBS groups are necessary, but not sufficient, for
antiproliferative activity. The results presented in Figure 3 suggest
that the primary role of the TBS groups may be to enhance mem-
brane permeability, assuming that BMPR1b is the primary target.
Hydrolysis of the TBS group of compound 3 within the intracellular
milieu could give rise to 16, which clearly has greater affinity for
BMPR1b (Fig. 3). BMPR1b is a transmembrane receptor whose
ATP-binding site domain lies within the cytoplasm. It is part of a
signaling cascade that regulates expression of Id-1.20 Aberrant
expression of Id-1 has been reported in over 20 cancers,21 and inhi-
bition, inactivation, or downregulation of Id-1 have been shown to
induce apoptosis in breast, ovarian, and prostate cancers.22 In
OTBS
O
6
H
5
m
N
N
H
7
6
6'
N
5'''
1
N
2
H
H
w
w
8
N
O
m
4
N
9
N
3
m
H
CH3
5'
O
H
H
1'
O
4'
2'
OTBS
H
H
3'
4
TBSO
Figure 4. NOESY correlation data for compounds 3 and 4: (s = strong, m = medium,
w = weak).

J. R. Shelton et al. / Bioorg. Med. Chem. 20 (2012) 1008–1019
1013
%N
Table 2
1H NMR and Keq data for 50-ureido and 50-carbamoyl derivativesa,b,c
b
b
0
H-10 (J1 ,2
)
H-20
H-30 (J3 ,4
)
H-40
H-50
H-500
H-5000
H-8
H-2
H-6
9.10
H-60
Keq
%S
0
0
0
Compound
3
6.17 (7.7 Hz)
6.14 (7.6 Hz)
6.14 (7.5 Hz)
6.11 (7.5 Hz)
6.15 (7.5 Hz)
6.07 (8.0 Hz)
6.09 (7.5 Hz)
6.10 (7.5 Hz)
6.01 (8.0 Hz)
5.92 (7.5 Hz)
6.20 (5.4 Hz)
6.19 (5.5 Hz)
6.20 (5.5 Hz)
6.22 (5.5 Hz)
6.17 (5.5 Hz)
6.16 (5.0 Hz)
6.18 (5.5 Hz)
6.16 (5.0 Hz)
6.19 (5.5 Hz)
6.18 (5.0 Hz)
4.62
4.66
5.01
4.53
4.41
4.54
4.52
4.52
4.63
4.72
4.54
4.62
4.98
4.58
4.51
4.55
4.53
4.55
4.62
4.64
4.34 (2.1 Hz)
4.34 (2.0 Hz)
4.55 (1.7 Hz)
4.43 (1.8 Hz)
4.48 (1.2 Hz)
4.44 (1.4 Hz)
4.44 (1.3 Hz)
4.46 (1.2 Hz)
4.38 (1.7 Hz)
4.31 (1.6 Hz)
4.32 (3.1 Hz)
4.31(2.8 Hz)
4.55 (3.0 Hz)
4.34 (2.9 Hz)
4.35 (3.1 Hz)
4.37 (3.2 Hz)
4.37 (3.1 Hz)
4.37 (3.0 Hz)
4.34 (3.0 Hz)
4.32 (2.9 Hz)
4.62
4.66
4.16
4.53
4.41
4.54
4.52
4.52
4.63
4.72
4.54
4.62
4.30
4.58
4.51
4.55
4.53
4.55
4.62
4.64
3.97, 3.18
3.99, 3.22
3.63, 3.59
3.98, l.14
3.93, 2.92
4.05, 3.12
4.04, 3.12
4.04, 3.12
4.01, 3.23
4.01, 3.23
4.48, 4.23
4.45, 4.28
4.43, 4.42
4.53, 4.03
4.56, 4.21
4.55, 4.26
4.57, 4.24
4.25,4.57
4.54, 4.28
4.46, 4.30
6.49
6.55
6.28
6.27
6.19
6.57
6.52
6.51
6.51
6.65
. . .
4.75
4.64
5.61
4.96
5.46
5.41
5.45
5.48
4.71
4.55
5.90
5.63
6.37
6.10
6.40
6.38
6.52
6.43
5.75
5.64
8.60
8.49
8.84
8.94
9.10
8.84
8.89
8.92
8.61
8.34
8.84
8.72
8.68
8.89
8.84
8.74
8.81
8.77
8.78
8.73
8.65
8.67
8.83
8.65
8.56
8.56
8.57
8.56
8.68
8.67
8.64
8.63
8.77
8.63
8.50
8.53
8.53
8.53
8.66
8.65
11.9
11.9
12.7
11.9
10.6
9.86
9.93
9.92
3.7
4.1
4.4
4.1
6.4
5.6
5.8
6.3
4.8
4.7
1.7
1.8
1.8
1.9
1.8
1.7
1.8
1.7
1.8
1.7
79
80
82
80
86
85
85
86
83
82
63
64
64
66
64
63
64
63
64
63
21
20
20
20
14
15
15
14
17
18
37
36
36
34
36
37
36
37
36
37
7a
8.92
9.50
9.52
9.61
9.03
9.15
9.19
9.08
8.65
7bd
7c
7d
10a
10b
10c
10d
10e
4
13a
13bd
13c
13d
15a
15b
15c
15d
15e
12.0
11.8
12.2
12.2
12.8
12.1
10.4
9.87
9.93
9.88
10.0
9.77
9.44
. . .
. . .
. . .
10.1
. . .
9.82
9.41
9.63
9.52
9.88
9.78
. . .
. . .
. . .
. . .
12.3
12.2
. . .
a
b
c
Spectra were obtained in CDCl3 at 500 MHz. Chemical shifts were assigned using 2D COSY spectra and are reported in ppm relative to TMS.
0
0
Coupling constants are in parentheses. J3
, were determined using HOMO-2DJ spectra.
4
For hydrogen numbering, see Figure 4.
Spectra for 7b and 13b were determined in acetone-d6.
d
addition, a majority of the protein kinases inhibited by 16 (Fig. 2a)
have been implicated in cancer. These data support the conclusion
that protein kinases may be key targets for the N6,50-bis-ureidoad-
enosine derivatives discussed here, and provide preliminary
evidence that the role of the TBS group may be to enhance mem-
brane permeability. In this context, compound 3 would be viewed
as a prodrug form of the active derivative, compound 16.
The SAR designed to probe the effects of varying N6 and 50 sub-
stituents revealed that a 50-urea is necessary for optimal antiprolif-
erative activity. Conformational analysis showed that the 50-
carbamate derivatives are substantially less conformationally rigid,
and this greater degree of conformational freedom may contribute
to the observed loss of activity relative to the more conformation-
ally constrained 50-ureas. Conformationally restricted nucleosides
have been demonstrated to have greater activities than less-re-
stricted analogs in a number of instances,13 and our results are in
harmony with these observations. Compounds 7b and 13b are
exceptions to this general trend, suggesting that primary targets
for compounds 7b and 13b may differ from other members of their
respective series.
complete conversion of starting material), and/or the required
use of Staudinger reduction conditions when working with H2/pal-
ladium-sensitive moieties such as C–Cl or NO2. In addition, the
number of derivatives that could be prepared by Method A is lim-
ited due to the somewhat restricted number of isocyanates that
are commercially available. A synthetically much more versatile
route was found in Method B. Treatment of compounds 8 or 12
with ethylchloroformate gave N6-ethoxycarbonyl derivatives 9
and 14 in good yields (55 and 63%, respectively). Compounds 9
and 14 could be converted to N6-ureido products (10a–e and
15a–e) by simple heating in the presence of a primary amine.
The relatively large selection of commercially available primary al-
kyl- and arylamines, together with the relative ease of preparation
of such precursors, make Method B a versatile route providing ac-
cess to a potentially vast library of compounds varying at the N6-
position.
Evaluation of compounds 4, 7a–d, 10a–e, 13a–d, and 15a–e,
against a number of cancer cell lines did not reveal any marked
improvement in antiproliferative activity relative to compound 3.
The 50-carbamoyl derivatives 4, 13a–d, and 15a–e were, generally
speaking, significantly less potent than the corresponding bis-ure-
ido derivatives 3, 7a–d, and 10a–e. The difference in antiprolifera-
tive activity may be at least partially attributed to a difference in
conformational flexibility between the 50-ureido and 50-carbamoyl
series.
The effect of varying the p-electron density of the phenyl rings
of the N6-ureido moiety ranged from somewhat modest to quite
significant, with the most notable effect on antiproliferative activ-
ity being exhibited by nitro derivative 7b. Compounds 7a, 7c, 7d,
and 10a–b had comparable activities to compound 3, in contrast
to compounds 10c–e which were approximately 10–20 times less
potent.
A 20,30-O-desilylated derivative (16) was shown to bind to
BMPR1b with a Kd = 11.5 0.7 lM. Compound 16 also inhibited
binding of several other cancer-related protein kinases to ATP-
binding site ligands in a single-dose competitive binding assay,
suggesting that protein kinases may be targets for this class of
compounds after intracellular hydrolysis of the 20,30-O-TBS ethers.
4. Conclusion
We have developed methods for efficient preparation of N6,50-
bis-ureido and 50-carbamoyl-N6-ureidoadenosine derivatives. Rep-
resentative compounds from each class were prepared via the
routes depicted (Schemes 1 and 2). Treatment of compounds 5 or
12 with isocyanates (Method A) gave N6-ureido products 3/7a–d
and 4/13a–d in good yields (49–86% and 45–90%, respectively).
However, preparation of these compounds via this route was com-
plicated by a number of factors, including labor-intensive chro-
matographic removal of diphenylurea byproducts (which
occurred due to hydrolysis of excess isocyanate used to ensure
5. Experimental
5.1. Biology
5.1.1. Antiproliferative assays
The cytostatic effects of the test compounds on murine leuke-
mia cells (L1210), murine mammary carcinoma cells (FM3A), hu-
man T-lymphocyte cells (CEM) and human cervix carcinoma cells

1014
J. R. Shelton et al. / Bioorg. Med. Chem. 20 (2012) 1008–1019
Table 3
1D-NOESY data for 50-ureido and 50-carbamoyl derivativesa,b
.
Compound
(H-10)b
(H-2)b
(H-8)b
Compound
(H-10)b
(H-2)b
(H-8)b
3
H-8: 4.02
H-20: 1.03
H-30: 0.21
H-40: 0.71
H-60: 0.40
H-500: 0.19
H-5000: 0.82
NCH3: 0.29
H-10: 3.15
4
H-8: 0.25
H-20: 0.22
H-30: 0.25
H-40: 0.25
H-60: 0.41
H-10: 0.94
H-5000: 0.54
H-20: 0.33
H-50: 0.45
H-50: 0.15
H-10: 2.00
H-5000: 0.77
H-20: 0.48
H-50: 0.56
H-50: 0.30
H-10: 1.83
H-5000: 0.24
H-20: 1.25
H-50: 0.40
H-50: 0.47
H-10: 0.42
H-5000: 0.76
7a
7b
H-8: 4.64
H-20: 1.31
H-30: 0.39
H-40: 1.00
H-60: 0.73
H-500: 0.86
H-5000: 1.63
NCH3: 0.58
H-10: 6.43
H-10: 1.18
13a
13b
H-8: 1.81
H-20: 1.77
H-30: 0.50
H-40: 0.50
H-60: 0.25
H-60: 0.39
H-8: 2.04
H-20: 0.76
H-30: 0.17
H-40: 0.55
H-60: 0.25
H-500: 0.16
H-5000: 0.17
NCH3: 0.10
H-8: 1.53
H-20: 0.89
H-30: 0.25
H-40: 0.56
7c
H-8: 2.93
H-20: 1.21
H-30: 0.00
H-40: 0.84
H-8: 4.02
H-20: 1.03
H-30: 0.21
H-40: 0.71
H-8: 1.90
H-20: 0.76
H-30: 0.30
H-40: 0.45
H-8: 2.79
H-20: 1.13
H-30: 0.57
H-40: 0.95
H-60: 0.00
H-500: 0.17
H-5000: 0.45
NCH3: 0.20
H-60: 0.00
H-500: 0.64
H-5000: 0.33
NCH3: 0.49
H-60: 0.00
H-500: 1.31
H-5000: 0.57
NCH3: 0.45
H-60: 0.62
H-500: 1.12
H-5000: 0.68
NCH3: 0.54
H-10: 3.23
H-10: 3.52
H-10: 3.46
H-10: 5.73
13c
13d
15a
15b
H-8: 1.10
H-20: 1.10
H-30: 0.23
H-40: 0.42
H-8: 0.96
H-20: 1.21
H-30: 0.23
H-40: 0.41
H-8: 1.50
H-20: 1.77
H-30: 0.43
H-40: 0.61
H-8: 1.45
H-20: 1.64
H-30: 0.32
H-40: 0.79
H-60: 0.33
H-60: 0.37
H-60: 0.64
H-60: 0.56
7d
H-10: 2.02
H-5000: 0.96
H-20: 0.56
H-30: 0.66
H-10: 2.49
H-20: 0.83
H-30: 0.96
10a
10b
H-10: 2.23
H-5000: 1.15
H-20: 1.10
H-30: 0.88
H-50: 0.43
H-10: 2.23
H-5000: 1.15
10c
10d
10e
H-8: 2.19
H-20: 0.97
H-30: 0.51
H-40: 0.75
H-8: 3.29
H-20: 1.21
H-30: 0.39
H-40: 0.91
H-8: 4.87
H-20: 1.45
H-30: 0.54
H-40: 1.21
H-60: 0.00
H-500: 0.60
H-5000: 1.15
NCH3: 0.65
H-60: 0.63
H-500: 1.12
H-5000: 0.60
NCH3: 0.71
H-60: 0.69
H-500: 1.98
H-5000: 0.40
NCH3: 0.75
H-10: 6.15
H-10: 6.77
H-10: 9.35
15c
15d
15e
H-8: 1.34
H-20: 1.47
H-30: 0.00
H-40: 0.60
H-8: 1.41
H-20: 1.41
H-30: 0.37
H-40: 0.61
H-8: 1.28
H-20: 1.12
H-30: 0.38
H-40: 0.36
H-60: 0.00
H-60: 0.60
H-60: 0.24
H-10: 2.23
H-5000: 1.15
H-10: 2.07
H-5000: 0.84
H-20: 0.61
H-30: 0.32
a
Data given as % enhancement when proton is irradiated.
Proton irradiated is in parentheses.
b
(HeLa) were evaluated as follows: an appropriate number of cells
suspended in growth medium were allowed to proliferate in
200-lL-wells of 96-well-microtiter plates in the presence of vari-
able amounts of test compounds at 37 °C in a humidified CO2-con-
trolled atmosphere. After 48 h (L1210, FM3A), 72 h (CEM) or 96 h
(HeLa), the number of cells was counted in a Coulter counter.
The IC50 value was defined as the compound concentration re-
quired to inhibit cell proliferation by 50%.
BSA, 0.05% Tween 20, 1 mM DTT) to remove unbound ligand and
to reduce non-specific binding. Binding reactions were assembled
by combining kinases, liganded affinity beads, and test compounds
in 1ꢁ binding buffer (20% SeaBlock, 0.17ꢁ PBS, 0.05% Tween 20,
6 mM DTT). All reactions were performed in polystyrene 96-well
plates in a final volume of 0.135 mL. The assay plates were incu-
bated at room temperature with shaking for 1 h and the affinity
beads were washed with wash buffer (1ꢁ PBS, 0.05% Tween 20).
The beads were then re-suspended in elution buffer (1ꢁ PBS,
5.1.2. Protein kinase assays
0.05% Tween 20, 0.5 lM non-biotinylated affinity ligand) and incu-
The competitive binding assays were performed by DiscoveRx,
Inc. according to the following general protocol. Kinase-tagged T7
phage strains were prepared in anEscherichia coli host derived from
the BL21 strain. E. coli were grown to log-phase and infected with
T7 phage and incubated with shaking at 32 °C until lysis. The ly-
sates were centrifuged and filtered to remove cell debris. The
remaining kinases were produced in HEK-293 cells and subse-
quently tagged with DNA for qPCR detection. Streptavidin-coated
magnetic beads were treated with biotinylated small molecule li-
gands for 30 min at room temperature to generate affinity resins
for kinase assays. The liganded beads were blocked with excess
biotin and washed with blocking buffer (SeaBlock (Pierce), 1%
bated at room temperature with shaking for 30 min. The kinase
concentration in the eluates was measured by qPCR. Binding con-
stants (Kds) were calculated with a standard dose–response curve
using the Hill equation. The Hill Slope was set to ꢂ1, and curves
were fitted using a non-linear least square fit with the Leven-
berg-Marquardt algorithm.
5.2. Chemistry
5.2.1. General experimental
Moisture sensitive reactions were performed in flame-dried
flasks under an inert atmosphere (N2 or Ar) at ambient

J. R. Shelton et al. / Bioorg. Med. Chem. 20 (2012) 1008–1019
1015
temperature unless otherwise indicated. Solvents (CH2Cl2, pyri-
dine, EtOAc, DMF, Et3N) were dried by passing through columns
of activated alumina under Ar. TLC was performed using Merck
Kieselgel 60 F254 sheets, and flash chromatography was performed
with silica gel (230–400 mesh) and reagent grade solvents. ‘Solvent
A’ for chromatography consisted of the separated organic phase of
EtOAc/i-PrOH/H2O (4:1:2). 1H NMR and 13C NMR spectra were
determined using internal references at d 7.24 (CDCl3), and d
77.23 (CDCl3), respectively. High resolution mass spectra were ob-
tained using fast atom bombardment (FAB, NaOAc/thioglycerol or
thioglycerol matrix) or electrospray (ES) ionization techniques.
Commercially available reagents were used as supplied. Com-
pounds 3–5,3a,c 11,12 and 163c were prepared as previously re-
ported. All compounds tested were >98% pure (as determined by
HPLC; 5–10% IPA/CH2Cl2).
osine (130 mg, 0.203 mmol, 85%). This material (123 mg,
0.192 mmol) was subjected to general procedure B [10% Pd–C
(50 mg), EtOAc (10 mL)] to give a crude product that was treated
with N-methyl-p-nitrophenylcarbamate, Et3N (60 lL), and CH2Cl2
(4 mL), by general procedure D [chromatography 75% EtOAc/hex-
anes?EtOAc] to give 3 (111 mg, 0.165 mmol, 86%). Method B. Treat-
ment of 9 (70 mg, 0.11 mmol), aniline (17 mg, 0.18 mmol), and
pyridine (1.0 mL) by general procedure F (chromatography EtOAc),
gave 3 (36 mg, 0.054 mmol, 49%). 1H NMR (CDCl3, 500 MHz) d
11.92 (br s, 1H), 9.03 (br s, 1H), 8.67 (s, 1H), 8.61 (s, 1H), 7.57 (d,
J = 7.5 Hz), 7.39 (t, J = 8.3 Hz, 2H), 7.18 (t, J = 7.3 Hz, 1H), 6.51 (d,
J = 6.0 Hz, 1 H), 6.01 (d, J = 7.7 Hz, 1H), 4.74–4.73 (m, 1H), 4.64
(dd, J = 7.5, 4.5 Hz, 1 H), 4.36 (d, J = 4.5 Hz, 1H), 4.18 (t, J = 2.5 Hz,
1H), 3.99 (ddd, J = 14.5, 9.0, 2.5 Hz, 1H), 3.19 (dt, J = 14.5, 3.1 Hz,
1H), 2.72 (d, J = 4.5 Hz, 3H), 0.95 (s, 9H), 0.70 (s, 9H), 0.15 (s, 3H),
0.13 (s, 3H), –0.13 (s, 3H), –0.49 (s, 3H); 13C NMR (CDCl3,
125 MHz) d 159.1, 152.9, 151.0, 150.4, 150.3, 144.1, 137.1, 129.2,
125.0, 121.8, 121.2, 88.0, 87.8, 75.9, 73.5, 41.6, 26.8, 25.9, 25.6,
18.0, 17.7, ꢂ4.53, ꢂ4.79, ꢂ5.65; MS (FAB) m/z 671.3525 (MH+
[C31H51N8O5Si2]) = 671.3516.
5.2.2. General procedure A (acylation with isocyanates)
A solution of the adenosine derivative (5 or 12) and R–N@C@O
(1.2 equiv.) in CH2Cl2 was stirred protected from moisture at ambi-
ent temperature until TLC showed complete consumption of start-
ing material (5–7d). The crude reaction mixture was added to a
flash chromatography column and chromatographed directly.
5.2.7.2. 20,30-Bis-O-tert-butyldimethylsilyl-50-(N-methylcarba-
moyl)-N6-(N-phenylcarbamoyl)adenosine (4). Method A
Treatment of 12 (100 mg, 0.181 mmol), phenylisocyanate
(33 mg, 0.28 mmol), and CH2Cl2 (2.2 mL), by general procedure A
5.2.3. General procedure B (hydrogenation)
A suspension of the 50-azido-50-deoxyadenosine derivative 6
and Pd–C (10%) in EtOAc was stirred for 12–15 h at ambient tem-
perature under H2 (balloon pressure). The catalyst was removed by
filtering through celite. Volatiles were evaporated under reduced
pressure and the crude product was used without further
purification.
[chromatography 30?50% EtOAc/hexanes] gave
4 (109 mg,
0.162 mmol, 90%). Method B. Treatment of 14 (50 mg, 0.09 mmol),
aniline (11 mg, 0.12 mmol), and pyridine (1 mL) by general proce-
dure F (chromatography 50% EtOAc/hexanes), gave 4 (33 mg,
0.049 mmol, 55%). 1H NMR (CDCl3, 500 MHz) d 12.25 (s, 1H), 9.86
(br s, 1H), 8.80 (s, 1H), 8.66 (s, 1H), 7.60 (d, J =7.5 Hz, 2H), 7.38
(t, J = 7.8 Hz, 2H), 7.16 (t, J = 7.3 Hz, 1H), 6.21 (d, J = 5.0 Hz, 1H),
5.82 (d, J = 4.0 Hz, 1H), 4.64 (t, J = 4.8 Hz, 1H), 4.50 (dd, J = 12.8,
3.8 Hz, 1H), 4.34 (t, J = 3.8 Hz, 1H), 4.31–4.29 (m, 2H), 2.47 (d,
J = 5.0 Hz, 3H), 0.95 (s, 9H), 0.82 (s, 9H), 0.12 (s, 6H), 0.00 (s, 3H),
ꢂ0.20 (s, 3H); 13C NMR (CDCl3, 125 MHz) d 157.0, 153.4, 151.4,
150.8, 150.4, 143.9, 137.8, 129.3, 124.7, 121.6, 120.6, 87.8, 84.5,
72.4, 72.9, 63.6, 29.9, 27.1, 26.0, 25.9, 18.2, 18.0, 4.29, ꢂ4.61,
ꢂ4.72, ꢂ5.15; MS (FAB) m/z 672.3353 (MH+ [C31H50N7O6Si2]) =
672.3356.
5.2.4. General procedure C (Staudinger reduction)
A solution of the 50-azido-50-deoxyadenosine derivative 6 and
Ph3P (1.5 equiv.) in THF–H2O (25:1) was heated at 85 °C for
1.5 h. Volatiles were evaporated under reduced pressure, and the
product was purified by flash chromatography.
5.2.5. General procedure D (acylation with N-methyl-p-
nitrophenylcarbamate)
A solution of the 50-amino-50-deoxyadenosine product derived
from reduction of 6, or compound 11, N-methyl-p-nitrophenylcar-
bamate, and Et3N (or Na2CO3), in CH2Cl2 (or EtOAc) was stirred at
ambient temperature until TLC indicated complete conversion to
product (4–6 h). Volatiles were evaporated under reduced pres-
sure, and the product was isolated by flash chromatography.
5.2.7.3.
50-Azido-20,30-bis-O-tert-butyldimethylsilyl-50-deoxy-
N6-[N-(4-chlorophenyl)-carbamoyl]adenosine (6a). Treatment
of 5 (60 mg, 0.12 mmol), 4-chlorophenylisocyanate (0.14 mmol),
and CH2Cl2 (1.8 mL) by general procedure A [chromatography
10% EtOAc/CH2Cl2] gave 6a (40 mg, 0.06 mmol, 50%). 1H NMR
(CDCl3, 300 MHz) d 11.91 (s, 1H), 8.81 (s, 1H), 8.63 (s, 1H), 8.43
(s, 1H), 7.61 (d, J = 8.9 Hz, 2H), 7.32 (d, J = 8.9 Hz, 2H), 6.00 (d,
J = 3.3 Hz, 1H), 4.85 (t, J = 4.2 Hz, 1H), 4.32 (t, J = 4.5 Hz, 1H), 4.23
(dd, J = 9.0, 4.8 Hz, 1H), 3.75 (dd, J = 13.1, 4.1 Hz, 1H), 3.69 (dd,
J = 13.2, 4.8 Hz, 1H), 0.94 (s, 9H), 0.84 (s, 9H), 0.13 (s, 3H), 0.11
(s, 3H), 0.00 (s, 3H), ꢂ0.15 (s, 3H); 13C NMR (CDCl3, 75 MHz) d
151.6, 150.9, 150.2, 143.0, 136.9, 129.2, 129.0, 121.7, 89.9, 83.1,
75.0, 72.5, 51.8, 26.00, 25.89, 18.26, 18.12, ꢂ4.17, ꢂ4.47, ꢂ4.63,
ꢂ4.67; MS (ES) m/z ([M+H]+ 674.2819 [C29H45ClN9O4Si2] =
674.2816).
5.2.6. General procedure E (acylation with ethylchloroformate)
A solution of adenosine derivatives 8 or 12, 4-(dimethyl-
amino)pyridine, and ethylchloroformate, in pyridine was stirred
at ambient temperature. Additional aliquots of ethylchloroformate
were added in order to achieve complete conversion to products 9
or 14, respectively. Volatiles were evaporated under reduced pres-
sure, and the product was purified by flash chromatography.
5.2.7. General procedure F (N6-Urea formation)
A solution of adenosine derivatives 9 or 14, and various primary
alkyl or arylamines, in pyridine was heated at 80 °C and the reac-
tion was followed by TLC. Volatiles were evaporated under reduced
pressure, and the product was purified by flash chromatography.
5.2.7.4.
50-Azido-20,30-bis-O-tert-butyldimethylsilyl-50-deoxy-
N6-[N-(4-nitrophenyl)carbamoyl]adenosine (6b). Treatment of
5 (100 mg, 0.192 mmol), 4-nitrophenylisocyanate (0.24 mmol),
and CH2Cl2 (2.4 mL), by general procedure A [chromatography
10% EtOAc/CH2Cl2] gave 6b (97 mg, 0.141 mmol, 73%). 1H NMR
(CDCl3, 500 MHz) d 12.39 (s, 1H), 8.69 (s, 1H), 8.64 (s, 1H), 8.38
(s, 1H), 8.27 (d, J = 9.3 Hz, 2H), 7.85 (d, J = 9.3 Hz, 2H), 6.02 (d,
J = 4.5 Hz, 1H), 4.86 (t, J = 4.3 Hz, 1H), 4.33 (t, J = 4.3 Hz, 1H), 4.23
(dd, J = 8.7, 4.2 Hz, 1H), 3.77 (dd, J = 13.5, 4.0 Hz, 1H), 3.72 (dd,
5.2.7.1. 20,30-Bis-O-tert-butyldimethylsilyl-50-deoxy-50-[(N-meth-
ylcarbamoyl)amino]-N6-(N-phenylcarbamoyl)adenosine (3).
Method A. Treatment of 5 (125 mg, 0.240 mmol), phenylisocya-
nate (0.29 mmol), and CH2Cl2 (2.9 mL) by general procedure A
[chromatography 20?30% EtOAc/hexanes] gave 50-azido-20,30-bis-
O-tert-butyldimethylsilyl-50-deoxy-N6-(N-phenylcarbamoyl)aden-

1016
J. R. Shelton et al. / Bioorg. Med. Chem. 20 (2012) 1008–1019
J = 13.5, 4.8 Hz, 1H), 0.95 (s, 9H), 0.85 (s, 9H), 0.14 (s, 3H), 0.13 (s,
3H), 0.02 (s, 3H), ꢂ0.14 (s, 3H); 13C NMR (CDCl3, 125 MHz) d 151.2,
150.9, 150.7, 149.9, 144.4, 143.6, 143.0, 125.3, 121.6, 119.7, 90.0,
83.3, 75.1, 72.5, 51.8, 26.0, 25.9, 18.3, 18.1, ꢂ4.14, ꢂ4.42, ꢂ4.58,
ꢂ4.67; MS 685.3057 (ES) m/z ([M+H]+ [C29H45N10O6Si2] =
685.3062).
mate (22 mg, 0.11 mmol), Et3N (0.29 mmol), and CH2Cl2 (1.9 mL),
by general procedure [chromatography 30% acetone/hex-
D
anes?3% MeOH/CH2Cl2] to give 7b (47 mg, 0.07 mmol, 78%). 1H
NMR (Acetone-d6, 300 MHz) d 12.77 (s, 1H), 9.60 (s, 1H), 8.94 (s,
1H), 8.82 (s, 1H), 8.26 (d, J = 9.3 Hz, 2H), 8.02 (d, J = 9.3 Hz, 2H),
6.33–6.30 (m, 1H), 6.14 (d, J = 7.6 Hz, 1H), 5.70 (d, J = 4.5 Hz, 1H),
5.00 (dd, J = 4.5, 2.7 Hz, 1H), 4.55 (d, J = 4.5 Hz, 1H), 4.15 (t,
J = 5.4 Hz, 1H), 3.64 (d, J = 5.1 Hz, 2H), 2.74 (d, J = 4.2 Hz, 3H),
0.98 (s, 9H), 0.72 (s, 9H), 0.19 (s, 3H), 0.17 (s, 3H), ꢂ0.04 (s, 3H),
ꢂ0.14 (s, 3H); 13C NMR (Acetone-d6, 75 MHz) d 159.9, 152.2,
152.0, 151.8, 150.9, 145.9, 145.0, 143.9, 125.8, 122.0, 120.2,
120.1, 88.9, 88.1, 75.9, 74.4, 42.8, 42.7, 27.3, 27.1, 26.4, 26.1,
18.7, 18.4, ꢂ4.2, ꢂ4.3, ꢂ4.4, ꢂ5.3; MS 716.3366 (ES) m/z ([M+H]+
[C31H50N9O7Si2] = 716.3353).
5.2.7.5. 50-Azido-20,30-bis-O-tert-butyldimethylsilyl-50-deoxy-N6-
[N-(4-methoxyphenyl)-carbamoyl]adenosine (6c). Treatment
of
5
(100 mg, 0.192 mmol), 4-methoxyphenylisocyanate
(0.24 mmol), and CH2Cl2 (2.4 mL), by general procedure A [chro-
matography 50% EtOAc/Hexanes] gave 6c (104 mg, 0.155 mmol,
81%). 1H NMR (CDCl3, 500 MHz) d 11.60 (s, 1H), 8.61 (s, 1H), 8.53
(s, 1H), 8.36 (s, 1H), 7.54 (d, J = 8.8 Hz, 2H), 6.91 (d, J = 8.8 Hz,
2H), 5.98 (d, J = 4.5 Hz, 1H), 4.86 (t, J = 4.0 Hz, 1H), 4.32 (t,
J = 4.5 Hz, 1H), 4.23 (dd, J = 9.5, 5.0 Hz, 1H), 3.82 (s, 3H), 3.72 (dd,
J = 13.0, 4.0 Hz, 1H), 3.70 (dd, J = 13.0, 5.0 Hz, 1H), 0.94 (s, 9H),
0.84 (s, 9H), 0.13 (s, 3H), 0.11 (s, 3H), 0.00 (s, 3H), ꢂ0.16 (s, 3H);
13C NMR (CDCl3, 125 MHz) d 156.3, 151.5, 150.8, 150.2, 150.1,
142.5, 131.0, 122.2, 121.2, 114.2, 89.7, 82.9, 74.7, 72.3, 55.5, 51.6,
25.8, 25.7, 18.0, 17.9, ꢂ4.4, ꢂ4.7, ꢂ4.85, ꢂ4.90; MS (ES) m/z
([M+H]+ 670.3335 [C30H48N9O5Si2] = 670.3317).
5.2.7.9.
20,30-Bis-O-tert-butyldimethylsilyl-50-deoxy-N6-[N-(4-
methoxyphenyl)carbamoyl]-50-[(N-methylcarbamoyl)
amino]adenosine (7c). Treatment of 6c (100 mg, 0.15 mmol),
10% Pd–C (50 mg), and EtOAc (10 mL) by general procedure B gave
a crude product that was treated with N-methyl-p-nitrophenylcar-
bamate, Et3N (60
lL), and CH2Cl2 (4 mL), by general procedure D
[chromatography 5% MeOH/CH2Cl2] to give 7c (60 mg, 0.086 mmol
57%). 1H NMR (Acetone-d6, 300 MHz) d 11.98 (s, 1H), 9.55 (br s,
1H), 9.00 (s, 1H), 8.90 (s, 1H), 7.67 (d, J = 9.0 Hz, 2H), 6.98 (d,
J = 9.0 Hz, 2H), 6.40–6.32 (m, 1H), 6.19 (d, J = 7.5 Hz, 1H), 5.71 (d,
J = 4.8 Hz, 1H), 4.97 (dd, J = 7.4, 4.4 Hz, 1H), 4.59 (d, J = 4.5 Hz,
1H), 4.19 (t, J = 4.7 Hz, 1H), 3.83 (s, 3H), 3.77–3.67 (m, 1H), 3.62–
3.54 (m, 1H), 2.72 (d, J = 4.2 Hz, 3H), 0.98 (s, 9H), 0.73 (s, 9H),
0.19 (s, 3H), 0.17 (s, 3H), 0.00 (s, 3H), ꢂ0.42 (s, 3H); 13C NMR (Ace-
tone-d6, 75 MHz) d 158.9, 156.3, 151.6, 151.4, 151.0, 150.9, 150.4,
143.9, 131.5, 131.4, 121.7, 121.6, 114.0, 87.9, 87.3, 75.2, 73.6,
54.8, 41.8, 25.5, 25.2, 17.8, 17.5, ꢂ5.14, ꢂ5.19, ꢂ5.33, ꢂ6.22; MS
701.3611 (ES) m/z ([M+H]+ [C32H53N8O6Si2] = 701.3621).
5.2.7.6. 50-Azido-20,30-bis-O-tert-butyldimethylsilyl-50-deoxy-N6-
(N-benzylcarbamoyl)adenosine (6d). Treatment of 5 (70 mg,
0.13 mmol), benzylisocyanate (0.16 mmol), and CH2Cl2 (1.8 mL)
by general procedure A [chromatography 10% EtOAc/CH2Cl2] gave
6d (65 mg, 75%). 1H NMR (CDCl3, 300 MHz) d 9.97 (br s, 1H), 8.78
(br s, 1H), 8.48 (s, 1H), 8.42 (s, 1H), 7.42–6.95 (m, 5H), 5.98 (d,
J = 3.6 Hz, 1H), 4.83 (t, J = 4.2 Hz, 1H), 4.66 (d, J = 5.4 Hz, 2H), 4.34
(dd, J = 10.5, 5.1 Hz, 1H), 4.32 (t, J = 4.4 Hz, 1H), 4.22 (dd, J = 9.3,
4.5 Hz, 1H), 3.73 (dd, J = 13.8, 4.5 Hz, 1H), 3.66 (dd, J = 13.7,
5.0 Hz, 1H), 0.93 (s, 9H), 0.84 (s, 9H), 0.12 (s, 3H), 0.11 (s, 3H),
0.00 (s, 3H), ꢂ0.15 (s, 3H); 13C NMR (CDCl3, 75 MHz) d 154.2,
151.0, 150.5, 142.4, 138.8, 128.6, 127.4, 127.3, 121.2, 89.7, 82.8,
74.8, 72.3, 51.6, 44.0, 29.8, 25.81, 25.70, 18.04, 17.90, ꢂ4.38,
ꢂ4.70, ꢂ4.85; MS 669.3609 (ES) m/z ([M+H]+ [C31H51N9O4Si2] =
669.3603).
5.2.7.10. N6-[N-Benzylcarbamoyl]-20,30-bis-O-tert-butyldimeth-
ylsilyl-50-deoxy-50-[(N-methylcarbamoyl)amino]
adenosine
(7d). Treatment of 6d (126 mg, 0.192 mmol), triphenylphosphine
(76 mg, 0.29 mmol), and THF–H2O (25:1, 1.2 mL) by general proce-
dure C [chromatography; solvent A] gave a crude product that was
treated with with N-methyl-p-nitrophenylcarbamate (57 mg,
0.29 mmol), Na2CO3 (53 mg, 0.5 mmol), and EtOAc (8.0 mL), by
general procedure D [chromatography 30% acetone/hexanes?3%
MeOH/CH2Cl2] to give 7d (65 mg, 0.095 mmol, 49%). 1H NMR
(CDCl3, 500 MHz) d 10.43 (br s, 1H), 9.33 (br s, 1H), 8.91 (br s,
1H), 8.55 (s, 1H), 7.39–7.36 (m, 3H), 7.32–7.29 (m, 2H), 6.34 (br
s, 1H), 6.10 (d, J = 8.0 Hz, 1H), 5.27 (br s, 1H), 4.65 (d, J = 6.0 Hz,
2H), 4.49 (dd, J = 7.8, 4.8 Hz, 1H), 4.45 (d, J = 5.0 Hz, 1H), 4.13 (t,
J = 5.4 Hz, 1H), 3.97 (ddd, J = 14.8, 8.0, 1.5 Hz, 1H), 2.97 (dt,
J = 11.5, 3.0 Hz, 1H), 2.71 (d, J = 5.0 Hz, 3H), 0.96 (s, 9H), 0.69 (s,
9H), 0.15 (s, 3H), 0.14 (s, 3H), ꢂ0.12 (s, 3H), ꢂ0.49 (s, 3H); 13C
NMR (CDCl3, 125 MHz) d 159.5, 156.2, 151.7, 150.9, 150.5, 144.1,
138.2, 128.9, 127.6, 126.9, 120.8, 88.6, 86.6, 77.3, 73.9, 44.3, 41.5,
29.9, 26.9, 26.1, 25.7, 18.2, 17.9, ꢂ4.3, ꢂ4.6, ꢂ5.5; MS 685.3666
(ES) m/z ([M+H]+ [C32H53N8O5Si2] = 685.3672).
5.2.7.7.
20,30-Bis-O-tert-butyldimethylsilyl-N6-[N-(4-chloro-
phenyl) carbamoyl]-50-deoxy-50-[(N-methylcarbamoyl)amino]
adenosine (7a). Treatment of 6a (60 mg, 0.09 mmol), triphenyl-
phosphine (35 mg, 0.13 mmol), THF–H2O (25:1, 0.6 mL) by general
procedure C [chromatography; solvent A] gave a crude product
that was treated with N-methyl-p-nitrophenylcarbamate (26 mg,
0.13 mmol), Et3N (0.36 mmol), and CH2Cl2 (2.3 mL), by general
procedure D [chromatography 30% acetone/hexanes?5% MeOH/
CH2Cl2] to give 7a (50 mg, 0.07 mmol, 78%). 1H NMR (Acetone-d6,
300 MHz) d 12.30 (s, 1H), 9.86 (s, 1H), 9.03 (s, 1H), 8.77 (s, 1H),
7.79 (d, J = 9.0 Hz, 2H), 7.37 (d, J = 8.7 Hz, 2H), 6.34 (t, J = 6.0 Hz,
1H), 6.15 (d, J = 7.5 Hz, 1H), 5.74 (d, J = 5.1 Hz, 1H), 4.96 (dd,
J = 7.1, 4.4 Hz, 1H), 4.54 (d, J = 4.2 Hz, 1H), 4.15 (t, J = 5.3 Hz, 1H),
3.70–3.60 (m, 2H), 2.72 (d, J = 4.5 Hz, 3H), 0.98 (s, 9H), 0.73 (s,
9H), 0.19 (s, 3H), 0.16 (s, 3H), ꢂ0.05 (s, 3H), ꢂ0.41 (s, 3H); 13C
NMR (Acetone-d6, 75 MHz) d 159.1, 151.5, 151.4, 151.0, 150.9,
150.2, 144.1, 137.6, 128.8, 128.5, 127.8, 121.3, 120.9, 87.9, 87.1,
75.2, 73.5, 41.9, 26.4, 26.3, 25.5, 25.3, 17.8, 17.5, ꢂ5.13, ꢂ5.19,
ꢂ5.32, ꢂ6.16; MS 705.3126 (ES) m/z ([M+H]+ [C31H50ClN8O5Si2] =
705.3131).
5.2.7.11.
methylcarbamoyl)amino]adenosine
20,30-Bis-O-tert-butyldimethylsilyl-50-deoxy-50-[(N-
(8). Treatment of
5
(100 mg, 0.192 mmol), 10% Pd–C (50 mg), and EtOAc (10 mL) by
general procedure B gave a crude product that was treated with
N-methyl-p-nitrophenylcarbamate (57 mg, 0.29 mmol), Et3N (60
5.2.7.8.
20,30-Bis-O-tert-butyldimethylsilyl-50-deoxy-50-[(N-
lL), and CH2Cl2 (4 mL), by general procedure D [chromatography
methylcarbamoyl)amino]-N6-[N-(4-nitro-phenyl)carbamoyl]
adenosine (7b). Treatment of 6b (60 mg, 0.09 mmol), triphenyl-
phosphine (29 mg, 0.11 mmol), and THF–H2O (25:1, 0.5 mL) by
general procedure C [chromatography; solvent A] gave a crude
product that was treated with with N-methyl-p-nitrophenylcarba-
5% MeOH/CH2Cl2] to give 8 (87 mg, 0.16 mmol, 83%). 1H NMR
(CDCl3, 500 MHz) d 8.35 (s, 1H), 7.84 (s, 1H), 7.42 (d, J = 9.5 Hz,
1H), 5.75 (d, J = 4.5 Hz, 1H), 5.65 (br s, 2H), 4.84 (dd, J = 8.3,
4.8 Hz, 1H), 4.50–4.42 (m, 1H), 4.23 (d, J = 5 Hz, 1H), 4.18 (s, 1H),
4.05 (dd, J = 14.3, 10.3 Hz, 1H), 3.17 (d, J = 14.5 Hz, 1H), 2.84 (d,

J. R. Shelton et al. / Bioorg. Med. Chem. 20 (2012) 1008–1019
1017
J = 4.5 Hz, 3H), 0.95 (s, 9H), 0.71 (s, 9H), 0.15 (s, 3H), 0.13 (s, 3H),
ꢂ0.15 (s, 3H), ꢂ0.52 (s, 3H); 13C NMR (CDCl3, 125 MHz) d 159.4,
156.4, 152.4, 149.3, 142.1, 121.9, 90.6, 88.3, 73.82, 73.80, 41.8,
27.4, 26.10, 25.8, 18.2, 18.0, ꢂ4.24, ꢂ4.35, ꢂ4.59, ꢂ5.58; MS
552.3153 (ES) m/z ([M+H]+ [C24H46N7O4Si2] = 552.3150).
J = 7.5 Hz, 1H), 5.60 (br s, 1H), 4.52–4.48 (m, 2H), 4.16 (s, 1H),
4.05 (ddd, J = 14.3, 8.8, 1.3 Hz, 1H), 3.40 (q, J = 6.5 Hz, 2H), 3.12
(dt, J = 14.8, 3.6 Hz, 1H), 2.84 (d, J = 4.5 Hz, 3H), 1.66 (pent,
J = 7.3 Hz, 2H), 1.46–1.42 (m, 2H), 1.38–1.32 (m, 2H), 0.98 (s, 9H),
0.91 (t, J = 6.5 Hz, 3H), 0.70 (s, 9H), 0.17 (s, 3H), 0.15 (s, 3H),
ꢂ0.10 (s, 3H), ꢂ0.46 (s, 3H); 13C NMR (CDCl3, 125 MHz) d 159.5,
155.3, 151.1, 150.8, 143.8, 121.2, 88.6, 87.6, 76.5, 73.8, 41.7, 40.7,
31.7, 29.9, 27.1, 27.0, 26.1, 26.0, 25.8, 22.8, 18.3, 18.0, 14.2,
ꢂ4.26, ꢂ4.30, ꢂ4.56, ꢂ5.46; MS (FAB) m/z 679.4142 ([M+H]+
[C31H59N8O5Si2]) = 679.4204.
5.2.7.12.
20,30-Bis-O-tert-butyldimethylsilyl-50-deoxy-N6-(eth-
oxycarbonyl)-50-[(N-methylcarbamoyl)amino]-adenosine
(9). Treatment of 8 (80 mg, 0.145 mmol), ethylchloroformate
(62 mg, 0.57 mmol), DMAP (27 mg, 0.22 mmol), and pyridine
(1 mL), by general procedure E [1 h; additional ethylchloroformate
(30 mg), 1 h; chromatography 30?50% acetone/hexanes] gave 9
(50 mg, 0.080 mmol, 55%). 1H NMR (CDCl3, 500 MHz) d 8.76 (s,
1H), 8.42 (br s, 1H), 8.03 (s, 1H), 7.09 (d, J = 8.0 Hz, 1H), 5.81 (d,
J = 8.5 Hz, 1H), 4.78 (dd, J = 8.0, 5.0 Hz, 1H), 4.49–4.46 (m, 1H),
4.35 (q, J = 7.2 Hz, 2H), 4.24 (d, J = 4.5 Hz, 1H), 4.19 (t, J = 2.8 Hz,
1H), 4.01 (ddd, J = 15.0, 9.5, 2.5 Hz, 1H), 3.22 (dt, J = 14.5, 2.8 Hz,
1H), 2.81 (d, J = 5.0 Hz, 3H), 1.37 (t, J = 7.3 Hz, 3H), 0.94 (s, 9H),
0.68 (s, 9H), 0.14 (s, 3H), 0.13 (s, 3H), ꢂ0.17 (s, 3H), ꢂ0.61 (s,
3H); 13C NMR (CDCl3, 125 MHz) d 159.2, 152.3, 150.9, 150.6,
150.4, 143.8, 123.8, 90.5, 88.4, 73.9, 73.6, 62.6, 41.8, 29.9, 29.5,
27.4, 26.0, 25.7, 18.2, 17.9, 14.6, ꢂ4.3, ꢂ4.4, ꢂ4.6, ꢂ5.6; MS (FAB)
m/z 624.3356 ([M+H]+ [C27H50N7O6Si2]) = 624.3358.
5.2.7.16. 20,30-Bis-O-tert-butyldimethylsilyl-50-deoxy-N6-[N-(m-
iodophenyl)carbamoyl]-50-[(N-methylcarbamoyl)amino]
adenosine (10d). Treatment of
9 (38 mg, 0.061 mmol) and
m-iodoaniline (36 mg, 0.16 mmol) in pyridine (1 mL) by general
procedure F [chromatography 2?4% MeOH/CH2Cl2 then 15?45%
Acetone/CH2Cl2] gave 10d (34 mg, 0.043 mmol, 70%). 1H NMR
(CDCl3, 500 MHz) d 12.13 (s, 1H), 9.26 (br s, 1H), 8.72 (s, 1H),
8.69 (s, 1H), 8.01 (t, J = 1.8 Hz, 1H), 7.55 (dd, J = 8.0, 1.0 Hz, 1H),
7.51 (d, J = 8.5 Hz, 1H), 7.11 (t, J = 7.8 Hz, 1H), 6.49–6.42 (m, 1H),
6.06 (d, J = 8.0 Hz, 1H), 4.81–4.76 (m, 1H), 4.61 (dd, J = 8.0, 4.5 Hz,
1H), 4.41 (d, J = 4.5 Hz, 1H), 4.20 (t, J = 2.5 Hz, 1H), 4.10 (ddd,
J = 15.0, 8.5, 2.5 Hz, 1H), 3.24 (dt, J = 14.8, 3.3 Hz, 1H), 2.75 (d,
J = 4.5 Hz, 3H), 0.97 (s, 9H), 0.71 (s, 9H), 0.16 (s, 3H), 0.15 (s, 3H),
ꢂ0.11 (s, 3H), ꢂ0.48(s, 3H); 13C NMR (CDCl3, 125 MHz) d 159.2,
152.3, 150.9, 150.6, 150.4, 144.3, 138.9, 133.8, 130.8, 129.9,
121.8, 120.4, 94.5, 88.8, 88.3, 75.7, 73.7, 41.9, 29.8, 27.3, 26.1,
25.8, 18.3, 18.0, ꢂ4.26, ꢂ4.32, ꢂ4.55, ꢂ5.46; MS (FAB) m/z
797.2482 (([M+H]+ [C31H50IN8O5Si2]) = 797.2445.
5.2.7.13.
20,30-Bis-O-tert-butyldimethylsilyl-N6-(N-cyclohexyl
carbamoyl)-50-deoxy-50-[(N-methylcarbamoyl) amino]adeno-
sine (10a). Treatment of 9 (38 mg, 0.060 mmol) and cyclohexyl-
amine (10 mg, 0.10 mmol) in pyridine (1 mL) by general
procedure F [chromatography 40?60% acetone/CH2Cl2] gave 10a
(19 mg, 0.028 mmol, 46%). 1H NMR (CDCl3, 500 MHz) d 10.00 (d,
J = 7.0 Hz, 1H), 9.29 (br s, 1H), 9.04 (br s, 1H), 8.57 (s, 1H), 6.48–
6.43 (m, 1H), 6.14 (d, J = 7.0 Hz, 1H), 5.63 (br s, 1H), 4.51–4.49 (m,
2H), 4.16 (s, 1H), 4.10 (dd, J = 14.3, 8.8 Hz, 1H), 3.82–3.74 (m, 1H),
3.11, (dt, J = 14.8, 3.4 Hz, 1H), 2.84 (d, J = 4.0 Hz, 3H), 2.04–1.96
(m, 2H), 1.82–1.74 (m, 2H), 1.68–1.62 (m, 2H), 1.48–1.42 (m, 4H),
0.97 (s, 9H), 0.70 (s, 9H), 0.17 (s, 3H), 0.15 (s, 3H), ꢂ0.11 (s, 3H),
ꢂ0.45 (s, 3H); 13C NMR (CDCl3, 125 MHz) d 159.5, 154.5, 151.1,
150.8, 143.8, 121.1, 88.6, 87.3, 77.4, 76.6, 73.7, 49.6, 41.6, 33.4,
33.3, 29.9, 27.1, 26.1, 25.8, 24.8, 18.3, 17.9, ꢂ4.29, ꢂ4.60, ꢂ5.45;
MS (FAB) m/z 677.3985 ([M+H]+ [C31H57N8O5Si2]) = 677.3949.
5.2.7.17. 20,30-Bis-O-tert-butyldimethylsilyl-50-deoxy-N6-[N-(p-
iodophenyl)carbamoyl]-50-[(N-methylcarbamoyl)amino] aden-
osine (10e). A solution of 9 (38 mg, 0.061 mmol) and p-iodoani-
line (39 mg, 0.18 mmol) in pyridine (1 mL) [chromatography
40?50% Acetone/hexanes then EtOAc] gave 10e (16 mg,
0.020 mmol, 34%). 1H NMR (CDCl3, 500 MHz) d 11.95 (s, 1H), 8.93
(br s, 1H), 8.67 (s, 1H), 8.49 (s, 1H), 7.68 (d, J = 8.5 Hz, 2H), 7.39
(d, J = 9.0 Hz, 2H), 6.57 (d, J = 6.0 Hz, 1H), 5.97 (d, J = 8.0 Hz, 1H),
4.70 (dd, J = 8.0, 4.5 Hz, 1H), 4.66–4.64 (m, 1H), 4.34 (d, J = 4.5 Hz,
1H), 4.22–4.19 (m, 1H), 4.00 (ddd, J = 15.0, 9.0, 2.5 Hz, 1H), 3.24
(dt, J = 15.0, 3.0 Hz, 1H), 2.78 (d, J = 5.0 Hz, 3H), 0.96 (s, 9H), 0.71
(s, 9H), 0.16 (s, 3H), 0.14 (s, 3H), ꢂ0.12 (s, 3H), ꢂ0.50 (s, 3H); 13C
NMR (CDCl3, 125 MHz) d 159.2, 151.7, 150.5, 144.3, 138.3, 137.6,
122.8, 89.5, 88.2, 87.9, 75.0, 73.6, 41.9, 29.9, 27.6, 26.1, 25.8,
18.3, 18.0, ꢂ4.28, ꢂ4.33, ꢂ4.55, ꢂ5.48; MS (FAB) m/z 797.2482
([M+H]+ [C31H50IN8O5Si2]) = 797.2474.
5.2.7.14.
20,30-Bis-O-tert-butyldimethylsilyl-50-deoxy-50-[(N-
methylcarbamoyl)amino]-N6-(N-propylcarbamoyl)adenosine
(10b). Treatment of 9 (38 mg, 0.061 mmol) and propylamine
(11 mg, 0.19 mmol) in pyridine (1 mL) by general procedure F
[chromatography 40?60% Acetone/CH2Cl2] gave 10b (28 mg,
0.044 mmol, 72%). 1H NMR (CDCl3, 500 MHz)
d 10.10 (t,
J = 5.0 Hz, 1H), 9.47 (s, 1H), 9.12 (s, 1H), 8.58 (s, 1H), 6.40 (q, J =
4.0 Hz, 1H), 6.17 (d, J = 7.5 Hz, 1H), 5.71, (br s, 1H), 4.50 (dd,
J = 13.3, 4.8 Hz, 1H), 4.48 (dd, J = 8.0, 5.0 Hz, 1H), 4.15 (s, 1H),
4.07 (dd, J = 14.3, 8.3 Hz, 1H), 3.38 (q, J = 6.5 Hz, 2H), 3.11 (dt,
J = 3.5, 15.0 Hz, 3H), 2.83 (d, J = 4.5 Hz, 3H), 1.70 (sext, J = 7.2 Hz,
2H), 1.04 (t, J = 7.5 Hz, 3H), 0.97 (s, 9H), 0.69 (s, 9H), 0.17 (s, 3H),
0.15 (s, 3H), 0.10 (s, 3H), ꢂ0.45 (s, 3H); 13C NMR (CDCl3,
125 MHz) d 159.6, 155.6, 151.3, 150.9, 150.7, 143.9, 121.4, 88.6,
87.1, 73.8, 42.4, 41.6, 29.9, 29.5, 27.1, 26.1, 25.8, 23.3, 18.3, 17.9,
11.8, 0.21, ꢂ4.10, ꢂ4.58, ꢂ5.47; MS (FAB) m/z 637.3678 ([M+H]+
[C28H53N8O5Si2Na]) = 637.3677.
5.2.7.18. 20,30-Bis-O-tert-butyldimethylsilyl-50-(N-methylcarba-
moyl) adenosine (12). Treatment of 11 (618, 1.25 mmol), N-
methyl-p-nitrophenylcarbamate (377 mg, 1.92 mmol), Et3N
(2.1 mL), and CH2Cl2 (9.5 mL) by general procedure D [60 °C over-
night; chromatography EtOAc] gave 12 (580 mg, 1.05 mmol, 84%).
1H NMR (CDCl3, 500 MHz) d 8.35 (s, 1H), 7.98 (s, 1H), 5.89 (d,
J = 4.5 Hz, 1H), 5.51 (br s, 2H), 4.93 (t, J = 4.0 Hz, 1H), 4.72 (br s,
1H), 4.50 (dd, J = 11.8, 4.3 Hz, 1H), 4.33 (dd, J = 11.8, 4.7 Hz, 1H),
4.32 (t, J = 4.5 Hz, 1H), 4.29 (t, J = 4.5 Hz, 1H), 2.82 (d, J = 5 Hz,
3H), 0.93 (s, 9H), 0.84 (s, 9H), 0.09 (s, 6H), 0.01 (s, 3H), ꢂ0.14 (s,
3H); 13C NMR (CDCl3, 125 MHz) d156.7, 155.9, 153.1, 149.7,
140.1, 120.6, 89.9, 82.7, 74.7, 72.0, 63.8, 29.8, 27.8, 25.9, 25.8,
18.2, 18.0, ꢂ4.25, ꢂ4.57, ꢂ4.75, ꢂ4.80; MS (FAB) m/z 553.2999
([M+H]+ [C24H45N6O5Si2]) = 553.2985.
5.2.7.15. 20,30-Bis-O-tert-butyldimethylsilyl-50-deoxy-N6-(N-hex-
ylcarbamoyl)-50-[(N-methylcarbamoyl)amino]adenosine
(10c). Treatment of
9 (19 mg, 0.031 mmol) and hexylamine
(12 mg 0.12 mmol) in pyridine (1 mL) by general procedure F
[chromatography 2% MeOH/CH2Cl2] gave 10c (8 mg, 0.012 mmol,
39%). 1H NMR (CDCl3, 500 MHz) d 10.00 (br s, 1H), 9.32 (br s,
1H), 9.02 (br s, 1H), 8.57 (s, 1H), 6.47 (d, J = 4.0 Hz,1H), 6.13 (d,
5.2.7.19.
20,30-Bis-O-tert-butyldimethylsilyl-N6-[N-(p-chloro-
phenyl)carbamoyl]-50-(N-methylcarbamoyl) adenosine (13a).
Treatment of 12 (100 mg, 0.181 mmol), p-chlorophenylisocya-
nate (43 mg, 0.28 mmol), and CH2Cl2 (2.2 mL) by general proce-

1018
J. R. Shelton et al. / Bioorg. Med. Chem. 20 (2012) 1008–1019
dure
A
[chromatography 30?50% EtOAc/hexanes] gave 13a
5.2.7.23. 20,30-Bis-O-tert-butyldimethylsilyl-N6-ethoxycarbonyl-
50-(N-methylcarbamoyl)adenosine (14). Treatment of 12
(150 mg, 0.271 mmol), ethylchloroformate (38 mg, 0.35 mmol),
DMAP (56 mg, 0. 46 mmol), and pyridine (1 mL) by general proce-
dure E [15 h; additional ethylchloroformate (48 mg); chromatogra-
phy 75% EtOAc/hexanes] gave 14 (107 mg, 0.171 mmol, 63%). 1H
NMR (CDCl3, 500 MHz) d 8.75 (s, 1H), 8.13 (br s, 1H), 8.12 (s, 1H),
5.95 (d, J = 4.5 Hz, 1H), 4.90 (t, J = 4.3 Hz, 1H), 4.72 (d, J = 2.0 Hz,
1H), 4.50 (dd, J = 11.5, 3.5 Hz, 1H), 4.37–4.32 (m, 3H), 4.31–4.27
(m, 2H), 2.83 (d, J = 5.0 Hz, 3H), 1.37 (t, J = 7.0 Hz, 3H), 0.93 (s,
9H), 0.88 (s, 9H), 0.09 (s, 6H), 0.00 (s, 3H), ꢂ0.16 (s, 3H); 13C
NMR (CDCl3, 125 MHz) d 156.6, 152.9, 151.4 (minor), 151.0,
149.8, 142.2, 123.1, 89.9, 82.9, 74.9, 72.0, 63.6, 62.4, 29.0, 27.9,
26.0, 25.9, 18.2, 18.1, 14.6, ꢂ4.2, ꢂ4.5, ꢂ4.72, ꢂ4.76; MS (FAB)
m/z 625.3182 ([M+H]+ [C27H49N6O7Si2]) = 625.3201.
(57 mg, 0.081 mmol, 45%). 1H NMR (CDCl3, 500 MHz) d 12.15 (s,
1H), 9.45 (br s, 1H), 8.65 (s, 1H), 8.63 (s, 1H), 7.56 (d, J =8.5 Hz,
2H), 7.33 (dt, J = 9.7, 2.5 Hz, 2H), 6.14 (d, J = 3.0 Hz, 1H), 5.48 (d,
J = 5.5 Hz, 1H), 4.68 (t, J = 4.5 Hz, 1H), 4.45 (dd, J = 12.8, 3.3 Hz,
1H), 4.35 (dd, J = 12.5, 3.0 Hz, 1H), 4.33–4.28 (m, 2H), 2.60 (d,
J = 5.0 Hz, 3H), 0.94 (s, 9H), 0.82 (s, 9H), 0.11 (s, 6H), 0.00 (s, 3H),
ꢂ0.21 (s, 3H); 13C NMR (CDCl3, 500 MHz) d 156.9, 153.2, 151.3,
150.8, 150.2, 143.9, 136.5, 129.6, 129.3, 122.5, 120.7, 88.1, 84.4,
77.7, 77.5, 72.8, 63.7, 29.9, 27.4, 26.0, 25.9, 18.2, 18.0, ꢂ3.42,
ꢂ3.77, ꢂ3.82, ꢂ4.24; MS (FAB) m/z 706.2971 ([M+H]+
[C31H49ClN7O6Si2]) = 706.2999.
5.2.7.20. 20,30-Bis-O-tert-butyldimethylsilyl-50-(N-methylcarba-
moyl)-N6-[N-(p-nitrophenyl)carbamoyl]adenosine (13b).
Treatment of 12 (100 mg, 0.181 mmol), p-nitrophenylisocya-
nate (45 mg, 0.27 mmol), and CH2Cl2 (2.2 mL) by general proce-
dure A [chromatography 30% EtOAc/hexanes?100% EtOAc] gave
13b (88 mg, 0.12 mmol, 66%). 1H NMR (Acetone-d6, 500 MHz) d
12.84 (s, 1H), 9.79 (br s, 1H), 8.83 (s, 1H), 8.75 (s, 1H), 8.22 (dt,
J = 9.5, 2.7 Hz, 2H), 7.99 (dt, J = 9.5, 2.3 Hz, 2H), 6.41 (q, J = 4.5 Hz,
1H), 6.19 (d, J = 5.5 Hz, 1H), 4.93 (t, J = 5.0 Hz, 1H), 4.53 (t, J
=4.0 Hz, 1H), 4.47 (dd, J = 12.3, 4.8 Hz, 1H), 4.44 (dd, J = 11.8,
4.8 Hz, 1H), 4.31 (dd, J = 8.3, 4.3 Hz, 1H), 2.72 (d, J = 4.5 Hz, 3H),
0.98 (s, 9H), 0.81 (s, 9H), 0.18 (s, 3H), 0.16 (s, 3H), 0.03 (s, 3H),
ꢂ0.20 (s, 3H); 13C NMR (Acetone-d6, 125 MHz) d 157.5, 152.3,
152.1, 151.6, 150.7, 145.8, 144.2, 143.9, 125.7, 121.7, 120.3,
120.2, 118.9 (minor), 89.1, 84.8, 76.6, 73.6, 64.4, 27.8, 26.4, 26.2,
18.7, 18.5, ꢂ4.2, ꢂ4.4, ꢂ4.5, ꢂ4.9; MS (FAB) m/z 717.3168
([M+H]+ [C31H49N8O8Si2]) = 717.3212.
5.2.7.24.
carbamoyl]-50-(N-methylcarbamoyl)adenosine
20,30-Bis-O-tert-butyldimethylsilyl-N6-[N-cyclohexyl-
(15a). Treat-
ment of 14 (50 mg, 0.08 mmol) and cyclohexylamine (12 mg,
0.12 mmol) in pyridine (1 mL) by general procedure F [chromatog-
raphy 2?4% MeOH/CH2Cl2] gave 15a (50 mg, 0.074 mmol, 93%). 1H
NMR (CDCl3, 500 MHz) d 10.00 (d, J = 7.5 Hz, 1H), 9.78 (br s, 1H),
8.89 (s, 1H), 8.53 (s, 1H), 6.76 (br s, 1H), 6.21 (d, J = 5.0 Hz, 1H),
4.60 (dd, J = 12.5, 1.5 Hz, 1H), 4.49 (t, J = 4.8 Hz, 1H), 4.40 (t,
J = 3.8 Hz, 1H), 4.26–4.21 (m, 1H), 3.84–3.76 (m, 1H), 2.84 (d,
J = 4.0 Hz, 3H), 2.06–1.98 (m, 2H), 1.81–1.76 (m, 2H), 1.69–1.62
(m, 2H), 1.48–1.38 (m, 4H), 0.95 (s, 9H), 0.79 (s, 9H), 0.14 (s, 3H),
0.13 (s, 3H), ꢂ0.04 (s, 3H), ꢂ0.26 (s, 3H); 13C NMR (CDCl3,
125 MHz) d 157.2, 154.4, 151.0, 150.9, 150.8, 143.1, 120.6, 87.8,
84.5, 77.1, 72.7, 63.3, 49.1, 33.4, 33.3, 29.9, 27.8, 26.1, 25.9, 24.9,
18.3, 18.0, ꢂ4.3, ꢂ4.6, ꢂ4.7, ꢂ5.1; MS (FAB) m/z 678.3825
([M+H]+ [C31H56N7O6Si2]) = 678.3839.
5.2.7.21. 20,30-Bis-O-tert-butyldimethylsilyl-N6-[N-(p-methoxy-
phenyl)carbamoyl]-50-(N-methylcarbamoyl)adenosine (13C).
Treatment of 12 (100 mg, 0.181 mmol), p-methoxyphenylisocy-
anate (53 mg, 0.36 mmol), and CH2Cl2 (2.2 mL) by general proce-
dure A [chromatography 30% EtOAc/hexanes?100% EtOAc] gave
13C (88 mg, 0.125 mmol, 69%). 1H NMR (CDCl3, 500 MHz) d 12.11
(s, 1H), 10.33 (br s, 1H), 8.99 (s, 1H), 8.65 (s, 1H), 7.47 (d, J
=9.5 Hz, 2H), 6.91 (d, J = 9.0 Hz, 2H), 6.27 (d, J = 5.5 Hz, 1H), 6.25
(br s, 1H), 4.57–4.55 (m, 2H), 4.35 (dd, J =3.8, 2.8 Hz, 1H), 4.28
(dd, J = 5.0, 2.5 Hz, 1H), 4.21 (dd, J = 12.8, 2.3 Hz, 1H), 3.83 (s,
3H), 2.38 (d, J = 4.0 Hz, 1H), 0.95 (s, 9H), 0.80 (s, 9H), 0.12 (s, 6H),
ꢂ0.01 (s, 3H), ꢂ0.25 (s, 3H); 13C NMR (CDCl3, 125 MHz) d 157.0,
156.9, 153.5, 151.3, 150.9, 150.5, 143.8, 130.7, 123.5, 120.7,
114.5, 87.8, 84.6, 72.9, 63.6, 55.8, 27.3, 26.1, 25.9, 18.3, 18.1,
5.2.7.25. 20,30-Bis-O-tert-butyldimethylsilyl-50-(N-methylcarba-
moyl)-N6-[N-propylcarbamoyl]adenosine (15b). Treatment of
14 (75 mg, 0.12 mmol) and propylamine (11 mg, 0.19 mmol) in
pyridine (1 mL) by general procedure F [chromatography 2?4%
MeOH/CH2Cl2] gave 15b (50 mg, 0.078 mmol, 65%). 1H NMR
(CDCl3, 500 MHz) d 10.08 (br s, 1H), 10.08–10.06 (m, 1H), 8.99 (s,
1H), 8.54 (s, 1H), 6.99–6.94 (m, 1H), 6.24 (d, J = 5.5 Hz, 1H), 4.64
(dd, J = 13.0, 2.0 Hz, 1H), 4.46 (t, J = 4.8 Hz, 1H), 4.40 (t, J = 3.8 Hz,
1H), 4.25 (d, J = 2.5 Hz, 1H), 4.19 (dd, J = 13.0, 2.5 Hz, 1H), 3.45–
3.32 (m, 2H), 2.83 (d, J = 4.5 Hz, 3H), 1.70 (sext, J = 7.2 Hz, 2H),
1.04 (t, J = 7.3 Hz, 3H), 0.95 (s, 9H), 0.78 (s, 9H), 0.14 (s, 3H), 0.12
(s, 3H), ꢂ0.04 (s, 3H), ꢂ0.28 (s, 3H); 13C NMR (CDCl3, 125 MHz) d
157.2, 155.5, 151.1, 150.9, 150.8, 143.4, 120.5, 87.6, 84.7, 77.3,
72.7, 63.3, 42.2, 29.5, 27.8, 26.0, 25.8, 23.2, 18.2, 18.0, 11.8,
ꢂ4.26, ꢂ4.63, ꢂ4.70, ꢂ5.20; MS (FAB) m/z 638.3512 ([M+H]+
[C28H52N7O6Si2]) = 638.3518.
ꢂ4.3, ꢂ4.6, ꢂ4.7, ꢂ5.1
;
MS (FAB) m/z 702.3461 ([M+H]+
[C32H52N7O7Si2]) = 702.3450.
5.2.7.22. 20,30-Bis-O-tert-butyldimethylsilyl-50-(N-methylcarba-
moyl) -N6-(N-benzylcarbamoyl)adenosine (13d). Treatment of
12 (100 mg, 0.181 mmol), benzylisocyanate (46 mg, 0.35 mmol),
and CH2Cl2 (2.2 mL) by general procedure A [chromatography
30% EtOAc/hexanes?100% EtOAc] gave 13d (58 mg, 0.085 mmol,
47%). 1H NMR (CDCl3, 500 MHz) d 10.47 (t, J = 5.5 Hz, 1H), 10.10
(br s, 1H), 8.94 (s, 1H), 8.52 (s, 1H), 7.40–7.30 (m, 5H), 6.63 (br s,
1H), 6.21 (d, J = 5.5 Hz, 1H), 4.69 (dd, J = 15.5, 6.0 Hz, 1H), 4.64
(dd, J = 15.8, 5.8 Hz, 1H), 4.60 (dd, J = 12.8, 2.3 Hz, 1H), 4.49 (t,
J = 4.8 Hz, 1H), 4.38 (t, J = 3.5 Hz, 1H), 4.25 (dd, J = 5.3, 2.3 Hz,
1H), 4.20 (dd, J = 13.0, 2.5 Hz, 1H), 2.69 (d, J = 4.5, 3H), 0.94 (s,
9H), 0.78 (s, 9H), 0.12 (s, 3H), 0.11 (s, 3H), ꢂ0.06 (s, 3H), ꢂ0.27
(s, 3H); 13C NMR (CDCl3, 125 MHz) d 156.9, 155.5, 150.9, 150.8,
150.4, 143.2, 138.4, 128.7, 127.5, 127.4, 127.0, 120.4, 87.6, 84.4,
76.9, 72.5, 63.1, 43.9, 27.5, 25.8, 25.6, 18.0, 17.8, ꢂ4.5, ꢂ4.85,
ꢂ4.89, ꢂ5.35; MS (FAB) m/z 686.3569 ([M+H]+ [C32H52N7O6Si2]) =
686.3518.
5.2.7.26. 20,30-Bis-O-tert-butyldimethylsilyl-N6-[N-hexylcarba-
moyl]-50-(N-methylcarbamoyl)adenosine (15c). Treatment of
14 (75 mg, 0.12 mmol) and hexylamine (14 mg 0.14 mmol) in pyri-
dine (1 mL) by general procedure F [chromatography 2?4% MeOH/
CH2Cl2] gave 15c (51 mg, 0.075 mmol, 63%). 1H NMR (CDCl3,
500 MHz) d 10.02 (t, J = 5.5 Hz, 1H), 9.98 (br s, 1H), 8.95 (s, 1H),
8.54 (s, 1H), 6.88 (br s, 1H), 6.23 (d, J = 6.0 Hz, 1H), 4.63 (dd,
J = 12.5, 2.0 Hz, 1H), 4.48 (t, J = 5.3 Hz, 1H), 4.40 (t, J = 3.8 Hz, 1H),
4.25 (dd, J = 4.5, 2.5 Hz, 1H), 4.20 (dd, J = 12.5, 2.5 Hz, 1H), 3.42–
3.38 (m, 2H), 2.83 (d, J = 5.0 Hz, 3H), 1.67 (sext, J = 7.5 Hz, 2H),
1.46–1.42 (m, 2H), 1.38–1.32 (m, 4H), 0.95 (s, 9H), 0.91 (t,
J = 6.8 Hz, 3H), 0.78 (s, 9H), 0.14 (s, 3H), 0.13 (s, 3H), ꢂ0.04 (s, 3H),
ꢂ0.27 (s, 3H); 13C NMR (CDCl3, 125 MHz) d 157.2, 155.4, 151.1,
151.0, 150.8, 143.3, 120.6, 87.7, 84.7, 72.7, 63.3, 40.5, 31.7, 29.9,
27.8, 27.0, 26.1, 25.8, 22.8, 18.3, 18.0, 14.2, ꢂ4.25, ꢂ4.62, ꢂ4.68,
ꢂ5.17; MS (FAB) m/z 680.3915 ([M+H]+ [C31H58N7O6Si2]) =
680.4004.

J. R. Shelton et al. / Bioorg. Med. Chem. 20 (2012) 1008–1019
1019
5.2.7.27. 20,30-Bis-O-tert-butyldimethylsilyl-50-(N-methylcarba-
moyl)-N6-[N-(m-iodophenyl)carbamoyl]-adenosine (15d).
Treatment of 14 (75 mg, 0.120 mmol) and m-iodoaniline
(36 mg, 0.17 mmol) in pyridine (1 mL) by general procedure F
[chromatography 2?4% MeOH/CH2Cl2] gave 15d (53 mg,
0.066 mmol, 55%). 1H NMR (CDCl3, 500 MHz) d 12.35 (s, 1H),
10.22 (s, 1H), 8.90 (s, 1H), 8.68 (s, 1H), 8.02 (s, 1H), 7.56 (d,
J = 10.5 Hz, 1H), 7.50 (d, J = 7.0 Hz, 1H), 7.10 (t, J = 8.3 Hz, 1H),
6.24 (d, J = 5.5 Hz, 1H), 5.97-5.92 (m, 1H), 4.59 (dd, J = 10.5,
5.0 Hz, 1H), 4.58 (dd, J = 8.5, 3.0 Hz, 1H), 4.36 (t, J = 3.5 Hz, 1H),
4.30–4.25 (m, 2H), 2.52 (d, J = 5.0 Hz, 3H), 0.96 (s, 9H), 0.80 (s,
9H), 0.13 (s, 6H), 0.00 (s, 3H), ꢂ0.24 (s, 3H); 13C NMR (CDCl3,
125 MHz) d 157.0, 152.9, 151.4, 150.9, 150.2, 143.7, 139.2, 133.5,
130.8, 130.0, 120.9, 120.5, 94.5, 88.3, 84.7, 72.9, 63.8, 30.0, 27.6,
26.1, 25.9, 18.3, 18.1, ꢂ3.72, ꢂ4.02, ꢂ4.05, ꢂ4.56; MS (FAB) m/z
798.2324 ([M+H]+ [C31H49IN7O6Si2]) = 798.2328.
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Treatment of 14 (75 mg, 0.12 mmol) and p-iodoaniline (40 mg,
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raphy 15?25% Acetone/CH2Cl2] gave 15e (37 mg, 0.046 mmol,
39%). 1H NMR (CDCl3, 500 MHz) d 12.35 (s, 1H), 10.22 (s, 1H),
8.90 (s, 1H), 8.68 (s, 1H), 7.67 (d, J = 8.7 Hz, 1H), 7.38 (d,
J = 8.7 Hz, 1H), 6.23 (d, J = 5.4 Hz, 1H), 5.97–5.92 (m, 1H), 4.59
(dd, J = 10.5, 5.0 Hz, 1H), 4.58 (dd, J = 8.5, 3.0 Hz, 1H), 4.36 (t,
J = 3.5 Hz, 1H), 4.30–4.25 (m, 2H), 2.52 (d, J = 5.0 Hz, 3H), 0.96 (s,
9H), 0.80 (s, 9H), 0.13 (s, 6H), 0.00 (s, 3H), ꢂ0.24 (s, 3H); 13C
NMR (CDCl3, 125 MHz) d 156.7, 153.0, 151.3, 150.9, 150.2, 143.4,
138.3, 137.8, 123.1, 120.1, 88.3, 87.7, 84.3, 72.8, 63.8, 30.0, 27.5,
26.1, 25.9, 18.3, 18.1, ꢂ3.74, ꢂ4.10, ꢂ4.53; MS (FAB) m/z
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The authors thank Mrs. Lizette van Berckelaer, Mrs. Leen Ingels,
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References and notes
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