Design and synthesis of 5′-deoxy-5′-phenyladenophostin A, a highly potent IP3 receptor ligand

Article abstract of DOI:10.1021/ol0602710

5′-Deoxy-5′-phenyladenophostin A (5), designed as a useful IP₃ receptor ligand based on the previous structure-activity relationship studies, was successfully synthesized via two key stereoselective glycosidation steps. This compound proved to

Full text of DOI:10.1021/ol0602710

ORGANIC
LETTERS
2006
Vol. 8, No. 7
1455-1458
Design and Synthesis of
5′-Deoxy-5′-Phenyladenophostin A,
a Highly Potent IP3 Receptor Ligand1
Tetsuya Mochizuki,† Yoshihiko Kondo,† Hiroshi Abe,† Colin W. Taylor,‡
Barry V. L. Potter,§ Akira Matsuda,† and Satoshi Shuto*,†
Graduate School of Pharmaceutical Sciences, Hokkaido UniVersity, Kita-12, Nishi-6,
Kita-ku, Sapporo 060-0812, Japan, Department of Pharmacology, Tennis Court Road,
UniVersity of Cambridge, Cambridge, CB 1PD, U.K., and Wolfson Laboratory for
Medicinal Chemistry, Department of Pharmacy and Pharmacology, UniVersity of Bath,
Bath BA2 7AY, U.K.
shu@pharm.hokudai.ac.jp
Received January 31, 2006 (Revised Manuscript Received March 4, 2006)
ABSTRACT
5′
-Deoxy-5
′
-phenyladenophostin A (5), designed as a useful IP3 receptor ligand based on the previous structure
−activity relationship studies,
was successfully synthesized via two key stereoselective glycosidation steps. This compound proved to be a highly potent IP3 receptor
agonist.
Adenophostin A (2),2 isolated from Penicillium breVicom-
pactum, is a very potent myo-inositol 1,4,5-trisphosphate (IP3,
1) receptor ligand, which is 10-100 times more potent than
the endogenous ligand IP3 in stimulating Ca2+ release and
in binding to IP3 receptors.2-4 We previously synthesized
an adenophostin A analogue 3 lacking the adenine moiety
and its des-hydroxymethyl derivative 4, and demonstrated
that the compounds not only bind to IP3 receptors but also
stimulate Ca2+ mobilization with potencies comparable to
IP3 itself.5 These results suggested that the pentofuranosyl
structure of the D-ribose would not be essential for the
activity but the tetrahydrofuran ring could effectively restrict
the three-dimensional positioning of the D-glucose 3,4-
bisphosphate, adenine, and the third phosphate moiety of the
ring. Therefore, the 5′-hydroxymethyl moiety of adenophos-
tin A seems to be unimportant for the binding and Ca2+
mobilization, suggesting that this moiety might be appropriate
† Hokkaido University.
‡ University of Cambridge.
§ University of Bath.
(1) This report constitutes Part 240 of Nucleosides and Nucleotides: for
Part 239, see Kudoh, T.; Maruyama, T.; Ogawa, Y.; Matsuda, A.; Shuto,
S. Nucleosides Nucleotide Nucleic Acids In press.
(2) (a) Takahashi, M.; Kagasaki, T.; Hosoya, T.; Takahashi, S. J. Antibiot.
1993, 46, 1643-1647. (b) Takahashi, M.; Tanzawa, K.; Takahashi, S. J.
Biol. Chem. 1994, 269, 369-372. (c) Hirota, J.; Michikawa, T.; Miyawaki,
A.; Takahashi, M.; Tanzawa, K.; Okura, I.; Furuichi, T.; Mikoshiba, K.
FEBS Lett. 1995, 368, 248-252.
(3) Total synthesis of adenophostin A: (a) Hotoda, H.; Takahashi, M.;
Tanzawa, K.; Takahashi, S.; Kaneko, M. Tetrahedron Lett. 1995, 36, 5037-
5040. (b) van Straten, N. C. R.; van der Marel, G. A.; van Boom,
J. H. Tetrahedron 1997, 53, 6509-6522. (c) Marwood, R. D.; Correa, V.;
Taylor, C. W.; Potter, B. V. L. Tetrahedron: Asymmetry 2000, 11, 397-
403.
(4) For synthesis of adenophostin A analogues, see: (a) Correa, V.;
Nerou, E. P.; Riley, A. M.; Marwood, R. D.; Shuto, S.; Rosenberg, H. J.;
Horne, G.; Potter, B. V. L.; Taylor, C. W. Mol. Pharmacol. 2001, 59, 1206-
1215. (b) Terauchi, M.; Yahiiro, Y.; Abe, H.; Ichikawa, S.; Tovey, S. C.;
Dedos, S. G.; Taylor, C. W.; Potter, V. B. L.; Matsuda, A.; Shuto, S.
Tetrahedron 2005, 61, 3697-3707, and references therein.
(5) (a) Tatani, K.; Shuto, S.; Ueno, Y.; Matsuda, A. Tetrahedron Lett.
1998, 39, 5065-5068. (b) Shuto, S.; Tatani, K.; Ueno, Y.; Matsuda, A. J.
Org. Chem. 1998, 63, 8815-8824. (c) Kashiwayanagi, M.; Tatani, K.;
Shuto, S.; Matsuda, A. Eur. J. Neurosci. 2000, 12, 606-612.
10.1021/ol0602710 CCC: $33.50
© 2006 American Chemical Society
Published on Web 03/11/2006

for further modification to develop novel adenophostin
analogues of biological importance.
Scheme 1
Bioactive ligands bearing an aromatic group, such as a
fluorescent or photoreactive aromatic residue, are useful as
biological tools in labeling target biomolecules and/or
investigating the biological mechanisms of action.6 Adeno-
phostin A might be even more suitable than IP3 itself as the
lead for this kind of modification to develop such biological
tools, because of its higher affinity for the receptor. Accord-
ingly, identification of a site for the modification of adeno-
phostin A without reducing the binding affinity is needed.
Consequently, introduction of an aromatic group into an
appropriate position of adenophostin A would be of biologi-
cal interest.
On the basis of these findings and considerations, we
designed a novel adenophostin A analogue 5 having a phenyl
group at the 5′-position. Biological evaluation of this
compound would clarify steric tolerability around the 5′-
hydroxymethyl moiety for introducing a bulky aromatic
group near the binding site of the IP3 receptors.
4C1 form by the 3,4-O-cyclic diketal protection.10 In this
restricted conformation, the kinetic anomeric effect is
enhanced, resulting in the high R-selectivity in these C-
glycosidation reactions.10 On the basis of these results, we
designed the sulfoxide donor 9 bearing a 3,4-O-cyclic diketal
protecting group to realize the desired R-selective glycosi-
dation due to the enhanced anomeric effect. The 3,4-O-cyclic
diketal protecting group was thought to be also advantageous
for selective phosphorylation of the hydroxyl groups at a
later stage in the synthesis.11
The glycosyl donor 9 was prepared as shown in Scheme
1. Phenyl 1-thio-â-D-glucoside (6) was heated with 2,2,3,3-
tetramethoxybutane, (MeO)3CH, and (+)-camphorsulfonic
acid (CSA) in MeOH under reflux12 to give the 3,4-O-cyclic
diketal derivative 7 in 49% yield, along with the correspond-
ing 2,3-O-protected isomer. Benzylation of the 2- and
6-hydroxyls of 7 followed by m-chloroperbenzoic acid
(m-CPBA) oxidation gave the sulfoxide donor 9.
The glycosidation of the donor 9 and the acceptor 10 (1.0
equiv), prepared according to the previously reported method,13
was investigated with Tf2O and 2,6-di-tert-butyl-4-meth-
ylpyridine (DTBMP) as the promoter9 under various condi-
tions. The R/â-selectivity was significantly affected by the
reaction conditions. Although the reaction with CH2Cl2 as
solvent gave non-stereoselectively a mixture of R/â-glycosi-
Figure 1. IP3 receptor ligands.
The synthesis of the target compound 5, shown in Schemes
1 and 2, includes the two key stereoselective glycosidation
steps, constructing the R-disaccharide 11 with a sulfoxide
donor and the â-nucleoside 16 by the Vorbru¨ggen glycosy-
lation.7
The sulfoxide donor 9 and the acceptor 10 were used for
the R-selective glycosidation preparing 11. Sulfoxide gly-
cosyl donors are known to be stable but can be activated
under mild Lewis acidic conditions.8,9 We recently developed
highly R-selective C-glycosidation reactions based on the
conformational restriction of the pyranosyl donor to the
(10) Stereoselective synthesis of glycosides based on the conformational
restriction strategy with the 3,4-O-cyclic diketal-protecting group (a) Abe,
H.; Shuto, S.; Matsuda, A. J. Am. Chem. Soc. 2001, 123, 11870-11882.
(b) Tamura, S.; Abe, H.; Matsuda, A.; Shuto, S. Angew. Chem., Int. Ed.
2003, 42, 1021-1023. (c) Abe, H.; Terauchi, M.; Matsuda, A.; Shuto, S.
J. Org. Chem. 2003, 68, 7439-7447. (d) Terauchi, M.; Abe, H.; Matsuda,
A.; Shuto, S. Org. Lett. 2004, 6, 3751-3754.
(11) During our study, the synthesis of adenophostin analogues using a
3,4-O-cyclic diketal glycosyl donor has been reported: de Kort, M.;
Regenbogen, A. D.; Overkleeft, H. S.; Challis, J.; Iwata, Y.; Miyamoto,
S.; van der Marel, G. A.; van Boom, J. Tetrahedron 2000, 56, 5915-5928.
(12) Montchamp, J. L.; Tian, F.; Hart, M. E.; Frost, J. W. J. Org. Chem.
1996, 61, 3897-3899.
(6) For an example, see: Nakanishi, W.; Kikuchi, K.; Inoue, T.; Hirose,
K.; Iino, M.; Nagano, T. Bioorg. Med. Chem. Lett. 2002, 12, 911-913.
(7) Niedballa, U.; Vorbru¨ggen, H. J. Org. Chem. 1974, 39, 3654-3660.
(8) Yan, L.; Kahne, D. J. Am. Chem. Soc. 1996, 118, 9239-9248.
(9) Crich, D.; Sun, S. J. Am. Chem. Soc. 1997, 119, 11217-11223.
(13) Parr, I. B.; Horenstein, B. A. J. Org. Chem. 1997, 62, 7489-7494.
1456
Org. Lett., Vol. 8, No. 7, 2006

groups of 14 followed by acylation produced the 1,2,3′,4′-
tetra-O-acetate 15a or the 1,2,3′,4′-tetra-O-i-butyrylate 15b.
The Vorbru¨ggen glycosylation of the acetate 15a was
examined (Table 1). The reaction was first carried out with
Scheme 2
Table 1. Vorbru¨ggen Glycosylation with Donors 15a and 15b
entry donor Lewis acid methoda
solvent
yield (R/â)b
1
2
3
4
5
15a
15a
15a
15b
15b
TMSOTf
TMSOTf
SnCl4
TMSOTf
SnCl4
A
A
B
A
B
MeCN
(ClH2C)2 26% (â)
MeCN
MeCN
MeCN
18% (â)
66% (R/â)
12% (â)
60% (â)
a A: N6-benzoyladenine (4 equiv), TMSOTf (10 equiv), and Et3N (4
equiv) at room temperature. B: silylated N6-Bz-adenine (5 equiv), prepared
by heating N-benzoyladenine in hexamethyldisilazane/pyridine and SnCl4
(6 equiv) at room temperature. b The R-anomer was not detected in the 1H
NMR spectrum in entries 1, 2, 4, and 5; and the R/â ratio was about 1:1
1
based on the H NMR spectrum in entry 3.
N6-benzoyladenine and TMSOTf/Et3N in MeCN or dichloro-
ethane (entries 1 and 2), where the silylated N6-benzoyl-
adenine was formed under the reaction conditions. Although
these reactions selectively produced the expected â-nucleo-
sidic product, the yield was low. The reaction using silylated
N6-benzoyladenine, prepared from N6-benzoyladenine and
hexamethyldisilazane/pyridine, as the acceptor and SnCl4 as
the promoter in MeCN improved the yield; however, the R/â-
mixture was produced non-stereoselectively (entry 3).14
We recently reported that, in the Vorbru¨ggen glycosylation
reaction with a sterically hindered ribosyl donor, high
â-selectivity was realized when the hydroxyl groups of the
donor were protected by i-butyryl groups.15 Since glycosy-
lation with the donor 15a might not work well because of
steric hindrance due to the 5-phenyl group, we therefore
investigated reactions using the tetra-O-i-butyryl donor 15b.
Although the reaction using the donor 15b under TMSOTf
conditions was unsuccessful (Table 1, entry 4), the desired
â-nucleoside 16b was selectively obtained in 60% yield,
when 15b and silylated N6-benzoyladenine were treated with
SnCl4 in MeCN at room temperature (entry 5).16 Thus, like
the previous case,15 the i-butyryl protection of the sterically
hindered ribosyl donor proved effective in this Vorbru¨ggen
glycosylation.
dation products, we found that the stereoselectivity improved
by using Et2O as the solvent. Thus, the desired R-glucoside
11 was obtained as the sole glycosidation product in 78%
yield, when the reaction was performed in Et2O at -78 °C
(Scheme 1).
The three O-i-butyryl and the N-benzoyl groups of 16b
were removed simultaneously with NaOMe/MeOH to give
17. The phosphate units were selectively introduced into the
three hydroxyls, using the phosphoramidite method with
o-xylene N,N-diethylphosphoramidite (XEPA).17 Thus, 17
was treated with XEPA in the presence of imidazolium
triflate as a promoter18 in CH2Cl2, followed by oxidation with
Synthesis of the target compound 5 from the R-glucoside
11 was accomplished as summarized in Scheme 2. After
removal of the 5-O-TBS group of 11, the 5-hydroxymethyl
moiety of the resulting 12 was oxidized by Moffatt oxidation
conditions. The aldehyde obtained was immediately treated
with PhMgBr in THF to give the 5-phenyl product 13.
Radical deoxygenation at the 5-position was performed by
the treatment of 13 with PhOCSCl/4-(dimethyamino)pyridine
(DMAP) in MeCN and then with Bu3SnH/AIBN in hot
benzene to give 14. Acidic removal of the ketal protecting
(14) For non-stereoselective examples of Vorbru¨ggen glycosylation,
see: Azuma, T.; Isono, K. Chem. Pharm. Bull. 1977, 25, 3347-3353.
(15) Nomura, M.; Sato, T.; Washinosu, M.; Tanaka, M.; Asao, T.; Shuto,
S.; Matsuda, A. Tetrahedron 2002, 58, 1279-1288.
(16) The regio- and stereochemistry of 16b was confirmed by its NOE
and HMBC spectra.
(17) Watanabe, Y.; Komoda, Y.; Ebisuya, K.; Ozaki, S. Tetrahedron
Lett. 1990, 31, 255-256.
Org. Lett., Vol. 8, No. 7, 2006
1457

m-CPBA to give the desired 2′,3′′,4′′-trisphosphate derivative
18 in 90% yield. Finally, the benzyl protecting groups were
all removed in one step by catalytic hydrogenation with Pd
black in aqueous MeOH/CHCl3 to furnish the target tris-
phosphate 5 as a sodium salt, after treatment with ion-
exchange resin.
The Ca2+-mobilizing activity of 5 was evaluated using
recombinant rat type 1 IP3 receptors expressed in DT40 cells
lacking endogenous IP3 receptors.19 The results show that
5′-deoxy-5′-phenyladenophostin A (5) is a potent full agonist,
mobilizing all of the IP3-sensitive Ca2+ pool in a concentra-
tion-dependent manner. The half-maximally effective con-
centration (EC50) for 5 was 2.1 ( 0.4 nM (n ) 5; Hill slope
) 1.62 ( 0.24), which is comparable to that for adenophostin
A (2.1 ( 0.2 nM; n ) 12; Hill slope ) 1.54 ( 0.13), and is
about 13-fold lower than the EC50 for the natural ligand IP3
(24.8 ( 2.1 nM; n ) 11; Hill slope ) 1.21 ( 0.06) in parallel
experiments.
conjugated with a phenyl group at the 5′-position designed
as a useful IP3 receptor ligand was effectively synthesized
via the two key stereoselective glycosidation steps. The
analogue 5 proved to have significant Ca2+-mobilizing
potency. Thus, the 5′-position of adenophostin A is identified
as a site suitable for the further modification to develop
biological tools, which are useful for investigating biological
mechanisms of action of Ca2+ mobilization.
Acknowledgment. We wish to acknowledge financial
support from Ministry of Education, Culture, Sports, Science
and Technology, Japan for Scientific Research 17659027 and
17390027 (to S.S.), the Japan Society for Promotion of
Science for Creative Scientific Research 13NP0401 (to
A.M.), and the Wellcome Trust for Program Grants 039662
(to C.W.T.) and 060554 (to B.V.L.P.).
Supporting Information Available: Synthetic procedures
and spectroscopic data of compounds, and NMR spectra (1H,
2D and/or 13C NMR) of the final compound 5 and the key
intermediates 12 and 16b. This material is available free of
charge via the Internet at http://pubs.acs.org.
In conclusion, the novel adenophostin A analogue 5
(18) Hayakawa, Y.; Kataoka, M. J. Am. Chem. Soc. 1998, 120, 12395-
12401.
(19) Laude, A. J.; Tovey, S. C.; Dedos, S. G.; Potter, B. V. L.; Lummis,
S. C. R.; Taylor, C. W. Cell Calcium 2005, 38, 45-51.
OL0602710
1458
Org. Lett., Vol. 8, No. 7, 2006