Asymmetric syntheses of phosphatidylinositol-3-phosphates with saturated and unsaturated side chains through catalytic asymmetric phosphorylation

Article abstract of DOI:10.1021/ja0466098

Highly direct asymmetric syntheses of phosphatidylinositol-3-phosphate (PI3P) in each enantiomerically pure form have been achieved. The key step involves catalytic asymmetric phosphorylation of meso-myo-inositol derivatives through desymmetrization. Prot

Full text of DOI:10.1021/ja0466098

Published on Web 09/23/2004
Asymmetric Syntheses of Phosphatidylinositol-3-Phosphates with Saturated
and Unsaturated Side Chains through Catalytic Asymmetric Phosphorylation
Bianca R. Sculimbrene, Yingju Xu, and Scott J. Miller*
Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467-3860
Received June 9, 2004; E-mail: scott.miller.1@bc.edu
Scheme 1
The chemistry and biology of the phosphatidylinositol phosphates
(PIPs) have emerged as a complex field due in part to the ubiquity
of PIP-dependent cellular signaling.1 In addition, the field has
benefited from synthetic studies of these molecules, with natural
products, synthetic probes, and analogues fueling chemical biologi-
cal investigations.2 Themes of the syntheses reported to date include
complex, multistep schemes resulting from manipulations of chiral
pool precursors such as D-glucose, the inositol ring system, which
contains six stereochemically unique sites, and/or classical resolu-
tions.3,4 A significant opportunity for study of atomic level, high-
resolution ligand-receptor interactions involving the PIPs and their
targets would be enhanced if highly efficient syntheses of PIPs and
their analogues, in each enantiomeric series, could be developed.
We report herein initial steps along these lines, culminating in rapid
total syntheses of optically pure PI3P and ent-PI3P with both
saturated and unsaturated side chains. PI3P has been implicated
as a product of phosphoinositide-3-kinase (PI3K), an important
player in the biochemistry of cell cycle progression.5 On the basis
of catalytic asymmetric phosphorylation, the schemes reported
herein provide access to either enantiomer of PI3P with equal
efficiency, on the basis of the choice of synthetic catalyst.
Scheme 2 a
As a first step toward improved access, we recently reported an
approach to the syntheses of D-myo-inositol-1-phosphate (D-I-1P,
1), and its enantiomer D-myo-inositol-3-phosphate (D-I-3P ) L-I-
1P, 2), employing peptide-catalyzed asymmetric phosphorylations
as the key step.6 For this purpose, we discovered peptides 3 and 4,
a Conditions: (a) 6a, Hunig’s Base, THF, -78 °C; then 30% H2O2/
H2O, 31%; (b) TBSCl, imidazole, DMF, 89%; (c) NaH, BnOH, THF, 84%;
which exhibited enantiodivergent catalysis as exhibited in Scheme
1, affording desymmetrized phosphates 5 and ent-5 with high optical
purity. A critical component of our strategy was the decision that
the synthetic schemes should originate with inositol, an achiral,
meso precursor that is readily available.
Our initial target for synthesis was ent-PI3P-(C8) with saturated
C8-side chains on the glycerol unit. PI3P-(C8) has been a staple
of chemical biological study. This compound also constitutes a more
straightforward target strategically since the saturated side chains
are compatible with global deprotection by hydrogenolysis.
Direct synthesis of the ent-PI3P-(C8) analogues from intermedi-
ate 5 required a swap of the phosphate ester protecting groups
(Scheme 2). Initially, desymmetrized phosphate 5 was subjected
to standard chlorophosphite coupling with 6a to deliver fully
(d) HF pyridine, THF, 86%; (e) dicyanoimidazole, toluene/CH2Cl2, (1:1),
6b; then 30% H2O2/H2O; (f) H2, Pd(OH)2/C, t-BuOH/H2O, NaHCO3, 85%.
protected ent-PI3P-(C8) analogue 7 (31% isolated yield).7,8 Com-
pound 7 is, in principle, one step from a fully deprotected ent-
PI3P-(C8), provided that catalytic cleavage of both the benzyl ethers
and phenyl phosphate esters could be achieved in one step.
However, under the conditions we explored (e.g., H2, PtO2), benzyl
ring hydrogenation intervened. As a result, a high-yielding three-
step sequence was developed to convert phenyl phosphate 5 to
benzyl phosphate 8. Coupling to phosphoramidite 6b then delivered
9,7,9 which was readily converted to ent-PI3P-(C8) in 85% yield.
Of note, the identical sequence initiated with the desymmetrization
of the meso-2,4,6-tris(O-benzyl)-myo-inositol substrate with peptide
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10.1021/ja0466098 CCC: $27.50 © 2004 American Chemical Society

C O M M U N I C A T I O N S
Scheme 3 a
4 was carried out to provide the naturally occurring enantiomer of
PI3P-(C8). (See Supporting Information for details.) These schemes,
despite the phosphate ester swap, may represent the most direct
access to PI3P-(C8) targets reported to date.
We then turned our attention to the more ambitious objective of
preparing PI3P compounds with the naturally implicated arachi-
donate ester side chains. For this objective, clearly the overall
protecting group scheme would require alteration, as catalytic
hydrogenation would surely reduce the alkenes resident in the side
chains. After considerable experimentation, we found that para-
methoxybenzyl (PMB) ethers were compatible with a similarly
direct scheme.
The first question to answer was the viability of catalytic
asymmetric phosphorylation of substrate 10, with the tris(PMB)-
array on the inositol ring. As before, peptide 3 proved to be highly
effective in the desymmetrization reaction, producing phosphate
11 in 65% isolated yield, with >98% ee (eq 1). Of note, the catalytic
phosphorylation proceeded at ambient temperature without a
decrease in selectivity. We also found that the desymmetrization
may be conducted with 1 mol % catalyst without loss of efficiency.
a Conditions: (a) TBSCl, imidazole, DMF, 89%; (b) NaH, BnOH, THF
99%; (c) HF pyridine, THF, 77%; (d) dicyanoimidazole, toluene/CH2Cl2
(1:1), 13; then 30% H2O2/H2O, 39%; (e) TMSBr (20 equiv)/PhCH3, 70
°C; then NH4OH, 61%.
pure targets and analogues in this family of natural products. In
addition, they serve as a starting place for the development of other
asymmetric phosphorylation catalysts that may provide direct access
to alternative isomers and more highly phosphorylated targets in
this series. Finally, these routes may prove to be useful in the
preparation of PI3P analogues of interest for chemical biological
study.
Phosphate 11 turned out to move through the phosphate ester
swap with equal facility in comparison to phosphate 5. Thus, bis-
silylation followed by transesterifcation and desilylation afforded
phosphate 12 (Scheme 3). Coupling of 12 to the arachidonic acid-
derived phosphoramidite 1310 afforded protected ent-PI3P with the
unsaturated side chains installed (14). As before, the yield of
coupled product 14 is somewhat compromised by competitive
phosphitylation at the 5-position of the inositol ring. Nevertheless,
chromatographic purification delivers pure 14 as a mixture of
phosphotriester diastereomers.
Acknowledgment. This work is supported by the NIH NIGMS-
68649 to S.J.M. We are also grateful to Pfizer Global Research for
research support.
Supporting Information Available: Experimental procedures and
product characterization for all new compounds synthesized (PDF). This
material is available free of charge via the Internet at http://pubs.acs.org.
References
(1) Irvine, R. F.; Schell, M. J. Nat. ReV. Mol. Cell. Biol. 2001, 2, 327-338.
(2) Prestwich, G. D. Chem. Biol. 2004, 11, 619-637.
The deprotection of 14 to deliver ent-PI3P with the unsaturated
side chains intact was achieved through careful optimization of
reaction conditions. Ultimately, one-step treatment of 14 with 20
equiv of TMSBr in toluene at 70 °C for 12 h delivered ent-PI3P.11
Initial attempts to achieve the deprotection in two steps (e.g., DDQ
oxidation of the PMB groups followed by TMSBr-mediated
cleavage of the benzyl phosphate esters) resulted in complicated
reaction mixtures, perhaps related to phosphate migration. In
addition, isolation of the final product proved to be difficult coming
out of the DDQ-promoted oxidation. Instead, the one-step protocol
enabled efficient removal of both the PMB and benzyl groups,
delivering a product that was amenable to direct analysis by mass
spectrometry and 1H and 31P NMR (solvent: CD3OD/CDCl3/D2O,
4:3:1). In addition, in accord with the original characterization of
these molecules, we found that we were able to purify these
amphiphilic compounds by conventional chromatography.12
In summary, we report enantioselective total syntheses of PI3P-
(C8) in each enantiomeric series, in addition to a synthesis of ent-
PI3P with the arachidonate side chain in place. The sequences are
rapid in terms of their overall step count and ease of operation.
Furthermore, because the syntheses depend on asymmetric catalysis,
the routes may be conducted in either enantiomeric series with
comparable facility and economic considerations. These syntheses
may provide an opportunity to deliver improved access to optically
(3) For representative syntheses of PI3P-compounds with saturated side
chains, see: (a) Morisaki, N.; Morita, K.; Nishikawa, A.; Nakatsu, N.;
Fukui, Y.; Hashimoto, Y.; Shirai, R. Tetrahedron 2000, 56, 2603-2614.
(b) Falck, J. R.; Krishna, U. M.; Capdevila, J. H. Bioorg. Med. Chem.
Lett. 2000, 10, 1711-1713. (c) Painter, G. F.; Grove, S. J. A.; Gilbert, I.
H.; Holmes, A. B.; Raithby, P. R.; Hill, M. L.; Hawkins, P. T.; Stephens,
L. R. J. Chem. Soc., Perkin Trans. 1 1999, 923-935. (d) Chen, J.; Feng,
L.; Prestwich, G. D. J. Org. Chem. 1998, 63, 6511-6522. (e) Wang, D.
S.; Chen, C. S. J. Org. Chem. 1996, 61, 5905-5910. (f) Bruzik, K. S.;
Kubiak, R. J. Tetrahedron Lett. 1995, 36, 2415-2418.
(4) For syntheses of PIP-compounds with unsaturated side chains, see: (a)
Kubiak, R. J.; Bruzik, K. S. J. Org. Chem. 2003, 68, 960-968. (b)
Gaffney, P. R. J.; Reese, C. B. J. Chem. Soc., Perkin Trans. 1 2001, 192-
205. (c) Watanabe, Y.; Nakatomi, M. Tetrahedron 1999, 55, 9743-9754.
(5) Vazquez, F.; Sellers, W. R. Biochim. Biophys. Acta 2000, 1470, M21-
M35.
(6) (a) Sculimbrene, B. R.; Miller, S. J. J. Am. Chem. Soc. 2001, 123, 10125-
10126. (b) Sculimbrene, B. R.; Morgan, A. J.; Miller, S. J. J. Am. Chem.
Soc. 2002, 124, 11653-11656. (c) Sculimbrene, B. R.; Morgan, A. J.;
Miller, S. J. Chem. Commun. 2003, 1781-1786.
(7) Martin, S. F.; Josey, J. A.; Wong, Y. L.; Dean, D. W. J. Org. Chem.
1994, 59, 4805-4820.
(8) Overall yield of the coupling is reduced due to competitive phosphitylation
at the C5-position. The minor products are removed by preparative
chromatography, and the reported yield refers to analytically pure 7 (or
9) as a mixture of phosphotriester diastereomers.
(9) Reddy, K. K.; Saady, M.; Falck, J. R.; Whited, G. J. Org. Chem. 1995,
60, 3385-3390.
(10) For a synthesis of phosphoramidites related to 13, see ref 4.
(11) For a related deprotection, see ref 4a.
(12) Auger, K. R.; Carpenter, C. L.; Cantley, L. C.; Varticovski, L. J. Biol.
Chem. 1989, 264, 20181-20184.
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