Synthesis and evaluation of 1-deoxy-D-xylulose 5-phosphoric acid analogues as alternate substrates for methylerythritol phosphate synthase

Article abstract of DOI:10.1021/jo048022h

(Chemical Equation Presented) Four deoxyxylulose phosphate (DXP) analogues were synthesized and evaluated as substrates/ inhibitors for methylerythritol phosphate (MEP) synthase. In analogues CF₃-DXP (1), CF ₂-DXP (2), and CF-DXP (3)

Full text of DOI:10.1021/jo048022h

Synthesis and Evaluation of 1-Deoxy-D-xylulose 5-Phosphoric Acid
Analogues as Alternate Substrates for Methylerythritol Phosphate
Synthase
David T. Fox and C. Dale Poulter*
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112
poulter@chem.utah.edu
Received November 5, 2004
Four deoxyxylulose phosphate (DXP) analogues were synthesized and evaluated as substrates/
inhibitors for methylerythritol phosphate (MEP) synthase. In analogues CF3-DXP (1), CF2-DXP
(2), and CF-DXP (3), the three methyl hydrogens at C1 of DXP were sequentially replaced by
fluorine. In the fourth analogue, Et-DXP (4), the methyl group in DXP was replaced by an ethyl
moiety. Analogues 1, 2, and 4 were not substrates for MEP synthase under normal catalytic
conditions and were instead modest inhibitors with IC50 values of 2.0, 3.4, and 6.2 mM, respectively.
In contrast, 3 was a good substrate (kcat ) 38 s-1, Km ) 227 µM) with a turnover rate similar to
that of the natural substrate. These results are consistent with a retro-aldol/aldol mechanism rather
than an R-ketol rearrangement for the enzyme-catalyzed conversion of DXP to MEP.
Introduction
glyceraldehyde 3-phosphate (GAP) and pyruvate in a
thiamine diphosphate-dependent reaction catalyzed by
DXP synthase (DXS).10,11 The branched carbon skeleton
typical of isoprenoid compounds is then constructed from
the linear deoxysugar by a reversible rearrangement-
NADPH-dependent reduction catalyzed by 2-C-methyl-
D-erythritol 4-phosphate (MEP) synthase.12,13 Since DXP
is also required for synthesis of vitamins B1 and B6,14,15
the rearrangement of DXP to MEP represents the first
committed step in the pathway for the biosynthesis of
isoprenoids. MEP is ultimately converted to both IPP and
DMAPP by the action of five enzymes (see Scheme 1).16
MEP synthase catalyzes both the rearrangement and
reduction of DXP. In the first step, the C3-C4 bond in
DXP is broken with concomitant formation of a new bond
between C2 and C4 of the substrate to produce a putative
aldehyde intermediate, 2-C-methyl-D-erythrose 4-phos-
phate, which is then reduced by NADPH. The stereo-
With greater than 30000 representative compounds,
the isoprenoid family is the largest and most chemically
diverse group of natural products.1 These molecules are
assembled from the simple five-carbon precursors iso-
pentenyl diphosphate (IPP) and dimethylallyl diphos-
phate (DMAPP). For several decades it was thought that
isoprenoid compounds were derived from acetyl-CoA by
the mevalonate biosynthetic pathway.2 Recently, an
alternative pathway based on pyruvate and D-glyceral-
dehyde 3-phosphate (GAP) was discovered in eubacteria,
algae, and plant chloroplasts.3-9 In this pathway, 1-deoxy-
D-xylulose 5-phosphate (DXP) is synthesized from D-
* To whom correspondence should be addressed. Phone: (801) 581-
6685. Fax: (801) 581-4391.
(1) Sacchettini, J. C.; Poulter, C. D. Science 1997, 277, 1788-1789.
(2) Bochar, D. A.; Freisen, J. A.; Stauffacher, C. V.; Rodwell, V. W.
Comprehensive Natural Products Chemistry; Elsevier: Oxford, 1999;
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10.1021/jo048022h CCC: $30.25 © 2005 American Chemical Society
Published on Web 02/19/2005
1978
J. Org. Chem. 2005, 70, 1978-1985

DXP Analogues as Substrates for MEP Synthase
SCHEME 1. Methylerythritol Phosphate Pathway
for Isoprenoid Biosynthesis
FIGURE 1. Structures of DXP analogues 1-4.
amino acid sequences. In addition, the X-ray crystal
structures of both MEP synthase and ketol-acid reduc-
toisomerase are quite dissimilar, although both enzymes
appear to follow an induced fit model.25 Ketol-acid re-
ductoisomerase and MEP synthase bind NADPH and
divalent cation, which causes a slight conformational
change, followed by binding of the substrate to cause a
more drastic conformational change prior to the enzy-
matic reaction. Due to similarities in the overall reactions
catalyzed by MEP synthase and the ketol-acid reductoi-
somerase, it was generally accepted that the mechanism
was also similar. However, Rohmer et al.26 recently
suggested that the aldehyde intermediate could be formed
by a retro-aldol/aldol mechanism. As part of an effort to
distinguish between the ketol-acid and retro-aldol/aldol
mechanisms, we synthesized four DXP analogues, CF3-
DXP (1), CF2-DXP (2), and CF-DXP (3), where hydrogen
atoms at C1 were replaced with fluorine, and Et-DXP
(4), where the methyl group was replaced by an ethyl
moiety (Figure 1). While this paper was being prepared,
related studies were reported by Liu et al.27 and Proteau
et al.28
Results and Discussion
chemistry for the reduction was studied by Proteau et
al.17 and Arigoni et al.,18 who found that the pro-S-
hydride from NADPH was delivered to the re face of the
aldehyde. Thus, MEP synthase can be classified as a class
B dehydrogenase.17,19 The coupled reactions catalyzed by
MEP synthase, while uncommon, are not unprecedented.
Ketol-acid reductoisomerase catalyzes a similar carbon
skeletal rearrangement and NADPH-dependent reduc-
tion of either 2-acetolactate or 2-acetohydroxybutyrate
to yield 2,3-dihydroxy-3-isovalerate or 2,3-dihydroxy-3-
methylvalerate, respectively, during biosynthesis of va-
line, isoleucine, and leucine.20-24 Although the two reac-
tions mediated by MEP synthase and ketol-acid reducto-
isomerase are similar, the enzymes do not share similar
Synthesis of CF3-DXP (1). The route used to syn-
thesize 1,1,1-trifluoro-1-deoxy-D-xylulose 5-phosphoric
acid (CF3-DXP, 1) is outlined in Scheme 2. Aldehyde 7
was obtained from (-)-2,3-O-isopropylidene-D-threitol (5)
according to the sequence reported by Blagg et al.29 The
trifluoromethyl moiety was introduced using (trifluoro-
methyl)trimethylsilane (TMS-CF3) and a catalytic amount
of potassium tert-butoxide, following the procedure of
Olah et al.,30 to give 8 as a 3:1 mixture of diastereomers.
The trifluoromethylated bissilyl ether 8 was unstable to
silica gel chromatography and therefore was treated
directly with 2 equiv of tetra(n-butyl)ammonium fluoride
(TBAF) to afford diol 9 as a mixture of diastereomers.
Regioselective phosphorylation of the primary alcohol
was accomplished using dibenzyl phosphoroiodidate
(DBPI), prepared in situ from tribenzyl phosphite and
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1999, 1, 921-923.
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M. H.; Kis, K.; Bacher, A.; Eisenreich, W. Chem. Commun. 1999, 1127-
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K.; Eisenreich, W.; Bacher, A.; Zenk, M. H.; Arigoni, D. FEBS Lett.
2000, 465, 157-160.
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359-410.
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M. Eur. J. Biochem. 2002, 269, 4446-4457.
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H.-w. Org. Lett. 2004, 6, 3625-3628.
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Biophys. 1973, 158, 132-138.
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5309-5312.
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Burns, R. O. J. Biol. Chem. 1975, 250, 877-882.
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J. Org. Chem, Vol. 70, No. 6, 2005 1979

Fox and Poulter
SCHEME 2. Synthesis of CF3-DXPa
SCHEME 3. Synthesis of CF2-DXPa
a Reagents and conditions: (a) NaBH4, MeOH, 0 °C, 35%; (b)
P(OBn)3, I2, pyridine, CH2Cl2, -40 °C to rt, 86%; (c) LDA, diethyl
(1,1-difluoromethyl)phosphonate, THF, -78 °C, 83%; (d) NaOMe,
MeOH, 0 °C, 83%; (e) (i) H2/10 wt % Pd/C, t-BuOH, (ii) H2O, 3 d,
86%.
et al. in their synthesis of 2-C-methyl-D-erythritol 4-phos-
phoric acid (MEP),36 resulted in the formation of a stable
methoxy hemiketal. However, a hemiketal did not form
when methanol was replaced by tert-butyl alcohol in the
hydrogenation step, presumably because of the bulky tert-
butyl group. After removal of palladium, the solution was
carefully concentrated with a stream of nitrogen. The
fluorinated analogues partially degraded if concentrated
by either rotory evaporation or lyophilization, giving a
complex mixture of products as judged by 19F NMR
spectroscopy. The isopropylidene group was then re-
moved by stirring in the water/tert-butyl alcohol system
for several days. The solution was then again carefully
concentrated with a stream of nitrogen to a final con-
centration of ∼25-75 mM to give 1 as the free acid.
a Reagents and conditions: (a) (TIPS)Cl, NaH, THF, 0 °C to rt,
90%; (b) oxalyl chloride, DMSO, NEt3, CH2Cl2, -78 °C, 95%; (c)
0.5 M CF3-TMS in THF, cat. t-BuOK, THF, 0 °C; (d) 1.0 M TBAF
in THF, THF, 0 °C, 80% (two steps); (e) P(OBn)3, I2, pyridine,
CH2Cl2, -40 °C to rt, 77%; (f) Dess-Martin reagent, CH2Cl2,
nonbasic workup, 90%; (g) (i) H2/10 wt % Pd/C, t-BuOH, (ii) H2O,
5 d, 96%.
iodine,31,32 to give phosphorus triester 10. Both Swern33
conditions and TPAP/NMO34 were not suitable for the
oxidation of alcohol 10; however, Dess-Martin35 oxida-
tion followed by a nonbasic workup afforded protected
CF3-DXP 11. The oxidation was monitored by 19F NMR
spectroscopy, and only one product, corresponding to the
protected trifluoromethyl ketone, was seen. Following
workup and silica gel flash chromatography, 11 existed
almost exclusively in the hydrate form (90:10) as judged
by both 19F and 13C NMR spectroscopy. Removal of the
protecting groups from 11 proved to be difficult. We found
that the isopropylidene moiety was unexpectedly stable
to acid (TFA/THF/H2O and AcOH/THF/H2O) even under
refluxing conditions. This problem was circumvented by
catalytic hydrogenation to deprotect the phosphate ester,
followed by hydrolysis of the isopropylidene group by the
resulting phosphoric acid moiety. Use of methanol/water
as the solvent for hydrogenation, as described by Bacher
Trifluoromethyl analogue 1, >95% pure as judged by 19
F
NMR spectroscopy, was obtained in five steps with a 53%
overall yield from known aldehdye 7. The concentration
of a solution of 1 was determined by comparison of the
intensity of the 19F resonance of the trifluoromethyl group
with that of an internal standard of trifluoroacetic acid
(TFA). The fluorinated analogues were found to be stable
for approximately six months when stored as an aqueous
solution (pH ≈ 1) at -20 °C.
Synthesis of CF2-DXP (2). 2 was prepared as il-
lustrated in Scheme 3. Synthesis of 2 was based on a
modification of the procedure reported by Bouvet and
O’Hagan37 in their synthesis of 1,1-difluoro-1-deoxy-D-
xylulose (CF2-DX). Following desymmetrization of (-)-
2,3-O-isopropylidene-D-tartrate (12) with NaBH4, monoal-
cohol 1338 was treated with DBPI to give phosphorus
triester 14. Monoester 14 was treated with lithiated
(31) Stowell, J. K.; Widlanski, T. S. Tetrahedron Lett. 1995, 36,
1825-1830.
(32) Gefflaut, T.; Lemaire, M.; Valetin, M.-L.; Bolte, J. J. Org. Chem.
1997, 62, 5920-5922.
(33) Omura, K.; Swern, D. Tetrahedron 1978, 1651-1660.
(34) Ley, S. V.; Norman, J.; Griffith, W. P.; Mardsen, S. P. Synthesis
1994, 639-666.
(36) Kis, K.; Wungsintaweekul, J.; Eisenreich, W.; Zenk, M. H.;
Bacher, A. J. Org. Chem. 2000, 65, 587-592.
(37) Bouvet, D.; O’Hagan, D. Tetrahedron 1999, 55, 10481-10486.
(38) Batsanov, A. S.; Begley, M. J.; Fletcher, R. J.; Murphy, J. A.;
Sherburn, M. S. J. Chem. Soc., Perkin Trans. 1 1995, 1281-1294.
(35) Martin, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155-
4156.
1980 J. Org. Chem., Vol. 70, No. 6, 2005

DXP Analogues as Substrates for MEP Synthase
SCHEME 4. Synthesis of CF-DXPa
SCHEME 5. Synthesis of Et-DXPa
a Reagents and conditions: (a) 3.0 M CH3MgBr, N,O-dimeth-
ylhydroxylamine hydrogen chloride, THF, -20 °C, 60%; (b)
P(OBn)3, I2, pyridine, CH2Cl2, -40 °C to rt, 87%; (c) 3.0 M EtMgBr,
Et2O, -40 °C, 85%; (d) (i) H2/10 wt % Pd/C, MeOH, (ii) H2O, 2 d,
NaHCO3 to pH 7.0, 99%.
to the corresponding aldehyde followed by treatment with
dimethyloxosulfonium methylide.41 Preparations of 18
routinely gave a 4:1 mixture of diastereomers in yields
of 45-55% over the two steps. Regioselective ring opening
of oxirane 18 with diisopropylamine trihydrogen fluo-
ride42 gave 47% of the C-1-monofluorinated alcohol 19.
The benzyl group was removed by hydrogenolysis (Pd/C,
H2), and the resulting diol 20 was regioselectively phos-
phorylated (21), followed by Dess-Martin oxidation, to
give fully protected CF-DXP 22. The ketone was depro-
tected as described for 1 and 2 to give a 77:23 mixture of
ketone/hydrate.
a Reagents and conditions: (a) BnBr, NaH, THF, 0 °C, 81%; (b)
Dess-Martin reagent, CH2Cl2, rt; (c) NaH, trimethyloxosulfonium
iodide, DMSO, rt, 50% (two steps); (d) (i-Pr)2NH‚3HF, neat, 100
°C, 47%; (e) H2/Pd/C, EtOH, rt, 95%; (f) P(OBn)3, I2, pyridine,
CH2Cl2, -40 °C to rt, 69%; (g) Dess-Martin reagent, CH2Cl2, rt,
89%; (h) (i) H2/10 wt % Pd/C, t-BuOH, (ii) H2O, 3 d, 90%.
Synthesis of Et-DXP (4). 4 was prepared as shown
in Scheme 5. Monoester 13 was converted to amide 23
in 60% yield, along with ∼10-15% of the corresponding
methyl ketone and ∼5% tertiary alcohol, by a modifica-
tion of the Weinreb43 protocol using methylmagnesium
bromide to prepare the N-methoxy-N-methylamide.44 The
methyl ketone, O-isopropylidene-protected deoxyxylulose
(DX), was isolated, phosphorylated, and deprotected to
give DXP. Phosphorylation of 23 followed by addition of
ethylmagnesium bromide to 24 gave protected Et-DXP
25. Deprotection of 25 and purification over cellulose gave
the disodium salt of 4.
Enzymatic Activity of DXP Analogues 1-4. Re-
combinant MEP synthase was obtained from an Escheri-
chia coli clone as previously reported.13 Details of the
enzyme assays are outlined in the Supporting Informa-
tion. 1 and 2 were not alternate substrates for DXP under
catalytic conditions. Since both analogues exist predomi-
nantly in the hydrate form (>99.9% for 1 and ∼98% for
2), we expected they might bind to the enzyme but
perhaps not serve as substrates. However, 1 and 2 were
relatively poor inhibitors, with IC50 values of 2.0 and 3.4
mM, respectively. 4 was also studied in an effort to sort
diethyl (difluoromethyl)phosphonate39 to give (difluoro-
methyl)phosphonate 15, and the phosphonate was cleaved
in the presence of the dibenzyl phosphate triester using
NaOMe. O’Hagan et al. reported a 49% yield for this step
with the base-stable tert-butyldimethylsiloxy (TBDMS)-
protected alcohol using 0.5 equiv of sodium methoxide
in dry methanol. We obtained a similar yield when 15
was used directly after silica gel chromatography. Ex-
amination of 15 by 19F NMR spectroscopy revealed an
80:20 mixture of hydrate/ketone forms. Since the ketone
is required for cleavage, the low yield observed by
O’Hagan may be due to a slow hydrate-ketone equilibra-
tion under the conditions for cleavage. We converted the
hydrate to the ketone by azeotropic removal of water from
15 with benzene and replaced benzene with dry methanol
and sodium methoxide. This method routinely gave the
fully protected CF2-DXP 16 in greater than 80% yield
with no detectable cleavage of the phosphate triester
moiety. The free acid 2 was obtained from 16 by the
procedure described for deprotection of 11. The ratio of
ketone to hydrate for 2 was ∼2:98, as judged by 19F NMR
spectroscopy.
Synthesis of CF-DXP (3). The synthesis of 1-fluoro-
DXP (CF-DXP, 3) from alcohol 17 is outlined in Scheme
4. After the monoprotection of 5 as the benzyl ether,40
17 was converted to oxirane 18 by oxidation of the alcohol
(41) Corey, E. J.; Chaykovsky, M. J. Am. Chem. Soc. 1965, 87, 1353-
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J. Org. Chem, Vol. 70, No. 6, 2005 1981

Fox and Poulter
whether the lack of turnover and poor inhibition were
due to the presence of the hydrate or an increase in steric
bulk at the methyl position upon substitution of hydrogen
with fluorine. The ethyl analogue was not turned over
under catalytic conditions and was a worse inhibitor, IC50
) 6.2 mM, than either 1 or 2. Proteau et al.28 reported
Ki ) 630 µM for Et-DXP for MEP synthase from Syn-
echocystis PCC6803, which is also considerably higher
than Km for DXP. We conclude that steric interactions
in the active site are primarily responsible for the lack
of turnover and poor inhibition observed for Et-DXP and
are probably responsible for similar behavior by the CF3
and CF2 analogues. Thus, it appears that the active site
pocket in MEP synthase has strict size requirements with
respect to the C-1 position of DXP and related ana-
logues.45
In contrast, 3 was an excellent substrate for the
enzyme, with kcat ) 38 s-1, Km ) 227 µM, and kcat/Km
)
0.17 s-1 µM-1. These values are similar to those for DXP,
with kcat ) 29 s-1, Km ) 50 µM, and kcat/Km ) 0.58 s-1
µM-1. Some of the increase in Km
might be due to
CF-DXP
the presence of the hydrated form (∼25%), which may
not bind as tightly as the ketone, and the increase in the
steric bulk at C-1. Liu et al.27 reported similar results
for CF-DXP and the E. coli enzyme, with kcat ) 4.5 s-1
and Km ) 100 µM.
Mechanistic Considerations. Only a few inhibitors
have been reported for enzymes in the MEP pathway.
Fosmidomycin and the related analogue FR-900098
specifically inhibit MEP synthase in E. coli46 and Zy-
momonas mobilis,47 and fosmidomycin has been used to
treat parasitic infections by Plasmodium falciparum and
Plasmodium vinckei in mice.48 A recent crystal structure
of E. coli MEP synthase complexed with manganese and
fosmidomycin has provided some insight about the
architecture of the active site of the enzyme.49 However,
an understanding of the detailed reaction mechanism can
also be important for the rational design of novel inhibi-
tors. An R-ketol rearrangement (mechanistically related
to acetoin and pinacol rearrangements) has been com-
monly favored for the rearrangement of DXP to MEP (see
Figure 2) and is similar to the mechanism proposed for
ketol-acid reductoisomerase.
FIGURE 2. Conversion of DXP to MEP catalyzed by MEP
synthase, R-ketol rearrangement vs retro-aldolization/aldoliza-
tion (X ) H+ or divalent metal).
deprotonation occurs at the C-4-hydroxyl group, followed
by cleavage of the C-3-C-4 bond to give glycoaldehyde
phosphate and the enol(ate) of hydroxyacetone (Figure
2). Subsequent aldolization then gives 2-C-methyl-D-
erythrose 4-phosphate, identical to the aldehyde inter-
mediate generated by an R-ketol rearrangement. Both
mechanisms utilize NADPH to reduce the aldehdye to
the primary alcohol to generate MEP.
Fluorine has been used to great advantage for mecha-
nistic studies and development of inhibitors in biological
and medicinal chemistry.54 In general, the development
of positive charge at a â-position is destabilized by the
powerful electron-withdrawing effect of a fluorine atom.
Conversely, a carbanionic center â to a fluorine atom is
stabilized.55 The similar values for kcat for DXP and CF-
DXP found by us and Liu et al.27 are more consistent with
the retro-aldol/aldol mechanism for the rearrangement
step catalyzed by MEP synthase. One would anticipate
that the rearrangement would be slower for the CF
analogue for an R-ketol mechanism because of the
development of positive charge at C-2 upon activation of
A retro-aldolization/aldolization mechanism also gives
the same aldehyde intermediate. This mechanism is also
well-documented by the reactions catalyzed by ribulose-
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lases.52,53 In the retro-aldolization mechanism, initial
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(54) Hiyama, T. In Organofluorine Compounds, Chemistry and
Applications; Yamamoto, H., Ed.; Springer-Verlag: New York, 2000;
pp 137-182.
(55) Allen, A. D.; Tidwell, T. T. In Advances in Carbocation
Chemistry; Creary, X., Ed.; JAI Press: Greenwich, CT, 1989; Vol. 1, p
1.
1982 J. Org. Chem., Vol. 70, No. 6, 2005

DXP Analogues as Substrates for MEP Synthase
form) 1.41 (s, 3H), 1.46 (s, 3H), 4.08-4.16 (m, 2H), 4.29-4.38
(m, 1H), 4.46-4.53 (m, 1H), 5.04 (d, J ) 8.0 Hz, 4H), 7.30-
7.39 (m, 10H). 13C NMR (ppm): (hydrate form) 26.89, 27.3,
67.5 (d, J ) 5.5 Hz), 69.9 (d, J ) 5.5 Hz), 70.0 (d, J ) 5.5 Hz),
75.4, 75.9 (d, J ) 6.8 Hz), 91.8 (q, J ) 31.8 Hz), 111.6, 123.0
the ketone by protonation. Thus, the mechanism of the
rearrangement catalyzed by MEP synthase appears to
be related to those of ribulose phosphate epimerase and
bacterial class II aldolases.
(q, J ) 288 Hz), 128.2, 128.8, 128.9, 135.6 (d, J ) 6.5 Hz). 19
F
NMR (ppm): -10.9 (s, 3F). 31P NMR (ppm): -2.87; [R]D25 +9.9
(c ) 2.2, EtOAc). HRMS (CI, M + H): m/z calcd for C22H25F3O7P
489.1285, found 489.1288.
Experimental Procedures
(3S,4R)-1,1,1-Trifluoro-2-hydroxy-3,4-(O-isopropylidene-
dioxy)pentan-5-ol (9). To a stirred solution of 830 mg of
aldehyde 7 (2.62 mmol, 1 equiv) and 5.77 mL of a 0.5 M
solution of (trifluoromethyl)trimethylsilane (2.88 mmol, 1.1
equiv) in 5 mL of THF cooled to 0 °C was added a catalytic
amount (∼1 mg) of potassium tert-butoxide. After 2 h, THF
was removed by rotory evaporation and the resulting oil
dissolved in 10 mL of 1:1 diethyl ether/water. The organic layer
was washed with brine, dried over anhydrous MgSO4, and
concentrated under reduced pressure. The pale yellow oil was
resuspended in 5 mL of THF, cooled to 0 °C, and then treated
with 5.50 mL of a 1.0 M solution of TBAF (5.50 mmol, 2.1
equiv). After the resulting solution was stirred for 2 h, THF
was removed by rotory evaporation, and the residual oil was
immediately chromatographed on silica (1:1 (v/v) ethyl acetate/
hexanes) to give 482 mg (80%) of a pale yellow oil as a 3:2
mixture of diasteromers. 1H NMR (ppm): 1.44-1.48 (3 s, 6H),
3.70-3.91 (m, 3H), 4.08-4.25 (m, 2H). 13C NMR (ppm): 26.8,
26.9, 27.2, 27.4, 61.2, 62.7, 68.3 (q, J ) 31.2 Hz), 71.2 (q, J )
31.2 Hz), 73.8 (q, J ) 1.5 Hz), 75.4, 78.5, 110.5, 111.1, 124.3
(q, J ) 283 Hz). 19F NMR (ppm): -3.49 (d, J ) 6.1 Hz), -4.42
(d, J ) 6.1 Hz). HRMS (CI, M + H): m/z calcd for C8H14F3O4
231.0839, found 231.0844.
Dibenzyl (3S,4R)-1,1,1-Trifluoro-2-hydroxy-3,4-(O-iso-
propylidenedioxy)pent-5-yl Phosphate (10). To a stirred
solution of 1.40 g of freshly prepared tribenzyl phosphite32 (3.97
mmol, 1.16 equiv) in 10 mL of CH2Cl2 at -40 °C was added
916 mg of I2 (3.61 mmol, 1.05 equiv). Once the I2 had
completely dissolved, the solution was cannulated over 10 min
to a separate flask containing 790 mg of diol 9 (3.43 mmol,
1.0 equiv) and 1.17 mL of freshly distilled pyridine (14.4 mmol,
4.2 equiv) in CH2Cl2 precooled to -40 °C. The solution was
allowed to warm to room temperature over 1 h, after which
the reaction was quenched with water and concentrated under
reduced pressure. The residue was resuspended into 10 mL
of diethyl ether, extracted with aqueous KHSO4, NaHCO3, and
brine, dried over MgSO4, and concentrated under reduced
pressure. Flash chromatography of the residue (3:2 (v/v) ethyl
acetate/hexanes) gave 1.30 g (77%) of a colorless oil as a 3:2
mixture of diastereomers. 1H NMR (ppm): 1.37-1.44 (3 s, 6H),
3.30 (d, J ) 9.9 Hz, OH) 3.80-4.30 (m, 5H), 5.05-5.09 (m,
4H), 7.30-7.40 (m, 10H). 13C NMR (ppm): 26.8, 26.9, 27.0,
27.1, 66.4 (d, J ) 5.5 Hz), 67.5 (d, J ) 5.5 Hz), 68.2 (q, J )
31.2 Hz), 69.8 (d, J ) 5.5 Hz), 69.9 (d, J ) 4.0 Hz), 71.6 (q, J
) 30.2 Hz), 73.8, 74.8 (q, J ) 1.5 Hz), 75.4 (d, J ) 8.6 Hz),
78.5 (d, J ) 6.1 Hz), 110.8, 111.5, 124.3 (q, J ) 283 Hz), 124.6
(q, J ) 283 Hz), 128.2, 128.3, 128.4, 128.8, 128.9, 129.0, 135.5
(d, J ) 7.0 Hz), 135.6 (d, J ) 7.0 Hz). 19F NMR (ppm): -3.73
(d, J ) 7.1 Hz), -4.01 (d, J ) 7.1 Hz). 31P NMR (ppm): -2.91,
-3.45. HRMS (CI, M + H): m/z calcd for C22H27F3O7P
491.1441, found 491.1435.
1,1,1-Trifluoro-1-deoxy-D-xylulose 5-Phosphoric Acid
(CF3-DXP, 1). To a solution of 27.0 mg of phosphotriester 11
(0.053 mmol (based on the hydrate form), 1.0 equiv) in 500 µL
of tert-butyl alcohol at room temperature was added 2.9 mg of
10 wt % Pd/C (0.0028 mmol, 0.05 equiv). The flask was
evacuated under vacuum, then hydrogen was introduced under
atmospheric pressure, and the reaction was stirred for 5 h.
The suspension was filtered, washed with H2O, concentrated
to approximately 2 mL under a stream of nitrogen, and stirred
for an additional 5-6 days. Upon completion, as determined
by 19F NMR, the concentration of 1 was verified by 19F NMR
against an internal standard of sodium trifluoroacetate pre-
pared in D2O (4 mM final). Integration revealed 14.7 mg (96%)
1
of 1 was present in the aqueous solution as the hydrate. H
NMR (ppm): 3.80-4.00 (m, 3H), 4.32 (t, J ) 6.5 Hz, 1H). 13
C
NMR (ppm): 65.9 (d, J ) 5.1 Hz), 68.2, 69.1 (d, J ) 8.8 Hz),
94.4 (q, J ) 29.8 Hz), 123.0 (q, J ) 288 Hz). 19F NMR (ppm):
-6.8 (s, 3F). 31P NMR (ppm): 0.61. [R]D -11.3 (c 0.4, H2O).
25
HRMS (FAB, M - OH, hydrate): m/z calcd for C5H9F3O7P
269.0033, found 269.0041.
Diethyl {Dibenzyl (3S,4R)-1,1-difluoro-2-oxo-3,4-(O-
isopropylidenedioxy)pent-5-yl phosphate}phosphonate
(15). To a solution of 1.78 mL of 1.5 M LDA (2.66 mmol, 1.2
equiv) in 10 mL of THF at -78 °C was added 399 µL of diethyl
(1,1-difluoromethyl)phosphonate (2.44 mmol, 1.1 equiv) via
syringe in 1 mL of THF very slowly over a 10 min period. The
solution was stirred for 45 min at the same temperature, at
which time 1.00 g of 14 (2.22 mmol, 1.0 equiv) was added very
slowly via syringe in 1 mL of THF, and the resulting solution
was stirred for 2 h at the same temperature. Note: It is
important to add these reagents slowly since lithiated difluo-
rophosphonate decomposes at temperatures >-70 °C. After
the reaction was completed as determined by TLC, 1 mL of
glacial acetic acid was added followed by saturated NH4Cl. The
solution was allowed to warm to room temperature over a 1 h
period and then extracted into CH2Cl2. The combined organic
extracts were dried and concentrated. Flash column chroma-
tography (3:2 (v/v) hexanes/ethyl acetate) gave 1.11 g (83%)
of a pale yellow oil (80:20 hydrate/ketone). For spectral
analysis, the hydrate was converted to the ketone by azeotropic
1
distillation with benzene. H NMR (ppm): 1.37 (2t, J ) 7.1,
1.6 Hz, 6H), 1.41 (s, 3H), 1.46 (s, 3H), 4.13-4.21 (m, 1H), 4.24-
4.37 (m, 5H), 4.47-4.54 (m, 1H), 4.90 (d, J ) 6.3 Hz, 1H) 5.07
(d, J ) 8.1 Hz, 4H), 7.31-7.39 (m, 10H). 13C NMR (ppm): 16.4,
16.5, 26.3, 27.2, 66.0 (2d, J ) 6.5 Hz), 66.4 (d, J ) 5.0 Hz),
76.7 (d, J ) 8.6 Hz), 78.3 (d, J ) 2.0 Hz), 113.1, 113.8 (dt, J )
274, 197 Hz), 128.2, 128.2, 128.8, 135.8 (d, J ) 2.0 Hz), 135.9
(d, J ) 2.0 Hz), 196.5 (dt, J ) 24.2, 13.6 Hz). 19F NMR (ppm):
-43.6 (AB system, J ) 326, 94.0 Hz, 2F). 31P NMR (ppm): 0.01
25
(t, J ) 94.0 Hz, 1P), -3.49 (s, 1P). [R]D +7.7 (c 0.4, MeOH).
Dibenzyl(3S,4R)-1,1,1-Trifluoro-1-deoxy-2-oxo-3,4-(O-iso-
propylidene)-D-xylulose Phosphate (11). To a solution of
4.22 mL (2.04 mmol, 2 equiv) of Dess-Martin reagent dis-
solved in 2 mL of CH2Cl2 was added 500 mg of alcohol 10 (1.02
mmol, 2 equiv) in 1 mL of CH2Cl2. Upon completion, as judged
by 19F NMR (∼1 h, 0.13 ppm relative to external TFA, 0.00
ppm), a saturated solution of NaHCO3 and a 10-fold excess of
solid Na2S2O3 were added, and the mixture was stirred until
the solution cleared. The solution was extracted with diethyl
ether and washed in succession with a mixture of saturated
NaHCO3, 2.0 g of Na2S2O3, and brine. The organic layer was
dried and concentrated under reduced pressure. Flash chro-
matography of the residual oil (1:1 (v/v) hexanes/ethyl acetate)
gave 448 mg (90%) of a colorless oil. 1H NMR (ppm): (hydrate
HRMS (FAB, M + H): m/z calcd for C26H35F2O10P2 607.1674,
found 607.1642.
Dibenzyl 1,1-Difluoro-1-deoxy-3,4-(O-isopropylidene)-
D-xylulose Phosphate (16). Benzene was added to 1.00 g of
ketophosphonate 15 (1.64 mmol, 1.0 equiv), and water was
removed by distillation using a Dean-Stark trap. When the
hydrate was converted to the ketone, as determined by 19F
NMR, dry MeOH was added, the flask was cooled to 0 °C, and
53.6 mg of sodium methoxide (0.988 mmol, 0.6 equiv) was
added. The reaction was monitored by TLC until the starting
material was consumed (∼2-4 h), then water was added, and
the mixture was extracted into CH2Cl2. The organic layers
were combined and dried, and solvent was removed under
J. Org. Chem, Vol. 70, No. 6, 2005 1983

Fox and Poulter
reduced pressure. The crude product was purified by flash
chromatography (3:2 (v/v) ethyl acetate/hexanes) to give 647
mg (83%) of a colorless oil as an 80:20 mixture of the hydrate/
ketone forms, respectively. 1H NMR (ppm): 1.39 (s, 3H), 1.44
(s, 3H), 4.06 (dd, J ) 7.9, 1.5 Hz, 0.8H), 4.09-4.25 (m, 1.2H),
4.28-4.40 (m, 1H), 4.47-4.54 (m, 0.8H), 4.56 (d, J ) 6.8 Hz,
0.2H), 4.80 (br s, 0.8H, hydrate OH), 5.05 (d, J ) 8.0 Hz, 3.2H),
5.06 (d, J ) 8.0 Hz, 0.8H), 5.77 (t, J ) 55.2 Hz, 0.8H), 6.11 (t,
J ) 53.0 Hz, 0.2H), 7.29-7.41 (m, 10H). 13C NMR (ppm): 26.2,
26.9, 26.9, 27.3, 66.1 (d, J ) 5.5 Hz), 67.7 (d, J ) 5.5 Hz), 69.9
(dt, J ) 5.5, 2.0 Hz), 75.4 (dd, J ) 8.1, 2.0 Hz), 76.2 (d, J ) 8.6
Hz), 76.5, 78.4, 92.2 (t, J ) 23.7 Hz), 108.5 (t, J ) 251 Hz),
111.1, 113.7 (t, J ) 248 Hz), 128.2, 128.3, 128.8, 128.9, 129.0,
135.6 (d, J ) 7.1 Hz), 135.7 (d, J ) 7.0 Hz), no CdO observed.
19F NMR (ppm): -56.4 (d, J ) 55.0 Hz, 0.4F), -63.4 (AB
system, J ) 286, 55.0 Hz, 1.6F). 31P NMR (ppm): -3.14 (s,
0.8P), -3.55 (s, 0.2P). [R]D25 +11.0 (c 0.8, EtOAc). HRMS (FAB,
M - OH): m/z calcd for C22H26F2O7P (hydrate - OH) 471.1384,
found 471.1387.
(3R,4R)-1,2-Epoxy-3,4-(O-isopropylidenedioxy)pentan-
5-ol Benzyl Ether (18). To a solution of 1.00 g of 17 (3.96
mmol, 1.0 equiv) in 20 mL of CH2Cl2 at room temperature was
added 2.52 g of Dess-Martin reagent (5.94 mmol, 1.5 equiv).
The reaction was stirred for 45 min, then saturated NaHCO3
and 5.0 g of Na2S2O3 were added in succession, and the
suspension was stirred until the solution cleared. The organic
layer was decanted, and the aqueous layer was extracted with
diethyl ether. The combined organic extracts were washed with
a mixture of saturated NaHCO3 and 10.0 g of Na2S2O3 and
then brine and dried. Concentration under reduced pressure
gave 940 mg of the crude aldehyde, which was used in the
next step without further purification.
To 86.0 mg of a 50% NaH dispersion in mineral oil (2.14
mmol, 1.2 equiv), previously washed with hexanes, and 471
mg of trimethyloxosulfonium iodide41 (2.14 mmol, 1.2 equiv)
was added 5 mL of dry DMSO. The solution was stirred for 2
h or until H2 evolution ceased, at which time the crude
aldehyde was added in 2 mL of DMSO. The mixture was
stirred until the starting material was consumed as judged
by TLC (∼2 h). The reaction was quenched with water and
extracted into diethyl ether. The combined organic layers were
washed with water and then brine, dried, and concentrated
under reduced pressure. Flash chromatography of the residue
(7:3 (v/v) hexanes/ethyl acetate) gave 510 mg (49%, two steps)
of a 4:1 ratio of diastereomers as a colorless oil. 1H NMR
(ppm): 1.43-1.45 (3 s, 6H), 2.66 (dd, J ) 2.4 Hz, 0.25H), 2.70
(dd, J ) 2.7 Hz, 0.75H), 2.78 (t, J ) 4.5 Hz, 0.25H), 2.82 (t, J
) 4.2 Hz, 0.75H), 3.03-3.07 (m, 0.25H), 3.08-3.13 (m, 0.75H),
3.57-3.75 (m, 3H), 4.16-4.22 (m, 1H), 4.60 (s, 0.5H), 4.61 (s,
1.5H), 7.28-7.39 (m, 5H). 13C NMR (ppm): (major diastereo-
mer) 26.9, 27.2, 45.2, 51.9, 70.7, 73.8, 78.2, 78.3, 110.3, 127.9,
127.9, 128.6, 138.1, (minor diastereomer) 26.8, 44.3, 51.8, 70.3,
73.8, 76.9, 79.4, 110.3, 128.0, 128.7, 137.9. HRMS (CI, M +
H): m/z calcd for C15H21O4 265.1440, found 265.1434.
reomer) 27.0, 27.0, 70.6, 72.1 (d, J ) 18.1 Hz), 74.0, 78.3 (d, J
) 6.5 Hz), 78.8, 84.6 (d, J ) 170 Hz), 109.8, 128.2, 128.2, 128.8,
137.2, (minor diastereomer) 27.0, 27.2, 68.7 (d, J ) 19.6 Hz),
70.2, 73.8, 75.8, 78.2 (d, J ) 5.0 Hz), 84.3 (d, J ) 171 Hz),
110.0, 127.9, 128.0, 128.7, 137.8. 19F NMR (ppm): -155.0 (dt,
J ) 45.8, 18.3 Hz, 0.25F), -162.3 (dt, J ) 45.8, 24.4 Hz, 0.75F).
HRMS (CI, M + H): m/z calcd for C15H22FO4 285.1502, found
285.1517.
(3S,4R)-1-Fluoro-2-hydroxy-3,4-(O-isopropylidenedi-
oxy)pentan-5-ol (20). To a solution of 80.0 mg of 19 (0.281
mmol, 1.0 equiv) in 1 mL of absolute EtOH at room temper-
ature was added 15.0 mg of 10 wt % Pd/C (0.014 mmol, 0.05
equiv). The flask was evacuated under vacuum, hydrogen was
introduced, and the reaction was stirred for 3 h. The suspen-
sion was filtered, and the filtrate was concentrated under
reduced pressure, which gave 52.0 mg (95%) of a colorless oil
as a mixture of diastereomers. 1H NMR (ppm): 1.38 (s, 2.25H),
1.39 (s, 2.25H), 1.42 (s, 0.75H), 1.43 (s, 0.75H), 3.78-3.90 (m,
4H), 4.05-4.15 (m, 1H), 4.40-4.72 (m, 2H). 13C NMR (ppm):
(major diastereomer) 27.0, 27.1, 63.0, 72.2 (d, J ) 18.1 Hz),
77.0 (d, J ) 6.6 Hz), 80.6, 84.9 (d, J ) 169 Hz), 109.8, (minor
diastereomer) 27.2, 61.9, 68.7 (d, J ) 19.6 Hz), 77.0 (d, J )
5.5 Hz), 77.3, 84.4 (d, J ) 171 Hz), 109.9. 19F NMR (ppm):
-156.1 (dt, J ) 48.8, 18.3 Hz, 0.25F), -161.8 (dt, J ) 48.8,
18.3 Hz, 0.75F). HRMS (CI, M + H): m/z calcd for C8H16FO4
195.1033, found 195.1010.
Dibenzyl (3S,4R)-1-Fluoro-1-deoxy-3,4-(O-isopropyl-
idene)-D-xylulose Phosphate (22). To a solution of 62.8 mg
of Dess-Martin reagent (0.148 mmol, 1.5 equiv) in 1 mL of
CH2Cl2 at room temperature was added 45.0 mg of alcohol 21
(0.099 mmol, 1.0 equiv). The reaction was monitored by 19F
NMR until completion (t, -162.58 ppm, ∼1 h), at which time
saturated NaHCO3 and a 10-fold excess of solid Na2S2O3 were
added, and the mixture was stirred until the solution cleared.
The solution was extracted with diethyl ether and washed in
succession with a mixture of saturated NaHCO3 and 2.0 g of
Na2S2O3 and then brine. The organic layer was dried and
concentrated under reduced pressure. Flash chromatography
of the oil (1:1 (v/v) hexanes/ethyl acetate) gave 42.8 mg (89%)
of a colorless oil as a 90:10 mixture of ketone/hydrate forms.
1H NMR (ppm): (ketone only) 1.38 (s, 3H), 1.42 (s, 3H), 4.11
(m, 1H), 4.15-4.40 (m, 3H), 5.06 (d, J ) 8.3 Hz, 4H), 5.19 (AB
system, J ) 47.1, 10.0 Hz, 2H), 7.36 (m, 10H); 13C NMR
(ppm): (ketone only) 26.3, 26.8, 66.3 (d, J ) 5.5 Hz), 69.7 (d,
J ) 5.5 Hz), 76.4 (d, J ) 8.0 Hz), 79.3, 83.6 (d, J ) 184 Hz),
112.1. 128.2, 128.8, 135.8 (d, J ) 2.2 Hz), 203.0 (d, J ) 5.0
Hz). 19F NMR (ppm): (hydrate) -158.5 (t, J ) 48.8 Hz),
(ketone) -162.5 (dd, J ) 48.8 Hz). 31P NMR (ppm): (hydrate)
25
-2.84, (ketone) -3.55. [R]D -6.7 (c 1.0, EtOAc). HRMS (CI,
M + H): m/z calcd for C22H27FO7P 453.1478, found 453.1434.
(2R,3S)-1-Hydroxy-2,3-(O-isopropylidenedioxy)-N-meth-
oxy-N-methylbutanamide (23). To a cooled (-20 °C) mix-
ture of 276 mg of N,O-dimethylhydroxylamine hydrogen
chloride (2.83 mmol, 3.0 equiv) and 180 mg of monoester 13
(0.946 mmol, 1.0 equiv) in 2 mL of THF was added 1.89 mL of
a 3.0 M solution of CH3MgBr (5.67 mmol, 6.0 equiv) over 20
min. The reaction was stirred for 2 h at the same temperature
and then at room temperature overnight. The reaction was
quenched by addition of saturated NH4Cl and the aqueous
layer extracted with diethyl ether and then CH2Cl2. The
combined organic layers were dried and concentrated under
reduced pressure. Flash chromatography of the residue (100%
(3S,4R)-1-Fluoro-2-hydroxy-3,4-(O-isopropylidenedi-
oxy)pentan-5-ol Benzyl Ether (19). Diisopropylamine tri-
hydrofluoride was prepared according to Muehlbacher.42 To
199 mg of diisopropylamine trihydrofluoride (1.23 mmol, 2.0
equiv) was added 163 mg of oxirane 18. The flask was tightly
stoppered with a plastic cap and the mixture heated as a
homogeneous melt at 100 °C. The starting material was
consumed after 19 h as observed by TLC. The flask was cooled
and the semisolid extracted with diethyl ether. The organic
layer was washed with water, dried, and concentrated under
reduced pressure. The oil was purified by flash chromatogra-
phy (4:1 (v/v) hexanes/ethyl acetate) to yield 81.6 mg (47%) of
1
diethyl ether) gave 124 mg (60%) of a colorless oil. H NMR
(ppm): 1.47 (s, 3H), 1.49 (s, 3H), 2.15 (br s, 1H, OH), 3.23 (br
s, 3H), 3.67-3.73 (m, 1H), 3.75 (s, 3H), 3.90 (dt, J ) 12.2, 3.4
Hz, 1H), 4.46 (br s, 1H), 4.77 (br d, J ) 5.9 Hz, 1H). 13C NMR
(ppm): 26.2, 27.3, 32.6, 61.9, 73.9, 77.4, 79.0, 111.2, 170.7.
1
a 72:28 mixture of diastereomers as a colorless oil. H NMR
25
[R]D +11.0 (c 18.4, EtOAc). HRMS (CI, M + H): m/z calcd
(ppm): 1.40 (s, 4.5 H), 1.43 (s, 0.75H), 1.45 (s, 0.75H), 2.55 (br
s, J ) 8.3 Hz, 0.25H, OH), 3.45 (br s, 0.75H, OH), 3.56-3.84
(m, 3.75H), 3.97 (dd, J ) 8.3, 2.7 Hz, 0.25H), 4.13 (dt, J ) 6.8,
4.9 Hz, 0.75H), 4.24 (dt, J ) 8.0, 6.1 Hz, 0.25H), 4.34-4.71
(m, 4H), 7.28-7.41 (m, 5H). 13C NMR (ppm): (major diaste-
for C9H18NO5 220.1185, found 220.1191.
Dibenzyl (4S,5R)-3-Oxo-4,5-(O-isopropylidenedioxy)-
hexan-6-yl Phosphate (25). To a solution of 360 mg of amide
24 (0.750 mmol, 1.0 equiv) in 5 mL of diethyl ether at -40 °C
1984 J. Org. Chem., Vol. 70, No. 6, 2005

DXP Analogues as Substrates for MEP Synthase
was added 300 µL of a 3.0 M solution of EtMgBr (0.900 mmol,
1.2 equiv). The reaction was stirred at the same temperature
for 1 h, quenched with saturated NH4Cl, and extracted into
diethyl ether. The organic layer was washed with brine, dried,
and concentrated under reduced pressure. Flash chromatog-
raphy of the residue (7:3 (v/v) ethyl acetate/hexanes) gave 286
free acid was converted to the sodium form by addition of solid
NaHCO3 to pH 7.0 and lyophilized. Cellulose column chroma-
tography (15-50% (v/v) 0.1% TFA in water/THF) of the residue
1
gave 55.0 mg (99%) of a white powder. H NMR (ppm): 1.01
(t, J ) 7.1 Hz, 3H), 2.54-2.74 (m, 2H), 3.82 (t, J ) 7.4 Hz,
2H), 4.28 (dt, J ) 6.6, 1.6 Hz, 1H), 4.48 (d, J ) 1.6 Hz, 1H).
13C NMR (ppm): 7.6, 32.6, 65.5 (d, J ) 5.5 Hz), 71.9 (d, J )
1
mg (85%) of a colorless oil. H NMR (ppm): 1.06 (t, J ) 7.3
25
Hz, 3H), 1.38 (s, 3H), 1.43 (s, 3H), 2.64 (ABX3 system, J )
7.3, 4.4 Hz, 2H), 4.07-4.30 (m, 4H), 5.07 (d, J ) 8.1 Hz, 4H),
7.29-7.40 (m, 10H). 13C NMR (ppm): 7.1, 26.5, 26.9, 32.4, 67.0
(d, J ) 5.8 Hz), 69.6 (d, J ) 5.5 Hz), 76.5 (d, J ) 7.9 Hz), 81.0,
111.3, 128.2, 128.7, 128.8, 135.9 (d, J ) 7.0 Hz), 210.37. 31P
8.4 Hz), 77.6, 216.9. 31P NMR (ppm): 4.40. [R]D +1.4 (c 1.0,
H2O). HRMS (FAB, M - H): m/z calcd for C6H12O7P 227.0326,
found 227.0321.
Acknowledgment. We thank Dr. J. Walker and Dr.
G. Labadie for insightful discussions. This work was
supported by the National Institutes of Health (Grant
GM25521).
25
NMR (ppm): -3.50. [R]D -8.5 (c 2.9, EtOAc). HRMS (CI, M
+ H): m/z calcd for C23H30O7P 449.1729, found 449.1722.
(4S,5R)-3-Oxo-4,5-dihydroxyhex-6-yl Phosphate (Et-
DXP, 4). To a solution of 100 mg of 25 (0.223 mmol, 1.0 equiv)
in 1 mL of freshly distilled MeOH at room temperature was
added 12.0 mg of 10 wt % Pd/C (0.011 mmol, 0.05 equiv). The
flask was evacuated under vacuum, hydrogen was introduced
under atmospheric pressure, and the suspension was stirred
for 6 h. The suspension was filtered and the filtrate concen-
trated under reduced pressure. The residue was resuspended
in 2 mL of water and the suspension stirred for 2 days. The
Supporting Information Available: General methods,
experimental protocols for synthesis of 2, 3, 14, 17, 21, and
24, and 1H, 13C, 19F, and 31P NMR spectra for compounds 1-4,
9-11, 14-16, 18-22, and 23-25 (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
JO048022H
J. Org. Chem, Vol. 70, No. 6, 2005 1985