Synthesis and biological evaluation of two mannose 6-phosphate analogs

Article abstract of DOI:10.1002/1099-0690(200010)2000:20<3433::AID-EJOC3433>3.0.CO;2-I

Two β-hydroxyphosphonate analogs of M6P have been prepared by condensation of the lithiated anion of methyldiethylphosphonate with the C-6 carbonyl of a mannose derivative. The diastereoisomers thus obtained have been separated and the absolute configurat

Full text of DOI:10.1002/1099-0690(200010)2000:20<3433::AID-EJOC3433>3.0.CO;2-I

FULL PAPER
Synthesis and Biological Evaluation of Two Mannose 6-Phosphate Analogs
[
a]
[a]
[a]
[b]
S e´ bastien Vidal, Carole Vidil, Alain Mor e` re,* Marcel Garcia,
and Jean-Louis Montero*[
a]
Keywords: Phosphonate analogs / Mannose 6-phosphate (M6P) / Receptors / Recognition markers / Phosphonates /
Natural products
Two β-hydroxyphosphonate analogs of M6P have been pre-
pared by condensation of the lithiated anion of methyldi- been determined by spectroscopic analysis in conjunction
ethylphosphonate with the C-6 carbonyl of a mannose deriv-
with theoretical calculations. Recognition phenomena by
ative. The diastereoisomers thus obtained have been separ- M6P/IGFIIR have been evaluated for both diastereoisomers.
ated and the absolute configuration at the 6-position has
Introduction
in which the PϪO bond was replaced by a PϪC bond in-
sensitive to phosphatase hydrolysis. Two analogs (A and B)
were synthesized with the aim of determining their affinities
The cation-dependent (46 kDa) and cation-independent
275 kDa) mannose 6-phosphate receptors[
1,2,3,4]
(CD-MPR
(
[8]
towards M6P/IGFIIR (Scheme 1).
and CI-MPR, respectively) belong to the P-type lectin fam-
ily. Their function is to sort and transport M6P-bearing gly-
coproteins on their N-linked oligosaccharides from the
trans-Golgi network (TGN) to lysosomes. The
receptorϪenzyme complex accumulates in clathrin-coated
vesicles and travels to an acidic pre-lysosomal compartment
where low pH leads to dissociation of the complex. The
receptor can then go back to the TGN and reinitiate an-
other cycle of enzyme transport.
Our interest has been focused on CI-MPR as, according
to its presence on the plasma membrane, this receptor is
also responsible for the binding and the specific endocytosis
of extracellular M6P-bearing glycoproteins. This receptor is
a type I multifunctional transmembrane glycoprotein also
called Mannose 6-Phosphate/Insulin-like Growth Factor II
Receptor (M6P/IGFIIR) which, apart from M6P, also
Scheme 1. Phosphonate analogs of M6P
[5]
binds IGF II and retinoic acid (RA) at different sites.
The isosteric compound A was shown to be as well recog-
M6P/IGFIIR is the first example of a receptor able to bind nized as natural M6P, whereas the non-isosteric compound
three different categories of ligands such as a saccharide B was weakly recognized by M6P/IGFIIR. These results
[
6]
(
M6P), a peptide (IGFII), and a lipid (RA). Moreover, suggest that such isosteric M6P analogs may have consider-
this receptor has been shown to play a fundamental role in able potential in targeting therapy. Thus, replacement of the
the control of cell growth in fetal development and carcino- phosphate group by a phosphonate moiety (compound A)
[
7]
genesis.
does not affect the recognition phenomenon. Moreover,
The presence of this receptor on cell surfaces is particu- when the chain between the phosphorus and the pyran ring
larly interesting since it offers a possible means for internal- was shortened by a methylene unit (compound B), only a
izing M6P-bearing compounds. However, the phosphomon- weak recognition was observed. In the light of these results
oester bond of M6P is easily hydrolyzed by phosphatases. and in order to determine the structural factors that govern
Thus, the transport of M6P-bearing molecules appears to recognition phenomenon, two β-hydroxyphosphonates
be delicately balanced. A first study carried out in our (4a,b) have been prepared and their affinities towards M6P/
laboratory led us to prepare phosphonate analogs of M6P IGFIIR have been evaluated.
[
a]
Laboratoire de Chimie Biomol e´ culaire CC073, Universit e´
Montpellier II,
Results and Discussion
Place Eug e` ne Bataillon, F-34095 Montpellier Cedex 05, France
E-mail: morere@crit.univ-montp2.fr
Synthesis of β-Hydroxyphosphonate Analogs of M6P
E-mail: montero@crit.univ-montp2.fr
[
b]
The starting alcohol 1 (Scheme 2) was prepared accord-
ing to classical protection-deprotection reactions as de-
NSERM, Unit e´ 540, EMCC, 60,
Rue de Navacelles, F-34090 Montpellier, France
Eur. J. Org. Chem. 2000, 3433Ϫ3437

WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ193X/00/1020Ϫ3433 $ 17.50ϩ.50/0
3433

S. Vidal, C. Vidil, A. Mor e` re, M. Garcia, J.-L. Montero
FULL PAPER
scribed in the literature.[9] The key step of this synthesis
involves attack of the lithiated methyldiethylphosphonate
anion on the aldehyde obtained from 1 by Swern oxida-
[
10]
tion.
The two diastereoisomers 2a,b were obtained in
4
0% overall yield with relative proportions of 45% and 55%,
respectively. Separation of these two diastereoisomers was
accomplished after removal of the benzyl groups by hydro-
genolysis. Deprotection of the diethylphosphonates 3a,b
was accomplished by well-known procedures[ to give 4a,b
in 65% yield (Scheme 2).
11]
Scheme 3. Two possibilities for the addition of nucleophiles to α-
chiral carbonyl compounds
NMR analysis and that these data have been confirmed by
a conformational study. The conformational behavior was
conveniently analyzed by means of a conformation map ob-
tained by plotting the relative energy of the conformation
vs. the dihedral angle. The relative energies of the con-
formations were calculated using the CFF91 force field as
implemented in the Discover program of the Insight II pro-
gram (MSI, San Diego), systematically varying the dihedral
angles in increments of 10°. The lowest-energy rotamers
thus obtained for 3a (6R) and 3b (6S) are shown in Figure 1
and Figure 2, respectively.
Scheme 2. Preparation of β-hydroxyphosphonate analogs of M6P
(
2 2
i) (COCl) , DMSO, iPr NEt, THF, Ϫ60 °C, 20 min; (ii) methyldie-
thylphosphonate, nBuLi, THF, Ϫ78 °C; (iii) EtOH/H
2
O (1:1), H
2
/
1
°
0% PdϪC, 20 °C, 4 days; (iv) (a) CH CN, pyridine, Me
3
3
SiBr, 20
2
C, 2 h; (b) H O, pyridine, 0 °C then 20 °C, 2 h then cation-ex-
change resin, 20 °C, 24 h
The observed absence of diastereoselectivity is in accord-
ance with the Cram chelate rule[
12,13]
when applied to α,β-
dialkyloxy carbonyl compounds. Indeed, there are two pos-
sibilities for chelate formation. The chelation may either oc-
cur between the lithium counterion and the oxygen atoms
of both the carbonyl and α-alkyloxy moieties leading to a
five-membered ring (Scheme 3), or a six-membered ring
may be generated by chelation of the lithium counterion
and the oxygen atoms of both the carbonyl and β-alkyloxy
moieties (Scheme 3).
Our results have shown that the β-alkyloxy carbonyl che-
late is slightly favored, leading to a slight predominance of
the (6S) diastereoisomer 3b (55%). The ratio 55:45 is in ac-
cordance with data for the acyclic series reported in the
[
12,13]
literature.
It is worth pointing out that the absolute
Figure 1. Stick representation of the minimum-energy conforma-
1
configuration at the 6-position has been determined by H tion of 3a (6R)
3434
Eur. J. Org. Chem. 2000, 3433Ϫ3437

Synthesis and Biological Evaluation of Two Mannose 6-Phosphate Analogs
FULL PAPER
A, whereas similar concentrations of the β-hydroxyphos-
phonates 4a and 4b were totally inactive. Therefore, irre-
spective of the stereochemistry at the 6-position of com-
pounds 4a,b, the presence of hydroxyl groups prevents bind-
ing to M6P/IGFIIR.
Figure 3. Affinity of mannose 6-phosphate analogs for M6P/IGFII
receptors; M6P/IGFII receptors from calf serum were retained on
phosphomannan Sepharose columns and eluted with the indicated
concentrations of mannose 6-phosphonate A (M6Pn) and β-hydro-
xyphosphonates 4a (6R) or 4b (6S) as described in the Experi-
mental Section; the eluted proteins were analyzed on 10% SDS po-
lyacrylamide gel with visualization by silver-staining; MW, molecu-
Figure 2. Stick representation of the minimum-energy conforma-
tion of 3b (6S)
The coupling constant values calculated by means of the lar weight markers, arrow indicates the eluted M6P/IGFIIR; this
Karplus equation from the dihedral angles in 3a (6R) and
experiment was repeated and similar results were obtained
3
b (6S) are listed in Table 1.
For compound 3b (6S), the H ϪH dihedral angle ap-
proaches 180° and the calculated coupling constant value is
.6 Hz, as compared with the experimental value of 5.4 Hz.
6
5
Conclusion
9
In summary, two β-hydroxyphosphonate analogs of M6P
have been prepared. The diastereoisomers have been separ-
ated and the absolute configuration at the 6-position has
been determined by spectroscopic analysis in conjunction
with theoretical calculations. However, no recognition phe-
nomena have been observed between the β-hydroxyphos-
phonates 4a,b and M6P/IGFIIR. It has already been estab-
On the other hand, for the diastereoisomer 3a (6R), the
calculated coupling constant value is 2.1 Hz whereas no
coupling constant is observed experimentally.
Biological Evaluation of the Two β-Hydroxyphosphonate
Analogs of M6P
The affinities of the β-hydroxyphosphonate analogs 4a lished that replacement of the phosphomonoester linkage
6R) and 4b (6S) for M6P/IGFIIR were compared to that by a methylene group does not affect the recognition phe-
(
of M6Pn A by affinity chromatography on a phosphoman- nomenon. On the other hand, further substitution at the 6-
nan Sepharose gel (Figure 3). M6P/IGFIIR was eluted with position seems to be critical with regard to the recognition
maximum efficacy using 5 or 10 m isosteric phosphonate phenomenon and the ineffectiveness of the β-hydroxyphos-
3
Table 1. Comparison of J coupling constant values
3
a (6-R)
3b (6-S)
Dihedral angle
(ϕ°)
[a]
3
[b]
[a]
3
[b]
3
Dihedral angle
Calculated J
Hz)
Experimental
Calculated J
Experimental J
3
(
J (Hz)
(Hz)
(Hz)
(ϕ°)
H5ϪH6
H6ϪH7
H6ϪH7Ј
Ϫ62.4
Ϫ61.2
Ϫ177.9
2.1
2.3
9.8
Ϫ
3.7
9.3
171.2
175.9
59.4
9.6
9.7
2.5
5.4
9.8
2.7
[
a]
According to Insight II measurements. Ϫ [b] According to Karplus equations.
Eur. J. Org. Chem. 2000, 3433Ϫ3437
3435

S. Vidal, C. Vidil, A. Mor e` re, M. Garcia, J.-L. Montero
FULL PAPER
phonates 4a,b could be due to steric hindrance. Thus, in the Methyl 7-Deoxy-7-diethyloxyphosphinyl-
L
-glycero-α-
topyranoside (3a) and Methyl 7-Deoxy-7-diethyloxyphosphinyl-
glycero-α- -manno-heptopyranoside (3b): The diastereoisomeric
mixture 2a,b (1.0 g, 1.63 mmol) was dissolved in ethanol/H O (1:1,
D-manno-hep-
D-
hope of gaining further insight into the molecular basis of
the interaction of M6P/IGFIIR with M6P, we are currently
developing new M6P mimetics.
D
2
v/v, 60 mL), 10% Pd/C (0.3 g) was added, and the mixture was
stirred under hydrogen atmosphere for 4 days. It was then filtered
through Celite and the filtrate was concentrated in vacuo. The res-
idue was purified by silica gel column chromatography (AcOEt/
MeOH, 9:1, v/v) to afford the separated diastereoisomers 3a and
3b (total yield 0.45 g, 80%) in relative amounts of 45% and 55%, re-
Experimental Section
General Aspects: Reactions were monitored by TLC using alumi-
num-backed plates coated with silica gel 60 F254 (Merck); spots spectively.
2
0
1
were visualized with UV light (254 nm) or by charring with H
2
SO
4
3a: [α]
1.25 (t, J ϭ 7.0 Hz, 6 H, 2 ϫ CH
3.7 Hz, J7Ϫ7Ј ϭ 16.1 Hz, J7-P ϭ 19.1 Hz, 1 H, 7-H), 2.29 (td, J7Ј-
ϭ 9.3 Hz, J7Ј-7 ϭ J7Ј-P ϭ 16.1 Hz, 1 H, 7Ј-H), 3.25 (s, 3 H, OCH ),
3.31 (d, J5Ϫ4 ϭ 9.6 Hz, 1 H, 5-H), 3.71 (dd, J3Ϫ2 ϭ 3.0 Hz, J3Ϫ4
9.6 Hz, 1 H, 3-H), 3.84 (t, 1 H, 4-H), 3.80Ϫ3.85 (m, 1 H, 2-H),
3.95Ϫ4.10 (m, 4 H, 2 ϫ CH CH OP), 4.40 (m, 1 H, 6-H), 4.66 (s,
): δ ϭ 16.7 (d, J ϭ 2.2 Hz,
OP), 16.8 (d, J ϭ 2.7 Hz, CH CH OP), 31.1 (d, J ϭ
141.4 Hz, C-7), 55.4 (OCH ), 62.1 (d, J ϭ 6.5 Hz, CH CH OP),
62.5 (d, J ϭ 6.2 Hz, CH CH OP), 64.5 (d, J ϭ 2.6 Hz, C-6), 67.1
(C-2), 71.1 (C-4), 71.9 (C-3), 74.5 (d, J ϭ 13.4 Hz, C-5), 101.8 (C-
D
ϭ ϩ38.0 (c ϭ 0.85, CHCl
3
). Ϫ H NMR (CDCl
3
): δ ϭ
(10% aqueous spray solution). Aldehyde spots were developed by
3
CH OP), 1.90 (ddd, J7Ϫ6
2
ϭ
spraying with 5% rhodanine solution in ethanol followed by heat-
ing. Molybdenum blue was used to develop phosphorus-containing
compounds. Ϫ Column chromatography was performed on Carlo
6
3
ϭ
1
31
Erba silica gel 60A (35Ϫ70 µm). Ϫ H and P NMR spectra were
recorded on an AC-250 Bruker spectrometer and 13C NMR spectra
3
2
1
3
on a WP-200-SY Bruker spectrometer. Chemical shifts are given 1 H, 1-H). Ϫ C NMR (CDCl
3
on the δ scale using residual solvent peaks as a reference relative
to TMS. Ϫ Specific rotations were measured with sodium D light
at 20 °C using a PerkinϪElmer polarimeter. Ϫ Mass spectra were
CH
3
CH
2
3
2
3
3
2
3
2
ϩ
measured on a DX 300 JEOL spectrometer in the FAB (NBA) or
Ϫ
31
ϩ
FAB (GT) ion modes. Ϫ The cation-exchange resin (Dowex
1). Ϫ P NMR (CDCl
3
): δ ϭ 31.94. Ϫ MS (FAB ): m/z (%)
ϩ
ϩ
ϩ
5
0WX2 H ) was washed with 1  NaOH solution and then with
(NBA) ϭ 711 (5) [2M ϩ Na] , 367 (100) [M ϩ Na] , 345 (10) [M
ϩ
distilled water prior to use. Ϫ The pentamannose 6-phosphate was
functionalized with β-(p-aminophenyl)ethylamine, then reduced
with sodium tetrahydroborate, and finally coupled on CNBr-activ-
ated Sepharose to give phosphomannan Sepharose.[ Ϫ The M6P/
IGFII receptor was purified from fetal calf serum on a phosphom-
annan-Sepharose affinity column according to the method de-
ϩ H] . Ϫ C12
H
25
O
9
P (344.3): calcd. C 41.86, H 7.32; found C
41.73, H 7.38.
2
0
1
3b: [α]
D
ϭ ϩ58.0 (c ϭ 0.6, CHCl
CH
7Ϫ7Ј ϭ J7-P ϭ 15.9 Hz, 1 H, 7-H), 2.29 (ddd, J7Ј-6 ϭ 2.7 Hz, J7Ј-
3
). Ϫ H NMR (CDCl
2
OP), 2.06 (td, J7Ϫ6 ϭ 9.8 Hz,
3
): δ ϭ 1.25
14]
(t, J ϭ 7.0 Hz, 6 H, 2 ϫ CH
J
3
P
ϭ 18.8 Hz, 1 H, 7Ј-H), 3.27 (s, 3 H, OCH
3
), 3.39 (dd, J4Ϫ5
ϭ
[
15]
scribed previously.
Ϫ SDS polyacrylamide gel electrophoresis
9.3 Hz, J5Ϫ6 ϭ 5.4 Hz, 1 H, 5-H), 3.72 (dd, J2Ϫ3 ϭ 3.2 Hz, J3Ϫ4
ϭ
was performed according to Laemmli[ and proteins were visual-
16]
9.3 Hz, 1 H, 3-H), 3.81 (t, 1 H, 4-H), 3.83 (dd, J1Ϫ2 ϭ 1.3 Hz, 1 H,
2-H), 4.00Ϫ4.10 (m, 4 H, 2 ϫ CH CH OP), 4.24 (m, 1 H, 6-H),
.62 (d, 1 H, 1-H). Ϫ C NMR (CDCl ): δ ϭ 16.7 (d, J ϭ 1.8 Hz,
CH CH OP), 16.8 (d, J ϭ 2.2 Hz, CH CH OP), 29.9 (d, J ϭ
40.8 Hz, C-7), 55.4 (OCH ), 62.3 (d, J ϭ 6.4 Hz, CH CH OP),
2.6 (d, J ϭ 6.2 Hz, CH CH OP), 69.2 (d, J ϭ 4.8 Hz, C-6), 70.4
ized using a silver-staining kit (Biorad).
3
2
1
3
4
3
Methyl
7-Deoxy-7-diethyloxyphosphinyl-2,3,4-tri-O-benzyl-(
D,L)-
3
2
3
2
glycero-α-D-manno-heptopyranoside (2a,b): In a two-necked round-
1
6
3
3
2
bottomed flask, oxalyl chloride (0.41 mL, 4.74 mmol) was dis-
solved in THF (5.2 mL) and then DMSO (0.73 mL, 10.34 mmol)
was added dropwise at Ϫ60 °C. The mixture was stirred for 15 min
and then a solution of methyl 2,3,4-tri-O-benzyl-α--mannopyr-
anoside (1) (2.0 g, 4.31 mmol) in THF (4.3 mL) was added drop-
wise by means of a cannula, also at Ϫ60 °C. The resulting mixture
3
2
(
1
C-2), 70.8 (C-4), 71.9 (C-3), 73.5 (d, J ϭ 15.1 Hz, C-5), 101.5 (C-
). Ϫ P NMR (CDCl ): δ ϭ 32.54. Ϫ MS (FAB ): m/z (%)
3
31
ϩ
ϩ
ϩ
(
25 9
NBA) ϭ 367 (90) [M ϩ Na] , 345 (12) [M ϩ H] . Ϫ C12H O P
(
344.3): calcd. C 41.86, H 7.32; found C 41.78, H 7.35.
was stirred for
1.55 mmol) was added dropwise at Ϫ60 °C and the mixture was
stirred at room temp. for 1 h. It was then concentrated in vacuo,
diluted with CH Cl , and the organic phase was washed with water,
dried (Na SO ), filtered, and concentrated in vacuo. The crude al-
2
a further 15 min. Then, iPr NEt (3.7 mL,
2
Methyl 7-Deoxy-7-dihydroxyphosphinyl-
topyranoside Disodium Salt (4a): To a solution of 3a (0.088 g,
0.256 mmol) in anhydrous CH CN (3.2 mL) under nitrogen atmo-
sphere was added pyridine (0.21 mL, 2.56 mmol) and Me SiBr
L-glycero-α-D-manno-hep-
2
2
3
2
4
3
dehyde thus obtained was used for the next reaction without fur-
ther purification.
In a two-necked round-bottomed flask, 1.6  butyllithium in hex-
ane (2.15 mL, 3.46 mmol) was diluted with anhydrous THF
(0.33 mL, 2.56 mmol). After stirring at room temperature for 2 h,
distilled water (5 mL) and pyridine (0.21 mL, 2.56 mmol) were ad-
ded at 0 °C. The organic layer was concentrated and then distilled
water (75 mL) and cation-exchange resin (35 g) were added. After
stirring at room temperature for 24 h, the resin was filtered off and
(7.8 mL). The solution was cooled to Ϫ78 °C, whereupon methyldi-
ethylphosphonate (0.5 mL, 3.46 mmol) was added. The resulting washed several times with water. The filtrate was concentrated in
mixture was stirred at Ϫ78 °C for 30 min and then a solution of the
aldehyde (1.0 g, 2.16 mmol) in anhydrous THF (9 mL) was added
dropwise by means of a cannula. The reaction was subsequently
vacuo and the residue was purified by reversed-phase chromato-
2
0
graphy (RP-18/H
(c ϭ 1.00, MeOH). Ϫ H NMR (D
7,7Ј-H), 3.50 (s, 3 H, OCH ), 3.51Ϫ4.07 (m, 4 H, 2,3,4,5-H),
Cl 4.30Ϫ4.47 (m, 1 H, 6-H), 4.88 (d, J1Ϫ2 ϭ 1.4 Hz, 1 H, 1-H). Ϫ
), filtered, and con- NMR (D O): δ ϭ 32.7 (d, J ϭ 132.0 Hz, C-7), 55.1 (OCH ), 65.2
2
O) to afford 4a (0.055 g, 65%). Ϫ [α]
D
ϭ Ϫ6.0
1
2
O): δ ϭ 1.90Ϫ2.25 (m, 2 H,
quenched by the addition of 1  NH
CH Cl was added. The organic layer was washed with 1  NH
solution then twice with water, dried (Na SO
4
Cl solution (10 mL) and then
3
1
3
2
2
4
C
2
4
2
3
centrated in vacuo. The residue was purified by silica gel column
chromatography (petroleum ether/AcOEt, 7:3) to afford com-
(d, J ϭ 4.3 Hz, C-6), 66.8, 67.6, 70.4 (C-2,3,4), 74.4 (d, J ϭ 11.3 Hz,
3
1
Ϫ
C-5), 101.5 (C-1). Ϫ P NMR (D
m/z (%) (GT) ϭ 287 (95) [M Ϫ 2 Na ϩ H] . Ϫ C H15Na O P
8 2 9
2
O): δ ϭ 23.57. Ϫ MS (FAB ):
3
1
Ϫ
pounds 2a,b (1.06 g, 40%) as a mixture of diastereoisomers. Ϫ
NMR (CDCl ): δ ϭ 31.14 (45%), 32.46 (55%) [2 s, PO(OEt) ].
P
3
2
(332.1): calcd. C 28.93, H 4.55; found C 28.68, H 4.65.
3436
Eur. J. Org. Chem. 2000, 3433Ϫ3437

Synthesis and Biological Evaluation of Two Mannose 6-Phosphate Analogs
FULL PAPER
[
[
5]
6]
J. X. Kang, Y. Li, A. Leaf, Proc. Natl. Acad. Sci. USA 1998,
Methyl 7-Deoxy-7-dihydroxyphosphinyl-
topyranoside Disodium Salt (4b): Using the same procedure as for
D-glycero-α-D-manno-hep-
9
5, 13671Ϫ13676.
B. Schmidt, C. Kiecke-Siemsen, A. Waheed, T. Braulke, K. von
Figura, J. Biol. Chem. 1995, 270, 14975Ϫ14982; P. G. Marron-
Terada, M. A. Brzycki-Wessel, N. M. Dahms, J. Biol. Chem.
2
0
4
1
a, compound 4b was obtained in 65% yield. Ϫ [α]
.02, MeOH). Ϫ H NMR (D
2
D
ϭ ϩ8.0 (c ϭ
O): δ ϭ 1.85Ϫ2.20 (m, 2 H, 7,7Ј-
3
), 3.66Ϫ4.09 (m, 4 H, 2,3,4,5-H), 4.38Ϫ4.42
1
1
998, 273, 22358Ϫ22366.
H), 3.49 (s, 3 H, OCH
m, 6-H), 4.89 (d, J1Ϫ2 ϭ 1.4 Hz, 1 H, 1-H). Ϫ 1 C NMR (D
2
O):
[
7]
3
J. X. Kang, J. Bell, A. Leaf, R. L. Beard, R. A. S. Chandrar-
atna, Proc. Natl. Acad. Sci. USA 1998, 95, 13687Ϫ13691 and
references therein.
(
δ ϭ 29.4 (d, J ϭ 131.6 Hz, C-7), 55.1 (OCH ), 67.2 (d, J ϭ 4.2 Hz,
C-6), 67.6, 70.1, 71.0 (C-2,3,4), 74.7 (d, J ϭ 13.3 Hz, C-5), 101.2
3
[
[
8]
9]
C. Vidil, A. Mor e` re, M. Garcia, V. Barragan, B. Hamdaoui, H.
Rochefort, J.-L. Montero, Eur. J. Org. Chem. 1999, 2, 447Ϫ450.
H. B. Bor e´ n, K. Eklind, P. J. Garegg, B. Lindberg, A. Pilotti,
Acta Chem. Scand. 1972, 26, 4143Ϫ4146.
K. Omura, D. Swern, Tetrahedron 1978, 34, 1651Ϫ1660; A.
J. Mancuso, S. L. Huang, D. Swern, J. Org. Chem. 1978, 43,
Ϫ
(
(
C-1). Ϫ 31P NMR (D
GT) ϭ 287 (90) [M Ϫ 2 Na ϩ H] . Ϫ C
2
O): δ ϭ 25.18. Ϫ MS (FAB ): m/z (%)
Ϫ
8 2 9
H15Na O P (332.1):
calcd. C 28.93, H 4.55; found C 28.57, H 4.62.
[10]
2
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