Synthesis of β-D-Galp-(1 →4)-α-D-Manp methanephosphonate, a substrate analogue for the elongating α-D-mannosyl phosphate transferase in the Leishmania

Article abstract of DOI:10.1016/S0040-4039(01)00961-3

An isosteric C-glycoside phosphono analogue of dec-9-enyl β-D-galactopyranosyl-(1 →4)-α-D-mannopyranosyl phosphate was synthesised and showed high biological activity in the Leishmania MPT assay. A one-step Horner-Emmons/Michael reaction was developed for the stereoselective preparation of α-D-mannosyl methanephosphonate derivatives.

Full text of DOI:10.1016/S0040-4039(01)00961-3

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 5305–5308
Synthesis of b-
D
-Galp-(1“4)-a-
D
-Manp methanephosphonate, a
substrate analogue for the elongating a-
D
-mannosyl phosphate
transferase in the Leishmania
Vladimir S. Borodkin,a Michael A. J. Fergusonb and Andrei V. Nikolaeva,*
aSchool of Life Sciences, Division of Biological Chemistry and Molecular Microbiology, Carnelley Building,
University of Dundee, Dundee DD1 4HN, UK
bSchool of Life Sciences, Division of Biological Chemistry and Molecular Microbiology, Wellcome Trust Building,
University of Dundee, Dundee DD1 4HN, UK
Received 24 April 2001; accepted 1 June 2001
Abstract—An isosteric C-glycoside phosphono analogue of dec-9-enyl b-
D
-galactopyranosyl-(1“4)-a-
D-mannopyranosyl phos-
phate was synthesised and showed high biological activity in the Leishmania MPT assay. A one-step Horner–Emmons/Michael
reaction was developed for the stereoselective preparation of a-
D
-mannosyl methanephosphonate derivatives. © 2001 Elsevier
Science Ltd. All rights reserved.
Recent reports from this laboratory disclosed the syn-
nate derivative as the key problem. The rest of the
synthetic plan comprised 4-O-glycosylation of the
above mannosyl methanephosphonate with a suitable
galactosyl donor and formation of phosphonic acid
dec-9-enyl ester.
thesis and biological evaluation of b-
D-galactopyran-
osyl-(1“4)-a- -mannopyranosyl phosphate 1 and a
D
number of its structural analogues.1,2 The parent com-
pound was shown to be an efficient exogenous acceptor
substrate for elongating a-mannosyl phosphate trans-
ferase (MPT) in the three species of Leishmania, while
biochemical assays performed with structural analogues
of 1 helped to define the true acceptor substrate specifi-
city of the enzyme.3 As the next step of the project,
which is targeting the preparation of selective bisub-
strate inhibitors4 of the MPT, a demand for hydrolyti-
cally stable analogues5 of compound 1 has been
recognised. Here we report the chemical synthesis of the
isosteric C-glycoside phosphono analogue 2, which
then was tested as an acceptor substrate for the MPT.
Although syntheses of phosphono analogues of natural
glycosyl phosphates are well documented,6 no reliable
approach to a-
derivatives has been reported.7 The closest analogy
-rhamnosyl
D-mannosyl methanephosphonate
available was the preparation of diethyl (a-
L
methanephosphonate) via one-step Horner–Emmons/
Michael reaction of tetraethyl methylenediphosphonate
sodium with 2,3,4-tri-O-benzyl-a,b-
hands, however, the reaction of 2,3,4,6-tetra-O-benzyl-
-mannose 3 with tetramethyl methylenediphosphonate
L
-rhamnose.8 In our
D
4 and NaH yielded the conjugated vinylphosphonate 5
exclusively (Scheme 1).9 Other combinations of solvents
and bases provided the same product, except LiHMDS
HO
O
HO
HO
O
HO
HO
HO
O
OH
in THF at 55°C: this time the desired a-D-mannosyl
X
O
O
methanephosphonate derivative 610 was isolated in 33%
yield accompanied by the isomerised starting material 7
(50%).
P
-
+HNEt3
O
1 X = O
2 X = CH2
A retrosynthetic analysis exposed the preparation of a
selectively protected a- -mannosyl methanephospho-
To exclude the unwanted elimination of the 3-benzyl-
oxy group, 2,3-O-isopropylidene-D-mannose derivatives
were tested in the above Horner–Emmons/Michael
reaction. To this end, the allyl mannoside 9 prepared by
BF3·Et2O mediated mannosylation of allyl alcohol with
D
Keywords: carbohydrates; phosphonic acids and derivatives.
* Corresponding author.
D
-mannose penta-acetate 8 was effectively processed
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00961-3

5306
V. S. Borodkin et al. / Tetrahedron Letters 42 (2001) 5305–5308
into differentially protected hemiacetals 11 and 12 via
The glycosylation reaction was the next step we
addressed. To ensure selective handling of the 6-OH
group in the galactosyl residue required for further
functionalisation at this position, judiciously protected
galactosyl donors were needed. These were prepared by
the acetolysis11 and further protective group modifica-
the common diisopropylidenated precursor 10 (Scheme
1).
Treatment of the bis-isopropylidene hemiacetal 11 with
4 and LiHMDS in THF at 55°C produced a mixture of
a- and b- -mannosyl methanephosphonates 14 and 13,
D
tion of methyl tetra-O-benzyl-b- -galactopyranoside 17
D
respectively, in 80% yield with the b-anomer 1310 pre-
dominating (a:b=1:2.5). Similar reaction of the
monoisopropylidene derivative 12 gave a separable
mixture of the methanephosphonates 15 and 16 with a
prevalence of the a-anomer 1510 (a:b=1.7:1). No elimi-
nation product was detected in either case. Base screen-
ing led to an improvement of the 15/16 ratio up to the
very acceptable 10:1 using t-BuOK in THF. The
which provided an anomeric mixture of 1,6-diacetates
18, which were further transformed into galactosyl bro-
mide 19 and trichloroacetimidate 20 (Scheme 2).
Two differently protected glycosyl acceptors 21 and 22
were synthesised from the methanephosphonate 15 in a
straightforward manner (Scheme 3). Selective benzoyla-
tion of the primary hydroxyl group was successfully
accomplished with benzoyl cyanide in both cases. The
presence of the 2,3-O-isopropylidene group in the gly-
cosyl acceptor 22 was found to influence dramatically
the stereoselectivity of the glycosylation reaction.
Indeed, only the required b-linked disaccharide 25 (75–
78% yield, J1,2=8.0 Hz) was formed in the reaction of
compound 22 with either galactosyl bromide 19 or
trichloroacetimidate 20. In contrast, an inseparable
desired a- -mannosyl methanephosphonate 15 was iso-
D
lated in 85% yield. For the 14/13 ratio, the figure did
not exceed 2.8:1 with the same reagent. These experi-
ments demonstrated that either of the
D-mannosyl
methanephosphonate anomers could be obtained
stereoselectively from -mannose hemiacetal deriva-
D
tives. The stereo outcome depends on the protective
group pattern and proper choice of the reaction
conditions.
OBn
BnO
O
i or ii or iii
BnO
BnO
P(OMe)2
BnO BnO
BnO
BnO
O
O
O
5
HO
(MeO)2P
P(OMe)2
OH
OBn
O
BnO
BnO
BnO
3
4
O
iv
BnO
BnO
O
BnO
7
OH
P(OMe)2
6
O
O
vii
ix
O
O
O
O
O
O
O
O
O
P(OMe)2
OH
O
AcO
AcO
O
vi
O
O
11
13
+
14 (α-anomer)
AcO
AcO
O
O
OR
OAll
BnO
BnO
O
BnO
BnO
O
viii
ix
O
O
10
8 R = Ac
9 R = All
v
O
O
O
OH
P(OMe)2
16 (β-anomer)
12
15
+
Scheme 1. Reagents and conditions: (i) NaH, diglyme or THF, 12 h; (ii) KHMDS, THF, 20 h; (iii) KOBu-t, THF, 2 h; (iv)
LiHMDS, THF, 55°C, 4 h; (v) AllOH, BF3·Et2O, 18 h, 80%; (vi) (a) MeOH, MeONa cat., 94%; (b) Me2CO, Me2C(OMe)2,
TsOH·H2O cat., 90%; (vii) KOBu-t, DMSO, 60°C, 1 h, then Hg(OAc)2, THF–H2O, 20 min, 97%; (viii) (a) AcOH–H2O 8:2, 12
h, 0°C, 78%; (b) NaH, DMF, BnBr, 2 h, 92%; (c) KOBu-t, DMSO, 60°C, 1 h, then Hg(OAc)2, THF–H2O, 20 min, 95%; (ix) 4,
base, THF; see text for details.
OAc
OBn
O
BzO
BzO
BnO
BnO
OAc
BzO
BzO
O
i
O
ii
OMe
BzO
BnO
OAc
BzO
X
17
18
19 X = Br
20 X = OC(NH)CCl3
iii
Scheme 2. Reagents and conditions: (i) (a) Ac2O–AcOH, H2SO4, 18 h, 80%; (b) H2/Pd(OH)2-C, MeOH; (c) BzCl, pyridine, 80%;
(ii) (a) HBr/AcOH, Ac2O, DCM, 85%; (iii) (a) Ag2CO3, acetone–water; (b) Cl3CCN, DBU, DCM, 85%.

V. S. Borodkin et al. / Tetrahedron Letters 42 (2001) 5305–5308
5307
BzO
HO
BzO
BzO
O
BzO
BzO
OBz
O
iii or iv
O
i
BzO
BzO
O
O
BzO
O
OAc
P(OMe)2
P(OMe)2
BnO
BnO
O
O
21
23 + 24
O
O
P(OMe)2
BzO
BzO
HO
O
RO
15
O
OBz
iii or iv
O
O
ii
BzO
BzO
O
R'O
O
O
O
OAc
P(OMe)2
P(OMe)2
22
25 R, R' = C(CH3)2
23 R = R' = Bz
v
RO
RO
RO
O
vi
RO
RO
O
RO
23
O
OR'
O
O
P
-
+HNEt3
O
26 R = Bz, R' = Ac
2 R = R' = H
vii
Scheme 3. Reagents and conditions: (i) (a) AcOH–H2O 8:2, 60°C, 3 h; (b) BzCl, pyridine, 78% for a, b; (c) H2/Pd(OH)2-C, MeOH,
95%; (d) BzCN, Et3N, MeCN–DCM, −30°C, 30 min, 78%; (ii) (a) H2/Pd(OH)2-C, MeOH; (b) BzCN, Et3N, MeCN–DCM, −30°C,
,
30 min, 73%; (iii) 19, AgOTf, sym-collidine, DCM, −30°C, 40 min, 80% for 19+21, 75% for 19+22; (iv) 20, TMSOTf, 4 A MS,
DCM, −30°C, 2 h, 86% for 20+21, 78% for 20+22; (v) (a) C5H5N·HClO4, CH3NO2–MeOH, 65°C, 8 h; (b) BzCl, DMAP, pyridine,
80%; (vi) (a) TMSBr, sym-collidine, DCM–CH3CN; (b) dec-9-en-1-ol, DCC, pyridine, 36 h, 58%; (vii) MeOH, MeONa cat.,
quantitative.
mixture of a- and b-anomers 24 and 23, respectively
(a:b=1:2 in each case) was isolated from the reaction
of 2,3,4-tribenzoate 21 with the same glycosyl donors.
Finally, the isopropylidene group in compound 25 was
replaced with benzoyl protection to yield the disaccha-
ride methanephosphonate 23.
1743; (b) Ross, A. J.; Higson, A. P.; Ferguson, M. A. J.;
Nikolaev, A. V. Tetrahedron Lett. 1999, 40, 6695.
2. Ross, A. J.; Ivanova, I. A.; Ferguson, M. A. J.; Niko-
laev, A. V. J. Chem. Soc., Perkin Trans. 1 2001, 72–81.
3. Routier, F. H.; Higson, A. P.; Ivanova, I. A.; Ross, A.
J.; Tsvetkov, Y. E.; Yashunsky, D. V.; Bates, P. A.;
Nikolaev, A. V.; Ferguson, M. A. J. Biochemistry 2000,
39, 8017.
4. (a) Sears, P.; Wong, C.-H. J. Chem. Soc., Chem. Com-
mun. 1998, 1161 and references cited therein; (b) Palcic,
M.; Heerze, L.; Srivastara, O. P.; Hindsgaul, O. J. Biol.
Chem. 1989, 264, 17174.
Demethylation of compound 23 with TMSBr in the
presence of sym-collidine as an acid scavenger12
afforded the corresponding phosphonic acid derivative,
which was then coupled with dec-9-enol in the presence
of DCC13 to give the protected phosphonic mono-ester
26 (lP 16.7) in a reliable 55–60% yield (Scheme 3).
Deacylation of 26 with catalytic sodium methoxide in
MeOH provided the targeted disaccharide methane-
phosphonate dec-9-enyl ester 214 quantitatively. This
compound was tested in a biochemical assay3 and was
shown to be an effective substrate acceptor for the
MPT in Leishmania donovani: compound 2 revealed
84( 3)% acceptor substrate activity compared with the
disaccharide phosphate 1.
5. Engel, R. Chem. Rev. 1977, 77, 349.
6. (a) Casero, F.; Cipolla, L.; Lay, L.; Nicotra, F.; Panza,
L.; Russo, G. J. Org. Chem. 1996, 61, 3428; (b) Frische,
K.; Schmidt, R. R. Liebigs Ann. Chem. 1994, 297; (c)
Qiao, L.; Vederas, J. C. J. Org. Chem. 1993, 58, 3480;
(d) Maryanoff, B. E.; Nortey, S. O.; Inners, R. R.;
Campbell, S. A.; Reitz, A. B. Carbohydr. Res. 1987, 171,
259; (e) Meyer, Jr., R. B.; Stone, T. E.; Jesthi, P. K. J.
Med. Chem. 1984, 27, 1095; (f) McClard, R. W. Tetra-
hedron Lett. 1983, 24, 2631; (g) Chmielewski, M.;
BeMiller, J. N.; Cerretti, D. P. Carbohydr. Res. 1981,
97, C1.
Acknowledgements
7. (a) Nicotra, F.; Perego, R.; Ronchetti, F.; Russo, G.;
Toma, L. Carbohydr. Res. 1984, 131, 180; (b) Nicotra,
F.; Panza, L.; Ronchetti, F.; Russo, G.; Toma, L. Car-
bohydr. Res. 1987, 171, 49; (c) Boschetti, A.; Nicotra,
F.; Panza, L.; Russo, G. J. Org. Chem. 1988, 53, 4181.
8. Cippola, L.; La Ferla, B.; Panza, L.; Nicotra, F. J.
Carbohydr. Chem. 1998, 17, 1003.
The Wellcome Trust International Grant supported this
work and V.S.B. The research of A.V.N. was supported
by an International Research Scholar’s award from the
Howard Hughes Medical Institute.
9. All new compounds showed satisfactory spectral and
analytical data.
References
10. The anomeric configurations of compounds 6, 14, 15
1. (a) Ivanova, I. A.; Ross, A. J.; Ferguson, M. A. J.;
Nikolaev, A. V. J. Chem. Soc., Perkin Trans. 1 1999,
(a-
D
-anomers) and 13, 16 (b-D-anomers) were deduced

5308
V. S. Borodkin et al. / Tetrahedron Letters 42 (2001) 5305–5308
28: 1H NMR (300 MHz, C6D6): l 2.05 (dt, 1H, 15,
from the NOESY spectra of their perbenzoylated deriva-
J1*a,1=4.5, J1*a,1*b=J1*a,P=15.0, H-1*a), 2.30 (ddd, 1H,
tives 27 and 28, respectively (characteristic NOE contacts
J1*b,1=9.0, J1*b,P=17.0, H-1*b), 3.47 (d, 3H, JH,P=11.0,
are shown by the curved arrows at the diagram below).
OCH3), 3.60 (d, 3H, JH,P=11.0, OCH3), 3.80 (ddd, 1H,
4,5=10.0, H-5), 4.40 (dd, 1H, J5,6a=4.0, J6a,6b=12.0,
H-6a), 4.50 (ddd, 1H, J1,P=9.0, H-1), 4.96 (dd, 1H,
5,6b=2.3, H-6b), 5.92 (dd, 1H, J2,3=3.0, H-3), 6.15 (d,
1H, H-2), 6.55 (t, 1H, J3,4=J4,5=10.0, H-4), 7.30–8.30
(m, 20H, aromatic); 13C NMR (75 MHz, CDCl3) l 27.5
(d, JC,P=143.7, C-1*), 52.2 (d, JC,P=6.0, OCH3), 52.8 (d,
6
3
6
BzO
BzO
BzO
J
BzO
4
4
O
H
O
5
5
BzO
BzO
O
BzO
BzO
1*
3
1
2
2
O
P(OMe)2
1
1*
J
H
H
P(OMe)2
H
H
H
H
27
28
A mixture of 13 and 14 was converted to compounds 27
and 28 in two steps: (a) AcOH–H2O, 60°C; (b) BzCl,
pyridine, DMAP; followed by separation on silica gel.
Compound 27 was also prepared from 15 in three steps:
(a) H2, Pd(OH)2/C, MeOH; (b) Dowex-50 (H+), MeOH;
(c) BzCl, pyridine, DMAP, and from 6 in two steps: (a)
H2, Pd(OH)2/C, MeOH; (b) BzCl, pyridine, DMAP.
Compound 28 was obtained from 16 as described for the
preparation of 27 from 15.
J
C,P=6.0, OCH3), 62.9 (C-6), 66.4 (C-4), 70.7 (d, JC,P=
11.1, C-2), 72.7 (C-1), 72.9 (C-3), 76.3 (C-5); 31P NMR
(121 MHz, CDCl3): l 29.0; [h]D −105.6 (c 1.02, CHCl3).
11. Eby, R.; Sondheimer, S.; Schuerch, C. Carbohydr. Res.
1979, 73, 273.
12. Biller, S. A.; Forster, C. Tetrahedron 1990, 46, 6645.
13. Robl, J. A.; Duncan, L. A.; Pluscec, J.; Karanewsky, D.
S.; Gordon, E. M.; Ciosek, Jr., C. P.; Rich, L. C.;
Dehmel, V. C.; Slusarchyk, D. A.; Harrity, T. W.;
Obrien, K. A. J. Med. Chem. 1991, 34, 2804.
27: 1H NMR (300 MHz, C6D6): l 2.02 (ddd, 1H,
1*a,1*b=15.3, J1*a,1=5.5, J1*a,P=15.3, H-1*a), 2.30 (ddd,
1H, J1*b,1=9.7, J1*b,P=18.0, H-1*b), 3.57 (d, 6H, JH,P
11.0, 2×OCH3), 4.48 (ddd, 1H, H-5), 4.70 (dd, 1H, J5,6a
14. 2: 13C NMR (75 MHz, D2O): l 8.5 (Et3N), 25.3
(CCH2C), 28.5 (CCH2C), 28.7 (CCH2C), 28.8 (CCH2C),
28.9 (CCH2C), 29.0 (d, JC,P=142.3, Man-1*), 30.5 (d,
J
=
=
3.7, J6a,6b=12.0, H-6a), 4.85 (ddd, 1H, J1,P=9.0, H-1),
5.05 (dd, 1H, J5,6b=2.5, H-6b), 6.12 (br, 1H, H-2), 6.15
(dd, 1H, J2,3=3.0, H-3), 6.62 (t, 1H, J3,4=J4,5=9.0, H-4),
7.30–8.30 (m, 20H, aromatic); 13C NMR (75 MHz,
J
C,P=6.5, OCH2CH2), 33.5 (CCH2C), 46.9 (Et3N), 60.7
(Man-6), 61.4 (Gal-6), 65.1 (br, OCH2CH2), 69.0 (Gal-4),
69.4 (Man-3), 71.2 (2C, Man-2, br and Gal-2), 72.8
(Gal-3), 73.0 (Man-5), 74.4 (Man-1), 75.7 (Gal-5), 77.3
(Man-4), 103.4 (Gal-1), 114.3 (CHꢀCH2), 140.7
(CHꢀCH2); 31P NMR (121 MHz, D2O) l 22.3; ES-MS
(−) data: m/z 557.03 (100%, [M−Et3N−H]−) (expected
m/z 557.24, C29H58NO13P requires M, 659.36); [h]D +12.8
(c 1.0, MeOH).
CDCl3): l 26.5 (d, JC,P=143.8, C-1*), 52.9 (d, 2C, JC,P
6.5, 2×OCH3), 62.6 (C-6), 67.3 (C-4), 69.5 (C-3), 70.6 (d,
C,P=3.9, C-1), 71.1 (C-5), 71.2 (d, JC,P=15.6, C-2); 31P
=
J
NMR (121 MHz, CDCl3): l 28.0; [a]D −73.8 (c 1.22,
CHCl3).
.