Analogues of D-glucosaminylphosphatidylinositol: Synthesis of the glycosyl donors

Article abstract of DOI:10.1016/S0040-4039(00)01900-6

Appropriately protected deoxy and other analogues of 2-azido-2-deoxy-D-glucopyranosyl fluoride have been synthesised preparatory to inclusion into analogues of the D-glucosaminylphosphatidylinositol 1.

Full text of DOI:10.1016/S0040-4039(00)01900-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 117–119
Analogues of
D
-glucosaminylphosphatidylinositol: synthesis of the
glycosyl donors
Alexander P. Dix,a Charles N. Borissow,a Michael A. J. Fergusonb and John S. Brimacombea,*
aDepartment of Chemistry, University of Dundee, Dundee DD1 4HN, UK
bDepartment of Biochemistry, University of Dundee, Dundee DD1 4HN, UK
Received 25 August 2000; accepted 26 October 2000
Abstract—Appropriately protected deoxy and other analogues of 2-azido-2-deoxy-
sised preparatory to inclusion into analogues of the
reserved.
D
-glucopyranosyl fluoride have been synthe-
D-glucosaminylphosphatidylinositol 1. © 2000 Elsevier Science Ltd. All rights
The essential features of glycosylphosphatidylinositol
(GPI) biosynthesis in the bloodstream form of Try-
panosoma brucei (the causative agent of African sleep-
ing sickness) have been established1 and start with the
transfer of N-acetylglucosamine (GlcNAc) to phos-
completed syntheses and, briefly, the results of the
enzymic studies.
phatidylinositol (PI) to form a-
D
-GlcpNAc-(1“6)-PI,
-GlcpN-
which is then de-N-acetylated to produce a-
D
(1“6)-PI. This step, catalysed by a de-N-acetylase, is a
prerequisite for further processing which, in T. brucei,
entails the addition of the first of three
residues to form a- -Manp-(1“4)-a- -GlcpN-(1“6)-
PI. The mannosyltransferase (MT-1) catalysing this
step has a requirement for dolichol phosphate -man-
D-mannose
D
D
D
nose. Further processing is required1 before the fully
assembled GPI precursor is transferred en bloc to newly
synthesised protein and thereafter to the plasma mem-
brane where it forms part of the dense protective coat-
ing of the trypanosome. The substrate requirements of
the de-N-acetylase and MT-1 of T. brucei have been
probed2 extensively in our laboratories utilising sub-
strate analogues in which changes and deletions have
The synthetic strategy is dictated by the need to locate
a non-participating azido group (a masked amino
group) at C-2 of the glycosyl donor, invariably the
glycosyl fluoride, to promote the formation of the
requisite a-glycosidic linkage in subsequent coupling
reactions.
been effected in the various components of the
D-glu-
cosaminylphosphatidylinositol 1.3 In furtherance of
these studies, 3%-, 4%- and 6%-deoxy and other analogues
of 1 were required to be tested as substrate analogues/
inhibitors of these enzymes. This Letter outlines the
synthesis of the various glycosyl donors required for
Either of two routes provided the 2-azido-2,3-dideoxy-
glycosyl fluoride 5.4 An azide displacement on the
tosylate 3, prepared from the known alcohol 2,5 fur-
nished the 2-azido compound 4, which was transformed
straightforwardly into the glycosyl fluoride 5 (Scheme
1). Alternatively, a Michael reaction of the enone 66
with azide ion resulted, after equilibration, in a 2:1
mixture of the azido ketones 7 and 8, respectively
(Scheme 2). Reduction of the mixture of 7 and 8 with
sodium borohydride gave, after careful radial-band
coupling with an appropriately protected
D-myo-inosi-
tol acceptor,3 whilst the following Letter describes the
Keywords: glycosylphosphatidylinositol (GPI) membrane anchors;
GPI analogues; GPI biosynthesis.
* Corresponding author. Fax: (44) 1382-345 517; e-mail:
j.s.brimacombe@dundee.ac.uk
chromatography,7 ethyl 2-azido-2,3-dideoxy-a-
hexopyranoside 96 as one of the products. Thereafter,
D-ribo-
0040-4039/01/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)01900-6

118
A. P. Dix et al. / Tetrahedron Letters 42 (2001) 117–119
Scheme 1. Reagents: i, TsCl, pyridine; ii, NaN3, 18-crown-6-ether, DMF, 60°C; iii, 70% AcOH; iv, BnBr, NaH, DMF; v, 1 M
HCl, 80% AcOH; vi, DAST, 1,2-dichloroethane
Scheme 2. Reagents: i, NaN3, AcOH, H2O; ii, (a) NaBH4, MeOH; (b) radial-band chromatography; iii, BnBr, NaH, DMF; iv,
1 M HCl, 80% AcOH; v, DAST, 1,2-dichloroethane
Scheme 3. Reagents: i, Tf2O, pyridine; ii, NaN3, DMF, 70°C; iii, 90% CF3CO2H; iv, BnBr, NaH, DMF; v, 1 M HCl, 80% AcOH;
vi, DAST, 1,2-dichloroethane
benzylation, acid hydrolysis and treatment of the re-
leased hemiacetal with DAST produced the glycosyl
fluoride 5.
compound, which is available in a few steps from
D
-glucal 16, was converted into the imidazolide 18 and
thence, by radical-induced deoxygenation,12 into the
4-deoxy derivative 19.13 Gratifyingly, there was no sig-
nificant reduction of the reducible azido group14 in this
step. Subsequent acetolysis provided the diacetate 20
(a:bꢀ3:1), which was transformed, via the hemiacetal
21, into the glycosyl fluoride 22. This approach also
provided the 4-O-methyl analogue 24 by way of the
methylated derivative 23 obtained from 17.
Our approach to the 2-azido-2,6-dideoxyglycosyl
fluoride 154 followed a literature procedure8 from the
3,4-diacetal 10 through to the 6-deoxy analogue 11,
which, in turn, was converted into the triflate 12
(Scheme 3). Despite the presence of the a-glycosidic
substituent,9 the triflate 12 reacted with azide ion in hot
DMF to give the crystalline 2-azido compound 134,10 in
58% yield (over the two steps from 11). Deacetalation
then provided the 3,4-diol 14, which was transformed
into the glycosyl fluoride 15 without incident.
Acknowledgements
The 1,6-anhydro compound 17,11 with the 2-azido
group already installed, provided access to the 2-azido-
2,4-dideoxyglycosyl fluoride 224 (Scheme 4). This key
We thank the BBSRC for research studentships (to
A.P.D. and C.N.B.) and the Wellcome Trust for addi-
tional funding.

A. P. Dix et al. / Tetrahedron Letters 42 (2001) 117–119
119
Scheme 4. Reagents: i, 1,1-Thiocarbonyldiimidazole, toluene; ii, Bu3SnH, AIBN, benzene, 80°C; iii, Ac2O, CF3CO2H; iv, Me2NH,
MeCN; v, DAST, 1,2-dichloroethane; vi, MeI, NaH, DMF
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