Synthesis of UDP-GalNAc analogues as probes for the study of polypeptide-α-GalNAc-transferases. Part 2

Article abstract of DOI:10.1016/j.tetlet.2004.04.074

The synthesis of four UDP-GalNAc analogues (1-4) is described. The 3-, 4- and 6-deoxygenated analogues 1-3 were obtained by way of a divergent strategy starting from a 3,6-di-O-pivaloyl GlcNAc derivative as a common precursor. Analogue 4 bearing a N-trifluoroacetamido group was prepared from the trifluoromethylated oxazoline 24 as key intermediate. These compounds were designed to probe the substrate specificity of polypeptide-α-GalNAc transferases.

Full text of DOI:10.1016/j.tetlet.2004.04.074

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 4433–4436
Synthesis of UDP-GalNAc analogues as probes for the study of
polypeptide-a-GalNAc-transferases. Part 2
Patricia Busca and Olivier R. Martin*
Institut de Chimie Organique et Analytique, Universitꢀe d’Orlꢀeans and CNRS UMR 6005, BP 6759, 45067 Orleans, France
Received 4 March 2004; revised 13 April 2004; accepted 14 April 2004
Abstract—The synthesis of four UDP-GalNAc analogues (1–4) is described. The 3-, 4- and 6-deoxygenated analogues 1–3 were
obtained by way of a divergent strategy starting from a 3,6-di-O-pivaloyl GlcNAc derivative as a common precursor. Analogue 4
bearing a N-trifluoroacetamido group was prepared from the trifluoromethylated oxazoline 24 as key intermediate. These com-
pounds were designed to probe the substrate specificity of polypeptide-a-GalNAc transferases.
ꢀ 2004 Published by Elsevier Ltd.
1. Introduction
no donor substrates for the transferase and only weak
competitive inhibitors. These results provided further
evidence for the very high affinity and high selectivity of
the sugar nucleotide binding site of the ppGalNAcT for
UDP-GalNAc, as indicated also by affinity chroma-
tography experiments.5
As molecular markers at the surface of cells, glycan
constituents of glycoproteins play a prominent role in
numerous important biological processes such as cell–
cell recognition or antigen–antibodies interactions. In
particular, a direct correlation between the progression
of cancer and the alteration of oligosaccharide struc-
tures N- or O-linked to proteins has been demon-
strated.1 While the comparatively more complex process
of protein N-glycosylation has been extensively studied,
little is known yet on the specific role of protein O-glyco-
sylation and the factors triggering the glycosylation
process.2
More recently, molecular modelling of the UDP-Gal-
NAc binding site, based on structural information taken
from the first X-ray crystallographic studies of retaining
glycosyl transferases,6 indicated that at least two of the
OH groups of the sugar unit are involved in substrate
binding and that the sugar nucleotide fits very tightly into
a deep binding pocket, mostly through the GalNAc
part.7 In addition, the N-acetyl group may be involved in
substrate recognition since UDP-Gal is not a substrate
for the ppGalNAc transferase T1 although another
member of this family has been shown to use UDP-Gal
as a substrate albeit very poorly.8 These findings
prompted us to further explore the donor substrate
specificity of ppGalNAc T1. Toward this goal, we syn-
thesised the three deoxygenated analogues of UDP-
GalNAc 1–3 as well as the N-trifluoroacetylated deriva-
tive 4 as probes of the sugar nucleotide–transferase
interactions. Related studies revealed for example that
the 2-, 4- and 6-deoxygenated analogues of UDP-Gal
could serve as substrate for the b-(1 fi 4)-galactosyl-
transferase,9 and that the 3-, 4- (identical to 2) and
6-deoxy derivatives of UDP-GlcNAc acted as donors in
N-acetylglucosaminyl-transferase I mediated glycosyl-
ation reactions.10 Last but not least, the N-trifluoro-
acetylated analogue of UDP-GlcNAc was shown to serve
The first step of the biosynthesis of O-glycosylated
proteins is catalysed by polypeptide-a-GalNAc-trans-
ferases (ppGalNAcTs),3 which transfer a GalNAc unit
from UDP-GalNAc to the hydroxyl group of a serine or
a threonine residue with retention of configuration.
Recently, we described the synthesis of three O-methyl-
ated UDP-GalNAc derivatives as probes for the study
of the polypeptide-a-GalNAc-transferase T1.4 Follow-
ing biological evaluation, these analogues proved to be
Keywords: Sugar nucleotides; Glycosyltransferases; Deoxy sugars.
* Corresponding author. Tel.: +33-2-3849-4581; fax: +33-2-3841-7281;
e-mail: olivier.martin@univ-orleans.fr
0040-4039/$ - see front matter ꢀ 2004 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2004.04.074

4434
P. Busca, O. R. Martin / Tetrahedron Letters 45 (2004) 4433–4436
S
OH
OH
HO
HO
HO
OH
HO
OPiv
OPiv
O
O
O
O
N
N
O
O
a
b
O
HO
O-UDP
HO
O-UDP
PivO
PivO
5
HN
O-UDP
HN
HN
HN
HN
OBn
HN
OBn
O-UDP
F3C
O
O
O
O
O
O
1
2
3
4
11
12
N
Figure 1. Analogues of UDP-GalNAc.
N
S
as a glycosyl donor for the ‘core-2’ GlcNAc transferase
and for the GlcNAcT-V transferase (Fig. 1).11
PivO
PivO
O
PivO
O
O
a
b
PivO
3
+
6
HN
OBn
HN
OBn
OPiv
OR2
PivO
R1O
O
O
O
O
HO
PivO
13
14
HN
OBn
HN
OBn
Scheme 2. (a) Im2CS, toluene, 90 ꢁC, 4 h, 11: 97%, 13: 94%; (b)
Bu3SnH, AIBN, toluene, 90%, 4 h, 12: 86%, 14: 30% (6: 50%).
O
O
5
6 R1 = Piv, R2 = H
7 R1 = H, R2 = Piv
N,N-dimethylaminopyridine to give the corresponding
thionocarbonate 8 (61%), which in turn led to the de-
sired deoxygenated compound 9 in 55% overall yield.
On the other hand, treatment of 7 with 1,10-thio-
carbonyldiimidazole nicely furnished the parent thiono-
carbamate 10 (96%), which underwent the expected
deoxygenation in 80% overall yield.
2. Synthesis of deoxygenated derivatives 1–3
Following the pathway previously developed for the
synthesis of the O-methylated analogues,4 deoxygenated
analogues 1–3 were prepared by way of a divergent
strategy starting from 3,6-di-O-pivaloyl GlcNAc deriva-
tive 5 as a common precursor. The latter compound as
well as the two key intermediates 6 and 7 were readily
obtained from GlcNAc.12 Deoxygenation was achieved
by the Barton–McCombie procedure using tributyltin
hydride and 2,20-azobis(2-methylpropionitrile).13 The
risk of pivaloyl migration under basic conditions
prompted us to consider thionocarbamates and thiono-
carbonates as intermediates, since these groups can be
introduced under essentially neutral conditions14 and
the imidazolylthiocarbonyl group has been used with
success for the deoxygenation of galactosides.15 Starting
from 7 as model compound, we compared the two
possible pathways (Scheme 1).
Hence we selected the latter conditions for further syn-
theses (Scheme 2). The 4-OH derivative 5 was success-
fully deoxygenated to give 1216 in 83% overall yield
whereas the 6-deoxygenated compound 14 was obtained
in a modest yield of 28% along with the starting alcohol
6 (50%) resulting from competitive hydrogen capture.
Radical deoxygenation at primary positions is known to
be difficult.17 In some cases it has been possible to
improve the yield by conducting the reaction at higher
temperature and adding the hydride dropwise.18
Unfortunately, in our hands the conversion never
exceeded 30%; similar results were reported in the
galactose series.19
Further elaboration to sugar-nucleotides was achieved
by the strategy outlined below (Scheme 3). Deprotection
of the anomeric position of benzyl glycosides 9, 12 and
14 was accomplished under standard hydrogenolytic
conditions in nearly quantitative yield. The resulting
pyranoses 15, 16 and 17 were phosphorylated using
dibenzyl diethyl-phosphoramidite and 1H-tetrazole as
catalyst.20 Oxidation of the intermediate phosphites
using hydrogen peroxide at )78 ꢁC afforded the corre-
sponding phosphotriesters 18–20 in yields ranging from
64 to 79%. The phosphorylation and anomeric config-
On one hand, compound 7 was reacted with phenyl
chlorothionoformate in the presence of pyridine and
OPiv
OPiv
PivO
HO
PivO
O
O
c
N
O
S
N
HN
OBn
HN
OBn
O
O
7
10
a
d
1
uration were unambiguously confirmed by H and 31P
NMR data.21 It should be noted that the di-O-acetylated
analog of 19 was reported to be too labile for purifica-
tion on silica gel.10 All three phosphotriesters 18-20
however could be purified by flash chromatography
without noticeable degradation. Debenzylation, fol-
lowed by removal of the pivaloyl groups under Zemplen
conditions, provided the parent sugar-monophosphates,
which were immediately converted into their triethyl-
ammonium salts 21, 2210 and 23 using a cationic
OPiv
PivO
OPiv
PivO
O
O
b
O
S
O
HN
OBn
HN
OBn
O
O
9
8
Scheme 1. (a) PhO-CS-Cl, DMAP, dichloromethane, pyridine, 4 h,
61%; (b) Bu3SnH, AIBN, toluene, 90 ꢁC, 3 h, 90%; (c) Im2CS, toluene,
90 ꢁC, 4 h, 96%; (d) Bu3SnH, AIBN, toluene, 90 ꢁC, 4 h, 83%.

P. Busca, O. R. Martin / Tetrahedron Letters 45 (2004) 4433–4436
4435
2 R3
2 R3
R
was obtained by ion exchange and finally, sugar nucleo-
tide 4 was prepared by the UMP-morpholidate proce-
dure (63%). Pyrophosphate bond formation was as-
signed on the basis of 31P NMR data.27
R
O
HN
O
O
a
b
9, 12, 14
R1
R1
OH
HN
O-PO(OBn)2
O
15 R1 = H, R2 = R3 = OPiv
16 R2 = H, R1 = R3 = OPiv
17 R3 = H, R1 = R2 = OPiv
18 R1 = H, R2 = R3 = OPiv
19 R2 = H, R1 = R3 = OPiv
20 R3 = H, R1 = R2 = OPiv
4. Conclusion
2 R3
2 R3
R
R
The synthesis of the 3-, 4- and 6-deoxy derivative of
UDP-GalNAc, and of its N-COCF3 analog, has been
achieved by short sequences. These analogues will be
useful for the study of the substrate specificity of
ppGalNAc transferases. Exploration of their activity as
substrate or inhibitors is currently in progress and will
be presented in due course.
O
O
c
d
R1
R1
HN
HN
O-PO3(Et3NH)2
O-UDP
O
O
21 R1 = H, R2 = R3 = OH
22 R2 = H, R1 = R3 = OH
23 R3 = H, R1 = R2 = OH
1 R1 = H, R2 = R3 = OH
2 R2 = H, R1 = R3 = OH
3 R3 = H, R1 = R2 = OH
Scheme 3. (a) H2, 10% Pd/C, EtOH, rt, 1 h, 15: 97%, 16: 99%, 17: 99%.
(b) (i) 1.5 equiv (BnO)2PNEt2, 1.5 equiv 1-H-tetrazole, THF, rt, 3 h; (ii)
3 equiv H2O2, )78 ꢁC, 1 h, 18: 79%, 19: 64%, 20: 70% (two steps). (c) (i)
H2, 10% Pd/C, EtOH, rt, 1 h; (ii) 2 equiv MeONa, MeOH, rt, over-
night; (iii) Amberliteꢂ IR-120 Et3NHþ form, 21: 92%, 22: 95%, 23:
90% (three steps). (d) 2 equiv UMP-morpholidate, 3 equiv 1H-tetra-
zole, pyridine, rt, 4 days, 1: 79%, 2: 31%, 3: 42%.
Acknowledgements
The present work was financially supported, in part, by
a grant from the CNRS (PCV program). The award of a
ꢁ
fellowship to P.B. by the ‘‘Ministere de l’Education
Nationale, de l’Enseignement Superieur et de la
ꢀ
Recherche’’ is also gratefully acknowledged.
exchange resin, in yields ranging from 90% to 95% over
three steps. Finally, UDP-GalNAc analogues 1–3 were
obtained using improved Khorana conditions.22 This
coupling step, involving uridine 50-monophospho-mor-
pholidate as the activated UMP source and 1H-tetrazole
provided the desired UDP-sugars in moderate to good
yield (not optimised). Formation of the pyrophosphate
was clearly established on the basis of 31P NMR spectra
showing two characteristic doublets.23 Compound 2 was
already reported as the 4-deoxy analog of UDP-GlcNAc
and shown to be substrate for GlcNAc transferases.10
References and notes
1. (a) Seitz, O. Chembiochem 2000, 1, 214; (b) Barchi, J. J.
Curr. Pharm. Des. 2000, 6, 485; (c) Dennis, J. W.;
Granovsky, M.; Warren, C. E. Biochim. Biophys. Acta
1999, 1473, 21; (d) Brockhausen, I. Biochim. Biophys. Acta
1999, 1473, 67; (e) Hakamori, S.; Zhang, Y. Chem. Biol.
1997, 4, 97; (f) Kim, Y. J.; Varki, A. Glycoconjugate J.
1997, 14, 569; (g) Brockhausen, I. Biochem. Soc. Trans.
1997, 25, 871; (h) Toyokuni, T.; Singhal, A. K. Chem. Soc.
Rev. 1995, 231; (i) Hakamori, S.-I. In Glycoproteins and
Disease; Montreuil, J., Vliegenthart, J., Schatcher, H.,
Eds.; Elsevier: New York, 1996; p 243; (j) Hakamori, S.
Adv. Cancer Res. 1989, 52, 257.
3. Synthesis of N-AcF3 analogue
2. (a) Dwek, R. A. Chem. Rev. 1996, 96, 683; (b) Clausen, H.;
Bennett, E. P. Glycobiology 1996, 6, 635.
Analogue 4 bearing a 2-N-trifluoroacetamido group was
prepared from the trifluoromethylated oxazoline 24 as
key intermediate (Scheme 4), of which we have already
reported the synthesis.24;25 Subsequent phosphorylation
was performed by opening 24 with dibenzyl phosphate,
the phosphate was then deprotected by hydrogenolysis
and selective O-deacetylation, was achieved by careful
treatment with guanidine.26 The triethylammonium salt
3. (a) Ten Hagen, K. G.; Tetaert, D.; Hagen, F. K.; Richet,
C.; Beres, T. M.; Gagnon, J.; Balys, M. M.; Van
Wuyckhuyse, B.; Bedi, G. S.; Degand, P.; Tabak, L. A.
J. Biol. Chem. 1999, 274, 27867; (b) Bennett, E. P.;
Hassan, H.; Mandel, U.; Hollingsworth, M. A.; Akisawa,
N.; Ikematsu, Y.; Merkx, G.; van Kessel, A. G.; Olofson,
S.; Clausen, H. J. Biol. Chem. 1999, 274, 25362; (c)
Bennett, E. P.; Hassan, H.; Mandel, U.; Mirgorodskaya,
E.; Roepstorff, P.; Burchell, J.; Taylor-Papadimitriou, J.;
Hollingsworth, M. A.; Merkx, G.; van Kessel, A. G.;
eiberg, H.; Steffsen, R.; Clausen, H. J. Biol. Chem. 1998,
273, 30472; (d) Ten Hagen, K. G.; Hagen, F. K.; Balys,
M. M.; Beres, T. M.; Van Wuyckhuyse, B.; Tabak, L. A.
J. Biol. Chem. 1998, 273, 27749; (e) Joziasse, D. H.
Glycobiology 1993, 3, 97.
OH
HO
OAc
AcO
AcO
a
O
O
HO
F3C
HN
O-UDP
O
N
O
CF3
24
4. Busca, P.; Piller, V.; Piller, F.; Martin, O. R. Bioorg. Med.
Chem. Lett. 2003, 13, 1853.
4
Scheme 4. (a) (i) 1.5 equiv HO–PO(OBn)2, dichloroethane, rt, 2 h then
reflux 10 h, 77%; (ii) 10% Pd/C, EtOH, rt, 1 h, 95%; (iii) 4 equiv gua-
nidine, MeOH, rt, 2 h; (iv) Amberliteꢂ IR-120 Et3NHþform, 95% (2
steps); (v) 2 equiv UMP-morpholidate, 3 equiv 1-H-tetrazole, pyridine,
rt, 4 days, 63%.
5. Wang, Y.; Abernethy, J. L.; Eckhardt, A. E.; Hill, R. L.
J. Biol. Chem. 1992, 267, 12709.
6. (a) Persson, K.; Ly, H. D.; Dieckelman, M.; Wakarchuk,
W. W.; Withers, S. G.; Strynadka, N. C. Nature Struct.
Biol. 2001, 8, 166; (b) Boix, E.; Zhang, Y.; Swaminathan,

4436
P. Busca, O. R. Martin / Tetrahedron Letters 45 (2004) 4433–4436
G. J.; Brew, K.; Acharya, K. R. J. Biol. Chem. 2002, 277,
(d, J2;P ¼ 7:0 Hz, C-2), 61.52 (C-6), 65.62, 68.30 (C-4,5),
69.74, 69.79 (2d, JC;P ¼ 5:5 Hz, 2 · CH2Ph), 96.38 (d,
J1;P ¼ 6:5 Hz, C-1), 127.97–128.79 (10 · CHPh), 135.19
(d, JC;P ¼ 6:5 Hz, Cq Ph), 135.37 (d, JC;P ¼ 6:0 Hz, Cq
Ph), 169.62 (CH3CO), 177.19, 177.63 (2 · tBuCO). 19
1H(CDCl3) d 1.15, 1.19 (2s, 2 · 9H, 2 · 3CH3), 1.70 (s, 3H,
CH3CO), 1.61–1.79 (m, 1H, H-4a), 1.93–2.05 (m, 1H, H-
4b), 4.01 (d, 2H, 2H-6), 4.06–4.17 (m, 1H, H-5), 4.25
28310; (c) Pedersen, L. C.; Dong, J.; Taniguchi, F.;
Kitagawa, H.; Krahn, J. M.; Pedersen, L. G.; Sugahara,
K.; Negishi, M. J. Biol. Chem. 2003, 278, 14420.
7. Duclos, S.; Da Silva, P.; Vovelle, F.; Piller, F.; Piller, V.
submitted for publication.
8. Wandall, H. H.; Hassan, H.; Mirgorodskaya, E.; Kristen-
sen, A. K.; Roepstorff, P.; Bennett, E. P.; Nielsen, P. A.;
Hollingsworth, M. A.; Burchell, J.; Taylor-Papadimitriou,
J.; Clausen, H. J. Biol. Chem. 1997, 272, 23503.
9. (a) Srivastava, G.; Hindsgaul, O.; Palcic, M. M. Carbo-
hydr. Res. 1993, 245, 137; (b) Berliner, L. J.; Robinson, R.
D. Biochemistry 1982, 21, 6340; (c) Kodama, H.; Kajihara,
Y.; Endo, T.; Hashimoto, H. Tetrahedron Lett. 1993, 34,
6419; (d) Palcic, M. M.; Hindsgaul, O. Glycobiology 1991,
1, 205.
10. Srivastava, G.; Alton, G.; Hindsgaul, O. Carbohydr. Res.
1990, 207, 259.
11. Sala, R. F.; MacKinnon, S. L.; Palcic, M. M.; Tanner,
M. E. Carbohydr. Res. 1998, 306, 127.
12. Rochepeau-Jobron, L.; Jacquinet, J.-C. Carbohydr. Res.
1998, 305, 181.
13. (a) Barton, D. H.; McCombie, S. W. J. Chem. Soc., Perkin
Trans. 1 1975, 1574; (b) Barton, D. H. R.; Subramanian,
R. J. J. Chem. Soc., Perkin Trans. 1 1977, 1718.
14. (a) Robins, M. J.; Wilson, S. J.; Hansske, F. J. Am. Chem.
Soc. 1983, 105, 4059; (b) Robins, M. J.; Wilson, S. J.
J. Am. Chem. Soc. 1981, 103, 932.
15. Lin, T.-H.; Kovac, P.; Glaudemans, C. P. J. Carbohydr.
Res. 1989, 188, 228.
16. For the synthesis of the 3,6-di-O-acetyl analog of 12 by a
different procedure, see: Arita, H.; Fukukawa, K.; Matsu-
shima, Y. Bull. Soc. Chim. Jpn. 1972, 45, 3614.
17. Hartwig, W. Tetrahedron 1983, 39, 2609.
18. Barton, D. H.; Motherwell, W. B.; Stange, A. Synthesis
1981, 743.
19. Rassmusen, J. R.; Slinger, C. J.; Kordish, R. J.; Newman-
Evans, D. D. J. Org. Chem. 1981, 46, 4843.
20. Sim, M. M.; Kondo, H.; Wong, C.-H. J. Am. Chem. Soc.
1993, 115, 2260.
(dddd, 1H, J2;1 ¼ J2;P ¼ 3:0 Hz, J2;NH ¼ 9:5 Hz, J2;3
¼
10.5 Hz, H-2), 4.98–5.16 (m, 5H, H-3, 2 · CH2Ph), 5.59
(d, 1H, NH), 5.70 (dd, 1H, J1;P ¼ 5:5 Hz, H-1), 7.2–7.5 (m,
10H, 2 · C6CH5); 13C (CDCl3) d 22.80 (CH3CO), 26.92,
27.13 (2 · 3CH3), 32.38 (C-4), 38.75, 38.80 (2 · C(CH3)3),
52.00 (d, J2;P ¼ 7:2 Hz, C-2), 64.98 (C-6), 66.84, 67.99 (C-
3,5), 69.71 (d, JC;P ¼ 5:0 Hz, CH2Ph), 69.79 (d,
JC;P ¼ 5:5 Hz, CH2Ph), 97.85 (d, J1;P ¼ 6:7 Hz, C-1),
128.06–128.80 (10 · CHPh), 135.34, 135.46 (2d,
JC;P ¼ 6:3 Hz, 2 · CqPh), 170.03 (CH3CO), 178.05, 178.51
(2 · tBuCO). 20 1H (CDCl3) d 1.12 (d, 3H, 3H-6), 1.27,
1.30 (2s, 2 · 9H, 2 · 3CH3), 1.70 (s, 3H, CH3CO), 4.15 (q,
1H, J5;6 ¼ 7:0 Hz, H-5), 4.63 (dddd, 1H, J2;P ¼ 3:0 Hz,
J2;1 ¼ 3:5 Hz, J2;NH ¼ 10:0 Hz, J2;3 ¼ 10:5 Hz, H-2), 5.00–
5.16 (m, 4H, 2 · CH2Ph), 5.19 (d, 1H, J4;3 ¼ 3:0 Hz, H-4),
5.22 (dd, 1H, H-3), 5.58 (d, 1H, NH), 5.71 (dd, 1H,
J1;P ¼ 5:5, H-1), 7.3–7.5 (m, 10H, 2 · C6H5); 13C (CDCl3) d
16.02 (C-6), 22.81 (C3CO), 26.90, 27.26 (2 · 3CH3), 38.82,
39.09 (2·C(CH3)3), 47.63 (d, J2;P ¼ 7:2 Hz, C-2), 66.22,
67.73, 70.25 (C-3–5), 69.72, 69.75 (2d, JC;P ¼ 5:5 Hz,
2 · CH2Ph), 97.98 (d, J1;P ¼ 6:5 Hz, C-1), 128.02–128.80
(10 · CHPh), 135.27, 135.49 (2d, JC;P ¼ 6:1 Hz, 2 · Cq Ph),
169.91 (CH3CO), 177.47, 178.38 (2 · tBuCO).
22. Wittmann, V.; Wong, C.-H. J. Org. Chem. 1997, 62, 2144.
23. NMR data: 1 31P (D2O) d )10.68 (d, 1P, JP;P ¼ 19:5 Hz,
Pa), )11.98 (d, 1P, Pb). 2 31P (D2O) d )10.74 (d, 1P,
JP;P ¼ 20:1 Hz, Pa), )12.27 (d, 1P, Pb). 3 31P (D2O) d
)10.71 (d, 1P, JP;P ¼ 20:3 Hz, Pa), )12.16 (d, 1P, Pb).
24. Busca, P.; Martin, O. R. Tetrahedron Lett. 1998, 39, 8101.
25. NMR data: 1H (CDCl3) d 2.07, 2.14 (2s, 3H and 6H,
3 ·CH3CO), 4.14 (dd, 1H, J6a;5 ¼ 6:0 Hz, J6a;6b ¼ 11:5 Hz,
H-6a), 4.21 (dd, 1H, J6b;5 ¼ 6:0 Hz, H-6b), 4.25 (dd, 1H,
J2;1 ¼ 7:0 Hz, J2;3 ¼ 7:5 Hz, H-2), 4.31 (ddd, 1H,
J5;4 ¼ 2:0 Hz, H-5), 4.92 (dd, 1H, J3;4 ¼ 3:5 Hz, H-3),
5.47 (ddd, 1H, H-4), 6.32 (d, 1H, H-1); 13C (CDCl3) d
20.23, 20.37 (3 · CH3CO), 61.24 (C-6), 62.37 (C-2), 64.24,
69.93, 70.83 (C-3–5), 104.97 (C-1), 115.74 (q,
JC;F ¼ 274:5 Hz, CF3CO), 156.06 (q, JC;F ¼ 41:0 Hz,
CF3C), 168.54, 169.63, 170.17 (3 · CH3O).
21. NMR data: 18 1H (CDCl3) d 1.15, 1.22 (2s, 2 · 9H,
2 · 3CH3), 1.75 (s, 3H, CH3CO), 1.74 (ddd, 1H,
J3a;4 ¼ 2:5 Hz, J3a;2 ¼ J3a;3eq ¼ 13:5 Hz, H-3ax), 1.97 (ddd,
1H, J3eq;2 ¼ J3eq;4 ¼ 3:0 Hz, H-3eq), 3.96 (dd, 1H,
J6a;6b ¼ 11:0 Hz, J6a;5 ¼ 7:0 Hz, H-6a), 4.03 (dd, 1H,
J6b;5 ¼ 7:0 Hz, H-6b), 4.17 (ddd, 1H, J5;4 ¼ 2:0 Hz, H-5),
4.40 (m, 1H, J2;1 ¼ 3:0 Hz, J2;NH ¼ 9:0 Hz, H-2), 5.01 (m,
1H, H-4), 5.03–5.16 (m, 4H, 2 · CH2Ph), 5.65 (dd, 1H,
J1;P ¼ 5.5 Hz, H-1), 5.72 (d, 1H, NH), 7.3–7.5 (m, 10H,
2 · C6CH5); 13C(CDCl3) d 22.83 (CH3CO), 26.93, 26.96
(2 · 3CH3), 27.84 (C-3), 38.54, 38.99 (2 · C(CH3)3), 43.35
26. Kunesh, N.; Miet, C.; Poisson, J. Tetrahedron Lett. 1987,
28, 3569.
27. NMR data 31P (D2O): d )10.76 (d, 1P, JP;P ¼ 20:7 Hz, Pa)
)12.32 (d, 1P, Pb).