Looking glass inhibitors: synthesis of a potent naringinase inhibitor l-DIM [1,4-dideoxy-1,4-imino-l-mannitol], the enantiomer of DIM [1,4-dideoxy-1,4-imino-d-mannitol] a potent α-d-mannosidase inhibitor

Article abstract of DOI:10.1016/j.tetasy.2007.01.010

The synthesis of l-DIM [1,4-dideoxy-1,4-imino-l-mannitol] and of 1,4-imino-d-glycero-l-talo-heptitol from d-glycero-d-gulo-heptono-1,4-lactone depends on the use of pentan-3-one to form two five ring ketals as described by Burke, rather than the formation

Full text of DOI:10.1016/j.tetasy.2007.01.010

Tetrahedron: Asymmetry 18 (2007) 282–289
Looking glass inhibitors: synthesis of a potent naringinase inhibitor
L-DIM [1,4-dideoxy-1,4-imino-L-mannitol], the enantiomer of
DIM [1,4-dideoxy-1,4-imino-D-mannitol] a potent
a-D-mannosidase inhibitor
a
a
a
a
˚
Anders E. Hakansson, Jeroen van Ameijde, Luisa Guglielmini, Graeme Horne,
Robert J. Nash,b Emma L. Evinson,b Atsushi Katoc and George W. J. Fleeta,*
aChemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
bVASTox plc, Institute for Grassland and Environmental Research, Plas Gogerddan, Aberystwyth SY23 3EB, Dyfed, Wales, UK
cDepartment of Pharmacy, Toyama University Hospital, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan
Received 19 December 2006; accepted 8 January 2007
Abstract—The synthesis of L-DIM [1,4-dideoxy-1,4-imino-L-mannitol] and of 1,4-imino-D-glycero-L-talo-heptitol from D-glycero-D-gulo-
heptono-1,4-lactone depends on the use of pentan-3-one to form two five ring ketals as described by Burke, rather than the formation of
one five ring and one six ring ketal formed with acetone. L-DIM, the enantiomer of the potent a-D-mannosidase inhibitor DIM [1,4-dide-
oxy-1,4-imino-D-mannitol] is a good inhibitor of naringinase (an a-L-rhamnosidase) with a Ki of 3.63 lM. 1,4-Imino-D-glycero-L-talo-
heptitol is a moderate inhibitor of naringinase.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
sidases1 and other sugar processing enzymes2—have con-
siderable therapeutic potential.3 D-Swainsonine 2,
a
Carbohydrate mimics in which the ring oxygen of a sugar is
replaced by nitrogen—because of their inhibition of glyco-
natural product isolated4 from Swainsona canescens, is
a powerful inhibitor of a-mannosidases that cleave the
OH
OH
OH
OH
4
OH
CH2OH
HO
HO
HO
HO
HO
O
HO
OH
HO
RO
OH
1
OH
OH
CH2OH
OH
CH2OH
4 DIM
OH
5
N
O
N
O
N
H
H
O
CH2OH
OH
HOH2C
1
2
3
5
11 DAB
OH
O
OH
OH
OH
OH
OH
HO
HO
HO
HO
HO
HO
HO
RO
OH
OH
OH
CH3
OH
CH2OH
OH
OH
CH2OH
N
O
N
N
H
N
H
CH3
H
HOH2C
6
7
8
9 L-DIM
10
12 LAB
*
Corresponding author. Tel.: +44 01865 277386; fax: +44 01865 277378; e-mail: george.fleet@chem.ox.ac.uk
0957-4166/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2007.01.010

˚
A. E. Hakansson et al. / Tetrahedron: Asymmetry 18 (2007) 282–289
283
glycosidic bond of a-D-mannopyranosides 1. In particular
swainsonine 2 inhibits a mannosidase of glycoprotein pro-
cessing;5 this may be the basis for the potential of 2 in the
chemotherapy of cancer6 and the reason why more than 40
syntheses of swainsonine have appeared.7 Swainsonine is a
mimic of mannofuranose 3; the nitrogen analogue DIM
[1,4-dideoxy-1,4-imino-D-mannitol] 48 is also a potent
inhibitor of a-mannosidases,9 including a mannosidase of
glycoprotein processing,10 and has been the subject of
considerable synthetic interest.11 The crystal structure of
the hydrochloride of DIM 4 has been reported.12 Mirror
images of glycosidase inhibitors can also be powerful inhib-
itors of either the same or different enzymes;13 for example,
natural product 11 DAB and its synthetic enantiomer 12
LAB are both powerful inhibitors of a-glucosidases.14
heptitols have been shown to act as glycosidase inhibitors,
no study of 1,4-imino-D-glycero-L-talo-heptitol 10 as an
enzyme inhibitor has been reported. L-Rhamnose is a
sugar, which does not occur in mammals but does occur
in various pathogens; thus the mimics of L-rhamnose
may have a therapeutic potential.
Herein the first synthesis of L-DIM 9, and of iminoheptitol
1017 in which there is an additional CHOH in the side chain
from D-glycero-D-gulo-heptono-1,4-lactone, the only
cheaply available seven carbon sugar lactone, 5. The paper
also reports that L-DIM 9 is a good—and iminoheptitol 10
is a moderate—inhibitor of naringinase.
2. Synthesis of L-DIM 9 and of 1,4-imino-D-
glycero-L-talo-heptitol 10
a-L-Rhamnopyranosides 6 are the enantiomers of a-D-
mannopyranosides 1 in which the C-6 hydroxymethyl is re-
placed by a methyl group. L-Swainsonine 7, the enantiomer
of the natural product 2, is the imino sugar mimic of
L-rhamnofuranose 8 and is a potent inhibitor of narin-
ginase—an a-rhamnosidase;15 there are a few syntheses16
of the enantiomeric L-swainsonine 7 and none of L-DIM
9, the mirror image of DIM 4. Although pyrrolidine imino-
The value of the seven carbohydrate lactone 5 as a starting
material has been illustrated by the syntheses of antibiotic
gonifurfuranone18 and a number of imino sugars;19 other-
wise the use of protected seven carbon sugars has been
rare.20 The synthesis of L-DIM 9 and of the related imino-
heptitol 10 from the seven carbon sugar lactone 5 required
O
O
O
O
O
O
O
O
(ii)
(H+)
OH
4
HO
O
OX
O
OX
O
O
1
OH
5
O
O
O
(iv)
O
O
O
O
HO
O
O
O
OH
O
HOH2C
OH
O
O
O
17 X = H
18
16
14 X = H
(v)
5
(iii)
19 X = [Si]
15 X = SO2CF3
(vi)
[Si] = tBuMe2Si
(i)
HO
O
O
O
O
O
O
O
O
O
O
(viii)
O
(x)
(ix)
O[Si]
OH
O[Si]
O
O[Si]
O
OR1
XO
O
N
N
XO
N
O
CH2OR2
Ph
Ph
Ph
O
OH
O
O
13
24 R1 = [Si], R2 = H
25 R1 = H, R2 =[Si]
23
22
20 X = H
21 X = MeSO2
(xiii)
(vii)
(xi)
(xii)
(xiv)
OH
HO
Ph
OH
HO
OH
OH
HO
HO
OH
OH
OH
OH
OH
N
H
N
N
N
H
CH2OH
CH2OH
Ph
OH
HOH2C
HOH2C
26
27
10
9
Scheme 1. Reagents and conditions: (i) Ref. 21; (ii) Ref. 22; (iii) (CF3SO2)2O, pyridine, CH2Cl2; (iv) 4 M KOH, dioxane, then Amberlyst 15, 60% (two
steps); (v) tert-BuMe2SiCl, imidazole, DMF, 140 ꢁC, 99%; (vi) LiBH4, THF, 85%; (vii) MeSO2Cl, DMAP, pyridine, 96%; (viii) BnNH2, 120 ꢁC, 89%; (ix)
80% AcOH (aq), 80 ꢁC, 57% (from 19: 47%, four steps); (x) NaIO4, MeOH/H2O; then NaBH4 81%; (xi) 90% CF3CO2H (aq), reflux, 97%; (xii) H2,
Pd(OH)2/C, dioxane/H2O, quant; (xiii) 90% CF3CO2H (aq), reflux, 68%; (xiv) H2, Pd(OH)2/C, dioxane/H2O, quant.

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A. E. Hakansson et al. / Tetrahedron: Asymmetry 18 (2007) 282–289
284
(a) the formation of the pyrrolidine ring by the introduc-
tion of nitrogen between C-1 and C-4 with the overall
retention of configuration and (b) the inversion of config-
uration at C-5. The required stereochemistry was efficiently
achieved by an initial double inversion at both C-4 and C-5
in 5 to give the protected lactone 17. Acetone protection of
lactone 5 gave diacetonide 13 in a good yield—containing
both a five and a six ring ketal—leaving the C-2 hydroxyl
group free.21 However treatment of 5 with pentan-3-one by
the procedure described by Burke22 gave the corresponding
diketal derivative 14 in a 55% yield in which the C-5 hydr-
oxyl group was unprotected, ideally set up for the required
double inversion of both C-4 and C-5 (Scheme 1).
20 with methanesulfonyl chloride in the presence of N,N-
dimethylamino pyridine (DMAP) gave dimesylate 21
(96% yield), which on treatment with neat benzylamine at
elevated temperatures for a prolonged time gave pyrroli-
dine 22 in an 89% yield. Some problems were encountered
during the removal of excess benzylamine but any impuri-
ties were easily removed after the selective deprotection of
6,7-diethylketal in 22 to afford diol 23 in a 57% yield [over-
all yield from 19 was 47% without purification of the inter-
mediates]. Sequential treatment of 23 with periodate
followed by reduction with sodium borohydride gave an
inseparable mixture of 24 and 25; migration of the TBDMS
ether in 24 to the primary position in 25 was unavoidable
under the basic conditions of the reduction. However,
treatment of the mixture of silyl ethers 24 and 25 with
aqueous trifluoroacetic acid gave 26 as a single product
in a 78% yield from 23. The benzyl group in 26 was
removed by hydrogenation in the presence of Pearlman’s
catalyst (palladium hydroxide on carbon) to afford L-
DIM 9 in a quantitative yield with identical physical and
spectral data [other than the specific rotation] to those of
DIM 4.11a The overall yield of the synthesis of L-DIM 9
from the protected lactone 17 was 12.1%.
Esterification of the free hydroxyl group at C-5 in 14 with
triflic anhydride in dichloromethane gave the correspond-
ing triflate 15, which with potassium hydroxide in dioxane
afforded epoxide 16. Epoxide 16 under acidic conditions
gave the doubly inverted lactone 17. The yield of 17 was
highly dependant on the precise experimental procedure,
since 6,7-diethylketal 17 was prone to acid catalysed equil-
ibration to the more stable 5,6-diethylketal 18; this isomer-
ism was minimised by the use of an acidic resin (Amberlyst
15), but other acidic work-up conditions gave substantial
amounts of 18. The structure of 18 is strongly supported
by the 13C NMR spectrum in which the singlets of the ketal
carbon are at 117.6 and 114.0, values not consistent with a
six-membered ring ketal. The doubly inverted lactone 17
was thus obtained in a 60% yield from 14; the structure
of 17 was firmly established by X-ray crystal analysis.23
Iminoheptitol 10 with an extra carbon in the side chain was
obtained by removal of the silyl and ketal protecting
groups in 23 with aqueous trifluoroacetic acid to give
benzyl derivative 27 (68% yield); subsequent hydrogenation
of 27 in the presence of Pearlman’s catalyst gave the seven
carbon sugar mimic 10 in a 76% yield.17
The benzylation at the C-5 position in 17 gave only a mod-
erate yield of the corresponding benzyl ether. However,
alcohol 17 could be efficiently protected as its tert-butyl-
dimethylsilyl (TBDMS) ether 19 in a 99% yield by treat-
ment with a very concentrated solution of TBDMS
chloride and imidazole in anhydrous DMF at 140 ꢁC over-
night. Silyl ether 19 was reduced by lithium borohydride in
tetrahydrofuran to diol 20 in a 85% yield; trace amounts of
a product in which the silyl group had migrated could be
removed by column chromatography. The reaction of diol
3. Glycosidase inhibition
Inhibition was tested using 1 mg mlꢀ1 aqueous solutions of
L-DIM 9 and L-swainsonine 7 (the concentration of the
compounds in the assays was 915.8 and 860.6 lM, respec-
tively) and compared with D-swainsonine 2. Assays were
carried out in triplicate, and the values of percentage inhi-
bition of the glycosidases are given in Table 1 and are
means of the three replicates per assay. The substrate con-
Table 1. % Inhibition of various glycosidases by L-DIM 9, L-7 and D-2 swainsonine
Assay (enzyme source)
pH
[Enzyme] working [Enzyme] in
Reaction conditions L-DIM 9 L-Swain 7 D-Swain 2
stock (U/ml)
assay (U/ml) (min at ꢁC)
a-D-Glucosidase (Yeast [S. cerevisiae])
a-D-Glucosidase (Bacillus)
a-D-Glucosidase (Rice)
6.0
6.8
4.0
5.0
6.5
7.3
5.5
4.5
6.5
1.0
0.5
5.0
0.25
0.2
0.1
0.25
0.1
1.0
0.0007
0.00035
0.0035
0.000175
0.00014
0.00007
0.000175
0.00007
0.0007
10 at 27
10 at 27
20 at 27
10 at 27
10 at 27
10 at 27
10 at 27
10 at 27
20 at 27 (10 min
for D-swain)
20 at 27 (10 min
for D-swain)
10 at 27
10 at 27
10 at 27
10 at 32
8.0
21.7
2.0
9.1
2.3
12.6
5.8
17.1
ꢀ7.3
ꢀ6.2
0.7
12.1
2.7
ꢀ4.1
ꢀ2.8
6.9
11.4
ꢀ2.0
3.19
15.04
2.08
2.43
0.89
7.07
9.92
99.65
ꢀ4.61
b-D-Glucosidase (Almond)
a-D-Galactosidase (Green coffee bean)
b-D-Galactosidase (Bovine liver)
a-L-Fucosidase (Bovine kidney)
a-D-Mannosidase (Jack bean)
b-D-Mannosidase (Cellulomonas fimi)
Naringinase (Penicillium decumbens)
4.0
0.1
0.00007
97.2
99.2
3.63
N-Acetyl-b-D-gluc. (Bovine kidney)
N-Acetyl-b-D-gluc. (Jack bean)
N-Acetyl-b-D-hexos. (Aspergillus oryzae) 5.0
Amyloglucosidase (Aspergillus niger) 4.5
4.25 0.25
7.0
0.000175
0.00035
0.000175
0.00035
17.0
ꢀ0.5
ꢀ3.3
0.6
13.2
2.9
4.93
23.76
14.38
0.09
0.5
0.25
0.5 (1 U mlꢀ1
for D-swain)
ꢀ0.7
ꢀ5.6

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A. E. Hakansson et al. / Tetrahedron: Asymmetry 18 (2007) 282–289
285
centration was 5 mM in all assays.24 The only significant
inhibition of glycosidases by the L-sugar mimics 7 and 9
is of naringinase, whereas only a-D-mannosidase was inhib-
ited by D-swainsonine 2.
good inhibition of naringinase. Further investigation of
the properties of these compounds is currently in progress.
5. Experimental
The IC50 and Ki values for the inhibition of naringinase for
L-DIM 9 and L-swainsonine 7 are shown in Table 2. The
IC50 values were determined using serial dilutions from
the 1 mg mlꢀ1 solutions used for screening glycosidase inhi-
bition. Inhibition was tested using 0.1 U mlꢀ1 enzyme solu-
tion and 5 mM substrate solution, using deionised water
(dH2O) as a control. Reactions were carried out at 28 ꢁC.
The Ki values for the inhibition were determined using a
substrate dilution series (0.5–5 mM substrate in 0.5 mM
steps) and 0.1 U mlꢀ1 enzyme solution. Three inhibitor
concentrations were tested for each compound, using the
IC50 concentration as the highest. Control (uninhibited)
reactions were carried out using dH2O. Reactions were car-
ried out at 28 ꢁC. Velocity (rate of PNP release) was calcu-
lated using an absorption coefficient for PNP in 0.4 M
glycine solution, pH 10.3, which was determined using the
same microplate reader as used for the inhibition assays.
Ki values were calculated from transformed absorbance
data using Lineweaver–Burke double reciprocal plots.
All solvents were used as supplied (Analytical or HPLC
grade), without further purification, except for DMF and
pyridine, which were dried on molecular sieves prior to
use. The reactions performed under a hydrogen atmo-
sphere were maintained by an inflated balloon. Flash chro-
matography was performed using Sorbsil C60 40/60 silica.
Thin layer chromatography (TLC) was carried out on alu-
minium backed sheets coated with 60 F254 silica from
Merck. Plates were developed using a spray of 0.2% w/v
cerium sulfate and 5% w/v ammonium molybdate in 2 M
sulfuric acid with subsequent heating or 6% w/v phospho-
molybdic acid in ethanol. Melting points were recorded on
a Kofler hot block and are corrected. NMR spectra were
recorded on a Bruker DQX 400 (400 MHz) instrument
and were calibrated according to the chemical shift of the
deuterated solvent. High resolution mass spectra (HRMS)
were recorded on a Micromass LCT (ESI) spectrometer.
Infrared spectra (IR) were recorded on a Bruker Tensor
Fourier Transform IR spectrometer using thin film on
NaCl plates. Optical rotations were measured on a Per-
kin–Elmer 241 polarimeter. Microanalyses were carried
out by the analytical service of the ICL in Oxford.
The IC50 (lM) values of naringinase inhibition of 7 and 9
were determined separately for comparison with the
homologous pyrrolidine 1,4-imino-D-glycero-L-talo-hepti-
tol 10 and its N-benzyl derivative 27 (Table 3).
5.1. 2,3:6,7-Di-O-diethylidene-D-glycero-L-talo-heptono-1,4-
lactone 17 and 2,3:5,6-di-O-diethylidene-D-glycero-L-talo-
heptono-1,4-lactone 18
There was still significant inhibition of naringinase by the
pyrrolidines 10 and 27 with an additional CHOH in the side
chain and these may have value as rhamnose mimics. None
of the rhamnose mimics have any significant inhibition of
other glycosidases and are thus highly specific inhibitors.
Triflic anhydride (0.96 ml, 5.71 mmol) was added to a solu-
tion of diethylidene ketal 1422 (1.31 g, 3.81 mmol) dissolved
in dichloromethane (25 ml) with pyridine (0.92 ml,
11.5 mmol) under argon at ꢀ20 ꢁC. The reaction mixture
was stirred for 2 h at ꢀ20 ꢁC, quenched with brine
(20 ml) and was washed with aqueous hydrochloric acid
(1 M, 20 ml). The organic layer was dried over sodium sul-
fate, filtered and concentrated in vacuo in the cold. The res-
idue of crude triflate 15 was dissolved in dioxane (25 ml)
and potassium hydroxide (4 M, 3 ml, 12.0 mmol) was
added. The mixture was stirred for 2 h at room tempera-
ture after which Amberlyst 15 (3 g) was added. After stir-
ring for an additional 75 min, the reaction mixture was
filtered and the resin was washed with ethyl acetate. The
combined organic layers were washed with a saturated
aqueous solution of sodium bicarbonate (50 ml), dried (so-
4. Conclusion
Herein we have reported the efficient synthesis of a number
of monocylic pyrrolidines, which are the mimics of
L-rhamnofuranose; the compounds show an excellent to
Table 2. Inhibition of naringinase by L-DIM 9 and L-swainsonine 7
L-DIM 9
L-Swainsonine 7
IC50 (lM)
27.47
0.52
Ki (lM)
3.63
0.08
Mode of inhibition
Competitive
Competitive
Table 3. IC50 (lM) of naringinase inhibition by L-DIM 9 and other rhamnose mimics
HO
OH
HO
OH
HO
OH
HO
OH
OH
OH
OH
OH
OH
OH
N
N
H
HO
N
N
H
Bn
OH
OH
10
IC50 125
27
IC50 528
7
9
IC50 0.134
IC50 52.8

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A. E. Hakansson et al. / Tetrahedron: Asymmetry 18 (2007) 282–289
286
dium sulfate), filtered and concentrated in vacuo. The res-
idue was purified by flash column chromatography (ethyl
acetate/cyclohexane, 1:4) to afford the doubly inverted
lactone 17 (781 mg, 60%) as a white, crystalline solid.
3H, SiCH3); 13C NMR (100 MHz, CDCl3) d = 173.6
(C@O), 117.6, 113.8 (C(CH2CH3)2), 83.2 (C-4), 78.5 (C-
2/C-3), 76.6 (C-6), 75.6 (C-2/C-3), 73.0 (C-5), 66.0 (C-7),
29.8, 29.7, 29.3 (2x) (C(CH2CH3)2), 25.7 (C(CH3)3), 18.1
(C(CH3)3), 8.2, 8.1, 8.0, 7.4 (C(CH2CH3)2), ꢀ4.3,
ꢀ4.6 ppm (SiCH3); HRMS m/z (ESI +ve) calcd for
C23H42O7SiNa: 481.2592 [M+Na]+; found: 481.2587.
Rf = 0.70 (ethyl acetate/cyclohexane, 1:1); mp 93–94 ꢁC
21
(heptane); ½aꢁD ¼ ꢀ28:4 (c 1.93, CHCl3); IR (film)
1
m = 3443 (OH), 1789 (C@O); H NMR (400 MHz, CDCl3)
d = 4.84 (d, J2,3 = 6.0 Hz, 1H, H-3), 4.79 (d, J2,3 = 6.0 Hz,
1H, H-2), 4.40 (s, 1H, H-4), 4.23 (q, J = 6.8 Hz, 1H, H-6),
4.15–4.07 (m, 1H, H-7a), 3.75–3.67 (m, 2H, H-5, H-7b),
2.82 (br s, 1H, 4-OH), 1.72–1.56 (m, 8H, CH2CH3),
0.87 ppm (m, 12H, CH2CH3); 13C NMR (100 MHz,
CDCl3) d = 174.1 (C@O), 117.5, 114.2 (C(CH2CH3)2),
81.2 (C-4), 79.0 (C-2), 75.5 (C-6), 75.4 (C-3), 73.0 (C-5),
66.1 (C-7), 29.8, 29.5, 29.3, 29.1 (C(CH2CH3)2), 8.3, 8.2,
7.9, 7.3 ppm (C(CH2CH3)2); HRMS m/z (ESI +ve) calcd
for C17H28O7Na: 367.1733 [M+Na]+; found: 367.1728; ele-
mental analysis calcd (%) for C17H28O7: C 59.29, H 8.19;
found: C 59.28, H 8.26.
5.3. 5-O-tert-Butyldimethylsilyl-2,3:6,7-di-O-diethylidene-D-
glycero-L-talo-heptitol 20
Lithium borohydride (624 mg, 28.7 mmol) was added to
the silylated lactone 19 (6.58 g, 14.3 mmol) in anhydrous
THF (70 ml) under argon at 0 ꢁC and the reaction mixture
stirred at room temperature for 27 h. Additional lithium
borohydride (232 mg, 10.7 mmol) was added at 0 ꢁC. After
a total of 50 h, the reaction mixture was quenched by the
slow addition of a saturated aqueous solution of ammo-
nium chloride (100 ml), extracted with dichloromethane
(3 · 100 ml) and the combined organic layers were dried
(sodium sulfate), filtered and concentrated in vacuo. The
residue was purified by flash column chromatography
(ethyl acetate/cyclohexane, 1:4) to afford diol 20 (5.604 g,
In the presence of acid catalysts, the 6,7-ketal 17 isomerised
to the slightly more polar isomeric 5,6-ketal 18 oil,
22
Rf = 0.59 (ethyl acetate/cyclohexane, 1:1); ½aꢁD ¼ ꢀ62:6 (c
1
1.60, CHCl3); IR (film) m = 3483 (OH), 1791 (C@O); H
85%) as an oil. Rf = 0.30 (ethyl acetate/cyclohexane, 1:3);
21
NMR (400 MHz, CDCl3) d = 4.79 (d, J2,3 = 5.6 Hz, 1H,
H-3), 4.77 (d, J2,3 = 5.6 Hz, 1H, H-2), 4.61 ( br s, 1H, H-
4), 4.17–4.07 (m, 2H, H-5, H-6), 3.89 (dd, J6,7a = 3.9 Hz,
J7a,7b = 12.1 Hz, 1H, H-7a), 3.73 (dd, J6,7b = 3.2 Hz,
J7a,7b = 12.1 Hz, 1H, H-7b), 1.72–1.48 (m, 8H, CH2CH3),
0.92–0.78 ppm (m, 12H, CH2CH3); 13C NMR (100 MHz,
CDCl3) d = 174.0 (C@O), 117.6, 114.0 (C(CH2CH3)2),
79.0 (C-2), 78.8 (C-4), 77.0, 75.9 (C-5, C-6), 75.2 (C-3),
60.9 (C-7), 29.9, 29.8, 29.6, 29.2 (C(CH2CH3)2), 8.2, 8.2,
7.7, 7.3 ppm (C(CH2CH3)2); HRMS m/z (ESI +ve) calcd
for C17H28O7Na: 367.1727 [M+Na]+; found: 367.1725.
½aꢁD ¼ þ24:1 (c 3.1, CHCl3); IR (film) m = 3424 (O–H)
cmꢀ1 1H NMR (400 MHz, CDCl3) d = 4.43–4.36 (m,
;
1H, H-2), 4.21–4.13 (m, 1H, H-6), 4.08–4.01 (m, 3H,
H-3, H-5, H-7a), 3.85 (dd, J1a,1b = 11.8 Hz, J = 7.7 Hz,
1H, H-1a), 3.77 (dd, J1a,1b = 11.8 Hz, J = 5.1 Hz, 1H,
H-1b), 3.60 (t, J = 8.2 Hz, 1H, H-7b), 3.46 (d, J =
9.8 Hz, 1H, H-4), 3.08 (br s, 2H, OH), 1.71–1.51 (m, 8H,
C(CH2CH3)2), 0.94–0.84 (m, 12H, C(CH2CH3)2), 0.92 (s,
9H, C(CH3)3), 0.17 (s, 3H, SiCH3), 0.15 ppm (s, 3H,
SiCH3); 13C NMR (100 MHz, CDCl3) d = 113.5, 112.7
(C(CH2CH3)2), 77.8 (C-6), 77.3 (C-2), 75.4, 72.3 (C-3, C-
5), 69.5 (C-4), 66.3 (C-7), 60.8 (C-1), 29.7, 29.5, 29.2, 28.6
(C(CH2CH3)2), 26.0 (C(CH3)3), 18.3 (C(CH3)3), 8.6, 8.2,
8.0, 7.8 (C(CH2CH3)2), ꢀ4.1, ꢀ4.9 ppm (SiCH3); HRMS
m/z (ESI +ve) calcd for C23H46O7SiNa: 485.2905
[M+Na]+; found: 485.2904.
5.2. 5-O-tert-Butyldimethylsilyl-2,3:6,7-di-O-diethylidene-D-
glycero-L-talo-heptono-1,4-lactone 19
Imidazole (7.29 g, 107 mmol) and TBDMS chloride
(8.20 g, 54.4 mmol) were added to a suspension of lactone
17 (6.13 g, 17.8 mmol) in anhydrous DMF (6 ml) under
argon. The reaction mixture was heated to 140 ꢁC for
15 h, concentrated in vacuo and the residue was partitioned
between ether and water (100 ml, 1:1). The aqueous layer
was extracted with ether (50 ml) and the combined organic
layers over dried sodium sulfate, filtered and concentrated
in vacuo. The residue was purified by flash column chroma-
tography (ethyl acetate/cyclohexane, 1:19) to afford silyl
ether 19 (8.097 g, 99%) as a white, crystalline solid.
5.4. 5-O-tert-Butyldimethylsilyl-2,3:6,7-di-O-diethylidene-
1,4-di-O-methanesulfonyl-D-glycero-L-talo-heptitol 21
Dimethylaminopyridine (66 mg, 0.54 mmol) was added to
a solution of diol 20 (1.02 g, 2.20 mmol) in anhydrous
pyridine (10 ml) under argon at 0 ꢁC. Methanesulfonyl
chloride (0.7 ml, 8.9 mmol) was then added and the reaction
mixture stirred at room temperature for 14 h. The reaction
mixture was concentrated in vacuo, the residue dissolved in
dicholoromethane (20 ml) and washed sequentially with
aqueous hydrochloric acid (1 M, 2 · 15 ml) and a saturated
aqueous solution of sodium bicarbonate (15 ml). The
organic layer was dried (sodium sulfate), filtered and con-
centrated in vacuo. The residue was purified by flash col-
umn chromatography (ethyl acetate/cyclohexane, 1:4) to
Rf = 0.55 (ethyl acetate/cyclohexane, 1:3); mp 92–94 ꢁC
21
(ethyl acetate/cyclohexane); ½aꢁD ¼ ꢀ14:6 (c 2.5, CHCl3);
IR (film) m = 1786 (C@O) cmꢀ1 1H NMR (400 MHz,
;
CDCl3) d = 4.79 (d, J2,3 = 5.9 Hz, 1H, H-2/H-3), 4.77 (d,
J2,3 = 5.9 Hz, 1H, H-2/H-3), 4.44 (d, J4,5 = 2.6 Hz, 1H,
H-4), 4.14 (app. dt, J = 6.1 Hz, J = 8.7 Hz, 1H, H-6),
4.07 (dd, J6,7a = 6.3 Hz, J7a,7b = 7.6 Hz, 1H, H-7a), 3.92
(dd, J4,5 = 2.6 Hz, J5,6 = 5.9 Hz, 1H, H-5), 3.67 (dd,
J7a,7b = 7.7 Hz, J6,7b = 8.7 Hz, 1H, H-7b), 1.67 (q,
JEt = 7.4 Hz, 4H, C(CH2CH3)2), 1.59 (q, JEt = 7.7 Hz,
4H, C(CH2CH3)2), 0.93–0.84 (m, 12H, C(CH2CH3)2),
0.89 (s, 9H, C(CH3)3), 0.15 (s, 3H, SiCH3), 0.13 ppm (s,
afford dimesylate 21 (1.307 g, 96%) as a clear oil. Rf =
20
0.30 (ethyl acetate/cyclohexane, 1:3); ½aꢁD ¼ ꢀ44:2 (c
0.85, CHCl3); IR (film) m = 1358 (O–SO2), 1177 (O–SO2)
cmꢀ1 1H NMR (400 MHz, CDCl3) d = 4.77 (t, J =
;
4.0 Hz, 1H, H-4), 4.65–4.57 (m, 2H, H-2, H-3), 4.48 (dd,
J1a,1b = 10.7 Hz, J = 2.5 Hz, 1H, H-1a), 4.33 (dd,

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A. E. Hakansson et al. / Tetrahedron: Asymmetry 18 (2007) 282–289
287
J1a,1b = 10.7 Hz, J = 7.3 Hz, 1H, H-1b), 4.30–4.24 (m, 1H,
H-6), 4.12 (dd, J = 7.7 Hz, J = 6.7 Hz, 1H, H-7a), 3.97 (t,
J = 4.1 Hz, 1H, H-5), 3.68 (t, J = 7.9 Hz, 1H, H-7b), 3.16
(s, 3H, SCH3), 3.06 (s, 3H, SCH3), 1.75–1.57 (m, 8H,
C(CH2CH3)2), 0.97–0.85 (m, 12H, C(CH2CH3)2), 0.92 (s,
9H, C(CH3)3), 0.16 (s, 3H, SiCH3), 0.14 ppm (s, 3H,
SiCH3); 13C NMR (100 MHz, CDCl3) d = 114.0, 112.5
(C(CH2CH3)2), 79.3 (C-4), 75.2 (C-6), 75.1, 73.7 (C-2,
C-3), 71.7 (C-5), 69.7 (C-1), 66.0 (C-7), 38.7, 37.7 (SCH3),
29.8, 29.4, 28.9, 27.9 (C(CH2CH3)2), 25.8 (C(CH3)3),
18.2 (C(CH3)3), 8.6, 8.3, 8.2, 8.1 (C(CH2CH3)2), ꢀ4.5,
ꢀ4.9 ppm (SiCH3); HRMS m/z (ESI +ve) calcd for
C25H50O11S2SiNa: 641.2456 [M+Na]+; found: 641.2454.
idue was purified by flash column chromatography (ethyl
acetate/cyclohexane, 1:4) to afford 23 (320 mg, 57%) as a
clear oil.
Procedure B: Lithium borohydride (798 mg, 36.6 mmol)
was added to a solution of silyl ether 19 (8.097 g,
17.6 mmol) in anhydrous THF (75 ml) under argon and
cooled to 0 ꢁC and stirred at room temperature for 23 h.
Additional lithium borohydride (382 mg, 17.5 mmol) was
added at 0 ꢁC and after a total of 49 h, the mixture was
quenched by the slow addition of a saturated aqueous solu-
tion of ammonium chloride (100 ml). The reaction mixture
was extracted with dichloromethane (3 · 100 ml) and the
combined organic layers dried (sodium sulfate), filtered
and concentrated in vacuo. The concentrate was filtered
through a plug of silica gel and concentrated in vacuo.
Crude diol 20 was dissolved in anhydrous pyridine
(70 ml) under Ar and cooled to 0 ꢁC, treated sequentially
with dimethylaminopyridine (434 mg, 3.56 mmol) and
methanesulfonyl chloride (5.5 ml, 69.7 mmol). The result-
ing reaction mixture was stirred at room temperature for
20 h, concentrated in vacuo, dissolved in dichloromethane
(20 ml) and washed with aqueous hydrochloric acid (1 M,
2 · 15 ml) and a saturated aqueous solution of sodium
bicarbonate (15 ml). The organic layer was dried over
sodium sulfate, filtered and concentrated in vacuo. Crude
dimesylate 21 was dissolved in benzylamine (50 ml) under
Ar and heated to 120 ꢁC for 24 h. The reaction mixture
was concentrated in vacuo; the residue was dissolved in
dicholoromethane (100 ml) and washed with a saturated
aqueous solution of sodium bicarbonate (50 ml). The or-
ganic layer was dried (sodium sulfate), filtered and concen-
trated in vacuo. The residue was filtered through a plug of
silica gel to remove excess benzylamine. Crude diethylidene
ketal 22 was dissolved in 80% aqueous acetic acid (225 ml)
and heated to 80 ꢁC for 15 h. The reaction mixture was
concentrated in vacuo, dissolved in dichloromethane
(100 ml) and washed with a saturated aqueous solution
of sodium bicarbonate (15 ml). The organic layer was dried
(sodium sulfate), filtered and concentrated in vacuo. The
residue was purified by flash column chromatography
(ethyl acetate/cyclohexane, 1:4) to afford monoacetonide
5.5. N-Benzyl 5-O-tert-butyldimethylsilyl-1,4-dideoxy-
2,3:6,7-di-O-diethylidene-1,4-imino-D-glycero-L-talo-
heptitol 22
A solution of dimesylate 21 (1.168 g, 1.89 mmol) in benzyl-
amine (5 ml) was heated under argon to 120 ꢁC for 40 h.
The reaction mixture was concentrated in vacuo, dissolved
in dichloromethane (20 ml) and washed with a saturated
aqueous solution of sodium bicarbonate (15 ml). The
organic layer was dried over sodium sulfate, filtered and
concentrated in vacuo. The residue was purified by flash
column chromatography (ethyl acetate/cyclohexane, 1:24)
to afford pyrrolidine 22 (0.900 g, 89%) as a clear oil.
20
Rf = 0.75 (ethyl acetate/cyclohexane, 1:3); ½aꢁD ¼ þ20:4 (c
0.85, CHCl3); IR (film) m = 2937, 1463, 1132 cmꢀ1 1H
;
NMR (400 MHz, CDCl3) d = 7.39 (d, J = 7.3 Hz, 2H,
ArH), 7.26 (t, J = 7.1 Hz, 2H, ArH), 7.18 (t, J = 7.2 Hz,
1H, ArH), 4.85 (d, JArCHa,ArCHb = 13.4 Hz, 1H, ArCHa),
4.69 (ddd, J6,7b = 9.0 Hz, J6,7a = 6.6 Hz, J5,6 = 2.5 Hz,
1H, H-6), 4.60–4.52 (m, 2H, H-2, H-3), 4.16–4.14 (m,
1H, H-5), 4.07 (dd, J7a,7b = 7.5 Hz, J6,7a = 6.6 Hz, 1H, H-
7a), 3.79 (dd, J6,7b = 9.0 Hz, J7a,7b = 7.5 Hz, 1H, H-7b),
3.05 (d, J = 11.4 Hz, 1H, H-1a), 2.77 (d, JArCHa,ArCHb
=
13.4 Hz, 1H, ArCHa), 2.43–2.41 (m, 1H, H-4), 1.91–1.70
(m, 3H, H-1b, C(CH2CH3)2), 1.62–1.51 (m, 6H,
C(CH2CH3)2), 0.98 (t, JEt = 7.5 Hz, 3H, C(CH2CH3)2),
0.93 (s, 9H, C(CH3)3), 0.90 (t, JEt = 7.4 Hz, 3H,
C(CH2CH3)2), 0.84 (t, JEt = 7.4 Hz, 3H, C(CH2CH3)2),
0.77 (t, JEt = 7.5 Hz, 3H, C(CH2CH3)2), 0.14 (s, 3H,
SiCH3), 0.10 ppm (s, 3H, SiCH3); 13C NMR (100 MHz,
CDCl3) d = 140.3, 128.3, 127.8, 126.3 (ArC), 115.8, 112.7
(C(CH2CH3)2), 81.6 (C-3), 78.1 (C-2), 77.2 (C-6), 73.9 (C-
4), 70.6 (C-5), 67.2 (C-7), 60.5 (C-1), 60.0 (ArCH2), 29.9,
29.1, 29.0, 28.0 (C(CH2CH3)2), 26.0 (C(CH3)3), 18.1
(C(CH3)3), 8.4, 8.4, 8.2, 8.0 (C(CH2CH3)2), ꢀ4.2,
ꢀ4.5 ppm (SiCH3); HRMS m/z (ESI +ve) calcd for
C30H52NO5Si: 534.3609 [M+H]+; found: 534.3600.
23 (3.84 g, 47%, four steps) as a clear oil. Rf = 0.32 (ethyl
23
acetate/cyclohexane, 1:3); ½aꢁD ¼ þ35:1 (c 1.05, CHCl3);
IR (film) m = 3447 (O–H) cmꢀ1 1H NMR (400 MHz,
;
CDCl3) d = 7.37–7.20 (m, 5H, ArH), 5.03 (br s, 1H, OH),
4.91 (d, JArCHa,ArCHb = 13.0 Hz, 1H, ArCHa), 4.65 (dd,
J = 6.3 Hz, J = 4.6 Hz, 1H, H-3), 4.59–4.55 (m, 1H, H-2),
4.47–4.41 (m, 1H, H-6), 4.19 (s, 1H, H-5), 3.83 (dd,
J7a,7b = 11.0 Hz, J6,7a = 6.3 Hz, 1H, H-7a), 3.65–3.60 (m,
1H, H-7b), 3.07 (d, J1a,1b = 11.7 Hz, 1H, H-1a), 2.98 (s,
1H, OH), 2.84 (d, JArCHa,ArCHb = 13.0 Hz, 1H, ArCHb),
2.57 (app. d, J = 4.0 Hz, 1H, H-4), 1.98 (dd,
J1b,2 = 5.3 Hz, J1a,1b = 11.7 Hz, 1H, H-1b), 1.80 (app. q,
JEt = 7.5 Hz, 2H, C(CH2CH3)2), 1.55 (q, JEt = 7.5 Hz,
5.6. N-Benzyl 5-O-tert-butyldimethylsilyl-1,4-dideoxy-2,3-
O-diethylidene-1,4-imino-D-glycero-L-talo-heptitol 23
Procedure A: Diethylidene ketal 22 (664 mg, 1.21 mmol) in
80% aqueous acetic acid (30 ml) was heated to 80 ꢁC for
16 h. The reaction mixture was concentrated in vacuo;
the residue was dissolved in dichloromethane (20 ml) and
the extract washed with a saturated aqueous solution of so-
dium bicarbonate (5 ml). The organic layer was dried over
sodium sulfate, filtered and concentrated in vacuo. The res-
2H,
C(CH2CH3)2),
0.97
(t,
JEt = 7.5 Hz,
3H,
C(CH2CH3)2), 0.92 (s, 9H, C(CH3)3), 0.84 (t, JEt = 7.5 Hz,
3H, C(CH2CH3)2), 0.15 (s, 3H, SiCH3), 0.12 ppm (s, 3H,
SiCH3); 13C NMR (100 MHz, CDCl3) d = 138.4, 128.5,
128.4, 127.1 (ArC), 116.0 (C(CH2CH3)2), 80.7 (C-3), 77.3
(C-2), 74.3 (C-4), 73.6 (C-6), 71.6 (C-5), 64.4 (C-7), 61.3
(ArCH2), 60.1 (C-1), 28.2, 27.1 (C(CH2CH3)2), 25.8

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A. E. Hakansson et al. / Tetrahedron: Asymmetry 18 (2007) 282–289
288
(C(CH3)3), 18.0 (C(CH3)3), 8.6, 8.2 (C(CH2CH3)2), ꢀ4.1,
ꢀ5.0 ppm (SiCH3); HRMS m/z (ESI +ve) calcd for
C25H44NO5Si: 466.2983 [M+H]+; found: 466.2977.
+ve) calcd for C6H13NO4Na: 186.0737 [M+Na]+; found:
186.0740.
5.9. N-Benzyl 1,4-imino-D-glycero-L-talo-heptitol 27
5.7. N-Benzyl 1,4-dideoxy-1,4-imino-L-mannitol 26
A solution of benzyl pyrrolidine 23 (192 mg, 0.41 mmol) in
aqueous trifluoroacetic acid (9 trifluoroacetic acid/1 water,
25 ml) was stirred for 7.5 h at reflux temperature after
which the solvents were evaporated in vacuo. The crude
material was purified using ion exchange resin Dowex
50WX8-200 (H+ form) and aqueous 2 M ammonium
hydroxide as eluent to afford benzyl N-benzyl pyrrolidine
Sodium periodate (620 mg, 2.90 mmol) was added to a
solution of the protected pyrrolidine 23 (1.031 g,
2.21 mmol) in a mixture of methanol/water (4:1, 50 ml).
The reaction mixture was stirred at room temperature for
1 h after which sodium borohydride (499 mg, 13.2 mmol)
was added slowly. The reaction mixture was stirred for an-
other 3 h, filtered and concentrated in vacuo. The residue
was partitioned between chloroform (30 ml) and water
(30 ml). The aqueous layer was extracted with chloroform
(2 · 20 ml) and the combined organic layers were dried
over sodium sulfate, filtered and concentrated in vacuo.
The residue was filtered through a plug of silica gel to give
a mixture of silyl ethers 24 and 25, which in aqueous triflu-
oroacetic acid (9 trifluoroacetic acid/1 water, 25 ml) were
stirred for 6.5 h at reflux temperature after which the sol-
vents were evaporated in vacuo. The residue was purified
using ion exchange resin Dowex 50WX8-200 (H+ form)
and aqueous 2 M ammonium hydroxide as an eluent to
afford benzyl pyrrolidine 26 (438 mg, 78%) as an off-white
27 (79 mg, 68%) as a clear glass. Rf = 0.44 (acetone/
21
n-BuOH/H2O, 5:4:1); ½aꢁ ¼ þ12:7 (c 2.04, MeOH); 1H
D
NMR (400 MHz, CD3OD) d = 7.50–7.36 (m, 5H, ArH),
4.65 (d, JArCHa,ArCHb = 13.1 Hz, 1H, ArCHa), 4.48 (dd,
J2,3 = 4.6 Hz, J3,4 = 6.8 Hz, 1H, H-3), 4.22 (dd, J2,3
4.6 Hz, J = 9.3 Hz, 1H, H-2), 4.17 (dt, J5,6 = 2.2 Hz,
J6,7 = 5.9 Hz, 1H, H-6), 4.11 (dd, J5,6 = 2.2 Hz, J4,5
=
=
4.2 Hz, 1H, H-5), 3.92 (d, JArCHa,ArCHb = 13.1 Hz, 1H,
ArCHb), 3.70 (d, J6,7 = 5.9 Hz, 2H, H-7), 3.62–3.54 (m,
1H, H-4), 3.09–2.96 ppm (m, 2H, H-1); 13C NMR
(100 MHz, CD3OD) d = 134.8, 131.1, 130.1, 130.0 (ArC),
73.5 (C-6), 73.3 (C-3), 71.1 (C-4), 70.9 (C-2), 69.8 (C-5),
64.7 (C-7), 60.7 (ArCH2), 57.1 ppm (C-1); HRMS m/z
(ESI +ve) calcd for C14H22NO5: 284.1492 [M+H]+; found:
284.1491.
solid. Rf = 0.56 (acetone/n-BuOH/H2O, 5:4:1); mp 108–
21
109 ꢁC (MeOH); ½aꢁD ¼ þ37:7 (c 1.20, H2O); 1H NMR
(400 MHz, D2O) d = 7.43–7.34 (m, 5H, ArH), 4.34–4.29
(m, 1H, H-3), 4.13 (dt, J1,2 = 6.6 Hz, J2,3 = 4.6 Hz, 1H,
H-2), 3.93 (dt, J5,6b = 6.3 Hz, J5,6a = 3.7 Hz, 1H, H-5),
3.89 (d, JArCHa,ArCHb = 13.3 Hz, 1H, ArCHa), 3.79 (dd,
J6a,6b = 11.8 Hz, J5,6a = 3.7 Hz, 1H, H-6a), 3.72 (dd,
J6a,6b = 11.8 Hz, J5,6b = 6.3 Hz, 1H, H-6b), 3.56 (d,
JArCHa,ArCHb = 13.3 Hz, 1H, ArCHb), 3.01–2.97 (m, 1H,
H-4), 2.83 (dd, J1a,1b = 11.4 Hz, J1a,2 = 6.6 Hz, 1H,
H-1a), 2.76 ppm (dd, J1a,1b = 11.4 Hz, J1b,2 = 6.6 Hz, 1H,
H-1b); 13C NMR (100 MHz, D2O) d = 137.1, 130.3,
129.0, 128.3 (ArC), 72.8 (C-3), 71.2 (C-5), 70.0 (C-2),
66.3 (C-4), 63.7 (C-6), 59.7 (ArCH2), 55.8 ppm (C-1);
HRMS m/z (ESI +ve) calcd for C13H19NO4Na: 276.1206
[M+Na]+; found: 276.1204.
5.10. 1,4-Imino-D-glycero-L-talo-heptitol 10
Benzyl pyrrolidine 27 (79 mg, 0.27 mmol) in dioxane/water
(4:1, 5 ml) was stirred under an atmosphere of hydrogen in
the presence of 20% palladium on carbon for 19 h and then
filtered through a plug of Celite. The filtrate was concen-
trated in vacuo and the residue purified using ion exchange
resin Dowex 50WX8-200 (H+ form) and aqueous 2 M
ammonium hydroxide as an eluent to afford 10 (41 mg,
23
76%) as a clear glasslike solid, ½aꢁD ¼ þ9:5 (c 1.70, H2O)
23
{lit.17 ½aꢁD ¼ þ27 (c 1, MeOH)}; 1H NMR (400 MHz,
D2O) d = 4.35 (app. dt, J = 8.2 Hz, J = 4.0 Hz, 1H, H-2),
4.23–4.19 (m, 1H, H-3), 3.84 (app. d, J = 9.5 Hz, 1H, H-
5), 3.75–3.69 (m, 1H, H-6), 3.68–3.64 (m, 2H, H-7), 3.35
(dd, J = 9.2 Hz, J = 2.6 Hz, 1H, H-4), 3.22 (dd,
J = 10.9 Hz, J = 8.3 Hz, 1H, H-1a), 2.79 ppm (app. t,
J = 10.1 Hz, 1H, H-1b); 13C NMR (100 MHz, D2O)
d = 72.2 (C-2), 71.6 (C-3), 71.3 (C-6), 69.2 (C-5), 63.4 (C-
7), 60.7 (C-4), 48.5 ppm (C-1); HRMS m/z (ESI +ve) calcd
for C7H16NO5: 194.1023 [M+H]+; found: 194.1022.
5.8. L-DIM (1,4-dideoxy-1,4-imino-L-mannitol) 9
Benzyl pyrrolidine 26 (389 mg, 1.54 mmol) in dioxane/
water (4:1, 10 ml) with 20% palladium on carbon was
stirred under an atmosphere of hydrogen for 19 h and then
filtered through a plug of Celite. The filtrate was
concentrated in vacuo to give L-DIM 9 (250 mg, quantita-
21
Acknowledgement
tive) as a clear glasslike solid. ½aꢁD ¼ þ10:3 (c 1.20, H2O);
20
1
[lit.11a ½aꢁD ¼ ꢀ10:4 (c 0.12, H2O)]; H NMR (400 MHz,
Financial support [to A.E.H.] provided through the
European Community’s Human Potential Programme
under contract HPRN-CT-2002-00173 is gratefully
acknowledged.
D2O) d = 4.29 (dt, J1,2 = 8.3 Hz, J2,3 = 4.1 Hz, 1H, H-2),
4.16 (app. t, J = 3.9 Hz, 1H, H-3), 3.81 (ddd, J4,5
=
9.4 Hz, J5,6b = 6.4 Hz, J5,6a = 2.8 Hz, 1H, H-5), 3.71
(dd, J6a,6b = 12.0 Hz, J5,6a = 2.8 Hz, 1H, H-6a), 3.51 (dd,
J6a,6b = 12.0 Hz, J5,6b = 6.4 Hz, 1H, H-6b), 3.12 (dd,
J1a,1b = 11.2 Hz, J1a,2 = 8.1 Hz, 1H, H-1a), 3.07 (dd,
J4,5 = 9.4 Hz, J3,4 = 3.5 Hz, 1H, H-4), 2.72 ppm (dd,
J1a,1b = 11.2 Hz, J1b,2 = 3.5 Hz, 1H, H-1b); 13C NMR
(100 MHz, D2O) d = 72.5 (C-3), 71.8 (C-2), 70.7 (C-5),
64.0 (C-6), 61.0 (C-4), 48.8 ppm (C-1); HRMS m/z (ESI
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