Observations on the oxirane ring opening reactions of a 2-acetamido-3,4-anhydro sugar and on the inversion of the derived alcohols

Article abstract of DOI:10.1016/S0957-4166(00)00452-3

A novel methodology for the preparation of L-enantiomers of 2,4- and 2,3-diacetamido-2,4,6- and 2,3,6-trideoxy-pyranoses is described. Factors influencing both the steric course of the epoxide ring opening and substitution are discussed.

Full text of DOI:10.1016/S0957-4166(00)00452-3

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 11 (2000) 4693–4700
Observations on the oxirane ring opening reactions of a
2-acetamido-3,4-anhydro sugar and on the inversion of the
derived alcohols
Anna Banaszek* and Boz; ena Janisz
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
Received 9 October 2000; accepted 14 November 2000
Abstract
A novel methodology for the preparation of L-enantiomers of 2,4- and 2,3-diacetamido-2,4,6- and
2,3,6-trideoxy-pyranoses is described. Factors influencing both the steric course of the epoxide ring
opening and substitution are discussed. © 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
Sugar epoxides have attracted a great amount of attention as very useful intermediates in the
synthesis and modification of the various mono- and oligosaccharides. An oxirane ring is able
to react with nucleophiles under neutral, basic or acidic conditions.1 Although factors directing
the regioselectivity of oxirane ring cleavage have been well recognized,2 the steric course of the
reaction is in many cases unpredictable.
Little is known about the influence of the allylic acetamido group on the stereochemistry of
the epoxide ring formation.3,4 We thought, some knowledge of this question could be gained by
application of a suitable starting material for the synthesis of isomeric 2,4-diamido-2,4,6-trideoxy-
pyranoses. These compounds of
D
-gluco and
D
-galacto configuration play important biological
roles as constituents of bacterial polysaccharides.5 All other isomers and their L-enantiomers have
been recognized as C-4−C-9 fragments of structure of the corresponding 5,7-diamino-3,5,7,9-
tetradeoxy-glycero-nonulosonic acids, identified as components of O-antigenic lipopolysaccharides
(LPS) of the clinically important gram-negative bacteria.6 One isomer, i.e. 2,4-diacetamido-2,4,6-
trideoxy-L-gulopyranose, has recently been utilized in the synthesis of 5,7-diacetamido-3,5,7,9-
tetradeoxy-L-glycero-
D
-talo- and L-glycero-
-galacto-nonulosonic acids.7
D
In a previous paper4 we have reported a methodology for synthesis of diamino sugars starting
from 2-acetamido-2,3,4,6-tetradeoxy-a-L-threo-hex-2-enopyranoside 1. This olefin was prepared
from L-rhamnal in a reaction sequence involving: (i) Ferrier rearrangement to the corresponding
* Corresponding author. Fax: +48 22 632 66 81; e-mail: habaru@icho.edu.pl
0957-4166/00/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(00)00452-3

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benzyl a-L-erythro-hex-2-enopyranoside;8 (ii) conversion of configuration at C-4 via Mitsunobu
reaction;9 (iii) Overman [3,3]-sigmatropic rearrangement of 4-trichloroacetamidate10 with subse-
quent hydrolysis/acetylation reaction to afford 1. Utilizing again olefin 1 as a key starting material,
a new synthesis of isomeric 2,4-diamino-2,4,6-trideoxy- and 2,3-diamino-2,3,6-trideoxy-a-L-pyra-
nosides was elaborated.
2. Results and discussion
It has been reported that ethyl 2,3,4-trideoxy-2-trichloro-acetamido-a- -threo-hex-3-
D
enopyranoside3 as well as benzyl 2-acetamido-2,3,4,6-tetradeoxy-hex-3-enopyranoside,4 upon
treatment with MCPBA, furnished the corresponding epoxides, syn-oriented to the vicinal
2-acetamido group. Analogously, the anomeric a-L-olefin 1, submitted to the reaction with
MCPBA, afforded epoxide 2 as a single product (Scheme 1).
Scheme 1.
All these results are consistent with an existence of a transistent hydrogen bond between an
oxygen of MCPBA and the allylic acetamido group, by an analogy to the directing role of the
allylic hydroxyl group in epoxidation reactions of allylic alcohols.11
Our study focused, in the next step, on the ring opening of epoxide 2 by an azide. Using two
different types of reagents, i.e. Me3SiN3/BF3·OEt2 or NaN3/NH4Cl it should be possible to
direct an attack of the reagent at C-4 or C-3 of epoxide 2. Although little is known on the use
of the first reagent for the opening of the sugar epoxides,12 this procedure is commonly applied
for oxirane ring cleavage of the various epoxy alcohols.13 The steric course of the reaction has
been rationalized by invoking coordination of the epoxy alcohol to the metal center of a Lewis
acid in a rigid bidentate manner.13 This is opposite to those in the dianion case (NaN3/NH4Cl)
involving the participation of a cis hydroxyl group in the direct course of epoxide opening.13,14
Indeed, reaction of 2 with TMSN3/BF3·OEt2, performed in CH2Cl2 solution proceeded very
quickly, to afford the trans-diequatorial product 4-azido sugar 3a highly predominantly; its
3-amido trans-diaxial isomer 4a was isolated as a minor product (3a:4aꢀ3:1) (Scheme 2).
Scheme 2.

A. Banaszek, B. Janisz / Tetrahedron: Asymmetry 11 (2000) 4693–4700
4695
It seems more probable that the ‘abnormal’ product 3a arises from a change of the less stable
0H1 conformation (steric and electrostatic interactions between the dipoles associated with the
1
oxirane and pyranoid ring oxygen atoms, supported by 2-OH pseudo-axial) to its H0 or an E
conformation, which results in a trans-diaxial opening of 2.
In contrast, the reaction of 2 with NaN3/NH4Cl reagents proceeded sluggishly at 90°C to give
0
mainly 3-azido sugar 3 (3a:4aꢀ3.5:1), presumably via the less favored H1 conformation (two
1,3-diaxial interactions in the transition state). Evidently, this is due to the stabilizing effect of
the hydrogen bond between the epoxide oxygen and 2-acetamido group, similar to that of the
2-hydroxyl group.14
Compounds 3 and 4 were considered to be converted to their epimers. Inversion of
configuration is one of the most important problems in carbohydrate chemistry. Among
different methodologies developed, a direct Mitsunobu reaction is usually applied.9 However,
attempts to invert the configuration at C-3 in 3a under Mitsunobu condition failed. More
forcing conditions (large excess of reagents, longer reaction time, higher temperature) caused the
formation of a p-nitrobenzoic ester with retention of configuration, albeit in a low yield.
Evidently, the vicinal axial acetamido group renders the approaching reagent to 3-OH difficult,
thus preventing an inversion.
Epimerization of 3a and 4a was successfully achieved by a nucleophilic displacement of the
triflate group in 3c and 4c by CsOAc.15 Compound 3a (4a) in CH2Cl2 solution, when treated
with Tf2O/Py at −10“0°C over 15 min afforded 3c (4c), which is stable enough to purify by
filtration through silica gel column. After drying by evaporation with toluene, 3c dissolved in
toluene was heated with CsOAc and 18-crown-6 at 60–70°C overnight, furnishing a single benzyl
2-acetamido-3-O-acetyl-2-azido-2,4,6-trideoxy-a-L-altropyranoside 5 in a moderate yield. The
substitution reaction of triflate 4c proceeded much faster to give enantiomer 6 after ꢀ3 h at
60°C.
All azido sugars 3, 4, 5 and 6 were converted to the corresponding diacetamido derivatives 7,
8, 9 and 10, respectively (Scheme 3). For reduction of the azido group, NaBH4/NiCl2 reagent
was the best choice.16 The reaction proceeded smoothly giving, after acetylation, benzyl
Scheme 3.

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A. Banaszek, B. Janisz / Tetrahedron: Asymmetry 11 (2000) 4693–4700
2,4-diacetamido- and/or 2,3-diacetamido-2,4,6-a-L-pyranosides. Their structure was confirmed
1
by NMR data. In the case of compound 8 C4 conformation was a little distorted, as it was
indicated by coupling constants (J2,3 4.7, J3,4 6.1, J4,5 3.6 Hz). This probably resulted from two
1
1,3-diaxial interactions in C4 conformation, exerted by 1,3 and 2,4 substituents.
It is noteworthy that the observations described here can be also suitable for preparation of
other isomeric diamino sugars.
3. Experimental
General information: Optical rotations were measured with a JASCO Dip-360 Digital
1
polarimeter at room temperature. H NMR spectra were recorded on Bruker AM-500 (500
MHz) and Varian AC-200 (200 MHz) spectrometers with Me4Si as internal standard. Mass
spectra were taken on a AMD-604 mass spectrometer. IR spectra were taken with a Perkin–
Elmer FT-IR-1600 spectrophotometer. Reactions were controlled by TLC on silica [Merck
alu-plates (0.2 mm)]. All reagents and solvents were purified and dried according to common
methods. CsOAc was dried by stirring with Ac2O overnight and evaporated with toluene.
Reaction products were purified and separated by flash chromatography, using Merck’s
Kieselgel 60 (240–400 mesh or 70–230 mesh).
3.1. Benzyl 2-acetamido-3,4-anhydro-2,6-dideoxy-h-L-talopyranoside 2
To a solution of 14 (2.61 g, 10 mmol) in CH2Cl2 (20 ml), MCPBA (4 g) and NaHCO3 (1 g)
were added and the mixture was stirred overnight (TLC hexane–AcOEt, 3:7). After filtration
through Celite, the filtrate was diluted with CH2Cl2 and the solution was washed with aqueous
NaHCO3. Evaporation left a syrup, which was purified by chromatography (hexane–AcOEt,
3:7“1:1) to yield 2 (2.56 g, 92%) as a colorless oil; HRMS (LSIMS): MH+, found 278.1400.
C15H19O4N requires 278.1392; [h]D −87.7 (c 0.7, CHCl3); wmax (CHCl3) 3300, 2934, 1659, 1144,
1090 cm−1; lH (500 MHz, CDCl3) 7.26–7.35 (5H, m, Ph), 6.01–5.59 (1H, d, J 8.8 Hz, NH), 4.66
(1H, d, J 11.8 Hz, CH2OBn), 4.57 (1H, bs, H-1), 4.34 (1H, qd, J 0.8, 5.5, 8.8 Hz, H-2), 4.11 (1H,
q, J 6.7 Hz, H-5), 3.48 (1H, dtd, J 1.1, 4.2, 5.5 Hz, H-3), 3.15 (1H, dd, J 1.0, 4.2 Hz, H-4), 2.02
(3H, s, NAc), 1.35 (3H, d, J 6.7 Hz, Me); lC (CDCl3) 169.7, 137.0, 128.5, 127.9, 127.8, 97.4,
69.6, 60.9, 53.9, 50.4, 43.9, 23.2, 17.4.
3.2. Benzyl 2-acetamido-4-azido-2,4,6-trideoxy-h-L-mannopyranoside 3a and benzyl
2-acetamido-3-azido-2,3,6-trideoxy-h-L-idopyranoside 4a
Method a: A solution of 2 (1.69 g, 6.1 mmol) in CH2Cl2 (5 ml) was treated with Me3SiN3 (2.47
ml, 27 mmol), then with BF3·OEt2 (0.66 ml, 3.47 mmol) and the mixture was stirred for 2 h
(TLC hexane–AcOEt, 3:7). After neutralization with triethylamine, the solvent was evaporated.
The residue was chromatographed on a silica gel column (hexane–AcOEt, 1:1). Eluted first was
3a (1.26 g, 64.5%): colorless oil; HRMS (LSIMS): MH+, found 321.1571. C15H20O4N4 requires
321.1563; [h]D −105.6 (c 0.96, CHCl3); wmax (CHCl3) 3313, 2929, 2112, 1726, 1652 cm−1; lH (500
MHz, CDCl3) 7.29–7.38 (5H, m, Ph), 5.74 (1H, d, J 7.7 Hz, NH), 4.76 (1H, d, J 1.4 Hz, H-1),
4.66 (1H, d, J 12.0 Hz, CH2OBn), 4.48 (1H, d, J 12.0 Hz, CH2OBn), 4.40 (1H, ddd, J 1.4, 4.4,
7.7 Hz, H-2), 4.18 (1H, dd, J 4.4, 9.8 Hz, H-3), 3.63 (1H, pq, J 6.3, 10.0 Hz, H-5), 3.38 (1H, bs,

A. Banaszek, B. Janisz / Tetrahedron: Asymmetry 11 (2000) 4693–4700
4697
OH), 3.09 (1H, t, J 10.0 Hz, H-4), 2.05 (3H, s, NAc), 1.31 (3H, d, J 6.3 Hz, Me); lC (CDCl3)
169.7, 137.0, 128.5, 127.9, 127.8, 97.4, 69.6, 60.9, 53.9, 50.4, 43.9, 23.2, 17.4.
Eluted second was 4a (0.42 g, 21.6%): colorless crystals; mp 131–132°C; HRMS (LSIMS):
MH+, found 321.1574. C15H20O4N4 requires 321.1563; [h]D −107.1 (c 0.76, CHCl3); wmax (CHCl3)
3419, 2926, 2112, 1671, 1515 cm−1; lH (500 MHz, CDCl3) 7.26–7.38 (5H, m, Ph), 6.73 (1H, d,
J 9.0 Hz, NH), 4.79 (1H, bs, H-1), 4.73 (1H, d, J 12.2 Hz, CH2OBn), 4.57 (1H, d, J 12.2 Hz,
CH2OBn), 4.29 (1H, dq, J 1.3, 2.6, 9.0 Hz, H-2), 4.22 (1H, qd, J 1.2, 6.7 Hz, H-5), 3.87 (1H,
td, J 1.0, 4.0 Hz, H-4), 3.47 (1H, m, H-3), 2.30 (1H, bs, OH), 1.98 (3H, s, NAc), 1.19 (3H, d,
J 6.7 Hz, Me); lC (CDCl3) 169.3, 137.5, 128.4, 127.6, 127.4, 98.4, 69.7, 69.6, 61.9, 59.1, 46.5,
23.4, 15.9.
Method b: To a solution of 2 (138 mg, 0.5 mmol) in DMF (5 ml) were added NaN3 (130 mg,
1 mmol) and NH4Cl (130 mg). The mixture was heated at ꢀ90°C overnight. Evaporation of the
solvent left a residue, which after usual work-up and chromatography gave 3a (29 mg, 18%) and
4a (97 mg, 60%).
3.3. Benzyl 2-acetamido-3-O-acetyl-4-azido-2,4,6-trideoxy-h-L-mannopyranoside 3b
Acetylation of 3a (32 mg, 0.1 mmol) was performed using pyridine and Ac2O. Usual work-up
and purification of the product by chromatography (CHCl3–Me2CO, 95:5) gave the title
compound 3b as a colourless oil: HRMS (LSIMS): MH+, found 363.1657. C17H23O5N4 requires
363.1668; [h]D −154.2 (c 0.90, CHCl3); wmax (CHCl3) 3442, 2110, 1748, 1678, 1512 cm−1; lH (200
MHz, CDCl3) 7.26−7.36 (5H, m, Ph), 5.55 (1H, d, J 9.4 Hz, NH), 5.25 (1H, dd, J 4.3, 10.4 Hz,
H-3), 4.69 (1H, d, J 1.5 Hz, H-1), 4.66 (1H, d, J 12.0 Hz, CH2OBn), 4.60 (1H, ddd, J 1.5, 4.3,
9.4 Hz, H-2), 4.51 (1H, d, J 12.0 Hz, CH2OBn), 3.70 (1H, pq, J 6.2, 10.3 Hz, H-5), 3.25 (1H,
t, J 10.3 Hz, H-4), 2.05, 2.02 (2×3H, 2s, OAc, NAc), 1.33 (3H, d, J 6.2 Hz, Me); lC (CDCl3)
169.7, 136.3, 128.5, 128.1, 128.0, 97.9, 70.8, 69.4, 67.7, 62.9, 49.7, 23.3, 20.8, 18.4.
3.4. Benzyl 2-acetamido-4-O-acetyl-3-azido-2,3,6-trideoxy-h-L-idopyranoside 4b
Compound 4a (32 mg, 0.1 mmol) was converted to the title 4b according to the above
described procedure: white solid; mp 151–152°C; HRMS (LSIMS): MH+, found 363.1651.
C17H23O5N4 requires 363.1668; [h]D −92.4 (c 1.14, CHCl3); wmax (CHCl3) 3442, 2110, 1748, 1679,
1512 cm−1; lH (200 MHz, CDCl3) 7.26–7.38 (5H, m, Ph), 6.10 (1H, d, J 9.3 Hz, NH), 4.81 (1H,
d, J 0.8 Hz, H-1), 4.81–4.72 (1H, m, H-4), 4.65, 4.56 (2×1H, 2d, J 12.2 Hz, 2×CH2OBn), 4.32
(1H, pq, J 1.8, 6.6 Hz, H-5), 4.23 (1H, pq, J 0.8, 3.3, 9.2 Hz, H-2), 3.85 (1H, td, J 0.8, 3.3 Hz,
H-3), 2.15, 1.99 (2×3H, 2s, OAc, NAc), 1.10 (3H, d, J 6.6 Hz, Me); lC (CDCl3) 169.3, 137.0,
128.5, 127.8, 127.6, 97.9, 70.3, 69.8, 61.5, 57.4, 46.9, 23.3, 20.8, 15.8.
3.5. Benzyl 2-acetamido-3-O-acetyl-4-azido-2,4,6-trideoxy-h-L-altropyranoside 5
To a stirred solution of 3a (320 mg, 1 mmol) in CH2Cl2 (10 ml) containing pyridine (2.25 ml,
3 mmol) triflic anhydride (0.22 ml, 1.3 mmol) was added dropwise at −10°C under Ar. Then the
temperature was allowed to rise to −5°C continuing stirring until no starting material remained
(ꢀ10 min. TLC, hexane–AcOEt, 1:1). The reaction was then diluted with CH2Cl2 and filtered
through a short silica gel column. The solvent was removed to give a relatively stable crude
triflate 3c, which was used directly for the conversion to 5. Thus, 3c was dried by evaporation

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A. Banaszek, B. Janisz / Tetrahedron: Asymmetry 11 (2000) 4693–4700
with dry toluene in vacuo, redissolved in toluene (15 ml) and the solution was treated with
18-crown-6 (790 mg, 3 mmol) followed by cesium acetate (580 mg, 3 mmol). The reaction
mixture was stirred at 60–70°C for ꢀ18 h (TLC), whereupon the solvent was evaporated in
vacuo and the product was isolated by column chromatography (hexane–AcOEt, 17:5) to afford
5 (220 mg, 61%) as a white solid: mp 61–62°C; HRMS (LSIMS): MNa+, found 385.1484.
C17H22O5N4Na requires 385.1487; [h]D −122.5 (c 1.02, CHCl3); wmax (CHCl3) 3281, 2932, 1744,
1656, 1548 cm−1; lH (200 MHz, CDCl3) 7.30–7.40 (5H, m, Ph), 5.63 (1H, d, J 8.8 Hz, NH), 5.23
(1H, t, J 3.5 Hz, H-5), 4.75 (1H, d, J 12.0 Hz, CH2OBn), 4.72 (1H, d, J 1.7 Hz, H-1), 4.49 (1H,
d, J 12.0 Hz, CH2OBn), 4.41 (1H, ddd, J 1.7, 4.0, 8.8 Hz, H-2), 4.21 (1H, pq, J 6.4, 9.6 Hz,
H-5), 3.23 (1H, dd, J 3.5, 9.6 Hz, H-4), 2.08, 2.01 (2×3H, 2s, OAc, NAc), 1.30 (3H, d, J 6.4 Hz,
Me); lC (CDCl3) 169.7, 169.1, 137.3, 128.4, 127.8, 127.4, 98.2, 69.6, 68.9, 63.5, 60.6, 49.6, 23.3,
20.8, 18.3.
3.6. Benzyl 2-acetamido-4-O-acetyl-3-azido-2,3,6-trideoxy-h-L-altropyranoside 6
Compound 4a (160 mg, 0.5 mmol) was converted into the title 6 according to the procedure
described for 5, using pyridine (1.2 ml, 1.5 mmol) and Tf2O (0.11 ml, 0.66 mmol) in CH2Cl2 to
give 4c. This was subjected to the substitution reaction with 18-crown-6 (400 mg), cesium acetate
(290 mg) in toluene (10 ml). The reaction proceed at 60°C for 3 h (TLC, hexane–Me2CO, 7:3),
furnishing after column chromatography compound 6 (115 mg, 63.5%) as a white solid: mp
112°C; HRMS (LSIMS): MNa+, found 385.1484. C17H22O5N4Na requires 385.1487; [h]D −119.5
(c 0.83, CHCl3); wmax (CHCl3) 3436, 2936, 2112, 1739, 1682 cm−1; lH (200 MHz, CDCl3)
7.15–7.30 (5H, m, Ph), 5.27 (1H, d, J 8.2 Hz, NH), 4.93 (1H, dd, J 4.0, 8.7 Hz, H-4), 4.59 (1H,
d, J 12.0.4 Hz, CH2OBn), 4.56 (1H, d, J 2.1 Hz, H-1), 4.38 (1H, ddd, J 2.1, 4.0, 8.2 Hz, H-2),
4.29 (1H, d, J 12.4 Hz, CH2OBn), 4.25 (1H, pq, J 6.4, 8.7 Hz, H-5), 4.10 (1H, t, J 4.0 Hz, H-3),
1.67, 1.40 (2×3H, 2s, OAc, NAc), 1.10 (3H, d, J 6.4 Hz, Me); lC (CDCl3) 169.9, 169.4, 136.8,
128.5, 127.9, 127.8, 97.2, 71.4, 69.6, 63.1, 58.4, 51.1, 23.3, 20.6, 17.0.
3.7. General procedure for the reduction of azido group in sugars
To a solution of azido sugar (1 mmol) in EtOH (10 ml) were added NaBH4 (160 mg) and a
0.16 M solution of NiCl2 in EtOH (0.2 ml). The mixture was stirred for 30 min at room
temperature, then neutralized with AcOH and evaporated in vacuo to dryness. The residue was
treated with Ac2O (5 ml) and anhydrous NaOAc (500 mg) and stirred at 40°C until TLC showed
consumption of the starting material. The solvent was removed, water was added to the residue
and the product was extracted with CHCl3. The combined organic extracts were washed with
brine, dried MgSO4 and evaporated. The residue was purified by flash column chromatography.
3.8. Benzyl 3-O-acetyl-2,4-diacetamido-2,4,6-trideoxy-h-L-mannopyranoside 7
Based on the general procedure compound 3a (160 mg, 0.5 mmol) afforded, after purification
by column chromatography (CHCl3–MeOH, 17:1) the title 7 (164 mg, 87%) as a colorless oil:
HRMS (LSIMS): MNa+, found 401.1692. C19H26O6N2Na requires 401.1689; [h]D −103.5 (c 0.57,
CHCl3); wmax (CHCl3) 3431, 2935, 1729, 1679 cm−1; lH (200 MHz, CDCl3) 7.32 (5H, m, Ph), 5.85
(1H, d, J 9.1 Hz, NH), 5.45 (1H, d, J 9.3 Hz, NH), 5.25 (1H, dd, J 4.5, 11.1 Hz, H-3), 4.79 (1H,
d, J 1.5 Hz, H-1), 4.66, 4.59 (2×1H, 2d, J 11.8 Hz, CH2OBn), 4.53 (1H, m, H-2), 4.39 (1H, dd,

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4699
J 10.2, 11.1 Hz, H-4), 3.68 (1H, pq, J 6.2, 10.0 Hz, H-5), 2.05, 2.01, 1.96 (3×3H, 3s, OAc,
2×NAc), 1.24 (3H, d, J 6.2 Hz, Me); lC (CDCl3) 171.3, 170.4, 170.1, 136.6, 128.5, 128.1, 128.0,
98.2, 69.6, 68.9, 68.1, 51.7, 50.0, 23.4, 23.3, 20.9, 17.8.
3.9. Benzyl 4-O-acetyl-2,3-diacetamido-2,3,6-trideoxy-h-L-idopyranoside 8
Prepared according to the general procedure from 4a (64 mg, 0.2 mmol). Chromatography
(CHCl3–MeOH, 17:1) afforded the title 8 (60 mg, 79.4%) as a white solid: mp 185°C
(destruction); HRMS (LSIMS): MNa+, found 401.1684. C19H26O6N2Na requires 401.1689; [h]D
−72.6 (c 0.70, CHCl3); wmax (CHCl3) 3446, 2928, 1751, 1678 cm−1; lH (500 MHz, CDCl3)
7.28–7.36 (5H, m, Ph), 4.93 (1H, dd, J 3.5, 6.0 Hz, H-4), 4.80 (3H, m, H-1, 2× NH), 4.74 (1H,
d, J 12.0 Hz, CH2OBn), 4.57 (1H, d, J 12.0 Hz, CH2OBn), 4.29 (1H, pq, J 3.5, 6.6 Hz, H-5),
4.09 (1H, dd, J 6.0, 7.8 Hz, H-3), 3.98 (1H, dd, J 4.7, 7.9 Hz, H-2), 2.08, 1.98, 1.93 (3×3H, 3s,
OAc, 2×NAc), 1.13 (3H, d, J 6.6 Hz, Me); lC (CDCl3) 168.8, 168.8, 168.3, 136.6, 128.7, 128.4,
127.8, 98.9, 69.9, 69.8, 61.9, 47.9, 47.0, 23.4, 23.2, 20.9, 16.3.
3.10. Benzyl 3-O-acetyl-2,4-diacetamido-2,4,6-trideoxy-h-L-altropyranoside 9
Prepared according to the general procedure from 5 (74 mg, 0.2 mmol). Chromatography
(AcOEt–EtOH, 17:1) gave the title 9 (66 mg, 87%) as a colorless oil: HRMS (LSIMS): MNa+,
found 401.1683. C19H26O6N2Na requires 401.1689; [h]D −115.0 (c 1.03, CHCl3); wmax (CHCl3)
3281, 2932, 1744, 1656 cm−1; lH (200 MHz, CDCl3) 7.25–7.30 (5H, m, Ph), 6.10 (1H, d, J 9.2
Hz, NH), 5.69 (1H, d, J 9.6 Hz, NH), 4.82 (1H, t, J 3.3 Hz, H-3), 4.75 (1H, s, H-1), 4.68 (1H,
d, J 11.7 Hz, CH2OBn), 4.52–4.44 (1H, m, H-2), 4.50–4.44 (1H, d, J 11.7 Hz, CH2OBn), 4.22
(1H, ddd, J 9.6, 9.4, 3.3 Hz, H-4), 4.05 (1H, pq, J 6.4, 9.4 Hz, H-5), 2.02, 2.00, 1.99 (3×3H, 3s,
OAc, 2×NAc), 1.23 (3H, d, J 6.6 Hz, Me); lC (CDCl3) 169.9, 169.8, 169.5, 137.4, 128.5, 128.3,
127.5, 98.4, 70.3, 69.9, 64.7, 48.8, 48.5, 23.3, 23.2, 20.9, 17.8.
3.11. Benzyl 4-O-acetyl-2,3-diacetamido-2,3,6-trideoxy-h-L-altropyranoside 10
Prepared according to the general procedure from 6 (100 mg, 0.27 mmol). Chromatography
(AcOEt–EtOH, 17:1) afforded the title compound (86 mg, 82.7%) as a white solid: HRMS
(LSIMS): MNa+, found 401.1683. C19H26O6N2Na requires 401.1689; [h]D −66.4 (c 1.03, CHCl3);
wmax (CHCl3) 3287, 2935, 1740, 1660, 1537 cm−1; lH (200 MHz, CDCl3) 7.32–7.41 (5H, m, Ph),
6.81 (1H, d, J 8.7 Hz, NH), 6.02 (1H, d, J 8.3 Hz, NH), 4.78 (1H, s, H-1), 4.75 (1H, d, J 11.4
Hz, CH2OBn), 4.69 (1H, dd, J 4.0, 9.6 Hz, H-4), 4.56 (1H, d, J 11.4 Hz, CH2OBn), 4.48 (1H,
ddd, J 3.6, 4.0, 8.3 Hz, H-3), 4.26 (1H, pq, J 1.9, 3.6, 8.7 Hz, H-2), 4.01 (1H, pq, J 6.3, 9.6, Hz,
H-5), 2.03, 2.02, 1.90 (3×3H, 3s, OAc, 2×NAc), 1.24 (3H, d, J 6.3 Hz, Me); lC (CDCl3) 170.3,
169.7, 169.6, 136.6, 128.7, 128.4, 128.1, 98.3, 70.6, 70.3, 69.9, 50.7, 47.4, 23.3, 23.2, 20.8, 17.3.
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