Large Scale Synthesis and Regioselective Protection Schemes of Ethyl 2-Azido-2-deoxy-1-thio--D-cellobioside for Preparation of Heparin Thiodisaccharide Building Blocks
Kevin Sheerin, Lorenzo Guazzelli, Stefan Oscarson*
School of chemistry, University College Dublin, Belfield, Dublin 4, Ireland
Abstract – Crystalline acetylated ethyl 2-azido-2-deoxy-1-thio--D-cellobioside has been prepared
on a multigram scale from cellobiose in an overall yield of 23% with no chromatography required and converted after deacetylation into the benzylidene and 4’,6’-O-benzylidene-6-O-TBDMS protected derivatives. Applying a number of regioselective benzylation methods on these gave access to a variety of regioselectively protected derivatives, both mono-ols (2’- and 3-OH), diols (2’,6-, 2’,3-, and 3,6-di-OH), and triols (2’,3,6- and 2’,3’,3-tri-OH). A number of these derivatives were further processed by benzoylation followed by removal or opening of the benzylidene acetal and selective oxidation of the exposed primary alcohol to give heparin building block intermediates comprising a range of possible sulfation patterns. Keywords: Heparin; heparan sulfate; azidonitration; regioselective benzylation; Phase transfer benzylation
1. Introduction
Heparin and heparan sulfate are polysaccharides involved in biologically important interactions with hundreds of proteins,1 but only in one of these interactions, the one between a pentasaccharide
and Antithrombin III, has the finer details of a specific interaction been possible to elucidate.2
Specificity studies are substantially hampered by the heterogeneity of native heparin and heparan sulfate structures why there is a major need for synthetic well-defined structures, both naturally occurring as well as non-natural analogues, and large efforts have gone into such syntheses. Most often the syntheses start from monosaccharide precursors,3 but disaccharide approaches have also
been investigated, e.g., using cellobiose as precursor. Earlier attempts have mainly used the 1,6-anhydro-2-azido-2-deoxy-derivative of cellobiose as an intermediate.4 Here we present our
approach to a number of orthogonally protected disaccharide building blocks for continued synthesis of heparin and heparin sulfate structures with variant sulfation patterns using ethyl 2-azido-2-deoxy-1-thio--D-cellobioside as an intermediate, and applying a variety of selective
benzylation and debenzylation reactions to obtain the regioselective orthogonal protecting group patterns.
*Corresponding Author: Prof Stefan Oscarson: e-mail: stefan.oscarson@ucd.ie.
2. Results and discussion
Large Scale Synthesis of peracetylated ethyl 2-azido-2-deoxy-1-thio--D-cellobioside (3). Cellobial
was prepared according to Haworth using the modification of Hansen, Daasbjerg, and Skrydstrup5
to give a crystalline product without chromatography in 66% yield. After azidonitration according to Lemieux and Ratcliffe6 the anomeric nitrate was removed with phenyl thiol and DIEA to yield a
product mixture from which the desired gluco-compound 2 could be crystallized out in a 55% yield over two steps (20% of the manno isomer was left in the mother liquor). Previous azidonitration reactions performed on cellobialrequired a chromatographic purification in order to isolate either 2 in a 36% yield7 or its anomeric nitrate precursor, together with the manno nitrate isomer as a 2:1
mixture, in a 34% yield.8 Hence, by avoiding the purification step a significant increase of yield of
the desired 2-azido-2-deoxy-hexa-O-acetyl-D-cellobiose 2 was obtained. The subsequent
transformation of the hemiacetal into a thioglycoside was not straight-forward. Acetylation followed by treatment with ethane thiol and a Lewis acid gave low yields of /-mixtures. Attempts to rearrange preformed anomeric ethyl xantates also failed. Eventually, formation of a trichloroacetimidate followed by reaction with ethane thiol and BF3-etherate afforded a mixture
from which the pure -anomer 3 could be crystallized in a 64% yield.
Scheme 1. Synthesis of common intermediates 3, 5 and 7.Reagents and conditions: i) (a) CAN, NaN3, MeCN, -20 oC,
24 h, (b) DIEA, PhSH, MeCN, 0 oC, 2 h; ii) (a) trichloroacetonitrile, K
2CO3, CH2Cl2, 17 h, (b) EtSH, BF3.Et2O, CH2Cl2,
17 h; iii) NaOMe, MeOH, 3 h; iv) PhCH(OMe)2, CSA, MeCN, 17 h; v) TBDPSCl, imidazole, DMF, 0 oC, 20 min.
Regioselective protection of ethyl 2-azido-2-deoxy-1-thio--D-cellobioside. Having installed the
thioglycoside and the 2-azido function our attention now turned to the selective protection of the hydroxyl groups. For protection of the 4’- and 6’-OH groups derivative 3 was first deacetylated using Zemplen conditions (→4) and then treated with 2 equivalents of benzaldehyde dimethyl
acetal and an acid (CSA) to yield the 4’,6’-O-benzylidene compound 5 (50%). The reaction was contaminated, especially on a large scale, by the concomitant formation of the open methyl benzylidene acetal at 6-OH [compound 6 (25%)]; therefore, the equivalents of dimethoxytoluene were reduced to 1.3 affording compound 5 in 72% yield (together with about 10% of 6). All reactions could be performed on a 20-50 g scale and only the last step required column chromatography. For regioselective protection of the other primary position (6-OH) compound 5 was silylated with tert-butyldiphenylsilyl chloride and imidazole yielding derivative 7 in 74% yield. For the continued selective protection a number of different regioselective benzylation and debenzylation methodologies were explored.
Selective benzylation and debenzylation. 1. Bu2SnO activation followed by benzylation. 3’-O-benzylation. In earlier approaches using 1,6-anhydro derivative of 2-azido-cellobiose it was found
that the 3’-position was selectively benzylated using dibutyltin oxide activation followed by treatment with benzyl bromide.9 Not only the 6-O-silyl protected thioglycoside derivative 7 but also
5 with a free 6-OH group showed the same regioselectivity using this methodology and the 3’-O-benzylated compounds 8 and 9 could be isolated in 75% and 85% yield, respectively (Scheme 2).
Scheme 2. Tin mediated benzylation of compounds 5 and 7. Reagents and conditions: i) (a) Bu2SnO, toluene, reflux, 17 h, (b) TBAB, BnBr, reflux, 3 h.
Phase Transfer Benzylation. 2’,3’- and 3,3’-di-O-benzylation. Phase transfer benzylation10 attempts
on compound 5 with four free hydroxyl groups led to a complex mixture with no major products. However, utilizing compound 7 (three free OH groups) as precursor, two major (and inseparable) products could be detected on TLC and isolated in around a 70% yield as a mixture (~2:1) (Scheme 3). NMR showed that the two compounds were both dibenzyl derivatives and both were benzylated at the 3’-position, the major compound was also benzylated in the 2’-position whereas the minor component was benzylated in the 3-position. Benzoylation of the mixture did not improve separation but removal of the TBDPS group did and 3,6-diol 10 and 2’,6-diol 11 were obtained respectively in a 21% and 48% yield over the two steps.
Scheme 3. Phase transfer benzylation of compound 7. Reagents and conditions: i) BnBr, NaOH, TBAHSO3, CH2Cl2,
H2O, 40 oC, 16 h; ii) TBAF, THF, 60 oC, 17h.
Silylation followed by benzylation with benzaldehyde, Et3SiH and a Lewis acid of derivative 5. Benzylation order 6 > 3’ > 3 >> 2’. Rather recently, Hung et al.11a reported the tandem protection
of per-O-silylated sugars. This strategy, by carefully tuning reaction conditions, gives access in a single pot to protected monosaccharides with either the 2-, 3-, 4- or 6-position as the only remaining free hydroxyl group. The TMS groups are necessary to solubilize the starting material and also regenerate the Lewis acid (TMSOTf) used in the benzylidene formation, the first step of the reaction sequence. Similar results have been obtained using different Lewis acids [Cu(OTf)2,11b
FeCl3·6H2O11c] and generating the per-O-silylated saccharides in situ.11d Using a similar strategy as
for monosaccharides (PhCHO, Et3SiH, FeCl3·6H2O), Beau and coworkers11c reported the insertion
of a benzylidene acetal onto the 4’- and 6’-position of per-O-silylated -methyl maltoside with concomitant benzylation of the 3’- and 6-positions in a 51% yield. The success of the reaction relies on the formation of different types of aryl acetals characterized by different stability, namely stable six membered rings or transient five membered rings or acyclic acetals that undergo reductive etherification. Applying this methodology on compound 7 gave, in contrast to the phase transfer benzylation, a complex mixture of products but when compound 5 was used as precursor four distinctive products could be spotted and isolated, the 6-O-monobenzyl (13), the 3’,6-di-O-benzyl (14), the 3,6-di-O-benzyl (15), and the 3,3’,6-tri-O-benzyl (16) derivatives establishing a reactivity order of the silylated hydroxy groups of 6 > 3’ > 3 >> 2’. The positions of the benzyl groups were determined by HMBC NMR using both the coupling from the benzylic carbon to the corresponding ring proton(s) and the coupling from the benzylic protons to the corresponding ring carbon. Further evidence for the correct assignments were obtained from the downfield shift of the expected ring proton signals after benzoylation of compounds (14 →32 H-2' 5.14 and H-3 5.45 ppm and 16 →35 H-2' 5.22 ppm). As has been shown before the obtained yields and ratio of the compounds were dependent on the amount of benzaldehyde and Et3SiH used as well as on the nature of the Lewis
acid combination which together with 2.5 equiv of both PhCHO and Et3SiH gave good yields of
2’,3,3’-triol 13 (32%) and 2’,3-diol 14 (41%) (Scheme 4 and Table 1). 4.5 equiv. of the same reagents afforded 2’-OH compound 16 in a 60% yield. In the presence of a Lewis acid thioglycosides can anomerize and the rate is enhanced in polar solvents, hence when acetonitrile was used as a solvent in this reaction a minor amount (< 10%) of anomerization was observed.
Table 1. Regioselective benzylation of compound 12
Lewis Acid PhCHO
Eq. Et3SiH Eq Solvent Yield 13 Yield 14 Yield 15 Yield 16 FeCl3·6H2O 2.5 2.5 CH2Cl2 5 11 - -Cu(OTf)2 2.5 2.5 MeCN/CH2Cl2 5 10 - -TMSOTf 2.5 2.5 MeCN/CH2Cl2 15 26 - -CuOTf/TMSOT f 2.5 2.5 MeCN/CH2Cl2 32 41 11 9 CuOTf/TMSOT f 4.5 4.5 MeCN/CH2Cl2 10 21 5 60
Scheme 4. Persilylation followed by regioselective benzylation of compound 5. Reagents and conditions: i) HMDS,
TMSOTf, CH2Cl2, 40 min; ii) PhCHO, Et3SiH, Lewis acid.
The same reaction conditions were also tried on the dibenzylidene acetal derivative (6) obtained as a side product in the formation of 5 and was found to efficiently reductively cleave the acyclic benzylidene acetal but not the cyclic one, to afford the 6-O-benzylated structure 13 in an 83% yield.
Scheme 5. Selective reductive cleavage of acyclic benzylidene acetal in compound 6.. Reagents and conditions: i)
Cu(OTf)2, Et3SiH, CH2Cl2, MeCN, / >10:1.
Selective debenzylation using I2/Et3SiH. 3-O-debenzylation. Treatment of perbenzylated allyl
cellobioside with I2/Et3SiH has been shown to produce exclusive debenzylation at the 3-position to
afford the 3-OH compound in almost quantitative yield (96%).12 However, the same reagent mixture
has been used for reductive opening of benzylidene acetals.13 When compound 5 was perbenzylated
(→17, 88%) and treated with I2/Et3SiH, both reported reactions took place but, to our surprise, the
4’-position was silylated in the obtained product and a 50% yield of compound 18 could be isolated (Scheme 6).
Scheme 6. Benzylation of compound 5 followed by I2/Et3SiH treatment.. Reagents and conditions: i) NaH, BnBr, DMF,
17 h; ii) Et3SiH, I2, CH2Cl2, 4 h, -60 oC ⟶ -10 oC.
Since derivatives with an orthogonal group in the 6’-position were desired the corresponding benzylated naphtylmethylidene acetal 20 was prepared and treated with I2/Et3SiH (Scheme 7). A
similar result as with compound 17 was achieved and a 60% yield of compound 21 could be obtained together with a 32% yield of the 6’-OH derivative 22. The NAP group in derivative 21 could be removed to give additional amounts of derivative 22.
Scheme 7. Preparation and I2/Et3SiH treatment of benzylated naphtylmethylidene acetal 20. Reagents and conditions: i)
(a) NaOMe, MeOH, 3 h, (b) NapDMA, p-TSA, DMF, 20 min, 80 oC; ii) BnBr, NaH, DMF, 3 h; iii) Et
3SiH, I2, CH2Cl2,
4 h, -60 oC ⟶ -10 oC; iv) DDQ, CH
2Cl2, tBuOH, 3 h, 72%.
Continued transformations. Our protecting group strategy of the disaccharide building blocks for
continued synthesis of heparin structures follows the usual approach, initially introduced by Petitou et al.14 with benzyl groups as permanent protection for OH groups in the target structures and
benzoyl groups as temporary protecting groups for positions that will be sulfated in the target structures. The TBDMS group can be used as both a temporary and a permanent protecting group. With the regioselective benzylation/debenzylation methodologies described, a large variety of
sulfation pattern can effectively be accomplished in the disaccharide structure. Phase transfer benzylation giving access to mono-2’ and 3 and di-2’,6 and 3,6-sulfation; tin activation to di-2’,3 and tri-2’,3,6-sulfation; the PhCHO/Et3SiH/CuOTf/ TMSOTf methodology mono-2’, di-2’,3, and
tri-2’,3’,3-sulfation; and the I2/Et3SiH debenzylation to mono-3-sulfation. To prove the feasibility
of the approach a number of the partially benzylated structures were further manipulated using standard techniques to afford disaccharide building blocks suitable for continued synthesis of heparin structures.
Benzoylation of the 2’,3-diol 9 (from the tin activation/benzylation reaction) followed by acid hydrolysis of benzylidene acetal afforded 4,6-diol 24 (81% over two steps, Scheme 8). Regioselective oxidation of 24 using the TEMPO/BAIB reagent system and subsequent methyl ester formation gave the glucuronic acid derivative 25 in a 78% yield. Compound 25 can be used as an acceptor or after 4’-OH protection as a donor.
b9:1 : mixture due to the anomerization observed during the previous silylation-benzylation sequence. Pure compound was
obtained after the benzoylation reaction.
Scheme 8. Preparation of Orthogonally Protected Heparin Building Blocks. Reagents and conditions: i) BzCl, DMAP,
pyridine; ii) CSA, MeOH; iii) (a) TEMPO, BAIB, H2O/CH2Cl2; (b) DMT-MM, NMM, MeOH.
The same reaction sequence was applied to precursors 10, 11, 13, and 15 to afford building blocks 28, 31, 34, 37, respectively, in high yields (>60% yield over 3 steps) (Scheme 8).
Regioselective reductive opening of the benzylidene acetal ring in compounds 17 and 42 (obtained from 7 in three steps), followed by the above mentioned oxidation-esterification sequence instead afforded two disaccharide donors, 39 and 44, respectively, suitable as terminal blocks in the preparation of heparin structures (Scheme 9).
Scheme 9. Preparation of orthogonally protected heparin building blocks 39 and 44. Reagents and conditions: i) BnBr,
NaH, DMF, 16 h; ii) TBAF, THF, 60 oC, 16 h; iii) BzCl, pyridine, 3 h; iv) BH
3.THF, TMSOTf, CH2Cl2; v) (a) TEMPO,
BAIB, H2O, CH2Cl2, (b) DMT-MM, NMM, MeOH.
A different 4’-orthogonally silyl protected disaccharide donor/acceptor building block (46) was obtained from compound 22 after oxidation of the 6’-OH, esterification of the formed carboxyl group (→45, 85%), and final benzoylation (96%) (Scheme 10).
Scheme 10. Preparation of orthogonally protected heparin building block 46. Reagents and conditions: i) (a) TEMPO, BAIB, CH2Cl2, H2O, 45 min, (b) DMT-MM, NMM, MeOH, 30 min; ii)
BzCl, DMAP, pyridine, 3 h.
An optimized pathway to prepare the common intermediate 5 on a 20 g scale comprising only one chromatography step has been developed. Methodologies for following regioselective protection to allow almost any kind of sulfation patterns, 3-, 6-, 2’ and 3’-monosulfation and 3,6-; 2’,6-; and di-sulfation, in the final structures have been worked out. Selective silylation protects the 6-position, tin activated benzylation protects the 3’-position, phase transfer benzylation protects the 3’,3-positions or the 2’,3’-3’,3-positions, benzylation of persilylated 5 with benzaldehyde/Et3SiH affords
3,3’,6-benzylation, whereas debenzylation of perbenzylated 5 using I2/Et3SiH yields
2’,3’,6-benzylation. A number of the selectively protected compounds have been further processed through oxidation and esterification reactions to afford disaccharide thioglycoside building blocks suitable both as donors and acceptors in continued synthesis of larger heparin and heparan sulfate structures. 3. Experimental
3.1. General methods
Normal workup means drying the organic phase with MgSO4 (s) or Na2SO4 (s),
filter-ing and evaporation of the solvent in vacuo at ~35 oC. CH
2Cl2 was distilled over calcium
out on 0.25 mm precoated silica-gel plates (Merck silica-gel 60 F254); detected with UV-abs
(254 nm) and/or by charring with 8% sulfuric acid or AMC (ammonium molybdate (10g) and cerium sulphate (2 g) dissolved in 10 % H2SO4 (200 mL)) followed by heating to ~250 oC. FC means Flash Column chromatography using silica gel (Amicon, (0.040 – 0.063
mm)). 1H-NMR and 13C-NMR spectra were performed on a Varian 300 MHz or 400 MHz
instrument at 25 oC. Chemical shifts are given in ppm relative to solvent peaksfor 13C and =7.26 for 1H) in CDCl
3 or (= 49.0 for 13Cand = 3.31 for 1H) in CD3OD.
Assign-ments were aided by homonuclear (1H-1H) (COSY) and heteronuclear (1H-13C) (DEPT,
HSQC, HMBC) two-dimensional correlation spectroscopies.
3.2. 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl-(1⟶4)-3,6-di-O-acetyl-2-azido-2-deoxy-D-glucopyranose (2).
Compound 1 (50 g, 89 mmol) was dissolved in MeCN (642 mL) under an argon at-mosphere and the temperature was reduced to -20 oC. CAN (147 g, 268 mmol) was added
followed by sodium azide (9.28 g, 143 mmol) and the reaction mixture was then stirred vig-orously with a mechanical stirrer for 24 h. The reaction was monitored by TLC (toluene/EtOAc, 1:1). Upon completion the reaction was diluted with EtOAc and washed twice with ice water. The aqueous phase was re-extracted again with EtOAc. The organic phases were combined and dried over MgSO4 and filtered. The filtrate was evaporated to
dryness. The resulting white solid was dissolved in MeCN (892 mL) and the solution was cooled to 0 oC. PhSH (27.9 mL, 268 mmol) and DIPEA (15.59 mL, 89 mmol) were added
and the solution was stirred for 2 h at 0 oC. Upon completion of the reaction (TLC:
toluene/EtOAc, 1:1) the solution was concentrated. The residue was dissolved in the mini-mum amount of boiling EtOH, a further 100 mL of EtOH was added and the solution was left to crystallize to yield 2 (26 g, 55%) as white crystals. M.p.: 69 - 71 oC; []
D20 +31.1, (c 1.0, CHCl3); (Selected peaks); 1H NMR (500 MHz, CDCl3) 5.50 (dd, J = 10.4, 9.3 Hz, 1H, H-3),5.34 (d, J = 2.1 Hz, 1H, H-1), 5.15 (dd, J = 12.5, 6.1 Hz, 1H, H-3’), 5.09 (apt t, J = 9.6 Hz, 1H, H-4’), 4.94 (dd, J = 9.2, 8.0 Hz, 1H, H-2’), 4.54 (d, J =7.9 Hz, 1H, H-1’), 4.50 (dd, J = 11.9, 2.0 Hz, 1H, H-6a), 4.39 (dd, J = 12.5, 4.2 Hz, 1H, H-6a’), 4.19 (ddd, J = 10.0, 4.4, 1.8Hz, 1H, 5), 4.13 (dd, J= 12.0, 4.5 Hz, 1H, 6b),4.07 (dd, J = 12.5, 2.4 Hz, 1H, H-6b’), 3.75 – 3.70 (m, 1H, H-4), 3.67 (ddd, J = 9.8, 4.0, 2.4 Hz, 1H, H-5’), 3.29 (dd, J = 3.09, 10.58 Hz, 1, H-2), 3.24 (d, J = 3.15 Hz, 1H, OH), 2.13 (s, 3H, COOCH3), 2.11 (s, 3H,
COOCH3), 2.10 (s, 3H, COOCH3), 2.03 (s, 3H, OOCH3), 2.01 (s, 3H, COOCH3), 1.99 (s,
100.7, 92.1, 76.5, 72.9, 72.0, 71.7, 69.7, 68.6, 67.9, 61.8, 61.7, 61.6, 20.8, 20.8, 20.6, 20.6, 20.5, 20.5; Anal. Calcd for C24H33N3O13: C, 46.53; H, 5.37; N, 6.78. Found: C, 46.8; H, 5.26;
N, 6.48; HRMS: m/z [M+Na+]+ calculated for C
24H33N3O16Na: 642.1759, found: 642.1786.
3.3. Ethyl 2,3,4,6-tetra-O-acetly--D-glucopyranosyl-(1⟶4)-3,6-di-O-acetyl-2-azido-2-deoxy-1-thio--D-glucopyranoside (3).
Compound 2 (50 g, 81 mmol) was dissolved in anhydrous CH2Cl2 (1.2 L). Potassium
carbonate (27.9 g, 202 mmol) was added followed by trichloroacetonitrile (52.6 mL, 525 mmol). The mixture was stirred vigorously for 17 h. Upon complete conversion of the starting material, the mixture was filtered through a pad of celite and the filtrate was concentrated and dried. The residue was then dissolved in anhydrous CH2Cl2 (1.3 L) and 4 Å molecular sieves were added. EtSH (65.6
mL, 888 mmol) and BF3·Et2O (11 mL, 89 mmol) were added and the solution was stirred for a
further 17 h. Upon completion of the reaction (TLC: toluene/EtOAc: 1:1) the solution was concentrated. The residue was recrystalized from EtOH to give 3 (35.6 g, 64%) as clear plates.
M.p.: 98 - 99 oC; [] D20 +72.4 (c 1.0 CHCl3); 1H NMR (500 MHz, CDCl3) 5.38 (d, J = 5.6 Hz, 1H, H-1), 5.25 (dd, J = 10.2, 9.4 Hz, 1H, H-3), 5.15 (apt t, J = 9.3 Hz, 1H, H-3'), 5.09 (apt t, J = 9.6 Hz, 1H, H-4’), 4.92 (dd, J = 9.1, 8.0 Hz, 1H, H-2’), 4.51 (d, J = 7.9 Hz, 1H, H-1’), 4.44 (dd, J = 12.0, 1.9 Hz, 1H, 6a), 4.39 (dd, J = 12.5, 4.2 Hz, 1H, 6a’), 4.34 (ddd, J = 10.1, 4.9, 1.8 Hz, 1H, H-5), 4.18 (dd, J = 12.0, 5.1 Hz, 1H, H-6b’), 4.07 (dd, J = 12.5, 2.3 Hz, 1H, H-6b), 3.89 (dd, J = 10.5, 5.6 Hz, 1H, H-2), 3.72 – 3.64 (m, 2H, H-4, H-5’), 2.68 – 2.53 (m, 2H, SCH2), 2.12 (s, 3H,
OCOCH3), 2.09 (m, 6H, OCOCH3), 2.04 (s, 3H, OCOCH3), 2.01 (s, 3H, OCOCH3), 1.98 (s, 3H,
OCOCH3), 1.30 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (125 MHz, CDCl3) 170.4, 170.2, 170.2,
169.2, 169.2, 168.9, 100.7, 83.0, 76.8, 73.0, 72.0, 71.7, 71.3, 69.0, 67.8, 61.9, 61.9, 61.6, 24.7, 20.8, 20.6, 20.6, 20.5, 20.5, 14.6; HRMS (ESI) m/z: [M - H+]- calcd for C
26H37N3O15S: 662.1867, found:
3.4. Ethyl 1-thio--D-glucopyranoside (5) and Ethyl 4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-2-deoxy-6-O-(methoxy-phenyl-methyl)-1-thio--D-glucopyranoside (6).
Compound 3 (35.6 g, 53.6 mmol) was suspended in MeOH (700 mL). This was treated with a freshly prepared solution of NaOMe and stirred for 3 h. Upon completion of the reaction the solution was neutralized with DOWEX-50Wx80 ion exchange resin. The solution was filtered, concentrated and co-evaporated with toluene three times. The residue was then dissolved in dry DMF (280 mL). Benzaldehyde dimethyl acetal (25.2 mL, 109 mmol) and CSA (6.5 g, 28.0 mmol) were added and the reaction mixture was stirred overnight at 60 oC. After 17 h, Et
3N was added and
the solution was evaporated. Silica gel chromatography (CH2Cl2/MeOH: 29:1) afforded compound
5 (19.32 g, 72%) as a white solid and compound 6 (3.32 g, 10%) as a colorless syrup. 5: []D20
+84.3 (c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3) 7.48 (m, 2H, Ar-H), 7.38 (m, 3H, Ar-H), 5.52 (s, 1H, PhCH), 5.32 (d, J = 5.5 Hz, 1H, H-1), 4.55 (d, J = 8.1 Hz, 1H, H-1’), 4.36 (dd, J = 10.7, 3.8 Hz, 1H, H-6a), 4.16 (ddd, J = 9.7, 3.0 Hz, 1H, H-5), 3.99 – 3.93 (m, 1H, H-6a’), 3.91 – 3.85 (m, 1H, H-3), 3.84 – 3.75 (m, 3H, H-6b, H-5’, H-6b’), 3.73 – 3.69 (m, 1H, H-2), 3.62 (apt t, J = 9.2 Hz, 1H, H-4), 3.56 – 3.52 (m, 3H, H-2’, H-3’, H-4’), 2.64 – 2.55 (m, 2H, SCH2), 1.29 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 129.4, 128.4, 126.2, 104.1, 102.0, 83.5, 82.6, 80.0, 74.2,
73.4, 71.8, 70.2, 68.2, 66.7, 63.2, 62.0, 25.0, 14.7; HRMS (ESI) m/z: [M - H+]- calcd for
C21H28N3O9S: 498.1546, found: 498.1575.
6: Diastereoisomers in about 1:1 ratio; 1H NMR (500 MHz, CDCl
3) selected signals: 7.49 – 7.34 (m, 20H, Ar-H), 5.53 (s, 2H, PhCH), 5.50 (s, 1H, PhCH), 5.48 (s, 1H, PhCH), 5.34 (d, J = 5.5 Hz, 1H, H-1), 5.31 (d, J = 5.5 Hz, 1H, H-1), 4.50 (d, J = 7.8 Hz, 1H, H-1’), 3.34 (s, 3H, OMe), 3.33 (s, 3H, OMe), 2.65 – 2.48 (m, 4H, SCH2), 1.30 – 1.24 (m, 6H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 137.8, 137.7, 136.8, 136.8, 129.5, 129.5, 129.0, 128.9, 128.5, 128.5, 126.9, 126.4, 126.4, 104.2, 104.1, 103.3, 103.3, 102.1, 102.1, 83.4, 83.4, 82.8, 82.4, 80.2, 80.1, 74.6, 74.4, 73.6, 73.5, 72.1, 72.0, 69.6, 69.5, 68.4, 68.3, 66.8, 66.7, 65.4, 64.4, 63.3, 63.2, 53.7, 53.1, 25.0, 25.0, 14.9, 14.8; HRMS (ESI) m/z: [M + Na]+ calcd for C
29H37N3O10NaS: 642.2097, found: 642.2124.
3.5. Ethyl 4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-2-deoxy-6-O-(tert-butyldiphenylsilyl)-1-thio--D-glucopyranoside (7).
Compound 5 (13 g, 26 mmol) was dissolved in DMF (133 mL) and cooled to 0 oC. Imidazole
(3.54 g, 52 mmol) was added followed by a drop wise addition of TBDPSCl over 5 mins. The solution was stirred at 0 oC for 1 h or until TLC showed completion of the reaction. MeOH (5 mL)
evaporated to dryness and purified by silica gel chromatography (cyclohexane/EtOAc: 4:1 to 1:4) to yield 7 (14.17 g, 74%) as white foam. []D20 +62.9 (c 1.0, CHCl3); 1H NMR (600 MHz, CDCl3)
7.71 (m, 4H, Ar-H), 7.50 – 7.31 (m, 10H, Ar-H), 5.52 (s, 1H, PhCH), 5.35 (d, J = 5.5 Hz, 1H, H-1), 4.53 (d, J = 7.8 Hz, 1H, H-1'), 4.36 (dd, J = 10.4, 5.0 Hz, 1H, H-6a'), 4.19 – 4.15 (m, 1H, H-5), 4.06 (dd, J = 11.6, 3.8 Hz, 1H, 6a), 3.91 (dd, J = 11.7, 1.9 Hz, 1H, 6b), 3.88 (d, J = 8.9 Hz, 1H, H-3), 3.85 (s, 1H, OH) 3.79 – 3.68 (m, 4H, H-2, H-4, H-3', H-6b'), 3.53 (apt t, J = 9.3 Hz, 1H, H-4'), 3.48 – 3.42 (m, 2H, H-2', H-5'), 2.67 (s, 1H, OH), 2.60 – 2.48 (m, 2H, SCH2), 2.39 (s, 1H, OH), 1.25 (t, J = 7.4 Hz, 3H, SCH2CH3), 1.07 (s, J = 6.3 Hz, 9H, SiC(CH3)3); 13C NMR (151 MHz, CDCl3) 136.7, 135.8, 135.6, 133.4, 133.0, 129.8 (2C), 129.4, 128.4, 127.8, 127.6, 126.3, 103.6, 102.0 , 82.8, 81.1, 80.1, 74.3, 73.4, 71.8, 71.0, 68.3, 66.7, 63.4, 62.5, 26.8, 24.7, 19.4, 14.6; HRMS (ESI) m/z: [M – H+]- calcd for C
37H46N3O9SSi: 736.2724, found: 736.2733
3.6. Ethyl 3-O-benzyl-4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-2-deoxy-1-thio--D-glucopyranoside (8).
Compound 5 (1 g, 2 mmol) and dibutlytin oxide (0.6 g, 2.4 mmol) were suspended in toluene (25 mL) and heated to reflux. Moisture was removed with a dean stark apparatus and the reaction was stirred vigorously overnight. After 17 h the reaction was concentrated to ~25 mL and BnBr (0.5) was added followed by Bu4NI (0.74 g, 2 mmol). The reaction was stirred for 3 h before it was
concentrated. Purification by silica gel chromatography (cyclohexane/EtOAc: 1:1 to 1:2) yielded 8 (0.89 g, 75%) as a white solid. []D20 +61.2 (c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3) 7.48 – 7.44 (m, 2H, Ar-H), 7.40 – 7.23 (m, 8H, Ar-H), 5.53 (s, 1H, PhCH), 5.29 (d, J = 5.5 Hz, 1H, H-1), 4.95 (d, J = 11.6 Hz, 1H, BnCH2), 4.74 (d, J = 11.7 Hz, 1H, BnCH2), 4.50 (d, J = 7.7 Hz, 1H, BnCH2), 4.33 (dd, J = 10.4, 4.9 Hz, 1H, H-6a), 4.13 (ddd, J = 9.7, 3.3 Hz, 1H, H-5), 4.05 (s, 1H, OH-3), 3.93 – 3.84 (m, 2H, H-3, H-6a'), 3.79 – 3.61 (m, 5H, H-2, H-6b, H-3', H-4', H-6b'), 3.61 – 3.53 (m, 2H, H-2', H-4), 3.52 – 3.47 (m, 1H, H-5'), 2.99 – 2.93 (m, 1H, OH-6), 2.62 – 2.48 (m, 2H, SCH2), 1.26 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 138.1, 137.0, 129.1, 128.5, 128.3, 128.1, 128.0, 126.0, 104.3, 101.3, 83.4, 82.9, 81.0, 80.5, 74.2, 73.7, 71.8, 70.3, 68.2, 66.6, 63.2, 61.9, 24.9, 14.7; HRMS (ESI) m/z: [M – H+]- calcd for C
28H36N3O9S: 590.2172, found:
590.2179.
3.7. Ethyl 3-O-benzyl-4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-2-deoxy-6-O-(tert-butyldiphenylsilyl)-1-thio--D-glucopyranoside (9).
Compound 7 (3.9 g, 5.29 mmol) and dibutlytin oxide (1.58 g, 6.34 mmol) were suspended in toluene (70 mL) and heated to reflux. Moisture was removed with a dean stark apparatus and the reaction was stirred vigorously overnight. After 17 h the reaction was concentrated to ~40 mL and BnBr (1.25 mL, 10.57 mmol) was added followed by Bu4NI (1.95 g, 5.3 mmol). The reaction was
stirred for 3 h before it was concentrated. Purification by silica gel chromatography (cyclohexane/EtOAc: 5:1 to 1:1) yielded 9 (3.5 g, 85%) as a white solid. []D20 +51.5 (c 1.0,
CHCl3); 1H NMR (500 MHz, CDCl3) 7.70 (m, 4H, Ar-H), 7.48 (m, 2H, Ar-H), 7.44 – 7.29 (m, 14H, Ar-H), 5.56 (s, 1H, PhCH), 5.36 (d, J = 5.5 Hz, 1H, H-1), 4.96 (d, J = 11.7 Hz, 1H, BnCH2), 4.75 (d, J = 11.7 Hz, 1H, BnCH2), 4.51 (d, J = 7.7 Hz, 1H, 1'), 4.36 (dd, J = 10.4, 5.0 Hz, 1H, 6a'), 4.18 – 4.13 (m, 1H, 5), 4.06 (dd, J = 11.6, 3.9 Hz, 1H, 6a), 3.93 – 3.87 (m, 2H, 3, H-6b), 3.87 (s, 1H, OH-3), 3.78 (apt t, J = 10.3 Hz, 1H, H-6b'), 3.74 (dd, J = 10.3, 5.5 Hz, 1H, H-2), 3.69 (apt t, J = 9.4 Hz, 1H, H-4), 3.55 (apt t, J = 9.0 Hz, 1H, H-3'), 3.50 – 3.46 (m, 1H, H-2'), 3.46 – 3.41 (m, 1H, H-5'), 2.62 – 2.47 (m, 2H, SCH2), 2.22 (d, J = 2.9 Hz, 1H, OH-2'), 1.25 (t, J = 7.4 Hz, 3H, SCH2CH3), 1.05 (s, 9H, SitBu); 13C NMR (126 MHz, CDCl3) 138.2, 137.0, 135.9, 135.6, 133.1, 129.8, 129.7, 129.1, 128.5, 128.3, 128.0, 128.0, 127.7, 127.6, 126.0, 103.8, 101.4, 82.1, 81.2, 81.0, 80.3, 74.7, 73.9, 71.8, 71.0, 68.3, 66.6, 63.4, 62.4, 26.8, 24.6, 19.3, 14.6; HRMS (ESI) m/z: [M + Na]+ calcd for C
44H53N3O9NaSiS: 850.3170, found: 850.3199.
3.8. Ethyl 2,3-di-O-benzyl-4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-2-deoxy-1-thio--D-glucopyranoside (10) and Ethyl 3-O-benzyl-4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-3-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (11).
Compound 7 (3.1 g, 4.20 mmol), 1 M NaOH (7.86 mL) and Bu4NHSO4 (0.35 g, 1.085 mmol)
were added to flask and dissolved in CH2Cl2 (90 mL), BnBr (1.74 mL, 14.7 mmol) was added and
the reaction and stirred vigorously at reflux (40 oC) overnight. The reaction was then diluted with
CH2Cl2, washed with water, dried with MgSO4 and filtered. The filtrate was then concentrated. The
mixture was purified by silica gel chromatography (pentane/EtOAc: 17:3) and the compound at Rf
0.7 (pentane/EtOAc; 17:3) was isolated as a white foam. The mixture (2.5 g, 2.72 mmol) was dissolved in THF (27.2 mL) at r.t. and TBAF (3.5 mL, 3.5 mmol, 1 M in THF) was added drop wise. The reaction was heated to 60 oC and stirred for 17 h. Upon completion of reaction the
solution was concentrated in vacuo. Purification by silica gel chromatography (pentane/EtOAc: 10:1 to 1:1) yielded 11 (1.78 g, 48%) as a white foam and 10 (0.8 g, 21%) also as a white foam. Data for Ethyl 3-O-benzyl-4,6-O-benzylidine--D -glucopyranosyl-(1⟶4)-2-azido-3-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (11). []D20 +78.7(c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3)
7.44 (m, 2H, Ar-H), 7.37 (m, 6H, Ar-H), 7.33 (m, 4H, Ar-H), 7.31 – 7.27 (m, 2H, Ar-H), 5.47 (s, 1H, PhCH), 5.37 (d, J = 5.5 Hz, 1H, H-1), 4.96 (m, 2H, BnCH2), 4.84 (d, J = 10.9 Hz, 1H, BnCH2), 4.75 – 4.68 (m, 2H, BnCH2, H-1'), 4.13 (dd, J = 7.1, 4.8 Hz, 1H, H-5), 4.07 (dd, J = 12.6, 4.5 Hz, 1H, H-6a), 3.96 (apt t, J = 9.3 Hz, 1H, H-4), 3.90 (dd, J = 10.5, 5.0 Hz, 1H, H-6b), 3.84 (dd, J = 10.1, 5.5 Hz, 1H, H-2), 3.75 (m 2H, H-3, H-6a'), 3.64 – 3.57 (m, 2H, H-3', H-4'), 3.53 (apt t, J = 8.0 Hz, 1H, H-2'), 3.47 (apt t, J = 10.3 Hz, 1H, H-6b'), 3.25 (ddd, J = 9.7, 5.0 Hz, 1H, H-5'), 2.94 (s, 1H, OH-2'), 2.65 – 2.50 (m, 3H, SCH2, OH-6), 1.29 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 138.3, 138.1, 137.2, 129.0, 128.6, 128.3, 128.3, 128.1, 128.0, 127.6, 126.9, 126.0, 103.9, 101.2, 83.4, 81.3, 80.7, 80.3, 77.8, 75.1, 75.0, 74.6, 71.5, 68.5, 66.6, 64.0, 61.0, 24.7, 14.7; HRMS (ESI) m/z: [M + Na]+ calcd for C
35H41N3O9NaS: 702.2461, found: 702.2482.
Data for ethyl 2,3-di-O-benzyl-4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-2-deoxy-1-thio--D-glucopyranoside (10): []D20 +68.2(c 1.0, CHCl3) 1H NMR (500 MHz, CDCl3) 8.06 –
8.02 (m, 2H, Ar-H), 7.93 – 7.89 (m, 2H, Ar-H), 7.57 (t, J = 7.4 Hz, 1H, Ar-H), 7.48 – 7.34 (m, 14H, Ar-H), 7.31 (t, J = 7.2 Hz, 1H, Ar-H), 7.13 – 7.02 (m, 5H, Ar-H), 5.49 (s, 1H, PhCH), 5.35 (apt t, J = 8.4 Hz, 1H, H-2'), 5.30 (d, J = 5.6 Hz, 1H, H-1), 5.03 (d, J = 10.5 Hz, 1H, BnCH2), 4.79 (m, 2H, BnCH2), 4.71 (d, J = 7.9 Hz, 1H, H-1'), 4.63 (d, J = 12.0 Hz, 1H, BnCH2), 4.45 (dd, J = 12.1, 4.6 Hz, 1H, H-6a), 4.36 (dd, J = 12.0, 1.4 Hz, 1H, H-6b), 4.18 (dd, J = 10.0, 3.0 Hz, 1H, H-5), 4.09 (dd, J = 10.5, 4.8 Hz, 1H, H-6'), 3.92 – 3.87 (m, 1H, H-4), 3.85 (dd, J = 10.2, 5.6 Hz, 1H, H-2), 3.80 (apt t, J = 9.0 Hz, 1H, H-3'), 3.78 – 3.71 (m, 2H, H-3, H-4'), 3.39 (apt t, J = 10.3 Hz, 1H, H-6'), 3.32 – 3.26 (m, 1H, H-5'), 2.49 (tdd, J = 12.8, 7.4, 5.4 Hz, 2H, SCH2), 1.19 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl 3) 165.9, 164.9, 138.1, 137.6, 137.1, 133.3, 133.3, 129.9, 129.6, 129.5, 129.2, 129.1, 128.5, 128.5, 128.3, 128.3, 128.1, 127.9, 127.8, 127.7, 127.6, 126.0, 101.6, 101.2, 82.9, 81.6, 79.6, 78.1, 78.1, 75.6, 74.2, 73.8, 69.4, 68.3, 66.4, 63.4, 62.6, 24.5, 14.5; HRMS (ESI) m/z: [M + Na]+ calcd for C
35H41N3O9NaS: 702.2461, found: 702.2473.
3.9. Ethyl 4,6-O-benzylidene-2,3-di-O-trimethylsilyl--D-glucopyranosyl-(1⟶4)-2-azido-2-deoxy-1-thio-3,6-di-O-trimethylsilyl--D-glucopyranoside (12).
Compound 5 (1.0 g, 2.0 mmol) was dissolved in CH2Cl2 (20 mL). HMDS (freshly distilled,
2.1 mL) was added and the reaction was cooled in an ice bath. TMSOTf (0.036 mL) was added and the reaction was stirred for 40 mins while allowing to warm to r.t. The reaction was diluted with CH2Cl2 and washed with water (3 times). The organic phase was dried with MgSO4 and filtered.
The filtrate was then concentrated to yield analytically pure 12 (1.56 g, 99%) as a white foam. []D20 +109.0 (c 1.0, CHCl3) 1H NMR (500 MHz, CDCl3) 7.48 (dd, J = 7.3, 2.4 Hz, 2H, Ar-H),
Hz, 1H, H-1'), 4.42 (dd, J = 10.4, 5.0 Hz, 1H, H-6a'), 4.07 (dd, J = 11.7, 2.6 Hz, 1H, H-6a), 4.01 (ddd, J = 9.8, 2.1 Hz, 1H, H-5), 3.80 (dd, J = 9.8, 8.3 Hz, 1H, H-3), 3.76 – 3.67 (m, 4H, H-2, H-4, H-6b, H-6b'), 3.65 (apt t, J = 8.7 Hz, 1H, H-3'), 3.43 – 3.38 (m, 2H, H-2', H-4'), 3.31 (ddd, J = 9.6, 4.9 Hz, 1H, H-5'), 2.64 – 2.53 (m, 2H, SCH2), 1.29 (t, J = 7.4 Hz, 3H, SCH2CH3), 0.20 (s, 9H, TMS), 0.15 (d, J = 2.9 Hz, 18H, TMS), 0.09 (s, 9H, TMS); 13C NMR (126 MHz, CDCl 3) 137.1, 128.8, 128.0, 126.2, 102.2, 101.8, 83.3, 81.4, 76.0, 75.5, 75.3, 72.9, 71.6, 68.9, 66.3, 65.3, 60.3, 24.6, 14.7, 0.8 (3C), 0.7 (3C), 0.3 (3C), -0.3 (3C); HRMS (ESI) m/z: [M + Na]+ calcd for
C33H61N3O9SSi4: 810.3103, found: 810.3093.
3.10. Ethyl 4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-6-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (13), Ethyl 3-O-benzyl-glucopyranosyl-(1⟶4)-2-azido-6-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (14), Ethyl 4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-3,6-di-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (15), Ethyl 3-O-benzyl-4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-3,6-di-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (16). Note: compounds 13, 14, 15 and 16 can be made in different ratios depending what method is used.
Method A: Compound 12 (1.5 g, 1.903 mmol) was dissolved in CH2Cl2 (3 mL) in the presence
of 4 Å molecular sieves and cooled to 0 oC in an ice bath. PhCHO (0.48 mL, 2.5 Eq) was added
followed by a solution of Cu(OTf)2 (0.07 g, 0.19 mmol) in MeCN (0.1 mL)and the reaction was
stirred for 15 mins. Triethylsilane (0.85 mL) was added drop wise followed by TMSOTF (0.1 mL) and the reaction was stirred for 30 mins. Upon complete disappearance of the starting material, TBAF in THF (4.5 mL, 1M) was added and the reaction was stirred for 5 mins. The reaction was diluted with CH2Cl2 and washed with NaHCO3 and brine. The organic layer was dried with MgSO4
and filtered. The filtrate was concentrated and the crude product mixture was purified by silica gel chromatography (cyclohexane/EtOAc: 15:1 to 0:1) to yield (in order of elution from column) 16 (0.132 g, 9%), 14 (0.530 g, 41%), 15 (0.142 g, 11%) and 13 (0.36 g, 32%), all as white foams.
Method B: Compound 12 (2 g, 2.54 mmol) was dissolved in CH2Cl2 (4 mL) in the presence of
molecular sieves and cooled in an ice bath. Benzaldehyde (1.16 mL, 4.5 Eq) was added followed by a solution of Cu(OTf)2 (0.09 g, 0.254 mmol)and the reaction was stirred for 15 mins. Triethylsilane
(1.85 mL) was added drop wise followed by TMSOTF (0.16 mL) and the reaction was stirred for 30 mins. Upon complete disappearance of the starting material TBAF in THF (1 M, 6 mL) was added and the reaction was stirred for 5 mins. The reaction was diluted with CH2Cl2 and washed with
NaHCO3 and brine. The organic layer was dried with MgSO4, filtered and concentrated. The crude
yield (in order of elution from column) 16 (1.17 g, 60%), 14 (0.362 g, 21%), 15 (0.086 g, 5%) and 13 (0.15 g, 10%), all as white foams in an / ratio of 10:1.
13: (Selected peaks for -thio anomer) 1H NMR (500 MHz, CDCl
3) 7.49 – 7.45 (m, 2H, Ar-H), 7.39 – 7.28 (m, 7H, Ar-H), 7.27 – 7.21 (m, 1H, Ar-H), 5.46 (s, 1H, PhCH), 5.32 (d, J = 5.4 Hz, 1H, H-1), 4.62 (d, J = 12.0 Hz, 1H, BnCH2), 4.52 (d, J = 11.9 Hz, 1H, BnCH2), 4.33 – 4.28 (m, 2H, H-1', H-6'), 4.23 (ddd, J = 9.8, 3.1 Hz, 1H, H-5), 3.93 – 3.89 (m, 1H, OH-3), 3.88 – 3.80 (m, 2H, H-3, H-4), 3.74 – 3.60 (m, 5H, H-2, H-6a, H-6b, H-3', H-6b'), 3.49 – 3.34 (m, 3H, H-2', H-4', H-5'), 3.28 (d, J = 3.2 Hz, 1H, OH-2'), 3.18 (d, J = 2.6 Hz, 1H, OH-3'), 2.66 – 2.49 (m, 2H, SCH2), 1.27 (t, J = 7.4 Hz, 3H, SCH2CH3);13C NMR (126 MHz, CDCl3) 137.7, 136.7, 129.4, 128.5, 128.4, 128.1, 128.0, 126.3, 103.7, 101.9, 83.4, 81.9, 80.0, 74.2, 73.5, 73.3, 71.7, 69.4, 68.6, 68.2, 66.6, 63.2, 25.0, 14.8; HRMS (ESI) m/z: [M + Na]+ calcd for C
28H35N3O9NaS: 612.1992, found: 612.1971.
14: (Selected peaks for -thio anomer) 1H NMR (500 MHz, CDCl
3) 7.47 (dd, J = 7.8, 2.0 Hz, 2H, Ar-H), 7.40 – 7.23 (m, 15H, Ar-H), 5.52 (s, 1H, PhCH), 5.33 (d, J = 5.5 Hz, 1H, H-1), 4.95 (d, J = 11.8 Hz, 1H, BnCH2), 4.76 (d, J = 11.7 Hz, 1H, BnCH2), 4.61 (d, J = 11.9 Hz, 1H, BnCH2), 4.48 (d, J = 11.9 Hz, 1H, BnCH2), 4.34 – 4.26 (m, 2H, H-1', H-6a'), 4.23 (ddd, J = 9.9, 2.9 Hz, 1H, H-5), 3.88 (dd, J = 10.9, 3.3 Hz, 1H, H-6a), 3.84 (dd, J = 10.3, 8.6 Hz, 1H, H-3), 3.75 – 3.65 (m, 3H, H-2, H-6, H-4'), 3.67 – 3.59 (m, 2H, H-4, H-6b'), 3.55 – 3.45 (m, 2H, H-2', H-3'), 3.36 (ddd, J = 9.8, 5.0 Hz, 1H, H-5'), 2.66 – 2.48 (m, 2H, SCH2), 1.26 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 138.2, 137.9, 137.1, 129.1, 128.5 (2C), 128.5, 128.3, 128.2, 128.1, 127.9, 126.1, 103.9, 101.3, 83.5, 81.6, 81.0, 80.2, 74.5, 73.9, 73.5, 71.8, 69.5, 68.4, 68.3, 66.6, 63.2, 25.0, 14.8; HRMS (ESI) m/z: [M + Na]+ calcd for C
35H41N3O9S: 702.2461, found: 702.2466.
15: (Selected peaks for -thio anomer) 1H NMR (500 MHz, CDCl
3) 7.46 – 7.43 (m, 2H, Ar-H), 7.39 – 7.25 (m, 14H, Ar-H), 5.39 (s, 1H, PhCH), 5.36 (d, J = 5.6 Hz, 1H, H-1, BnCH2), 4.95 (d, J = 10.6 Hz, 1H, BnCH2), 4.73 (d, J = 10.5 Hz, 1H, BnCH2), 4.68 (d, J = 12.0 Hz, 1H, BnCH), 4.51 – 4.45 (m, 2H, BnCH2, H-1’), 4.21 (ddd, J = 2.43, 2.43, 9.98 Hz, 1H, H-5), 4.07 – 3.99 (m, 3H), 3.85 (dd, J = 10.1, 5.5 Hz, 1H), 3.73 – 3.63 (m, 2H), 3.54 (ddd, J = 9.1, 2.2 Hz, 1H), 3.42 – 3.34 (m, 3H), 3.25 (d, J = 3.1 Hz, 1H), 3.10 – 3.04 (ddd, J = 4.98, 9.74, 9.78 Hz, 1H, H-5’), 2.64 – 2.50 (m, 2H, SCH2), 1.28 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 138.2, 137.6, 137.0, 129.3, 128.6, 128.4, 128.3, 128.0, 128.0, 127.7, 127.6, 126.3, 103.0, 101.8, 83.3, 80.5, 80.2, 77.5, 75.2, 75.1, 73.5, 73.4, 70.9, 68.5, 68.2, 66.3, 63.5, 24.7, 14.8; HRMS (ESI) m/z: [M + Na]+ calcd
16: (Selected peaks for -thio anomer) 1H NMR (500 MHz, CDCl 3) 7.55 – 7.17 (m, 20H, Ar-H), 5.45 (s, 1H, PhCH), 5.38 (d, J = 5.6 Hz, 1H, H-1), 4.99 – 4.91 (m, 2H, BnCH2), 4.78 – 4.70 (m, 2H, BnCH2), 4.68 (d, J = 12.0 Hz, 1H, BnCH2), 4.48 – 4.42 (m, 2H, H-1', BnCH2), 4.22 (ddd, J = 9.8, 2.4 Hz, 1H, H-5), 4.09 – 4.00 (m, 3H, H-4, H-6a, H-6a'), 3.86 (dd, J = 10.2, 5.6 Hz, 1H, H-2), 3.71 (dd, J = 10.2, 8.9 Hz, 1H, H-3), 3.65 (dd, J = 11.1, 2.0 Hz, 1H, H-6b), 3.56 (apt t, J = 9.0 Hz, 1H, H-4'), 3.48 – 3.36 (m, 3H, H-2', H-3', H-6b'), 3.08 (ddd, J = 9.6, 4.9 Hz, 1H, H-5'), 2.67 – 2.51 (m, 2H, SCH2), 1.28 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 138.4, 138.3, 137.7, 137.3, 129.0, 128.5, 128.5, 128.2, 128.2, 128.1, 128.0, 128.0, 127.8, 127.6, 127.6, 126.1, 103.0, 101.2, 83.4, 81.4, 80.3, 80.2, 77.5, 75.2, 74.8, 74.5, 73.5, 70.9, 68.6, 68.1, 66.3, 63.5, 24.7, 14.7; HRMS (ESI) m/z: [M + Na]+ calcd for C
42H47N3O9NaS: 792.2933, found: 792.2933.
Alternative synthesis of 13 from 6: compound 6 (0.2 g, 0.323 mmol) was dissolved in dry CH2Cl2
(1.3ml) and cooled to 0 oC. Copper triflate (5.8 mg, 0.016 mmol) was dissolved in the minimum
amount of dry MeCN with sonication. Triethylsilane (0.062 ml) was added followed by the addition of copper triflate. The reaction was stirred for 30 mins and then quenched with Et3N (0.5 ml). The
reaction mixture was diluted with EtOAc and washed with sat NaHCO3, 1 M HCl, and brine.
Purification by silica gel column chromatography (cyclohexane/EtOAc: 5:1 to 0:1) yielded 13 (0.158 g, 83%) as a white foam in an alpha/beta mixture of 9:1.
3.11. Ethyl 2,3-di-O-benzyl-4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-2,3-di-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (17).
Compound 5 (2 g, 4.00 mmol) was dissolved in DMF (40 mL) and cooled to 0 oC. NaH (1.25
g, 32.6 mmol) was added and the solution was stirred for 20 mins. BnBr (8.5 mL) was added and the reaction mixture was stirred overnight at r.t. MeOH (5 mL) was then added to quench the reaction and the mixture was concentrated. The crude residue was dissolved/suspended in EtOAc and a large volume of water was added. This was then extracted 5 times with EtOAc. The organic phases were combined and washed once with brine, dried over MgSO4 and filtered. The filtrate was
then concentrated. Purification was by column chromatography (pentane/EtOAc: 20:1 to 1:1) to give 17 (3.03 g, 88%) as a colourless oil. []D20 +44.5 (c 1.0, CHCl3);1H NMR (500 MHz, CDCl3)
7.48 (dd, J = 7.7, 1.9 Hz, 2H, Ar-H), 7.42 – 7.22 (m, 23H, Ar-H), 5.46 (s, 1H, PhCH), 5.37 (d, J = 5.6 Hz, 1H, H-1), 4.97 (d, J = 10.3 Hz, 1H, BnCH2), 4.90 (d, J = 11.4 Hz, 1H, BnCH2), 4.84 (d, J = 11.2 Hz, 1H, BnCH2), 4.81 – 4.74 (m, 2H, BnCH2), 4.69 (d, J = 10.3 Hz, 1H, BnCH2), 4.60 (d, J = 11.9 Hz, 1H, BnCH2), 4.39 (d, J = 7.8 Hz, 1H, H-1'), 4.32 (d, J = 12.0 Hz, 1H, BnCH2), 4.13 (dd, J = 10.5, 5.0 Hz, 1H, H-6a'), 4.08 – 4.00 (m, 2H, H-4, H-5), 3.91 (dd, J = 11.0, 2.5 Hz, 1H, H-6a), 3.85 (dd, J = 10.2, 5.6 Hz, 1H, H-2), 3.66 (dd, J = 10.3, 7.9 Hz, 1H. H-3), 3.59 – 3.51 (m, 2H, H-3',
H-4'), 3.43 (dd, J = 11.0, 1.5 Hz, 1H, H-6b), 3.39 – 3.33 (m, 2H, H-2', H-6b'), 3.08 (ddd, J = 9.3, 4.9 Hz, 1H, H-5'), 2.67 – 2.52 (m, 2H, SCH2), 1.31 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126
MHz, CDCl3) 138.5, 138.3, 138.2, 137.7, 137.4, 128.9, 128.5, 128.3, 128.2, 128.2, 128.2, 128.0,
128.0, 127.9, 127.9 (2C), 127.7, 127.6, 127.6, 126.0, 102.8, 101.1, 83.3, 82.5, 81.7, 81.0, 79.8, 77.0, 75.6, 75.3, 74.9, 73.3, 71.1, 68.6, 67.6, 65.8, 63.2, 24.7, 14.7; HRMS (ESI) m/z: [M + Na]+ calcd
for C49H53N3O9NaS: 882.3400, found: 882.3417.
3.12. Ethyl 2,3,6-tri-O-benzyl-4-O-triethylsilyl--D-glucopyranosyl-(1⟶4)-2-azido-6-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (18).
Compound 17 (0.1 g, 0.116 mmol) was dissolved in CH2Cl2 (1.2 mL) and cooled to -60 oC. I2
(0.038 g, 0.151 mmol) was added followed by the slow addition of Et3SiH (0.023 mL). The reaction
was stirred while allowing to slowly warm to -10 oC over 4 h. Et
3N (0.1 mL) was added followed by
MeOH (0.1 mL) and the reaction was allowed to warm to r.t. The reaction was then diluted with CH2Cl2 and washed with satd. NaHCO3. The organic phase was dried with MgSO4 and filtered. The
filtrate was then concentrated and purified by silica gel chromatography (pentane/Et2O; 8:1 to 0:1)
to afford 18 (0.052 g, 50%) as a white foam. []D20 +96.3, (c 1.0, CHCl3), 1H NMR (500 MHz,
CDCl3) 7.40 – 7.31 (m, 5H, Ar-H), 7.33 – 7.15 (m, 15H, Ar-H), 5.33 (d, J = 5.5 Hz, 1H, H-1), 4.96 (d, J = 11.3 Hz, 1H, BnCH2), 4.76 (d, J = 11.3 Hz, 1H, BnCH2), 4.71 (d, J = 11.3 Hz, 1H, BnCH2), 4.69 – 4.63 (m, 2H, BnCH2, OH-3), 4.61 (d, J = 11.9 Hz, 1H, BnCH2), 4.51 (d, J = 12.0 Hz, 1H, BnCH2), 4.38 (d, J = 12.0 Hz, 1H, BnCH2), 4.30 (d, J = 7.1 Hz, 1H, H-1'), 4.26 (d, J = 12.1 Hz, 1H, BnCH2), 4.16 (ddd, J = 10.0, 4.0, 1.8 Hz, 1H, 5), 3.90 (ddd, J = 9.8, 8.3, 1.3 Hz, 1H, H-3), 3.76 (dd, J = 10.1, 5.5 Hz, 1H, H-2), 3.72 – 3.61 (m, 3H, H-4, H-6a, H-6a'), 3.59 (dd, J = 9.4, 8.1 Hz, 1H, H-3'), 3.55 – 3.48 (m, 2H, H-6b, H-6b'), 3.43 (ddd, J = 9.1, 6.7, 2.1 Hz, 1H, H-5'), 3.41 – 3.31 (m, 2H, H-2', H-4'), 2.67 – 2.51 (m, 2H, SCH2), 1.29 (t, J = 7.4 Hz, 3H, SCH2CH3), 0.87 (t, J = 8.0 Hz, 9H, Si(CH2CH3)3), 0.60 – 0.45 (m, 6H, Si(CH2)3);13C NMR (126 MHz, CDCl3) 138.6, 138.1, 138.0, 137.5, 128.4, 128.3, 128.2, 128.2, 128.1, 127.8, 127.8, 127.6, 127.5, 127.4, 127.2, 126.9, 103.1, 84.7, 83.2, 82.3, 80.9, 75.8, 75.1, 74.9, 73.8, 73.2, 72.2, 71.2, 70.0, 69.1, 68.1, 63.4, 24.8, 14.7, 6.9, 5.1. HRMS: m/z [M+Na+]+ calculated for C
48H63N3O9SSiNa: 908.3952 found:
908.3996.
3.13. Ethyl 4,6-O-[(R)-1-naphthalenylmethylene]--D-glucopyranosyl-(1⟶4)-2-azido-2-deoxy-1-thio--D-glucopyranoside (19).
Compound 3 (2 g, 3.31 mmol) was suspended in MeOH (33 mL). This was treated with a freshly prepared solution of NaOMe and stirred for 3 h. Upon completion of the reaction the solution was neutralised with DOWEX-50Wx80 ion exchange resin. The solution was filtered, concentrated and dried. The crude solid was co-evapourated 3 times with toluene. The crude mixture was then dissolved in DMF (33.1 mL), p-TSA (0.44 g, 2.314 mmol) and naphthaldehyde dimethyl acetal (0.8 g, 3.97 mmol) were added and the reaction was heated to 80 oC via microwave
irradiation for 20 mins. The reaction was then neutralized with Et3N and concentrated to dryness.
The crude mixture was purified by silica gel chromatography (CH2Cl2/MeOH: 1:0 to 8:2) to give 19
(1.35 g, 74%) as a white foam. []D20 +33.5 (c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3) 8.11 (d, J = 8.5 Hz, 1H, Ar-H), 7.86 (dd, J = 8.3, 1.6 Hz, 2H, Ar-H), 7.71 (dd, J = 7.1, 1.1 Hz, 1H, Ar-H),
7.54 (ddd, J = 8.4, 6.8, 1.4 Hz, 1H, Ar-H), 7.51 – 7.43 (m, 2H, Ar-H), 5.90 (s, 1H, PhCH), 5.20 (d, J = 5.5 Hz, 1H, H-1), 4.52 (d, J = 3.7 Hz, 1H, OH), 4.33 – 4.22 (m, 3H, H-1'), 4.07 – 4.00 (m, 2H), 3.87 – 3.76 (m, 2H), 3.72 – 3.58 (m, 4H, H-2, H-6a, H-6a'), 3.44 – 3.31 (m, 4H), 3.13 (dd, J = 7.7, 4.5 Hz, 1H), 2.60 – 2.48 (m, 2H, SCH2), 2.04 (s, 1H, OH), 1.26 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 133.8, 131.9, 130.3, 130.1, 128.8, 126.6, 125.9, 125.1, 124.7, 124.0, 103.9, 101.1, 83.4, 82.6, 80.3, 74.0, 73.0, 71.7, 70.1, 68.3, 66.4, 63.0, 61.8, 25.0, 14.7; HRMS (ESI) m/z: [M + Na]+ calcd for C
25H31N3O9NaS: 572.1679, found: 572.1694.
3.14. Ethyl 2,3-di-O-benzyl-4,6-O-((R)-1-naphthalenylmethylene)--D-glucopyranosyl-(1⟶4)-2-azido-3,6-di-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (20).
Compound 19 (1.35 mL, 2.456 mmol) was dissolved in DMF (25 mL) and cooled on an ice bath. NaH (0.48 g, 20.88 mmol) was added and the reaction was stirred for 30 mins. BnBr (2.3 mL, 19.34 mmol) was then added and the reaction was allowed to warm to r.t. over 3 h. The reaction was then quenched by the drop wise addition of MeOH until the evolution of H2 stopped. The
reaction was then diluted with EtOAc and washed 3 times with H2O. The organic phase was dried
with MgSO4 and filtered. The filtrate was then concentrated and purified by silica gel
chromatography (pentane/Et2O: 8:1 to 1:2) to give 20 (2.146 g, 96%) as a white foam. []D20 +66.6
(c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3) 8.16 – 8.11 (m, 1H, Ar-H), 7.87 (m, 2H, Ar-H), 7.78
(d, J = 7.1 Hz, 1H, H), 7.52 – 7.46 (m, 3H, H), 7.42 (m, 2H, H), 7.39 – 7.27 (m, 11H, Ar-H), 7.25 – 7.17 (m, 5H, Ar-Ar-H), 5.99 (s, 1H, NapCAr-H), 5.38 (d, J = 5.6 Hz, 1H, H-1), 5.01 (d, J = 10.4 Hz, 1H, BnCH2), 4.85 (d, J = 11.2 Hz, 1H, BnCH2), 4.80 (m, 2H, BnCH2), 4.72 (d, J = 10.4 Hz, 1H,
BnCH2), 4.66 (d, J = 11.2 Hz, 1H, BnCH2), 4.62 (d, J = 12.0 Hz, 1H, BnCH2), 4.42 (d, J = 7.8 Hz,
2H, H-4, H-5), 3.95 – 3.90 (m, 1H, H-6a), 3.87 (dd, J = 10.2, 5.6 Hz, 1H, H-2), 3.74 – 3.66 (m, 2H, H, H-3, H-4'), 3.55 (apt t, J = 9.0 Hz, 1H, H-3'), 3.46 (m, 2H, H-6b, H-6b'), 3.40 (apt t, J = 8.3 Hz, 1H, H-2'), 3.19 (ddd, J = 9.8, 5.0 Hz, 1H, H-5'), 2.67 – 2.52 (m, 2H, SCH2), 1.31 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 138.4, 138.4, 138.4, 137.8, 133.8, 132.6, 130.6, 129.7, 128.6, 128.5, 128.3, 128.2, 128.2, 128.1, 128.1, 128.1, 128.0, 128.0, 127.7, 127.7, 127.6, 126.3, 125.7, 125.0, 124.1, 124.0, 102.8, 100.3, 83.3, 82.6, 82.2, 81.0, 79.9, 77.0, 75.7, 75.3, 75.0, 73.4, 71.1, 68.9, 67.6, 65.8, 63.2, 24.7, 14.8; HRMS m/z: [M + Na]+ calcd for C
53H55N3O9NaS: 932.3557,
found: 932.3560.
3.15. Ethyl 2,3-di-O-benzyl-6-O-[1-naphthylmethylene]-4-O-triethylsilyl--D-glucopyranosyl-(1⟶4)-2-azido-6-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (21); Ethyl
2,3-di-O-benzyl-4-O-triethylsilyl-
-D-glucopyranosyl-(1⟶4)-2-azido-6-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (22).
Compound 20 (0.8 g, 0.879 mmol) was dissolved in CH2Cl2 (8.8 mL) and cooled to -60 oC. I2
(0.355 g, 1.319 mmol) was added followed by the slow addition of Et3SiH (0.21 mL, 1.319 mmol).
The reaction was stirred while allowing to slowly warm to -10 oC over 4 h. Et
3N (0.185 mL) was
added followed by MeOH (0.1 mL) and the reaction was allowed to warm to r.t. The reaction was then diluted with CH2Cl2 and washed with satd. NaHCO3. The organic phase was dried with MgSO4
and filtered. The filtrate was then concentrated and purified by silica gel chromatography (pentane/Et2O; 8:1 to 0:1) and the compound with a very similar Rf to the starting material was
isolated 21 (0.495 g, 60%) as a white foam and 22 (0.230 g, 32%) as a white foam. Compound 21 could be converted into 22 as follows: Compound 21 (0.495 g, 0.529 mmol) was dissolved in CH2Cl2 and tBuOH (10 mL, 10:1). DDQ (0.18 g, 0.793 mmol) was added and the reaction was
stirred for 3 h. The solution was then diluted with CH2Cl2 and washed with 1 M NaS2O3. The
organic phase was dried over MgSO4 and concentrated. Purification by column chromatography
(pentane/Et2O: 1:1 to 0:1) gave 22 (0.3 g, 72%) as a white foam.
21: []D20 +50.2(c 1.1, CHCl3); 1H NMR (500 MHz, CDCl3) 8.17 (d, J = 8.4 Hz, 1H, Ar-H), 7.83
(dd, J = 22.1, 8.1 Hz, 2H, Ar-H), 7.58 (dd, J = 11.2, 4.0 Hz, 1H, Ar-H), 7.52 – 7.47 (m, 2H, Ar-H), 7.45 – 7.40 (m, 1H, Ar-H), 7.34 – 7.13 (m, 17H, Ar-H), 5.34 (d, J = 5.5 Hz, 1H, H-1), 5.04 (s, 2H, NapCH2), 4.93 (d, J = 11.4 Hz, 1H, BnCH2), 4.75 (d, J = 11.3 Hz, 1H, BnCH2), 4.72 – 4.62 (m, 3H, BnCH2), 4.37 (d, J = 12.1 Hz, 1H, BnCH2), 4.30 (d, J = 7.3 Hz, 1H, H-1'), 4.26 (d, J = 12.0 Hz, 1H, BnCH2), 4.16 (dd, J = 9.9, 2.0 Hz, 1H, H-5), 3.91 (apt t, J = 9.2 Hz, 1H, H-3), 3.76 (dd, J = 10.1, 5.5 Hz, 1H, H-2), 3.72 (dd, J = 10.3, 1.8 Hz, 1H, H-6a'), 3.68 – 3.62 (m, 2H, H-4, H-6a), 3.54 (m, 3H, H-6b, H-5', H-6b'), 3.45 – 3.39 (m, 1H, H-3'), 3.38 – 3.30 (m, 2H, H-2', H-4'), 2.66 – 2.52 (m,
2H, SCH2), 1.29 (t, J = 7.4 Hz, 3H, SCH2CH3), 0.80 (t, J = 8.0 Hz, 9H, Si(CH2)3(CH3)3), 0.49 – 0.40
(m, 6H, Si(CH2)3); 13C NMR (126 MHz, CDCl3) 138.6, 138.1, 138.1, 133.8, 133.1, 131.8, 128.8,
128.4, 128.3, 128.3, 128.1, 127.8, 127.6, 127.5, 127.4, 127.2, 126.9, 126.9, 126.4, 125.9, 125.1, 124.1, 103.2, 84.7, 83.2, 82.3, 80.9, 75.9, 75.1, 75.0, 73.2, 72.3, 72.1, 71.2, 70.0, 69.1, 68.2, 63.4, 24.9, 14.7, 6.8, 5.1; HRMS (ESI) m/z: [M + Na]+ calcd for C
52H65N3O9NaS: 958.4109, found: 958.4135. 22:[]D20 +51.5 (c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3) 7.36 – 7.22 (m, 16H, Ar-H), 7.18 (m, 2H, Ar-H), 5.34 (d, J = 5.4 Hz, 1H, H-1), 4.91 (d, J = 11.4 Hz, 1H, BnCH2), 4.76 – 4.70 (m, 2H, BnCH2), 4.64 (d, J = 11.2 Hz, 1H, BnCH2), 4.49 (d, J = 12.0 Hz, 1H, BnCH2), 4.31 – 4.27 (m, 2H, H-1', BnCH2), 4.12 – 4.07 (m, 1H, H-5), 3.93 (apt t, J = 8.7 Hz, 1H, H-4'), 3.88 (s, 1H, OH), 3.86 – 3.78 (m, 5H, H-3, H-5', OCH3), 3.74 (dd, J = 10.2, 5.5 Hz, 1H, H-2), 3.70 – 3.64 (m, 2H, H-4, H-4, H-6a), 3.46 (dd, J = 10.8, 1.6 Hz, 1H, H-6b), 3.43 – 3.38 (m, 1H, H-2'), 3.33 (apt t, J = 8.5 Hz, 1H, H-3'), 2.59 (tdd, J = 12.8, 7.4, 5.4 Hz, 2H, SCH2), 1.29 (t, J = 7.4 Hz, 3H, SCH2CH3), 0.89 (t, J = 8.0 Hz, 9H, Si(CH2CH3)3), 0.57 – 0.51 (m, 6H, Si(CH2)3);13C NMR (126 MHz, CDCl3) 168.4, 138.3, 137.9, 137.9, 128.4, 128.3, 128.2, 128.0, 127.8, 127.6, 127.6, 127.3, 126.9, 102.8, 83.9, 83.4, 81.7, 79.9, 76.0, 75.1, 74.9, 73.3, 72.1, 71.6, 69.9, 67.6, 63.2, 52.5, 25.0, 14.7, 6.7, 4.9; HRMS (ESI) m/z: [M + Na]+ calcd for C
52H65N3O9NaS: 818.3483, found: 818.3449.
3.16. Ethyl
2-O-benzoyl-3-O-benzyl-4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-3-O-benzoyl-2-deoxy-6-O-(tert-butyldiphenylsilyl)-1-thio--D-glucopyranoside (23).
Compound 9 (3.5 g, 4.23 mmol) was dissolved in pyridine (42 mL) and cooled in an ice bath. DMAP (0.026 g, 0.211 mmol) was added followed by the drop wise addition of BzCl (1.5 mL, 16.8 mmol). The reaction was then stirred for 3 h while allowing to warm to r.t. On completion of the reaction, it was diluted with EtOAc, washed twice with a solution of satd. NaHCO3, twice with a 1
M solution of HCl and once with brine. The organic phase was dried with MgSO4 and filtered. The
filtrate was then concentrated and purified by silica gel chromatography (pentane/EtOAc: 10:1 to 1:1) to give 23 (3.94 g, 90%) as a white foam. []D20 +95.6 (c 1.0, CHCl3);1H NMR (500 MHz,
CDCl3) 8.16 – 8.10 (m, 5H, Ar-H), 7.80 – 7.76 (m, 2H, Ar-H), 7.70 (m, 3H, Ar-H), 7.61 (m, 3H,
H), 7.53 – 7.45 (m, 6H, H), 7.42 (m, 3H, H), 7.39 – 7.30 (m, 6H, H), 7.27 (m, 1H, Ar-H), 7.24 (d, J = 2.6 Hz, 1H, Ar-Ar-H), 7.14 (dd, J = 9.5, 4.3 Hz, 1H, Ar-Ar-H), 7.05 (m, 3H, Ar-Ar-H), 5.46 (apt t, J = 9.9 Hz, 1H, H-3), 5.39 (d, J = 5.6 Hz, 1H, H-1), 5.27 (d, J = 0.8 Hz, 1H, PhCH), 5.20 (dd,
J = 9.0, 8.2 Hz, 1H, H-2'), 4.85 (d, J = 8.0 Hz, 1H, H-1'), 4.76 (d, J = 12.2 Hz, 1H, BnCH2), 4.62 (d,
3.96 – 3.80 (m, 3H, H-5, H-6a, H-6a'), 3.73 – 3.62 (m, 2H, H-6b, H-3'), 3.52 (apt t, J = 9.3 Hz, 1H, H-4'), 3.22 (ddd, J = 9.7, 5.0 Hz, 1H, H-5'), 2.71 (d, J = 10.3 Hz, 1H, H-6b'), 2.51 – 2.37 (m, 2H, SCH2), 1.22 – 1.16 (m, 3H, SCH2CH3), 1.09 (s, 9H, SiC(CH3)3);13C NMR (126 MHz, CDCl3) 172.0, 164.9, 137.9, 137.1, 135.9, 133.8, 133.6, 133.1, 132.9, 132.7, 130.5, 130.2, 129.9, 129.8, 129.3, 129.0, 128.5, 128.3, 128.3, 128.2, 128.1, 127.9, 127.9, 127.6, 127.5, 126.0, 101.0, 100.7, 83.0, 81.4, 78.1, 74.5, 73.7, 73.3, 72.6, 71.5, 68.0, 66.0, 62.2, 61.2, 26.9, 24.7, 19.5, 14.5; HRMS (ESI) m/z: [M + Na]+ calcd for C
58H61N3O11NaSiS: 1058.3694, found: 1058.3744.
3.17. Ethyl 2-O-benzoyl-3-O-benzyl--D-glucopyranosyl-(1⟶4)-2-azido-3-O-benzoyl-2-deoxy-6-O-(tert-butyldiphenylsilyl)-1-thio--D-glucopyranoside (24).
Compound 23 (3.6 g, 3.47 mmol) was suspended in MeOH (50 mL). CH2Cl2 was added drop
wise with stirring until the solids had dissolved. CSA (0.4 g, 1.722 mmol) was added and the solution was stirred for 17 h. Upon completion of the reaction the solution was neutralized with Et3N (0.5 mL, 3.56 mmol) and evaporated to dryness. Purification was by silica gel chromatography
(pentane/EtOAc: 10:1 to 1:1) to give compound 24 (2.88 g, 90%) as a white foam. []D20 +72.7(c
1.0, CHCl3); 1H NMR (500 MHz, CDCl3) 8.15 – 8.11 (m, 2H, Ar-H), 7.85 – 7.80 (m, 2H, Ar-H),
7.77 (m, 2H, Ar-H), 7.72 – 7.68 (m, 2H, Ar-H), 7.64 – 7.59 (m, 1H, Ar-H), 7.54 – 7.36 (m, 10H, Ar-H), 7.29 (m, 2H, Ar-H), 7.21 – 7.17 (m, 3H, Ar-H), 7.14 (m, 2H, Ar-H), 5.42 (d, J = 5.6 Hz, 1H, H-1), 5.34 (apt t, J = 9.8 Hz, 1H, H-3), 5.15 (dd, J = 10.9, 6.4 Hz, 1H, H-2'), 4.85 (d, J = 8.0 Hz, 1H, H-1'), 4.63 (d, J = 11.5 Hz, 1H, BnCH2), 4.53 (d, J = 11.5 Hz, 1H, BnCH2), 4.35 (apt t, J = 9.2 Hz, 1H, 4), 4.16 (d, J = 4.1 Hz, 1H, 2), 3.95 – 3.88 (m, 2H, 5, 6a), 3.78 – 3.72 (m, 1H, H-6b), 3.50 – 3.40 (m, 3H, H-3', H-4', H-6a'), 3.22 – 3.17 (m, 1H, H-5'), 3.11 (dd, J = 12.0, 5.1 Hz, 1H, H-6b'), 2.53 – 2.39 (m, 2H, SCH2), 1.20 (t, J = 7.4 Hz, 3H, SCH2CH3), 1.12 (s, 9H, SiC(CH3)3); 13C NMR (126 MHz, CDCl 3) 165.2, 164.5, 137.8, 135.8, 135.5, 133.7, 133.4, 133.1, 132.7, 130.2, 130.2, 130.0, 129.9, 129.7, 129.6, 129.5, 128.7, 128.5, 128.4, 127.9, 127.8, 127.7, 100.1, 83.1, 82.9, 75.5, 74.4, 73.4, 73.4, 73.4, 71.7, 70.1, 62.0, 61.9, 61.3, 27.0, 24.7, 19.5, 14.5; Anal. Calcd for C51H57N3O11SSi: C, 64.60; H, 6.06; N, 4.43; S, 3.38. Found: C, 64.80; H, 5.95; N, 4.15; S 3.56.
3.18. Ethyl (methyl (2-O-benzoyl-3-O-benzyl--D-glucopyranosyl)uronate)-(1⟶4)-2-azido-3-O-benzoyl-2-deoxy-6-O-(tert-butyldiphenylsilyl)-1-thio--D-glucopyranoside (25).
Compound 24 (2.5 g, 2.64 mmol) was dissolved in a mixture of CH2Cl2 (50 mL) and H2O (16
reaction was stirred for 1.5 h. The reaction was then diluted with CH2Cl2 (50 mL) washed with a 1
M solution of Na2S2O3 (50 mL). The organic phase was separated, dried with MgSO4 and filtered.
The filtrate was then concentrated. The resulting yellow solid was dissolved in MeOH (26.4 mL), NMM (0.6 mL, 5.28 mmol) was added followed by the addition of DMT-MM (1.46 g, 5.28 mmol). The reaction was stirred for 1 hr. and concentrated. Purification by silica gel chromatography (pentane/EtOAc: 6:1 to 1:1) yielded compound 25 (2 g, 78%) as a white foam. []D20 +63.9(c 1.2,
CHCl3); 1H NMR (500 MHz, CDCl3) 8.09 – 8.05 (m, 2H, Ar-H), 7.79 – 7.73 (m, 4H, Ar-H), 7.72
– 7.69 (m, 2H, Ar-H), 7.55 (m, 1H, Ar-H), 7.50 – 7.41 (m, 6H, Ar-H), 7.41 – 7.35 (m, 4H, Ar-H), 7.30 – 7.25 (m, 2H, Ar-H), 7.13 (dd, J = 7.8, 2.4 Hz, 1H, Ar-H), 7.09 (t, J = 4.2 Hz, 1H, Ar-H), 5.48 – 5.43 (m, 1H, H-3), 5.42 (d, J = 5.6 Hz, 1H, H-1), 5.13 (dd, J = 9.4, 8.2 Hz, 1H, H-2'), 4.91 (d, J = 8.1 Hz, 1H, H-1'), 4.71 (d, J = 11.7 Hz, 1H, BnCH2), 4.63 (d, J = 11.7 Hz, 1H, BnCH2), 4.31 (apt t, J = 9.6 Hz, 1H, H-4), 4.02 (dd, J = 8.4, 7.9 Hz, 1H, H-2), 3.96 (d, J = 9.7 Hz, 1H, H-5), 3.92 (dd, J = 11.8, 1.9 Hz, 1H, H-6a), 3.84 (apt t, J = 9.3 Hz, 1H, H-4'), 3.77 (d, J = 10.9 Hz, 1H, H-6b), 3.69 (d, J = 9.8 Hz, 1H, H-5'), 3.58 (m, 3H, COOCH3), 3.50 (apt t, J = 9.2 Hz, 1H, H-3'), 2.52 – 2.39 (m, 3H, SCH2), 1.19 (t, J = 7.4 Hz, 3H, SCH2CH3), 1.12 (s, 9H, SiC(CH3)3); 13C NMR (126 MHz, CDCl3) 168.7, 165.3, 164.3, 137.9, 135.8, 135.5, 133.6, 132.9, 132.7, 132.7, 130.2, 130.0, 129.9, 129.8, 129.7, 129.5, 128.3, 128.2, 128.2, 127.9, 127.8, 127.6, 127.5, 100.2, 82.9, 81.1, 74.2, 74.2, 73.7, 72.7, 72.1, 71.8, 71.5, 62.5, 61.3, 52.4, 26.9, 24.6, 19.5, 14.5; HRMS (ESI) m/z: [M -H+]- calcd for C 51H54N3O12SiS: 960.3198, found: 960.3213. 3.19. Ethyl 2,3-di-O-benzyl-4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-3,6-di-O-benzoyl-2-deoxy-1-thio--D-glucopyranoside (26).
Compound 10 (0.56 g, 0.824 mmol) was dissolved in pyridine (8.5 mL) and cooled to 0 oC in
an ice bath. DMAP (0.001 g, 8.24 μmol) was added followed by the drop wise addition of BzCl (0.3 mL, 3.31 mmol). The reaction was then stirred for 3 h while allowing to warm to r.t. On completion of the reaction it was diluted with CH2Cl2, washed twice with a solution of satd. NaHCO3, twice
with a 1 M solution of HCl and once with brine. The organic phase was then dried with MgSO4 and
filtered. The filtrate was then concentrated. Purification by silica gel chromatography (pentane/Et2O: 3:1 to 1:3) gave 26 (0.7 g, 96%) as a white waxy solid. []D20 +60.2(c 1.0, CHCl3); 1H NMR (500 MHz, CDCl
3) 8.19 – 8.09 (m, 2H, Ar-H), 8.03 – 7.92 (m, 2H, Ar-H), 7.62 – 7.27
(m, 15H, Ar-H), 7.23 – 7.01 (m, 5H Ar-H), 5.60 – 5.54 (m, 1H, H-3), 5.45 (d, J = 5.6 Hz, 1H, H-1), 5.21 (s, 1H, PhCH), 4.87 – 4.80 (m, 3H, BnCH2), 4.69 (d, J = 8.0 Hz, 1H, BnCH2), 4.61 (dd, J =
(dd, J = 10.7, 5.5 Hz, 1H, H-2), 3.88 (apt t, J = 9.4 Hz, 1H, H-4), 3.66 – 3.59 (m, 2H, H-3', H-6a'), 3.42 – 3.37 (m, 1H, H-2'), 3.33 (apt t, J = 9.3 Hz, 1H, H-4'), 3.11 (ddd, J = 9.7, 5.0 Hz, 1H, H-5'), 2.68 – 2.56 (m, 3H, SCH2, H-6b'), 1.30 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3)
165.7, 165.0, 138.4, 138.1, 137.1, 133.3, 133.2, 130.2, 129.9, 129.8, 129.5, 128.9, 128.4, 128.2, 128.2, 128.2, 127.9, 127.8, 127.8, 127.6, 127.5, 125.9, 103.6, 100.9, 82.8, 82.3, 81.1, 81.0, 77.0, 75.9, 74.9, 72.4, 69.6, 67.9, 65.9, 62.5, 62.0, 24.6, 14.6; HRMS (ESI) m/z: [M + Na]+ calcd for
C49H49N3O11NaS: 910.2986, found: 910.2977.
3.20. Ethyl 2,3-di-O-benzyl--D-glucopyranosyl-(1⟶4)-2-azido-3,6-di-O-benzoyl-2-deoxy-1-thio--D-glucopyranoside (27).
Compound 26 (0.7 g, 1.03 mmol) was dissolved in MeOH (14 mL) and CH2Cl2 (1.4 mL).
CSA (0.1 g, 0.430 mmol) was added and the reaction was stirred for 17 h. After completion of the reaction (TLC pentane/EtOAc; 1:1) the reaction was neutralized with Et3N and concentrated.
Purification by silica gel chromatography (pentane/EtOAc: 2:1 to 1:4) afforded compound 27 (0.59 g, 94%) as a white foam. []D20 +46.6 (c 1.00, CHCl3);1H NMR (500 MHz, CDCl3) 8.13 – 8.06
(m, 2H, Ar-H), 8.03 – 7.95 (m, 2H, Ar-H), 7.65 – 7.55 (m, 2H, Ar-H), 7.48 (m, 4H, Ar-H), 7.37 – 7.16 (m, 10H, Ar-H), 5.52 (apt t, J = 9.7 Hz, 1H, H-3), 5.46 (d, J = 5.4 Hz, 1H, H-1), 4.87 (m, 2H, BnCH2), 4.78 (d, J = 11.5 Hz, 1H, BnCH2), 4.68 – 4.62 (m, 1H, H-6a), 4.59 (d, J = 11.7 Hz, 1H, BnCH2), 4.50 – 4.36 (m, 3H, H-5, H-6b, H-1'), 4.17 (dd, J = 10.5, 5.6 Hz, 1H, H-2), 4.01 (apt t, J = 9.1 Hz, 1H, H-4), 3.36 – 3.26 (m, 3H, H-2', H-5', H-6a'), 3.24 – 3.17 (m, 1H, H-4'), 3.08 – 2.96 (m, 2H, H-3', H-6'), 2.69 – 2.55 (m, 2H, SCH2), 1.31 (t, J = 7.5 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 165.8, 165.2, 138.4, 138.1, 133.6, 133.3, 129.9, 129.7, 129.5, 129.5, 128.7, 128.6, 128.5, 128.3, 127.9, 127.9, 127.8, 127.7, 103.0, 83.9, 82.9, 82.3, 75.7, 75.3, 75.2, 75.1, 72.8, 70.1, 69.7, 62.5, 62.1, 61.9, 24.6, 14.6; HRMS (ESI) m/z: [M + Na]+ calcd for C
42H45N3O11NaS:
822.2692, found: 822.2673.
3.21. Ethyl (methyl (2,3-di-O-benzyl--D -glucopyranosyl)uronate)-(1⟶4)-2-azido-3,6-di-O-benzoyl-2-deoxy-1-thio--D-glucopyranoside (28).
Compound 27 (0.5 g, 0.625 mmol) was dissolved in a mixture of CH2Cl2 and water (3:1, 3
mL). TEMPO (0.020 g, 0.125 mmol) and BAIB (0.5 g, 1.5 mmol) were added to the solution and the reaction was stirred vigorously for 45 mins. On completion of the reaction the solution was diluted with EtOAc and washed with a 1 M solution of Na2S2O3. The aqueous phase was
re-extracted twice with EtOAcand the organic phases were combined dried over MgSO4 and filtered.
The filtrate was then concentrated. The crude solid was dissolved in MeOH (6.25 mL). DMT-MM (0.346 g, 1.25 mmol) was added followed by NMM (0.08 mL) and the solution was stirred for a further 45 mins. The reaction mixture was then diluted with CH2Cl2, extracted once with water,
once with 1 M HCl and once with brine. The organic phase was dried over MgSO4 and filtered. The
filtrate was concentrated and purified by silica gel chromatography (pentane/EtOAc: 5:1 to 1:3) to give compound 28 (0.4 g, 77%) as a white foam. []D20 +11.5 (c 1.0, CHCl3); 1H NMR (500 MHz,
CDCl3) 8.06 – 8.00 (m, 4H, H), 7.59 (dd, J = 12.5, 5.0 Hz, 1H, H), 7.57 – 7.53 (m, 1H,
Ar-H), 7.49 – 7.42 (m, 4H, Ar-Ar-H), 7.31 m, 2H, Ar-Ar-H), 7.27 (m, 4H, Ar-Ar-H), 7.20 (m, 2H, Ar-Ar-H), 5.55 (dd, J = 10.1, 9.4 Hz, 1H, H-3), 5.45 (d, J = 5.6 Hz, 1H, H-1), 4.84 – 4.76 (m, 3H, BnCH2), 4.72 (d, J = 11.4 Hz, 1H, BnCH2), 4.64 (dd, J = 12.0, 1.4 Hz, 1H, H-6a), 4.46 (m, 2H, H-6b, H-1'), 4.44 – 4.39 (m, 1H, H-5), 4.11 – 4.05 (m, 2H, H-2, H-4), 3.62 – 3.57 (m, 1H, H-4'), 3.55 (d, J = 9.8 Hz, 1H, H-5'), 3.49 (s, 3H, COOCH3), 3.39 (apt t, J = 8.7 Hz, 1H, H-3'), 3.34 – 3.30 (dd, J = 7.90, 8.80 Hz, 1H, H-2'), 2.69 – 2.56 (m, 2H, SCH2), 2.54 (d, J = 2.6 Hz, 1H, OH), 1.33 – 1.29 (t, J = 7.44 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 168.5, 165.7, 165.4, 138.3, 138.2, 133.3, 132.9, 129.9, 129.8, 129.7, 129.6, 128.5, 128.4, 128.3, 128.0, 127.9, 127.8, 127.7, 127.6, 102.7, 83.1, 83.0, 81.7, 75.4, 75.3, 75.1, 74.3, 72.1, 71.4, 69.5, 62.5, 62.2, 52.3, 24.6, 14.6; HRMS (ESI) m/z: [M + Na]+ calcd for C
43H45N3O12NaS: 850.2622, found: 850.2612.
3.22. Ethyl
2-O-benzoyl-3-O-benzyl-4,6-O-benzylidene--D-glucopyranosyl-(1⟶4)-2-azido-6-O-benzoyl-3-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (29).
Compound 11 was dissolved in pyridine (22 mL) and cooled in an ice bath. DMAP (0.03 g, 0.246 mmol) was added followed by the drop wise addition of BzCl (0.66 mL, 7.28 mmol). The reaction was then stirred for 3 h while allowing to warm to r.t. On completion of the reaction it was diluted with CH2Cl2 washed twice with a solution of satd. NaHCO3, twice with a 1 M solution of
HCl and once with brine. The organic phase was dried with MgSO4 and filtered. The filtrate was
then concentrated. Purification by silica gel chromatography (pentane/Et2O: 3:1 to 1:1) yielded 29
(1.74 g, 89%) as a white foam. []D20 +72.8 (c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3) 8.06 –
8.02 (m, 2H, Ar-H), 7.93 – 7.89 (m, 2H, Ar-H), 7.57 (t, J = 7.4 Hz, 1H, Ar-H), 7.48 – 7.34 (m, 14H, Ar-H), 7.31 (t, J = 7.2 Hz, 1H, Ar-H), 7.13 – 7.02 (m, 5H, Ar-H), 5.49 (s, 1H, PhCH), 5.35 (apt t, J = 8.4 Hz, 1H, H-2'), 5.30 (d, J = 5.6 Hz, 1H, H-1), 5.03 (d, J = 10.5 Hz, 1H, BnCH2), 4.81 – 4.76
(m, 2H, BnCH2), 4.71 (d, J = 7.9 Hz, 1H, H-1'), 4.63 (d, J = 12.0 Hz, 1H, BnCH2), 4.45 (dd, J =
4.09 (dd, J = 10.5, 4.8 Hz, 1H, H-6'), 3.92 – 3.87 (m, 1H, H-4), 3.85 (dd, J = 10.2, 5.6 Hz, 1H, H-2), 3.80 (apt t, J = 9.0 Hz, 1H, H-3'), 3.78 – 3.71 (m, 2H, H-3, H-4'), 3.39 (apt t, J = 10.3 Hz, 1H, H-6'), 3.32 – 3.26 (m, 1H, H-5'), 2.49 (tdd, J = 12.8, 7.4, 5.4 Hz, 2H, SCH2), 1.19 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 165.9, 164.9, 138.1, 137.6, 137.1, 133.3, 133.3, 129.9, 129.6, 129.5, 129.2, 129.1, 128.5, 128.5, 128.3, 128.3, 128.1, 127.9, 127.8, 127.7, 127.6, 126.0, 101.6, 101.2, 82.9, 81.6, 79.6, 78.1, 78.1, 75.6, 74.2, 73.8, 69.4, 68.3, 66.4, 63.4, 62.6, 24.5, 14.5; HRMS (ESI) m/z: [M + Na]+ calcd for C
49H49N3O11NaS: 910.2986, found: 910.3022.
3.23. Ethyl 2-O-benzoyl-3-O-benzyl--D-glucopyranosyl-(1⟶4)-2-azido-6-O-benzoyl-3-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (30).
Compound 29 (1.7 g) was dissolved in MeOH (38 mL) and CH2Cl2 (3.8 mL). CSA (0.22 g,
0.947 mmol) was added and the reaction was stirred for 17 h. After completion of the reaction (TLC pentane/EtOAc; 1:1) the reaction was neutralized with Et3N (0.27 mL) and concentrated.
Purification was by silica gel chromatography (pentane/EtOAc: 2:1 to 1:4) yielded compound 30 (1.47 g, 96%) as a white foam. []D20 +48.2 (c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3) 8.12 –
8.08 (m, 2H, Ar-H), 7.94 (dd, J = 8.2, 1.1 Hz, 2H, Ar-H), 7.62 – 7.56 (m, 1H, Ar-H), 7.48 – 7.44 (m, 2H, Ar-H), 7.41 (m, 4H, Ar-H), 7.36 (m, 2H, Ar-H), 7.31 (d, J = 7.2 Hz, 1H, Ar-H), 7.21 – 7.18 (m, 2H, Ar-H), 7.17 – 7.14 (m, 2H, Ar-H), 5.33 – 5.28 (m, 2H, H-1, H-2'), 5.02 (d, J = 10.8 Hz, 1H, BnCH2), 4.82 (d, J = 10.8 Hz, 1H, BnCH2), 4.68 (d, J = 11.5 Hz, 1H, BnCH2), 4.61 (d, J = 8.0 Hz, 1H, H-1'), 4.56 (d, J = 11.5 Hz, 1H, BnCH2), 4.45 (dd, J = 12.1, 4.7 Hz, 1H, H-6b), 4.40 (dd, J = 12.1, 1.8 Hz, 1H, 6b), 4.23 – 4.17 (m, 1H, 5), 3.86 (m, 2H, 2, 4), 3.76 – 3.70 (m, 1H, H-3), 3.61 – 3.54 (m, 3H, H-6a', H-4', H-3'), 3.28 (dd, J = 12.1, 5.8 Hz, 1H, H-6b'), 3.16 (ddd, J = 8.9, 5.6, 3.1 Hz, 1H, H-5'), 2.51 (tdd, J = 12.8, 7.4, 5.4 Hz, 2H, SCH2), 1.20 (t, J = 7.4 Hz, 3H, SCH2CH3); 13C NMR (126 MHz, CDCl3) 166.0, 165.0, 138.2, 137.6, 133.4, 129.8, 129.5, 129.5, 129.2, 128.6, 128.5, 128.5, 128.0, 127.9, 127.8, 127.2, 101.1, 82.9, 82.7, 79.5, 78.0, 75.6, 75.4, 74.8, 73.8, 70.6, 69.4, 63.5, 62.7, 62.0, 24.5, 14.5; HRMS (ESI) m/z: [M + Na]+ calcd for
C42H45N3O11NaS: 822.2673, found: 822.2654.
3.24. Ethyl (methyl (2-O-benzoyl-3-O-benzyl--D-glucopyranosyl)uronate)-(1⟶4)-2-azido-6-O-benzoyl-3-O-benzyl-2-deoxy-1-thio--D-glucopyranoside (31).
Compound 30 (1.4 g, 1.75 mmol) was dissolved in a mixture of CH2Cl2 (5.8 mL) and water
