Convergent Synthesis of a β-(1→3)-Mannohexaose

Abstract

An as yet unknown β-(1→3)-mannohexaose has been synthesized by a block route involving the coupling of two trisaccharides. Comparison of three closely related attempted mannohexaose syntheses reinforces the influence of subtle matching and/or mismatching interactions on the outcome of convergent oligosaccharide synthesis.

Introduction

Insofar as the β-mannopyranosides have traditionally been considered to be one of the more challenging classes of glycosidic bond to synthesize in a stereocontrolled manner,^1–6 the β-mannans are the ultimate proving ground for methodology development in this area. Over the course of the last decade we have developed in our laboratory a direct stereocontrolled route to the synthesis of the β-mannopyranosides,⁷ based on the in situ generation and coupling of 4,6-O-alkylidene protected α-mannosyl triflates,^8–11 and have applied it successfully to the synthesis of the β-(1→2)-mannan from Candida albicans,¹² to the β-(1→4)-mannan from hard and soft woods, and guar gum,¹² and to the alternating β-(1→3)-β-(1→4)-mannan from Rhodotorula glutinis and mucilaginosa, and Leptospira biflexa.^13,14 An analogous synthesis of the β-(1→2)-mannan was also reported by Mallet and coworkers,^{15,16,17–20} and the general approach to β-mannosides has been applied widely to the synthesis of other complex oligosaccharides.^21–30

In this Article we turn our attention to the β-(1→3)-mannan which, to our knowledge, and in contrast to the closely related β-(1→3)-d-rhamnan,^30,31 has yet to be found in Nature. We do so because the synthesis and provision of samples to glycomics databases should assist in the future identification of such substances in Nature, and because of the challenge this particular mannan presents to our chemistry, especially when considered from a convergent or block synthesis standpoint. In effect, the size and nature of the O-3 substituent in 4,6-O-benzylidene protected mannosyl donors has been found to influence critically the stereochemical outcome of these reactions, with the benzyl ether being ideal and both smaller and larger groups detrimental.^14,32–38

Results and Discussion

Background

The negative influence of sterically bulky protecting groups on O-3 of the mannosyl donors was first noticed with the 3-O-tert-butyldimethylsilyl protected system 1, which was less selective than the corresponding regioisomer 2.^36,38 Subsequently, the phenomenon reared its head in the convergent synthesis of the alternating β-(1→3)-β-(1→4)-mannan when coupling of 3 with 4 resulted in the formation of the trisaccharide 5, but with only a 1:1 β:α ratio,¹⁴ and that of trisaccharides 6 and 7 to give hexasaccharide 8 with a disappointing 0.67:1 β:α ratio.¹⁴ We rationalized the influence of the size of the O-3 protecting group in terms of a steric buttressing effect between the O-2 and O-3 protecting groups, which causes undue hindrance of the β-face of the glycosyl donor and leads to the observed reduction in selectivity.^36,37,39

Taking a hint from the highly β-selective coupling observed by the van Boom group with the 2-azido-2-deoxy donor 9 we developed the propargyl ethers as sterically minimal protecting groups for O-2 capable of overcoming the influence of the bulky group on O-3.^40,41 On this basis we were able to demonstrate the coupling of the disaccharide donor 10 to acceptor 11 when trisaccharide 12 was obtained in 80% yield with 5.2:1 β:α ratio.³⁷

First Approach to the β-(1→3)-Mannohexaose

With this in mind we embarked on a convergent synthesis of the β-(1→3)-mannohexaose featuring extensive use of the 2-O-propagryl ether protecting system. Accordingly, phenyl 4,6-O-benzylidene-α-d-thiomannopyranoside was converted first to the 3-O-naphthylmethyl ether 13, by means of the stannylene acetal formed in situ with dibutyltin oxide, and then to the corresponding 2-O-propargyl ether 14. Removal of the naphthylmethyl ether from 14 with DDQ afforded the key building block 15 in 93% yield.^42–44 Activation of 14 with BSP^11,45 and triflic anhydride in the presence of TTBP⁴⁶ at −60 °C in dichloromethane, followed by quenching with methanol afforded the β-mannoside 16 in 85% yield (Scheme 1). Removal of the naphthylmethyl ether with DDQ then provided the acceptor 17 in 89% yield (Scheme 1).

Scheme 1.

Synthesis of 15 and 17

Activation of donor 14 with the BSP/triflic anhydride/TTBP combination followed by addition of acceptor 15 at −78 °C and then, before warming to room temperature, triethyl phosphite to quench any extraneous thiophiles and prevent premature activation of the new thioglycoside,^41,47 afforded disaccharide 18 in 91% yield and 25:1 β:α selectivity (Scheme 2). Treatment with DDQ then provided the alcohol 19 (Scheme 2). In the same manner coupling of donor 14 to acceptor 19 provided trisaccharide 20 in 82% yield as a single β-anomer (Scheme 2). Under the same conditions coupling of donor 18 with acceptor 17 gave the trisaccharide 21 in 84% yield with 7:1 β:α ratio (Scheme 2), from which removal of the naphthylmethyl group afforded acceptor 22 (Scheme 2). In contrast activation of donor 18 followed by reaction with acceptor 15 gave trisaccharide 20 in 88% yield but with the unexpected β:α ratio of 1:20 (Scheme 2). The complete reversal of selectivity in going from acceptor 15 to acceptor 17 in coupling to donor 18 is remarkable and draws attention to the still poorly understood influence of acceptor structure on the outcome of glycosylation reactions.^48–50

Scheme 2.

Synthesis of Trisaccharide Donor 20 and Acceptor 22

Unfortunately, despite repeated attempts, we were unable to realize the coupling of trisaccharide 20 with trisaccharide acceptor 22 and, thus, were forced to reconsider our approach.

Synthesis of the β-(1→3)-Mannohexaose

In redesigning our approach to the target mannan we elected to incorporate the use of the naphthylpropargyl ethers, developed in the interim,⁵¹ as sterically minimal protecting groups cleavable in a single step with DDQ. On the basis of the developmental work, it was known that these ethers afford excellent selectivity when used as O-3 protecting groups for donors in conjunction with 2-O-benzyl ethers. Additionally, because the more electron-rich naphthylpropargyl system is susceptible to electrophilic attack by the activated Ph₂SO/triflic anhydride combination,⁵¹ the use of glycosyl sulfoxides^52–55 as donors was recommended.⁵¹ Thus, the previously described sulfoxide 23⁵¹ was activated with triflic anhydride in the presence of TTBP and 1-octene at −78 °C in dichloromethane before addition of methanol, resulting in the formation of the β-mannoside 24 as a single anomer (Scheme 3). In this and subsequent coupling reactions 1-octene serves as a sacrificial alkene for the trapping of electrophilic species that otherwise diminish the overall yields by reaction with one or other of the naphthylpropargyl ethers or the thioglycoside containing acceptors.⁵⁶ Removal of the naphthylpropargyl group from 24 with DDQ gave 25 (Scheme 3) which, on coupling to 23 gave disaccharide 26 as a single anomer (Scheme 3). A sequence of treatment with DDQ, coupling to 23, and further treatment with DDQ gave the trisaccharide mono-ol 29 (Scheme 3).

Scheme 3.

Synthesis of Trisaccharide Acceptor 29

The second trisaccharide required for the convergent synthesis was assembled by activation of donor 23 in the presence of 1-octene, and introduction of the known acceptor 30,¹⁴ when disaccharide 31 was obtained as a single anomer in 76% yield (Scheme 4). Removal of the naphthylpropargyl group from 31 gave 32, and coupling to a second aliquot of 23 then afforded the trisaccharide 33 as a β only isomer in 78% yield (Scheme 4). Oxidation of 33 with mCPBA gave sulfoxide 34 as a single diastereomer at sulfur, which is assigned the (R)-configuration on the basis of previous crystallographic work.^57,58 Coupling of 34 with methanol and subsequent removal of the naphthylpropargyl protecting group provided a second more convenient entry into the acceptor trisaccharide 29 (Scheme 4). The ability to prepare the trisaccharide acceptor 29 from the donor 34 in this manner considerably enhances the efficiency of the overall protocol.

Scheme 4.

Convergent Synthesis of Trisaccharide Donor 34 and Acceptor 29

Finally, activation of 34 (1.2 eq) with triflic anhydride in the presence of 1-octene and TTBP at −78 °C in dichloromethane, followed by the addition of 29 (1.0 eq) smoothly afforded the hexasaccharide 35 as an approximately 1:1 mixture of anomers in 61% yield, Although the two anomers of 35 could be separated with difficulty by reverse phase HPLC, it was found to be more convenient to process the mixture with DDQ, giving the mono-ols 36, which were much more amenable to separation. Hydrogenolysis of each anomer over Pearlman’s catalysis gave the mannans 37 and 38, respectively (Scheme 5). In this manner the synthesis of the β-(1→3)-mannohexaose 37 was completed in 8% overall yield in a highly convergent manner from two monosaccharide building blocks 23 and 30, with only four glycosidic bond forming steps required, which, with the exception of the joining of 29 and 34 were all completely β-selective.

Scheme 5.

Synthesis of the Mannans 37 and 38 and Completion of the Synthesis

Structure of the β-(1→3)-mannohexaose

Inspection of the ¹³C-NMR spectrum of 37 at 125 MHz revealed the presence of only three anomeric carbon signals at δ 100.8 (¹J_CH = 157.9), δ 96.6 (¹J_CH = 158.6), and δ 96.4 (¹J_CH = 159.4) indicative of a highly regular open polymer. In this 37 resembles the β-(1→4)-mannohexaose synthesized previously,¹² but is distinct from the β-(1→2)-mannooctaose in which all eight anomeric carbons were discernible owing to its disordered, collapsed helical structure.^12,59 The ¹³C-NMR of spectrum of 38 exhibited two well resolved anomeric carbon signals at δ 102.1 (¹J_CH = 165.0) and 100.8 (¹J_CH = 155.0), indicative of α and β configured anomeric positions respectively; the remaining four anomeric signals resonated between δ 96.5 and 96.9 but were insufficiently resolved to permit determination of the one bond C-H coupling constants.

Influence of the 3-O-Naphthylpropargyl Protecting on β-Mannosylation

In addition to the preliminary results described previously,⁵¹ the coupling reactions summarized in Scheme 3 and Scheme 4 highlight the excellent β-selectivities obtained with the mannosyl donor 23, which are comparable to those provided by corresponding 3-O-benzyl and naphthylmethyl ethers.⁵⁵ More noteworthy, however, is the contrast between the highly β-selective 23 and the somewhat unselective 3-O-propargyl system 39,³⁷ which again highlights the sensitivity of these coupling reactions to substitution at the 3-position.

By means of the standard low temperature NMR methods,⁶⁰ we determined the steric A-value of the 1-naphthylpropargyloxy group in the cyclohexyl ether 40 to be 1.21, which is somewhat larger than of the simple propargyloxy group (1.10),³⁷ comparable to the allyloxy group (1.25),³⁷ a little smaller than the benzyloxy group (1.39),³⁷ and substantially smaller than the tert-butyldimethylsilylether group (1.50).³⁷ Taking into account the lack of selectivity seen with each of the 3-deoxy system 41,³² the 3-deoxy-3-fluoro system 42³³ (A value for fluoride = 0.27),^60–65 and the 3-azido-3-deoxy system 43⁶⁶ (A value for azide = 0.75),^61,67 but the excellent selectivity for the 3-benzylideneimino-3-deoxy system 44,⁶⁶ we are led to the conclusion that there is a relatively narrow window for the steric bulk of the group at the 3-position, centered around the benzyloxy group, in which excellent β-selectivity is observed. As we have previously discussed,^32,33 groups that are significantly smaller than the benzyloxy ether function result in a loss of selectivity due to minimization of the developing torsional interaction between the O2 and O3 groups as the covalent triflate¹⁰ flattens to the oxacarbenium ion,⁶⁸ thereby facilitating oxacarbenium ion formation and ultimately leading to a loss of selectivity. Larger groups than the benzyloxy ether result in the buttressing interaction discussed above, which also results in a loss of selectivity.

Conclusion

Trisaccharide donor 34 was successfully coupled to trisaccharide acceptor 29 to give hexasaccharide 35 in 61% yield as a 1:1 β:α mixture of anomers, whereas the closely related pair of 20 and 22 failed to give any appreciable amount of hexasaccharide under comparable conditions. As previously reported,¹⁴ trisaccharide donor 6 was coupled to trisaccharide acceptor 7 to give hexasaccharide 8 in 88% yield but only 0.67:1 β:α ratio. These three reactions, which all involved the attempted coupling of closely related 3-O-glycosyl-4,6-O-benzylidene protected mannopyranosyl donors to the non-reducing 3-OH of mannotrioses, serve to highlight the continuing difficulty in predicting the outcome of block approaches to oligosaccharide synthesis. As the molecular weight of the donors and acceptors increase with chain length (e.g., the MW of 29 and 34 are 1053.15 and 1310.47 Daltons, respectively), and the concentration of the reaction mixture inevitably decreases, subtle steric and matching/mismatching effects play increasingly important roles and influence the outcome considerably.

Experimental Section

Phenyl 4,6-O-benzylidene-3-O-(2-naphthylmethyl)-1-thio-α-d-mannopyranoside (13)

A stirred solution of phenyl 4,6-O-benzylidene-1-thio-α-d-mannopyranoside⁶⁹ (5.25 g, 14.6 mmol) in toluene (500 mL) was treated with Bu₂SnO (5.43 g, 21.8 mmol). The reaction mixture was refluxed for 4 h followed by removal of the solvent, affording a residue which was dissolved in DMF (50 mL). CsF (4.43g, 29.1 mmol) and 2-bromomethylnaphthalene (4.83 g, 21.8) were then successively added into the reaction mixture, which then was stirred at 95 °C for 6 h. DMF was then removed by rotary evaporation under reduced pressure. The residue was redissolved in CH₂Cl₂ (200 mL), washed with saturated aq. Na₂CO₃, brine, dried over anhydrous Na₂SO₄ and concentrated. The crude product was purified by flash chromatography on silica gel (hexane:ethyl acetate; 4:1) to give 13 (6.76 g, 94%), [α]²² + 176.5 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 2.80 (br. s, 1H), 3.89 (t, J = 10.0 Hz, 1H), 4.04 (dd, J = 3.5, 9.5 Hz, 1H), 4.23–4.27 (m, 2H), 4.33 (dd, J = 1.0, 3.5 Hz, 1H), 4.37 (dt, J = 4.5, 9.5 Hz, 1H), 4.93 (d, J = 12.0 Hz, 1H), 5.04 (d, J = 12.5 Hz, 1H), 5.62 (d, J = 1.5 Hz, 1H), 5.66 (s, 1H), 7.26–7.37 (m, 13H), 7.76–7.86 (m, 4H); ¹³C NMR (125 MHz, CDCl₃) δ: 64.7, 68.6, 71.4, 73.2, 75.8, 79.0, 87.8, 101.8, 125.7, 126.1, 126.2, 126.3, 126.4, 127.7, 128.0, 128.3, 128.4, 128.5, 129.1, 129.2, 129.3, 131.7, 133.1, 133.3, 135.2, 137.5; ESIHRMS Calcd for C₃₀H₂₈O₅SNa [M+Na]⁺: 523.1555. Found 523.1545.

Phenyl 4,6-O-benzylidene-3-O-(2-naphthylmethyl)-2-O-(prop-2-ynyl)-1-thio-α-d-mannopyranoside (14)

To a stirred solution of compound 13 (4.66 g, 9.3mmol) in dry DMF (25 mL) at 0 °C, was added NaH (60% in oil, 0.93 g, 18.6 mmol). The reaction mixture was stirred for 15 min before propargyl bromide (1.97 mL, 18.6 mmol) was added dropwise to the mixture, and the stirring was continued for 3 h. The reaction mixture was then quenched by addition of methanol, diluted with CH₂Cl₂ (75 mL) and washed with sat. NaHCO₃. The organic layer was separated, dried over anhydrous Na₂SO₄, and concentrated under vacuum. The crude product was purified by chromatography on silica gel (hexane:ethyl acetate; 5:1) to give 14 (5.01 g, 91%), [α]²⁴_D + 124.8 (c, 2.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 2.45 (t, J = 2.3 Hz, 1H), 3.89 (t, J = 10.0 Hz, 1H), 4.07 (dd, J = 3.1, 9.5 Hz, 1H), 4.22–4.32 (m, 3H), 4.35 (dd, J = 1.4, 3.2 Hz, 1H), 4.4 (dd, J = 2.3, 16.1 Hz, 1H), 4.49 (dd, J = 2.3, 16.1 Hz, 1H), 4.93 (dd, J = 12.4 Hz, 1H), 5.03 (d, J = 12.4 Hz, 1H), 5.63 (d, J = 1.4 Hz, 1H), 5.67 (s, 1H), 7.26–7.45 (m, 3H), 7.42–7.58 (m, 10H), 7.84–7.89 (m, 4H); ¹³C NMR (125 MHz, CDCl₃) δ: 58.8, 65.4, 68.5, 73.2, 75.4, 76.2, 77.5, 79.1, 79.4, 87.3, 101.6, 125.7, 125.0, 126.1, 126.2, 126.4, 127.7, 128.0, 128.2, 128.9, 129.2, 131.6, 133.0, 133.3, 133.6, 135.6, 137.6; ESIHRMS Calcd for C₃₃H₃₀O₅SNa [M+Na]⁺: 561.1712. Found 561.1722.

Phenyl 4,6-O-benzylidene-2-O-(prop-2-ynyl)-1-thio-α-d-mannopyranoside (15)

To a stirred solution of compound 14 (1.25 g, 2.3 mmol) in CH₂Cl₂ (40 mL) and water (2 mL) was added DDQ (1.05 g, 4.6 mmol) at rt. After the reaction mixture was stirred for 3 h, sat. NaHCO₃ was added, and the mixture was extracted with CH₂Cl₂. The extracts were washed several times with sat NaHCO₃, and dried over Na₂SO₄. Evaporation of the solvent in vacuo gave an oil, which was chromatographed on silica gel (hexane:ethyl acetate; 4:1) to give 15 (852 mg, 93%) as a white solid. MP 128 °C. [α]²⁷_D + 119 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 2.49 (t, J = 2.4 Hz, 1H), 2.5 (bs, 1H), 3.84 (t, J = 10.2 Hz, 1H), 3.9 (t, J = 9.6 Hz, 1H), 4.16 (dd, J = 3.6, 10.0 Hz, 1H), 4.21–4.24 (m, 2H), 4.27–4.32 (m, 1H), 4.34 (dd, J = 2.4, 16.1 Hz, 1H), 4.42 (dd, J = 2.4, 16.1 Hz, 1H), 5.59 (s, 1H), 5.68 (s, 1H), 7.32–7.53 (m, 10H); ¹³C NMR (125 MHz, CDCl₃) δ: 58.6, 64.7, 68.4, 68.9, 75.7, 78.9, 79.3, 79.4, 86.4, 102.2, 126.3, 127.7, 128.3, 129.2, 131.7, 133.8, 137.2; ESIHRMS Calcd for C₂₂H₂₂O₅SNa [M+Na]⁺: 421.1086. Found 421.1095.

Methyl 4,6-O-benzylidene-3-O-(2-naphthylmethyl)-2-O-(prop-2-ynyl)-β-d-mannopyranoside (16)

To a stirred solution of donor 14 (122 mg, 0.23 mmol), BSP (57 mg, 0.27 mmol) TTBP (84.6 mg, 0.34 mmol), and 4 Å molecular sieves in CH₂Cl₂ (6 mL), at −60 °C under an Ar atmosphere, was added Tf₂O (50 µL, 0.29 mmol). After 30 min. of stirring at −60 °C, dry methanol (28 µL, 0.68 mmol) was added. The reaction mixture was stirred for further 2 h. at −60 °C, and then allowed to warm up to room temperature. The reaction mixture was diluted with CH₂Cl₂ (10 mL), the molecular sieves were filtered off and washed with saturated NaHCO₃. The organic layer was separated, dried and concentrated. The crude product was purified by chromatography on silica gel (hexane:ethyl acetate; 5:1) to give 16 (89 mg, 85%) as a colorless oil. [α]²⁷_D − 29.8 (c, 2.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 2.53 (t, J = 2.4 Hz, 1H), 3.30–3.35 (m, 1H), 3.52 (s, 3H), 3.67 (dd, J = 3.1, 9.9 Hz, 1H), 3.93 (t, J = 10.3 Hz, 1H), 4.17 (t, J = 9.6 Hz, 1H), 4.21 (d, J = 3.0, Hz, 1H), 4.34 (dd, J = 4.9, 10.4 Hz, 1H), 4.39 (s, 1H), 4.61 (dd, J = 2.4, 16.1 Hz, 1H), 4.65 (dd, J = 2.4, 16.1 Hz, 1H), 4.98 (d, J = 12.9 Hz, 1H), 5.0 (d, J = 12.9 Hz, 1H), 5.64 (s, 1H), 7.40–7.54 (m, 8H), 7.71–7.87 (m, 4H); ¹³C NMR (125 MHz, CDCl₃) δ: 50.5, 60.0, 67.5, 68.6, 72.5, 74.9, 75.0, 78.4, 80.0, 101.5, 102.9, 125.7, 125.9, 126.0, 126.4, 127.7, 127.9, 128.1, 128.2, 128.9, 132.9, 133.2, 135.7, 137.6; ESIHRMS Calcd for C₂₈H₂₈O₆Na [M+Na]⁺: 483.1784. Found 483.1805.

Methyl 4,6-O-benzylidene-2-O-(prop-2-ynyl)-β-d-mannopyranoside (17)

To stirred solution of 16 (82 mg, 0.18mmol) in CH₂Cl₂ (5 mL) and water (0.1 mL) was added DDQ (81 mg, 0.36 mmol) at rt. After the reaction mixture was stirred for 3 h, sat. NaHCO₃ was added, and the mixture was extracted with CH₂Cl₂. The extract was washed several times with sat NaHCO₃, and dried over Na₂SO₄, and concentrated on a rotary evaporator. The crude product was purified by chromatography on silica gel (hexane:ethyl acetate; 7:3) to give 17 (51 mg, 89%) as a white solid. MP 126 °C. [α]²⁷_D − 119.9 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 2.5 (t, J = 2.4 Hz, 1H), 3.31–3.36 (m, 1H), 3.5 (s, 3H), 3.76–3.83 (m, 2H), 3.87 (t, J = 10.3 Hz, 1H), 4.0 (dd, J = 0.5, 3.2 Hz, 1H), 4.3 (dd, J = 4.9, 10.5 Hz, 1H), 4.46 (dd, J = 2.4, 16.1 1H), 4.48 (s, 1H), 4.6 (dd, J = 2.4, 16.1 1H), 5.5 (s, 1H), 7.26–7.38 (m, 3H), 7.48–7.5 (m, 2H); ¹³C NMR (125 MHz, CDCl₃) δ: 57.5, 60.6, 67.0, 68.4, 70.3, 75.5, 77.2, 79.1, 79.7, 102.0, 103.0, 126.3, 128.2, 129.1, 137.2; ESIHRMS Calcd for C₁₇H₂₁O₆ [M+H]⁺: 321.1338. Found 321.1347.

Phenyl 4,6-O-benzylidene-2-O-(prop-2-ynyl)-3-O-(2-naphthylmethyl)-β-d-mannopyranosyl (1→3)-4,6-O-benzylidene-2-O-(prop-2-ynyl)-1-thio-α-d-mannopyranoside (18)

To a stirred solution of donor 14 (270 mg, 0.50 mmol), BSP (126 mg, 0.6 mmol), TTBP (187 mg, 0.8 mmol), and 4 Å molecular sieves in CH₂Cl₂ (5 mL), at −60 °C under an Ar atmosphere, was added Tf₂O (110 µL, 0.65 mmol). After 30 min. the temperature was brought down to −78 °C, and then acceptor 15 (240 mg, 0.60 mmol) in CH₂Cl₂ (3 mL) was slowly added. The reaction mixture was stirred for 2 h. at −78 °C, and then quenched by the addition of triethyl phosphite (255 µL, 1.5 mmol), and stirring for 1 h at −78 °C before it was allowed to reach room temperature. The reaction mixture was diluted with CH₂Cl₂ (10 mL) and the molecular sieves were filtered off and washed with saturated NaHCO₃. The organic layer was separated, dried, and concentrated. The crude product was purified by column chromatography on neutral alumina (hexane:ethyl acetate; 7:3) to give 18 (380 mg, α:β; 1:25, 91%). For β-anomer: [α]²⁷_D + 51.1 (c, 2.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 2.28 (t, J = 2.4 Hz, 1H), 2.56 (t, J = 2.3 Hz, 1H), 3.24–3.29 (m, 1H), 3.67 (dd, J = 3.1, 9.8 Hz, 1H), 3.85–3.90 (m, 2H), 4.16–4.21 (m, 3H), 4.23 (t, J = 4.8, 10.2 Hz, 1H), 4.27–4.31 (m, 3H), 4.34 (dd, J = 1.5, 3.0 Hz, 1H), 4.37 (dd, J = 2.4, 16.3 Hz, 1H), 4.47 (dd, J = 2.4, 16.3 Hz, 1H), 4.65 (dd, J = 2.4, 16.0 Hz, 1H), 4.69 (dd, J = 2.4, 16.0 Hz, 1H), 4.80 (s, 1H), 4.95 (d, J = 12.8 Hz, 1H), 4.98 (d, J = 13.7 Hz, 1H), 5.57 (s, 2H), 5.63 (s, 1H), 7.26–7.53 (m, 18H), 7.80–7.86 (m, 4H); ¹³C NMR (125 MHz, CDCl₃) δ: 58.3, 59.8, 65.2, 67.7, 68.4, 68.6, 72.5, 75.0, 75.2, 75.5, 77.9, 78.4, 79.3, 80.5, 86.6, 100.0, 101.3, 101.7, 125.7, 125.9, 126.1, 126.2, 126.4, 127.7, 127.8, 127.9, 128.1, 128.2, 128.3, 128.9, 129.1, 129.3, 131.7, 132.9, 133.5, 137.3, 137.6; ESIHRMS Calcd for C₄₉H₄₆O₁₀SNa [M+Na]⁺: 849.2710. Found 849.2729

Phenyl 4,6-O-benzylidene-2-O-(prop-2-ynyl)-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-(prop-2-ynyl)-1-thio-α-d-mannopyranoside (19)

To stirred solution of 18β (72 mg, 0.09 mmol) in CH₂Cl₂ (10 mL) and water (0.5 mL) was added DDQ (49.4 mg, 0.22 mmol) at room temperature. After 3 h, sat. NaHCO₃ was added, and the mixture was extracted with CH₂Cl₂. The extracts were washed several times with sat NaHCO₃, and dried over Na₂SO₄. Evaporation of the solvent in vacuo gave an oil, which was chromatographed on silica gel (hexane:ethyl acetate; 3:2) to give 19 (55 mg, 94%). [α]²²_D + 27.8 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 2.5 (t, J = 2.4 Hz, 1H), 3.31–3.34 (m, 1H), 3.78 (t, J = 10.0 Hz, 1H), 3.82–3.89 (m, 3H), 4.19–4.26 (m, 2H), 4.31–4.37 (m, 3H), 4.36 (dd, J = 2.5, 16.5 Hz, 1H), 4.47 (dd, J = 2.5, 16.5 Hz, 1H), 4.55 (dd, J = 2.0, 16.0 Hz, 1H), 4.58 (dd, J = 2.0, 16.0 Hz, 1H), 4.94 (s, 1H), 5.37 (s, 1H), 5.57 (s, 1H), 5.66 (s, 1H), 7.26–7.41 (m, 9H), 7.44–7.52 (m, 6H); ¹³C NMR (125 MHz, CDCl₃) δ: 57.8, 59.9, 65.3, 67.1, 68.5, 70.2, 74.1, 75.6, 75.8, 76.1, 76.5, 77.4, 79.0, 79.5, 79.8, 86.1, 98.9, 101.8, 126.2, 126.3, 127.9, 128.3, 129.1, 129.3, 131.7, 133.5, 137.2, 137.3; ESIHRMS Calcd for C₃₈H₃₈O₁₀SNa [M+Na]⁺:709.2084. Found 709.2068.

Phenyl 4,6-O-benzylidene-2-O-(prop-2-ynyl)-3-O-(2-naphthylmethyl)-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-(prop-2-ynyl)-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-(prop-2-ynyl)-1-thio-α-d-mannopyranoside (20α)

To a stirred solution of donor 18β (179 mg, 0.22 mmol), BSP (54.4 mg 0.26 mmol), TTBP (80.5 mg, 0.32 mmol), and 4 Å molecular sieves in CH₂Cl₂ (3 mL), at −60 °C under an Ar atmosphere, was added Tf₂O (47 µL, 0.28 mmol). After 30 min. the temperature was brought down to −78 °C, and then acceptor 15 (103 mg, 0.26 mmol) in CH₂Cl₂ (2 mL) was slowly added. The reaction mixture was stirred for 2 h. at −78 °C, and quenched by the addition of triethyl phosphite (72 µL, 0.43 mmol), and stirred for 1 h at −78 °C before it was allowed to reach room temperature. The reaction mixture was diluted with CH₂Cl₂ (10 mL) and the molecular sieves were filtered off and washed with saturated NaHCO₃. The organic layer was separated, dried and concentrated. The crude product was purified by column chromatography on neutral alumina (hexane:ethyl acetate; 3:1) to give 20 (210 mg, α:β; 20:1, 88%). For α-anomer: [α]²⁰_D + 37.6 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 1.62 (t, J = 2.0 Hz, 1H), 2.53 (t, J = 2.5 Hz, 1H), 2.57 (t, J = 2.0 Hz, 1H), 3.21–3.26 (m, 1H), 3.64 (dd, J = 3.5, 10.0 Hz, 1H), 3.81–3.89 (m, 3H), 4.0–4.07 (m, 1H), 4.09–4.31 (m, 15H), 4.41 (dd, J = 2.5, 16.0 Hz, 1H), 4.63 (dd, J = 2.5, 16.0 Hz, 1H), 4.68 (dd, J = 2.5, 16.5 Hz, 1H), 4.73 (s, 1H), 4.94 (d, J = 12.5 Hz, 1H), 4.98 (d, J = 13.0 Hz, 1H), 5.31 (s, 1H), 5.50 (s, 2H), 5.65 (s, 1H), 7.26–7.53 (m, 23H), 7.80–7.89 (m, 4H); ¹³C NMR (125 MHz, CDCl₃) δ: 57.9, 58.6, 59.8, 64.2, 64.5, 65.2, 67.7, 68.5, 68.7, 72.2, 72.4, 74.9, 75.1, 75.2, 75.3, 76.6, 77.2, 77.8, 78.4, 79.0, 79.1, 79.2, 80.5, 86.4, 99.6, 100.5, 101.5, 101.6, 102.0, 125.7, 125.9, 126.2, 126.3, 126.5, 127.7, 127.9, 128.2, 128.3, 128.4, 128.9, 129.0, 129.3, 129.4, 131.7, 133.0, 133.2, 133.4, 134.5, 134.6, 135.7, 137.3, 137.5, 137.6; ESIHRMS Calcd for C₆₅H₆₂O₁₅SNa [M+Na]⁺: 1137.3702. Found 1137.3699.

Phenyl 4,6-O-benzylidene-2-O-(prop-2-ynyl)-3-O-(2-naphthylmethyl)-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-(prop-2-ynyl)-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-(prop-2-ynyl)-1-thio-α-d-mannopyranoside (20β)

To a stirred solution of donor 14 (400 mg, 0.074 mmol), BSP (18.6 mg 0.09 mmol), TTBP (27.6 mg, 0.11 mmol), and 4 Å molecular sieves in CH₂Cl₂ (2.5 mL), at −60 °C under an Ar atmosphere, was added Tf₂O (16 µL, 0.65 mmol). After 30 min. the temperature was brought down to −78 °C, and then acceptor 19 (55 mg 0.081 mmol) in CH₂Cl₂ (2 mL) was slowly added. The reaction mixture was stirred for 2 h. at −78 °C, and then quenched by the addition of triethyl phosphite (24 µL, 0.15 mmol), and stirred for 1 h at −78 °C before it was allowed to reach room temperature. The reaction mixture was diluted with CH₂Cl₂ (10 mL) and molecular sieves were filtered off and washed with saturated NaHCO₃. The organic layer was separated, dried and concentrated. The crude product was purified by column chromatography on neutral alumina (hexane:ethyl acetate; 7:3) to give 20β (69 mg, 82%). [α]²⁷_D − 10.7 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 2.08 (t, J = 2.5 Hz, 1H), 2.47 (t, J = 2.5 Hz, 1H), 2.51 (t, J = 2.5 Hz, 1H), 3.25–3.34 (m, 2H), 3.62 (dd, J = 3.0, 10.0 Hz, 1H), 3.84 (t, J = 11.0 Hz, 1H), 3.86 (t, J = 10.0 Hz, 1H), 3.90 (t, J = 10.0 Hz, 1H), 4.03–4.04 (m, 2H), 4.14 (t, J = 10.0 Hz, 1H), 4.17 (t, J = 10.0 Hz, 1H), 4.21–4.25 (m, 5H), 4.30–4.35 (m, 2H), 4.36–4.37 (m, 2H), 4.46 (dd, J = 2.5, 16.5 Hz, 1H), 4.51 (dd, J = 2.5, 16.0 Hz, 1H), 4.62 (dd, J = 3.0, 15.0 Hz, 1H), 4.65 (dd, J = 2.5, 16.5 Hz, 1H), 4.87 (s, 1H), 4.91 (s, 1H), 4.95 (d, J = 13.5 Hz, 1H), 4.99 (d, J = 14.0 Hz, 1H), 5.43 (br. s, 1H), 5.58 (s, 1H), 5.59 (s, 1H), 5.64 (d, J = 1.5 Hz, 1H), 7.26–7.54 (m, 23H), 7.76–7.87 (m, 4H); ¹³C NMR (125 MHz, CDCl₃) δ: 57.1, 59.5, 60.0, 65.3, 67.8, 68.5, 68.6, 72.2, 73.2, 73.9, 74.8, 74.9, 75.2, 75.3, 75.8, 75.9, 76.5, 76.9, 77.6, 78.3, 79.3, 80.3, 80.7, 86.2, 98.6, 99.1, 101.5, 101.8, 125.8, 125.9, 126.1, 126.2, 126.5, 127.7, 127.9, 128.2, 128.2, 128.3, 128.9, 129.2, 129.3, 131.7, 132.9, 133.2, 133.4, 135.7, 137.3, 137.6; ESIHRMS Calcd for C₆₅H₆₂O₁₅SNa [M+Na]⁺: 1137.3702. Found 1137.3698.

Methyl 4,6-O-benzylidene-2-O-(prop-2-ynyl)-3-O-(2-naphthylmethyl)-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-(prop-2-ynyl)-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-(prop-2-ynyl)-β-d-mannopyranoside (21)

To a stirred solution of donor 18β (124 mg, 0.15 mmol), BSP (37.6 mg 0.18 mmol), TTBP (55.8 mg, 0.23 mmol), and 4 Å molecular sieves in CH₂Cl₂ (3 mL), at −60 °C under an Ar atmosphere, was added Tf₂O (32.8 µL 0.19 mmol). After 30 min. of stirring at −60 °C, acceptor 17 (72 mg, 0.23 mmol) in CH₂Cl₂ (2 mL), was added slowly. The reaction mixture was stirred for further 2 h. at −60 °C, and then allowed to reach room temperature. The reaction mixture was diluted with CH₂Cl₂ (10 mL), the molecular sieves were filtered off and washed with saturated NaHCO₃. The organic layer was separated, dried and concentrated. The crude product was purified by chromatography on silica gel (toluene: ethyl actate: CH₂Cl₂; 7:2:1) to give 21 (130 mg, α:β; 1:7, 84%). For β-anomer: [α]²²_D − 82.2 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 1.94 (t, J = 2.3 Hz, 1H), 2.48–2.52 (m, 2H), 3.29–3.40 (m, 3H), 3.55 (s, 3H), 3.61 (dd, J = 3.0, 10.0 Hz, 1H), 3.84–3.93 (m, 3H), 3.97 (t, J = 10.0 Hz, 1H), 4.0–4.05 (m, 2H), 4.08 (dd, J = 3.0, 10.0 Hz, 1H), 4.17 (t, J = 10.0 Hz, 1H), 4.21 (d, J = 3.0 Hz, 1H), 4.23–4.28 (m, 3H), 4.35 (dd, J = 4.5, 10.0 Hz, 1H), 4.47 (dd, J = 2.5, 16.0 Hz, 1H), 4.49 (s, 1H), 4.55 (dd, J = 2.5, 17.0 Hz, 1H), 4.61 (dd, J = 2.5, 16.5 Hz, 1H), 4.65 (dd, J = 2.5, 16.0 Hz, 1H), 4.93 (s, 1H), 4.97 (s, 2H), 5.03 (s, 1H), 5.48 (s, 1H), 5.54 (s, 1H), 5.59 (s, 1H), 7.26–7.46 (m, 18H), 7.62–7.71 (m, 4H); ¹³C NMR (125 MHz, CDCl₃) δ: 57.6, 59.4, 59.5, 60.0, 67.5, 67.8, 68.5, 72.0, 72.1, 72.8, 73.7, 73.8, 74.7, 74.8, 75.2, 75.3, 76.2, 76.4, 76.6, 78.2, 80.4, 80.6, 97.6, 97.8, 101.4, 101.5, 103.4, 125.8, 125.9, 125.99, 126.0, 126.1, 126.5, 127.6, 127.8, 128.1, 128.2, 128.3, 128.9, 129.9, 132.9, 133.1, 135.6, 137.2, 137.5; ESIHRMS Calcd for C₆₀H₆₀O₁₆Na [M+Na]⁺: 1059.3779. Found 1059.3792.

Methyl 4,6-O-benzylidene-2-O-(prop-2-ynyl)-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-(prop-2-ynyl)-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-(prop-2-ynyl)-β-d-mannopyranoside (22)

To a stirred solution of 21β (72 mg, 0.069 mmol) in CH₂Cl₂ (10 mL) and water (0.5 mL) was added DDQ (40 mg, 0.18 mmol) at room temperature. After 3 h, sat. NaHCO₃ was added, and the mixture was extracted with CH₂Cl₂. The extracts were washed several times with sat NaHCO₃, and dried over Na₂SO₄. Evaporation of the solvent in vacuo gave an oil, which was purified by column chromatographed on neutral alumina (hexane:ethyl acetate; 2:1) to give 22 (51 mg, 81%) [α]²⁰_D −116.1 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 2.05 (t, J = 2.0 Hz, 1H), 2.48–2.50 (m, 2H), 2.59 (br. s, 1H), 3.35–3.45 (m, 3H), 3.56 (s, 3H), 3.76–3.86 (m, 3H), 3.91 (t, J = 10.0 Hz, 1H), 4.0 (t, J = 10.0 Hz, 1H), 4.0–4.05 (m, 2H), 4.09–4.13 (m, 2H), 4.25–4.30 (m, 4H), 4.36 (dd, J = 4.5, 10.5 Hz, 1H), 4.50 (s, 1H), 4.53 (dd, J = 2.5, 16.0 Hz, 1H), 4.55 (dd, J = 2.5, 16.0 Hz, 1H), 4.57 (dd, J = 2.5, 16.0 Hz, 1H), 4.63 (dd, J = 2.5, 16.0 Hz, 1H), 4.69 (dd, J = 2.5, 16.0 Hz, 1H), 4.70 (dd, J = 2.5, 16.0 Hz, 1H), 5.07 (s, 2H), 5.47 (s, 1H), 5.49 (s, 1H), 5.57 (s, 1H), 7.26–7.48 (m, 15H); ¹³C NMR (125 MHz, CDCl₃) δ: 57.7, 59.4, 59.5, 60.5, 67.2, 67.7, 68.4, 68.5, 70.2, 72.1, 72.8, 73.8, 73.9, 75.1, 75.2, 76.6, 77.2, 79.3, 80.0, 80.4, 80.6, 97.6, 97.8, 101.4, 101.6, 101.9, 103.4, 126.0, 126.2, 128.1, 128.18, 128.2, 128.3, 128.9, 129.0, 129.1, 137.1, 137.2; ESIHRMS Calcd for C₄₉H₅₂O₁₆Na [M+Na]⁺: 919.3148. Found 919.3143.

Standard procedure for coupling reactions of the sulfoxide donor 23 with the corresponding sugar acceptors using TTBP and Tf₂O

To a stirred solution of sulfoxide donor 23 (0.05 M in mixed solvent, 1.2 eq), TTBP (1.6 eq), 4Å molecular sieves in a mixed solvent of CH₂Cl₂ and 1-octene (v/v, 4/1), at −78 °C under argon atmosphere, was added Tf₂O (1.2 eq). After the reaction mixture was stirred at −78 °C for 30 minutes, a solution of sugar acceptors (0.1 M, 1.0 eq) in CH₂Cl₂ was added. Stirring was maintained for another 30 minutes at −78°C before the reaction temperature was then allowed to warm up to −20 °C slowly. The reaction mixture was poured into aq NaHCO₃ solution, diluted with CH₂Cl₂, and filtered through Celite. The organic layer was separated from the filtrate, washed with brine, dried over anhydrous Na₂SO₄, and concentrated. The residue was purified by chromatography on silica gel to give the coupled products.

Methyl 4,6-O-benzylidene-2-O-benzyl-3-O-[3-(naphthalen-1-yl)-prop-2-ynyl]-β-d-mannopyranoside (24)

To a stirred solution of sulfoxide 23 (0.15 g, 0.23 mmol), TTBP (0.094 g, 0.38 mmol), and 4Å molecular sieves in a mixed solvent of CH₂Cl₂ and 1-octene (5 mL, v/v, 4:1), at −78 °C under argon atmosphere, was added Tf₂O (48 µL, 0.28 mmol). After the reaction mixture was stirred at −78 °C for 30 minutes, 1 mL of anhydrous methanol was added. The reaction mixture was stirred at −78 °C for another 30 minutes before pouring into aq NaHCO₃ solution, then diluted with CH₂Cl₂, and filtered through Celite. The organic layer was washed with brine, dried over Na₂SO₄, and concentrated. The residue was purified by chromatography on silica gel (hexane:ethyl acetate; 4:1) to give the β coupled product 24 (0.087 g, 68%): [α]²⁰_D −33.8 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 8.30 (d, J = 8.0 Hz, 1H), 7.85 (t, J = 8.0 Hz, 2H), 7.64 (d, J = 7.0 Hz, 1H), 7.48–7.54 (m, 6H), 7.41–7.44 (dd, J = 7.0, 8.0 Hz, 1H), 7.33–7.36 (m, 5H), 7.28–7.29 (m, 1H), 5.65 (s, 1H), 5.03(d, J = 12.0 Hz 1H), 4.91 (d, J = 12.0 Hz, 1H), 4.60–4.68 (m, 2H), 4.48 (s, 1H), 4.36 (dd, J = 4.5, 10.5 Hz, 1H), 4.24 (t, J = 9.5 Hz, 1H), 4.09 (d, J = 3.0 Hz, 1H), 3.95–4.00 (m, 2H), 3.56 (s, 3H), 3.44 (dt, J = 5.0, 10.0 Hz, 1H); ¹³C NMR (125 MHz, CDCl₃) δ: 138.5, 137.5, 133.4, 133.1, 130.7, 129.0, 128.9, 128.4, 128.32, 128.25, 128.2, 127.5, 126.9, 126.5, 126.2, 126.1, 125.2, 120.2, 103.3, 101.6, 90.2, 84.5, 78.6, 76.3, 75.1, 68.7, 67.6, 59.0, 57.5; ESIHRMS Calcd for C₃₄H₃₂O₆Na [M+Na]⁺: 559.2097. Found 559.2094.

Standard procedure for removal of the 1-naphthylpropargyl protecting group with DDQ

To a stirred solution of the 1-naphthylpropargyl protected saccharide (0.06 M) in CH₂Cl₂ and water (CH₂Cl₂:water, v/v, 20:1) was added DDQ (1.5 eq). The resulting mixture was stirred at rt for 2–3 h. When the reaction was over as monitored by TLC, the reaction mixture was quenched by adding aq NaHCO₃ solution, then diuted with CH₂Cl₂. The organic layer was separated, and the aqueous layer was extracted twice with CH₂Cl₂ The combined organic layer was washed with brine, dried and concentrated. The residue was purified by chromatography on silica gel to give the deprotected product.

Methyl 4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranoside (25)

Removal of naphthylpropargyl protecting group from 24 (0.42 g, 0.78 mmol) by the standard protocol gave compound 25 (0.21 g, 0.56 mmol) in 74% yield. [α]²⁰_D −122.3 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 7.48–7.50 (m, 2H), 7.30–7.42 (m, 8H), 5.55 (s, 1H), 5.08 (d, J = 12.0 Hz, 1H), 4.65 (d, J = 12.0 Hz, 1H), 4.49 (s, 1H), 4.34 (dd, J = 5.0, 10.5 Hz, 1H), 3.76–3.93 (m, 4H), 3.59 (s, 3H), 3.35 (dt, J = 5.0, 9.5 Hz, 1H), 2.31 (br. s, 1H); ¹³C NMR (125 MHz, CDCl₃) δ: 138.3, 137.3, 129.1, 128.6, 128.3, 128.24, 128.15, 128.0, 126.3, 103.5, 102.0, 79.4, 78.4, 75.7, 70.8, 68.6, 67.1, 57.6; ESIHRMS Calcd for C₂₁H₂₄O₆Na [M+Na]⁺: 395.1471. Found 395. 1486.

Methyl 4,6-O-benzylidene-2-O-benzyl-3-O-[3-(naphthalen-1-yl)-prop-2-ynyl]-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranoside(26)

Coupling of sulfoxide 23 (0.16 g, 0.25 mmol) with donor 25 (0.08 g, 0.21 mmol) by the standard coupling protocol gave disaccharide 26 (0.17 g, 0.19 mmol) in 93% yield. [α]²⁰_D −81.8 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 8.34 (d, J = 8.0 Hz, 1H), 7.85 (t, J = 7.5 Hz, 2H), 7.65 (d, J = 7.0 Hz, 1H), 7.18–7.54 (m, 23H), 5.62 (s, 1H), 5.53 (s, 1H), 4.98 (d, J = 12.0, Hz, 1H), 4.93 (d, J = 12.5 Hz, 1H), 4.74 (t, J = 12.5 Hz, 2H), 4.58–4.66 (m, 2H), 4.48 (s, 1H), 4.36 (dd, J = 4.5, 10.5 Hz, 1H), 4.20 (dd, J = 5.0, 10.5 Hz, 1H), 4.07–4.15 (m, 4H), 3.94–3.98 (m, 2H), 3.86 (t, J = 10.5 Hz, 1H), 3.76 (d, J = 3.0 Hz, 1H), 3.60 (s, 4H), 3.41 (dt, J = 5.0, 10.0 Hz, 1H), 3.02 (dt, J = 5.0, 9.5 Hz, 1H); ¹³C NMR (125 MHz, CDCl₃) F: 138.8, 138.1, 137.5, 137.4, 133.4, 133.2, 130.7, 129.1, 128.9, 128.8, 128.4, 128.3, 128.2, 128.1, 127.3, 127.0, 126.5, 126.3, 126.2, 125.2, 120.3, 103.7, 101.8, 101.5, 97.4, 90.5, 84.4, 78.3, 77.0, 76.0, 74.8, 74.3, 73.5, 72.9; ESIHRMS Calcd for C₅₄H₅₂O₁₁Na [M+Na]⁺: 899.3408. Found 899.3444.

Methyl 4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranoside (27)

Removal of the naphthylpropargyl protecting group from 26 (0.135 g, 0.15 mmol) by the standard protocol gave deprotected compound 27 (0.091 g, 1.28 mmol) in 77% yield. [α]²¹_D −113.4 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 7.41–7.46 (m, 6H), 7.21–7.7.38 (m, 10H), 7.17–7.20 (m, 4H), 5.05 (d, J = 11.0 Hz, 1H), 5.00 (d, J = 12.5 Hz, 1H), 4.53 (d, 11.0 Hz, 1H), 4.52 (s, 1H), 4.38 (dd, J = 4.5, 10.5 Hz, 1H), 4.18 (dd, J = 5.0, 10.5 Hz, 1H), 4.07–4.15 (m, 3H), 4.02 (d, J = 2.5 Hz, 1H), 3.96 (t, J = 10.5 Hz, 1H), 3.71–3.76 (m, 2H), 3.62 (s, 3H), 3.57 (d, J = 4.0 Hz, 1H), 3.41–3.48 (m, 2H), 2.98 (dt, J = 4.5, 9.5 Hz, 1H); ¹³C NMR (125 MHz, CDCl₃) δ: 138.2, 137.4, 137.2, 129.1, 129.0, 128.5, 128.4, 128.2, 127.8, 126.2, 103.8, 101.84, 101.80, 97.0, 79.5, 77.6, 75.1, 74.4, 73.3, 72.6, 70.2, 68.7, 68.5, 67.8, 67.0; ESIHRMS Calcd for C₄₁H₄₄O₁₁Na [M+Na]⁺: 735.2782. Found 735.2761.

Methyl 4,6-O-benzylidene-2-O-benzyl-3-O-[3-(naphthalen-1-yl)-prop-2-ynyl]-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(l→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranoside (28)

Method 1: Coupling of sulfoxide 23 (0.095g, 0.15 mmol) with donor 27 (0.09 g, 0.13 mmol) by the standard coupling protocol gave trisaccharide 28 (0.12 g, 0.10 mmol) in 78% yield. Method 2: Coupling of sulfoxide donor 34 (0.07 g, 0.05 mmol) with methanol (1 mL, excess) by standard coupling protocol gave trisaccharide 28 (0.061 g, 0.05 mmol) in 94% yield. [α]²⁴_D −100.8 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 8.35 (d, J = 8.0 Hz, 1H), 7.84 (t, J = 8.0 Hz, 2H), 7.64 (d, J = 7.0 Hz, 1H), 7.28–7.53 (m, 25H), 7.17–7.20 (m, 5H), 7.11–7.12 (m, 3H), 5.60 (s, 1H), 5.57 (s, 1H), 5.51 (s, 1H), 5.04 (d, J = 12.5 Hz, 1H), 5.01 (d, J = 12.0 Hz, 1H), 4.92 (d, 12.0 Hz, 1H), 4.80 (d, J = 13.0 Hz, 1H), 4.77 (d, J = 12.0 Hz, 1H), 4.60–4.70 (m, 3H), 4.52–4.54 (m, 1H), 4.38 (dd, J = 4.5, 10.0 Hz, 1H), 3.72–4.25 (m, 17H), 3.62 (s, 3H), 3.44 (dt, J = 4.5, 9.5 Hz, 1H), 3.12 (dt, J = 4.5, 9.5 Hz, 1H), 3.02 (dt, J = 4.5, 9.5 Hz, 1H); ¹³C NMR (125 MHz, CDCl₃) δ: 138.8, 138.3, 138.2, 137.5, 137.43, 137.38, 133.4, 133.2, 130.7, 129.0, 128.9, 128.6, 128.44, 128.39, 128.2, 128.11, 128.08, 127.8, 127.3, 126.9, 126.5, 126.23, 126.18, 126.15, 125.2, 120.3, 103.8, 101.72, 101.67, 101.5, 97.7, 97.3, 90.4, 84.4, 78.4, 76.97, 76.93, 76.2, 74.9, 74.2, 74.1, 73.8, 73.3, 73.0, 72.7, 68.7, 68.6, 67.8, 58.7, 57.7; ESIHRMS Calcd for C₇₄H₇₂O₁₆Na [M+Na]⁺: 1239.4713. Found 1239.4680.

Methyl 4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(l→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranoside (29)

Removal of protecting group from compound 28 (0.094 g, 0.08 mmol) by the standard deprotection protocol gave trisaccharide 29 (0.065 g, 0.06 mmol) in 77% yield. [α]²⁹_D −120.8 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 7.43–7.47 (m, 9H), 7.19–7.36 (m, 21H), 5.60 (s, 1H), 5.47 (s, 1H), 5.37 (s, 1H), 5.03–5.07 (m, 2H), 4.97 (d, J = 12.0 Hz, 1H), 4.81 (d, J = 12.5 Hz, 1H), 4.72 (d, J = 11.0 Hz, 1H), 4.55 (d, J = 12.5 Hz, 1H), 4.54 (s, 1H), 4.38 (dd, J = 5.0, 10.5 Hz, 1H), 4.30 (s, 1H), 4.10–4.23 (m, 5H), 4.00–4.04 (m, 2H), 3.96 (t, J = 10.0 Hz, 1H), 3.75–3.86 (m, 5H), 3.70 (d, J = 4.0 Hz, 1H), 3.63 (s, 3H), 3.60–3.63 (m, 1H), 3.42–3.48 (m, 1H), 3.01–3.12 (m, 2H), 2.47 (d, J = 9.0 Hz, 1H); ¹³C NMR (125 MHz, CDCl₃) δ: 138.3, 138.2, 137.4, 137.4, 129.1, 129.0, 128.60, 128.55, 128.4, 128.2, 128.1, 127.9, 127.8, 126.3, 126.22, 126.16, 103.8, 101.80, 101.75, 101.7, 97.4, 97.2, 79.6, 77.6, 77.3, 75.1, 74.3, 73.6, 73.3, 72.9, 72.7, 70.2, 68.7, 68.6, 67.8, 67.1, 57.7; ESIHRMS Calcd for C₆₁H₆₄O₁₆Na [M+Na]⁺: 1075.4087. Found 1075.4090.

Phenyl 4,6-O-benzylidene-2-O-benzyl-3-O-[3-(naphthalen-1-yl)-prop-2-ynyl]-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-1-thio-α-d-mannopyranoside(31)

Coupling of sulfoxide donor 23 (0.105 g, 0.17 mmol) with thioglycoside 30 (0.050 g, 0.11 mmol) by the standard coupling protocol gave disaccharide 31 (0.081 g, 0.085 mmol) as a colorless syrup in 76% yield. [α]²⁴_D +37.6 (c, 2.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 8.35 (d, J = 8.5 Hz, 1H), 7.85 (t, J = 7.5 Hz, 2H), 7.67 (d, J = 7.0 Hz, 1H), 7.20–7.53 (m, 28H), 5.64 (s, 1H), 5.63 (s, 1H), 5.56 (s, 1H), 5.02 (d, J = 11.5 Hz, 1H), 4.83 (d, J = 11.5 Hz, 1H), 4.65–4.72 (m, 3H), 4.48 (d, J = 12.5 Hz, 1H), 4.41(dd, J = 3.0, 10.0 Hz, 1H), 4.24–4.36 (m, 5H), 4.18 (t, J = 9.5 Hz, 1H), 4.07–4.08 (m, 1H), 3.95 (d, J = 3.0 Hz, 1H), 3.91 (t, J = 10.0 Hz, 2H), 3.77 (dd, J = 3.5, 10.0 Hz, 1H), 3.12 (dt, J = 4.5, 9.5 Hz, 1H); ¹³C NMR (125 MHz, CDCl₃) δ: 138.8, 137.6, 137.5, 137.1, 133.8, 133.4, 133.2, 131.8, 130.7, 129.3, 129.1, 129.0, 128.9, 128.61, 128.55, 128.4, 128.2, 128.1, 127.9, 127.3, 127.0, 126.5, 126.3, 126.2, 126.1, 125.2, 120.3, 101.9, 101.5, 98.4, 90.5, 86.0, 84.5, 78.4, 77.4, 76.6, 75.7, 75.0, 72.7, 72.1, 68.64, 68.56, 67.7, 65.5, 58.8; ESIHRMS Calcd for C₅₉H₅₄O₁₀SNa [M+Na]⁺: 977.3336. Found 977.3380.

Phenyl 4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-1-thio-α-d-mannopyranoside (32)

Removal of the naphthylpropargyl group from compound 31 (1.30 g, 1.36 mmol) by the standard protocol gave product 32 (0.95 g, 1.20 mmol) in 88% yield. [α]²⁵_D −2.2 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 7.45–7.49 (m, 6H), 7.24–7.38 (m, 19H), 5.68 (s, 1H), 5.64 (s, 1H), 5.33 (s, 1H), 5.06 (d, J = 11.0 Hz, 1H), 4.77 (d, J = 12.0 Hz, 1H), 4.62 (d, J = 12.0 Hz, 1H), 4.55 (d, J = 12.0 Hz, 1H), 4.42 (dd, J = 3.0, 10.0 Hz, 1H), 4.35–4.40 (m, 2H), 4.22–4.30 (m, 3H), 4.12–4.13 (m, 1H), 3.92 (t, J = 10.0 Hz, 1H), 3.83 (t, J = 9.0 Hz, 1H), 3.74–3.78 (m, 2H), 3.58–3.66 (m, 1H), 3.10 (dt, J = 4.5, 9.5 Hz, 1H), 2.53 (d, J = 9.5 Hz, 1H); ¹³C NMR (125 MHz, CDCl₃) δ: 138.1, 137.44, 137.36, 137.1, 133.7, 131.8, 129.3, 129.08, 129.05, 128.7, 128.6, 128.5, 128.4, 128.2, 127.9, 127.8, 126.3, 102.0, 101.8, 97.8, 86.1, 79.8, 77.5, 77.30, 77.25, 75.4, 74.9, 72.4, 72.2, 70.2, 68.7, 68.6, 67.0, 65.6; ESIHRMS Calcd for C₄₆H₄₆O₁₀SNa[M+Na]⁺: 813.2704. Found 813.2694.

Phenyl 4,6-O-benzylidene-2-O-benzyl-3-O-[3-(naphthalen-1-yl)-prop-2-ynyl]-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-1-thio-α-d-mannopyranoside (33)

Coupling of sulfoxide donor 23 (0.063 g, 0.10 mmol) with thioglycoside 32 (0.062 g, 0.08 mmol) by the standard coupling protocol gave trisaccharide 33 (0.074 g, 0.06 mmol) as a colorless syrup in 73% yield. [α]²⁷_D −40.5(c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 8.33 (d, J = 8.0 Hz, 1H), 7.84 (t, J = 7.5 Hz, 2H), 7.63 (d, J = 7.0 Hz, 1H), 7.44–7.52 (m, 10H), 7.28–7.40 (m, 20H), 7.18–7.23 (m, 5H), 7.11–7.12 (m, 3H), 5.66 (s, 1H), 5.60 (s, 1H), 5.56 (s, 1H), 5.49 (s, 1H), 4.99 (d, J = 12.0 Hz, 1H), 4.93 (d, J = 12.0 Hz, 1H), 4.77 (t, J = 12.0 Hz, 2H), 4.53–4.70 (m, 4H), 4.43 (dd, J = 3.0, 10.0 Hz, 1H), 4.06–4.35 (m, 10H), 3.85–3.94 (m, 6H), 3.71 (dd, J = 3.0, 10.0 Hz, 1H), 3.08–3.14 (m, 2H); ¹³C NMR (125 MHz, CDCl₃) δ: 138.8, 138.2, 137.5, 137.4, 137.0, 133.7, 133.4, 133.2, 131.9, 130.7, 129.3, 129.0, 128.9, 128.7, 128.5, 128.4, 128.3, 128.2, 128.1, 127.9, 127.8, 127.3, 126.9, 126.5, 126.3, 126.2, 125.2, 120.3, 101.8, 101.7, 101.5, 98.0, 90.4, 85.8, 84.4, 78.4, 76.1, 75.4, 74.9, 74.2, 73.9, 73.4, 72.3, 71.9, 68.6, 67.8, 65.5, 58.7; ESIHRMS Calcd for C₇₉H₇₄O₁₅SNa[M+Na]⁺: 1317.4641. Found 1317.4630.

Phenyl 4,6-O-benzylidene-2-O-benzyl-3-O-[3-(naphthalen-1-yl)-prop-2-ynyl]-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-1-thio-α-d-mannopyranoside-S-oxide (34)

To a stirred solution of 33 (0.98 g, 0.76 mmol) in CH₂Cl₂ (40 mL) was added a solution of mCPBA (77%, 0.17 g, 0.76 mmol) in CH₂Cl₂ (2 mL) dropwise at −78 °C. The resultant mixture was stirred for 1 h during which the temperature was allowed to warm up to −20 °C slowly. The reaction mixture was then quenched by pouring into aq NaHCO₃ solution, and was diluted with CH₂Cl₂. The organic layer was separated, washed with 1 M aq NaOH solution, brine, dried over anhydrous Na₂SO₄, and concentrated. The residue was purified by chromatography on silica gel (hexane:ethyl acetate; 1.5:1) to give the title compound 34 (0.98 g, 98%). [α]²⁵_D −103.9 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 8.34 (d, J = 8.0 Hz, 1H), 7.84 (t, J = 8.0 Hz, 2H), 7.11–7.65 (m, 39H), 5.58 (s, 2H), 5.48 (s, 1H), 5.01 (d, J = 12.0 Hz, 1H), 4.93 (d, J = 12.0 Hz, 1H), 4.58–4.77 (m, 7H), 4.43–4.52 (m, 2H), 4.11–4.31 (m, 8H), 4.08 (t, J = 9.5 Hz, 1H), 3.94 (t, J = 10.0 Hz, 1H), 3.85–3.88 (m, 4H), 3.71–3.78 (m, 2H), 3.15 (dt, J = 5.0, 10.0 Hz, 1H), 3.08 (dt, J = 5.0, 10.0 Hz, 1H); ¹³C NMR (125 MHz, CDCl₃) δ: 141.6, 138.8, 138.3, 137.5, 137.1, 136.6, 133.4, 133.2, 131.9, 130.7, 129.6, 129.2, 129.0, 128.9, 128.7, 128.5, 128.3, 128.23, 128.19, 128.1, 127.8, 127.4, 127.0, 126.5, 126.3, 126.2, 125.2, 124.4, 120.3, 101.9, 101.7, 101.5, 98.4, 97.9, 96.3, 90.4, 84.4, 78.4, 77.3, 77.0, 76.4, 76.1, 74.9, 74.3, 73.9, 73.7, 72.7, 72.1, 70.7, 70.2, 68.6, 68.2, 67.8, 58.6; ESIHRMS Calcd for C₇₉H₇₄O₁₆SNa [M+Na]⁺: 1333.4590. Found 1333.4589.

Methyl 4,6-O-benzylidene-2-O-benzyl-3-O-[3-(naphthalen-1-yl)-prop-2-ynyl]-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-α-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranoside (35α) and Methyl 4,6-O-benzylidene-2-O-benzyl-3-O-[3-(naphthalen-1-yl)-prop-2-ynyl]-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranoside (35β)

To a stirred solution of sulfoxide donor 34 (120 mg, 0.09 mmol), TTBP (40 mg, 0.16 mmol), 4Å molecular sieves in a mixed solvent of CH₂Cl₂ and 1-octene (7.5 mL, v/v, 4:1), at −78 °C under argon atmosphere, was added Tf₂O (15 µL, 0.09 mmol). After the reaction mixture was stirred at −78 °C for 30 minutes, a solution of acceptor 29 (80 mg, 0.075mmol) in CH₂Cl₂ (1.5 mL) was added. The stirring was maintained for 30 minutes at −78°C, the the reaction temperature was allowed to warm up to −20 °C slowly over 30 minutes. The resultant mixture was stirred for another 30 minutes at −20 °C before it was quenched by pouring into aq NaHCO₃ solution. The mixture was diluted with CH₂Cl₂ and filtered through Celite. The organic layer was washed with brine, dried over Na₂SO₄, and concentrated. The residue was purified by chromatography on silica gel (hexane:ethyl acetate; 2:1→1.5:1) to give a mixture of hexasaccharides 35α, 35β (103 mg, 61%) in 1:1 ratio as estimated by ¹H NMR spectroscopy of the mixture. Separation of 30 mg of the mixture by RP HPLC using a gradient of 90% A to 100% A over 144 minutes (A: CH₃CN, B: H₂O; Varian Microsorb C₁₈ 250*21.4mm; flow rate: 5 mL/min; UV detection: 215 nm) gave pure samples of 35α, 35β.

Hexasaccharide 35α

[α]²⁰_D −127.7 (c, 0.5, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 8.33 (d, J = 8.5 Hz, 1H), 7.82 (t, J = 8.0 Hz, 2H), 7.62 (d, J = 7.0 Hz, 1H), 7.05–7.50 (m, 61H), 6.97 (d, J = 7.5 Hz, 2H), 5.63 (s, 1H), 5.57 (s, 1H), 5.56 (s, 1H), 5.55 (s, 1H), 5.45 (s, 1H), 5.39 (s, 1H), 4.45–5.07 (m, 15H), 4.39 (dd, J = 3.5, 9.0 Hz, 2H), 3.68–4.25 (m, 33H), 3.63 (s, 3H), 3.60–3.65 (m, 1H), 3.45 (dt, J = 4.5, 9.0 Hz, 1H), 3.05–3.12 (m, 3H), 3.01 (dt, J = 4.5, 9.5 Hz, 1H); ¹³C NMR (125 MHz, CDCl₃) δ: 138.8, 138.29, 138.27, 138.2, 137.9, 137.7, 137.5, 137.4, 137.3, 133.4, 133.2, 130.7, 129.5, 129.00, 128.96, 128.91, 128.85, 128.7, 128.6, 128.47, 128.45, 128.4, 128.34, 128.29, 128.24, 128.21, 128.16, 128.1, 128.0, 127.88, 127.85, 127.8, 127.3, 126.9, 126.5, 126.3, 126.2, 125.2, 120.3, 103.9, 102.2, 101.8, 101.69, 101.65, 101.5, 98.8, 98.5, 97.6, 97.3, 90.4, 84.4, 78.8, 78.3, 77.3, 76.9, 76.1, 76.0, 75.1, 74.8, 74.24, 74.16, 74.1, 73.9, 73.8, 73.7, 73.5, 73.3, 73.2, 72.6, 72.4, 72.1, 71.8, 68.7, 68.6, 67.8, 67.7, 67.5, 64.6, 58.6, 57.7; ESIHRMS Calcd for C₁₃₄H₁₃₂O₃₁Na [M+Na]⁺: 2259.8645. Found 2259.8513.

Hexasaccharide 35β

[α]²⁰_D −132.2 (c, 0.5, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 8.33 (d, J = 8.0 Hz, 1H), 7.83 (t, J = 7.5 Hz, 2H), 7.63 (d, J = 7.0 Hz, 1H), 7.09–7.51 (m, 63H), 5.62 (s, 1H), 5.55 (s, 1H), 5.53 (s, 1H), 5.51 (s, 1H), 5.50 (s, 1H), 5.48 (s, 1H), 4.98–5.08 (m, 5H), 4.89 (d, J = 12.0 Hz, 1H), 4.66–4.83 (m, 7H), 4.59–4.63 (m, 2H), 4.53–4.54 (m, 1H), 4.39 (dd, J = 4.5, 10.5 Hz, 2H), 3.78–4.24 (m, 30H), 3.68 (dd, J = 3.0, 9.5 Hz, 1H), 3.63 (m, 4H), 3.45 (dt, J = 5.0, 9.5 Hz, 1H), 3.13 (dt, J = 5.0, 9.5 Hz, 1H), 3.01–3.08 (m, 4H); ¹³C NMR (125 MHz, CDCl₃) δ: 138.8, 138.3, 138.2, 138.1, 137.5, 137.43, 137.37, 137.3, 133.4, 133.2, 130.6, 128.99, 128.95, 128.91, 128.8, 128.7, 128.5, 128.42, 128.35, 128.3, 128.21, 128.19, 128.1, 127.93, 127.87, 127.3, 126.9, 126.5, 126.24, 126.17, 126.1, 125.2, 120.3, 103.9, 101.8, 101.70, 101.63, 101.5, 97.5, 97.3, 90.4, 84.4, 78.4, 76.9, 76.1, 74.9, 74.2, 73.9, 73.8, 73.5, 73.3, 73.2, 72.5, 72.4, 72.1, 72.0, 68.7, 68.5, 67.8, 58.6, 57.7; ESIHRMS Calcd for C₁₃₄H₁₃₂O₃₁Na [M+Na]⁺: 2259.8645. Found 2259.8560.

Methyl 4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-α-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranoside (36α) and Methyl 4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranosyl-(1→3)-4,6-O-benzylidene-2-O-benzyl-β-d-mannopyranoside (36β)

Removal of the naphthylpropargyl group from a 1:1 mixture of 35α and 35β (85 mg, 0.038mmol) by the standard deprotection protocol gave 36 as a mixture of anomers (55 mg, 70%). Separation by RP HPLC using a gradient of 80% A to 100% A over 144 minutes (A: CH₃CN, B: H₂O; Varian Microsorb C₁₈ 250*21.4mm; flow rate: 10 mL/min; UV detection: 215 nm) gave pure samples of 36α, 36β respectively. Hexasaccharide 36α: [α]²¹_D −122.7 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 7.43–7.52 (m, 11H), 7.12–7.41 (m, 47H), 7.01 (d, J = 7.5 Hz, 2H), 5.64 (s, 1H), 5.59 (s, 1H), 5.55 (s, 2H), 5.41 (s, 1H), 5.36 (s, 1H), 4.81–5.08 (m, 7H), 4.76 (d, J = 3.5 Hz, 1H), 4.73 (d, J = 3.5 Hz, 1H), 4.48–4.55 (m, 2H), 4.41 (dt, J = 4.5, 10.0 Hz, 2H), 3.74–4.32 (m, 30H), 3.70 (d, 3.5 Hz, 1H), 3.66–3.68 (m, 1H), 3.64 (s, 3H), 3.57–3.58 (m, 1H), 3.45 (dt, J = 5.0, 10.0 Hz, 1H), 3.00–3.16 (m, 4H), 2.47 (s, 1H); ¹³C NMR (125 MHz, CDCl₃) δ: 138.3, 138.2, 138.1, 137.9, 137.7, 137.4, 137.34, 137.30, 137.2, 129.5, 129.1, 128.94, 128.90, 128.7, 128.6, 128.43, 128.38, 128.3, 128.23, 128.18, 128.15, 128.1, 128.0, 127.94, 127.90, 127.8, 126.24, 126.21, 126.1, 103.8, 102.1, 101.8, 101.7, 101.6, 98.8, 98.2, 97.5, 97.3, 79.6, 78.7, 77.6, 77.2, 76.9, 76.0, 75.0, 74.23, 74.19, 74.1, 73.9, 73.72, 73.67, 73.5, 73.1, 72.5, 72.3, 72.0, 71.8, 70.2, 68.7, 68.6, 68.5, 67.7, 67.6, 67.5, 67.0, 64.6, 64.2, 57.7; ESIHRMS Calcd for C₁₂₁H₁₂₄O₃₁Na [M+Na]⁺: 2095.8019. Found 2095.7938. Hexasaccharide 36β: [α]²¹_D −152.5 (c, 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃) δ: 7.44–7.47 (m, 14H), 7.22–7.36 (m, 49H), 5.63 (s, 1H), 5.49–5.53 (m, 4H), 5.37 (s, 1H), 4.97–5.08 (m, 6H), 4.75–4.84 (m, 5H), 4.53–4.55 (m, 2H), 4.40 (dd, J = 4.5, 10.0 Hz, 1H), 3.70–4.26(m, 33H), 3.64 (s, 3H), 3.55–3.58 (m, 1H), 3.45 (dt, J = 4.5, 9.0 Hz, 1H), 3.01–3.17 (m, 5H), 2.47 (br. s, 1H); ¹³C NMR (125 MHz, CDCl₃) δ: 138.3, 138.22, 138.16, 137.4, 137.3, 129.1, 129.0, 128.72, 128.66, 128.5, 128.4, 128.3, 128.2, 128.1, 128.0, 127.8, 126.3, 126.2, 126.1, 103.9, 101.81, 101.79, 101.7, 101.6, 97.5, 97.4, 97.3, 79.6, 77.7, 75.1, 74.2, 74.0, 73.9, 73.5, 73.3, 73.2, 72.5, 72.4, 72.0, 70.2, 68.7, 68.6, 67.8, 67.7, 67.1, 57.7; ESIHRMS Calcd for C₁₂₁H₁₂₄O₃₁Na [M+Na]⁺: 2095.8019. Found 2095.7932.

Methyl β-d-mannopyranosyl-(1→3)-β-d-mannopyranosyl-(1→3)-β-d-mannopyranosyl-(1→3)-β-d-mannopyranosyl-(1→3)-β-d-mannopyranosyl-(1→3)-β-d-mannopyranosyl-(1→3)-β-d-mannopyranoside (37)

A mixture of hexasaccharide 36β (19 mg, 0.01mmol) and 10% Pd(OH)₂/C (30 mg) in a mixed solvent of methanol (2.0 mL) and ethyl acetate (0.5 mL) was shaken under 50 psi of H₂ for 40 h. The mixture was filtered through Celite, followed by removal of the solvent under reduced pressure to, to give mannohexose 37 (10 mg, 100%). [α]¹⁹_D −68.9 (c, 0.25, MeOH:H₂O, 1:1); ¹H NMR (500 MHz, D₂O) δ: 4.65–4.74 (m, 6H), 4.42 (s, 1H), 4.13 (s, 3H), 4.04 (s, 1H), 3.92 (s, 1H), 3.79–3.85 (m, 11H), 3.40–3.43 (m, 1H), 3.40 (s, 3H), 3.26–3.29 (m, 6H); ¹³C NMR (500 MHz, D₂O) δ: 100.8 (¹J_CH = 157.9) , 96.6 (¹J_CH = 158.6), 96.4 (¹JCH = 159.4), 81.7, 78.9, 78.8, 78.7, 76.3, 76.0, 75.8, 72.8, 70.7, 67.7, 67.6, 67.1, 66.8, 65.2, 65.1, 61.0, 56.8. ESIHRMS Calcd for C₃₇H₆₄O₃₁Na [M+Na]⁺: 1027.3324. Found 1027.3334.

Methyl β-d-mannopyranosyl-(1→3)-β-d-mannopyranosyl-(1→3)-α-d-mannopyranosyl-(1→3)-β-d-mannopyranosyl-(1→3)-β-d-mannopyranosyl-(1→3)-β-d-mannopyranosyl-(1→3)-β-d-mannopyranoside (38)

A mixture of hexasaccharide 36α(23 mg, 0.01mmol) and 10% Pd(OH)₂/C (30 mg) in a mixed solvent of methanol (2.0 mL) and ethyl acetate (0.5 mL) was shaken under 50 psi of H₂ for 21 hr until the reaction was over as monitored by TLC. The mixture was filtered through Celite followed by removal of the solvent under reduced pressure to give target Mannohexose 38 (12 mg, 100%). [α]¹⁹_D −40.0 (c, 0.5, MeOH:H₂O, 1:1); ¹H NMR (500 MHz, D₂O) δ: 5.03 (s, 1H), 4.43 (s, 1H), 4.05–4.12 (m, 5H), 3.93 (s, 1H), 3.80–3.81 (m, 7H), 3.53–3.68 (m, 12H), 3.39–3.44 (m, 4H), 3.20–3.30 (m, 7H); ¹³C NMR (500 MHz, D₂O) δ: 102.1 (¹J_CH = 165.0), 100.8 (¹J_CH = 155), 96.9, 96.7, 96.54, 96.49, 80.2, 79.0, 77.2, 76.4, 76.2, 76.1, 76.0, 75.9, 73.1, 72.9, 72.1, 70.8, 70.5, 67.83, 67.78, 67.2, 66.9, 66.3, 65.3, 65.2, 62.5, 61.1, 61.0, 57.4, 56.9, 48.9; ESIHRMS Calcd for C₃₇H₆₄O₃₁Na [M+Na]⁺: 1027.3324. Found 1027.3338.

1-Naphthylpropargylcyclohexyl ether (40)

A mixed solution of propargyl cyclohexyl ether⁷⁰ (0.94 g, 6.8 mmol) and 1-bromonaphthalene (1.05 mL, 7.5 mmol) in triethylamine (20 mL) was degassed by bubbling Ar gas for 30 minutes, then PdCl₂(PPh₃)₂ (0.24 g, 0.34 mmol) and CuI (0.064 g, 0.34mmol) were successively added into the reaction mixture. The resulting mixture was stirred at 50–55 °C overnight under Ar, then was filtered through Celite. The filter cake was washed with CH₂Cl₂ and the filtrate was concentrated under vacuum and residue was purified by chromatography on silica gel (hexane: ethyl acetate; 20:1) to afford the title compound 40 (0.80 g, 44%) as a colorless oil. ¹H NMR (500 MHz, CD₂Cl₂) δ: 1.25–1.42 (m, 5H), 1.55–1.60 (m, 1H), 1.78–1.79 (m, 2H), 2.00–2.03 (m, 2H), 3.62–3.66 (m, 1H), 4.55 (d, J = 2.5 Hz, 2H), 7.43–7.47 (m, 1H), 7.54–7.61 (m, 2H), 7.69–7.70 (m, 1H), 7.86–7.90 (m, 2H), 8.33 (d, J = 8.0 Hz, 1H); ¹³C NMR (125 MHz, CD₂Cl₂) δ: 24.1, 25.8, 32.1, 55.8, 76.7, 83.0, 91.4, 91.4, 120.5, 125.2, 126.0, 126.4, 126.8, 128.3, 128.8, 130.5, 133.2, 133.3. ESIHRMS (EI) Calcd for C₁₉H₂₀O[M]⁺: 264.1514. Found 264.1521.

Supplementary Material

1. Supporting Information Available.

Copies of spectra of all compounds. This material is available free of charge via the Internet at http://pubs.acs.org.