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Synthesis 2024; 56(07): 1175-1182
DOI: 10.1055/a-2218-7604
paper
Emerging Trends in Glycoscience

Efficient Preparation of O-Isopropylidene Derivatives of Carbohydrates Catalyzed by Sulfonated Graphene (GR-SO3H) as a Sustainable Acid Catalyst

Padmashri Rabha
,
Rajib Panchadhayee∗
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Abstract

Sulfonated graphene (GR-SO3H) has emerged as a mild, efficient and sustainable catalyst for the preparation of O-isopropylidene derivatives of unprotected and anomeric-protected carbohydrates with acetone and 2,2-dimethoxypropane at room temperature. This methodology not only provides excellent yields but also reduces reaction times, and it demonstrates exceptional recyclability, allowing the catalyst to be reused multiple times.


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Key words

acetone - carbohydrates - 2,2-dimethoxypropane - GR-SO3H - O-isopropylidene acetals - sustainability

In carbohydrate chemistry, the O-isopropylidene acetal group is frequently used as a common protecting group to protect free hydroxyl groups.[1] Typically, depending upon the nature of the sugar, acetonation by O-isopropylidene groups of an aldohexose results in the formation of an carbohydrate derivative with a selective unmasked hydroxyl group.[2] For example d-glucose is converted into 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose on reaction with anhydrous acetone and catalyst, leaving one hydroxyl group unprotected at the C-3 position.[3] However, on acetonation, d-mannose gives 2,3:5,6-di-O-isopropylidene-α-d-mannofuranose with a free hydroxyl group at the anomeric position.[3] The O-isopropylidene derivatives of sugars play a significant role in the synthesis of complex oligosaccharide, especially for the preparation of valuable building blocks, such as glycosyl acceptors[4] and glycosyl donors.[5] Some O-isopropylidene derivatives of aldohexose have been used for structural studies as well as in theoretical calculations.[6] For example, the O-isopropylidene derivative of galactose, 1,2:3,4-di-O-isopropylidene-α-d-galactopyranose, has recently been employed in theoretical calculations and conformational studies.[7] In addition, some O-isopropylidene derivatives of carbohydrates are significant starting material for the synthesis of various natural products with pharmacological activity.[8] For example, 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose is in high demand commercially as a starting material for a wide range of bioactive molecules, including antibiotics, cytotoxic, anti-inflammatory, and antipyretic agents with very low toxicity.[9] Also, 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose has been utilized as a starting material for the total synthesis of 1-deoxynajirimycin, an α-glucosidase inhibitor for diabetes treatment.[10] In addition, 1,2:3,4:5,6-tri-O-isopropylidene-d-mannitol and 2,3:4,5-di-O-isopropylidene-d-xylose diethyl dithioacetal have been utilized for the total synthesis of a potent cytostatic agent (+)-7-epi-goniofufurone and (+)-phorboxazole A, respectively.[11] Therefore, in recent years, O-isopropylidene derivatives have become important research fields for the large-scale preparation of these important compounds in the pharmaceutical industry.

There are several methods available for O-isopropylidenation of sugar derivatives. Traditionally, the O-isopropylidene derivatives are prepared from the corresponding sugar diol with anhydrous acetone in the presence of an acid catalyst such as conc. H2SO4.[12] Also, this condensation reaction can be performed by using other acetonide-forming agents such as 2,2-dimethoxypropane (DMP) in solvents such as acetonitrile or N,N-dimethylformamide (DMF) with an acid catalyst. Many catalysts have been reported for the O-isopropylidenation of sugar derivatives, which include anhydrous ZnCl2 with H3PO4,[13] pyridinium p-toluenesulfonate (PPTS),[14] zeolite HY,[15] montmorillonite clay,[16] iodine,[17] ion exchange resins,[18] and boron trifluoride etherate,[19] and Lewis acidic metal salts, such as anhydrous ferric chloride,[20] anhydrous copper(II) sulfate,[21] anhydrous aluminium chloride,[22] ceric ammonium nitrate (CAN),[23] and SnCl2.[24] In the past few years, catalysts have also been reported for the O-isopropylidenation reaction including sulfuric acid immobilized on silica,[25] triphenylphosphine polymer-bound/iodine complex,[26] vanadyl triflate (VO(OTf)2·xH2O),[27] tetrabutylammonium tribromide (TBATB),[28] bromodimethylsulfonium bromide (BDMS),[29] [Cp*IrCl2]2 (Cp* = pentamethylcyclopentadienyl),[30] phosphotungstic acid (PTA).[31] Although some of the reported methods have been used extensively, many of these methods have drawbacks such as long reaction time, low yields, the requirement of extra neutralization steps, tedious work-up, and the use of a large excess of reagents and organic solvents.[17] [25] Therefore, a straightforward and practical synthetic strategy is required for the synthesis of O-isopropylidene derivatives of carbohydrates under appropriate reaction conditions.

Oger et al. reported the acetalization of glycerol in the presence of sulfonated graphene under acid-free conditions.[32] A wide range of organic transformations also have been reported by using sulfonated graphene.[33] [34] [35] [36] There has been growing interest in graphene-based catalysts due to their excellent physical, chemical and mechanical properties. Graphene is a 2D carbon material with a large surface area and is prepared from graphite. Recently, we reported the successful preparation of benzylidene acetal of carbohydrate using GR-SO3H as a solid-acid catalyst.[37] As the use of reusable catalysts is important from a green chemistry point of view, we thought it might be an efficient catalyst for the O-isopropylidenation of sugar derivatives. Herein, we report the successful preparation of O-isopropylidene derivatives by using sulfonated graphene (GR-SO3H), as shown in Scheme [1].

Zoom Image
Scheme 1 Isopropylidenation of d-glucose
Zoom Image
Figure 1 Chemical structure of sulfonated graphene (GR-SO3H)

In this work, we prepared sulfonated graphene (GR-SO3H) catalyst according to a standard literature procedure.[32] [38] Graphene oxide (GO) was prepared from graphite sheet by oxidation with KMnO4 in the presence of a mixture of sulfuric acid and phosphoric acid. Following this, GO was reduced to graphene (GR) by using hydrazine hydrate. Subsequently, the GR was functionalized by introducing benzene sulfonic groups, yielding the GR-SO3H catalyst (Figure [1]). The prepared catalyst was characterized by XRD and FT-IR spectroscopic analyses to confirm the formation of the catalyst. The appearance of a broad peak at 2θ=24° in XRD data and characteristic peaks in FT-IR spectra confirmed the formation of the GR-SO3H catalyst. The total amount of sulfonated groups in the GR-SO3H catalyst can be measured by acid-base back-titration; thus, the acidity of the sulfonated graphene catalyst is calculated to be 1.80 mmol H+·g–1.

Initially, the commercially available d-glucose was selected as the starting material for O-isopropylidenation by using anhydrous acetone and 2,2-dimethoxypropane (DMP) separately in the presence of GR-SO3H catalyst. For the test reaction, d-glucose (1) was allowed to react with anhydrous acetone (5 mL) or 3 equiv of DMP (in 2 mL CH3CN) in the presence of 5 mg of sulfonated graphene (GR-SO3H) catalyst at room temperature. The reaction was incomplete and did not give a satisfactory yield even after 9 h of stirring. The same reaction was carried out using different catalyst loadings to obtain the optimal results (Table [1]). The best result was obtained by using 10 mg GR-SO3H, with complete conversion within 1 h, which furnished the product 1a in 96% yield. The formation of the isopropylidene group was confirmed by 1H and 13C NMR spectroscopy, which give four characteristic methyl peaks in the range δ = 1–1.5 ppm and δ = 15–30 ppm, respectively. Both of the acetonating reagents, anhydrous acetone and DMP, were used for acetonation under the optimized reaction conditions, and d-glucose (1) gave product 1a with yields of 95% and 96%, respectively (Table [2], entry 1).

Table 1 GR-SO3H Catalyst Loading for O-Isopropylidenation of d-Glucose at Room Temperature

Entry

Catalyst (mg)

Time (h)

Yield (%)a

1

 0

24

 0

2

 5

 9

40

3

 5

12

65

4

 5

24

67

5

10

 1

96

6

15

 1

96

a Reaction conditions: d-glucose (1 mmol), DMP (3 equiv), CH3CN.

After optimizing the reaction conditions, commercially available free sugar and sugar derivatives were subjected to O-isopropylidenation reaction with both acetonationing reagent, anhydrous acetone and DMP under the optimized reaction conditions. The O-isopropylidenation of other aldohexoses, for example, d-galactose (2) and d-mannose (3), gave the product 1,2;3,4-di-O-isopropylidene-α-d-galactopyranose (2a) and 2,3:4,6-di-O-isopropylidene-α-d-mannopyranose (3a) with yields of 92–95%. Similarly, aldopentoses such as l-arabinose (4) and d-xylose (5) also smoothly give the corresponding acetonides 4a and 5a with good yields. Further, l-rhamnose (6) and d-mannitol (7) were converted into the corresponding O-isopropylidene derivatives 2,3-O-isopropylidene-α-l-rhamnofuranose (6a) and 1,2:3,4:5,6-tri-O-isopropylidene-d-mannitol (7a) under the same reaction conditions (Table [2]).

Table 2 Synthesis of O-Isopropylidene Derivatives from Free Sugars and Their Derivatives Using GR-SO3H as Catalyst

Entry

Substrate

Product

Reagenta

Time (h)

Yield (%)b,c

Ref.

1

DMP
acetone

1
1

96
95

[15]

2

DMP
acetone

1
2

95
92

[15]

3

DMP
acetone

1
1

96
96

[40]

4

DMP
acetone

1
1.5

92
90

[15]

5

DMP
acetone

1
2

93
90

[15]

6

DMP
acetone

1
2

90
89

[41]

7

DMP
acetone

1
1.5

95
92

[29]

8

DMP
acetone

2
2.5

93
89

–

9

DMP
acetone

2
3

92
89

[42]

10

DMP
acetone

2
2.5

91
87

–

11

DMP
acetone

1.5
2

92
87

–

12

DMP
acetone

2.5
3

90
89

–

a Reaction conditions: Acetone (5 mL) or DMP (3 equiv) in CH3CN.

b All compounds were characterized by 1H NMR and 13C NMR spectroscopy.

c The reaction was performed with unprotected sugar (1 mmol) in anhydrous acetone or DMP in the presence of GR-SO3H catalyst (10 mg).

To explore the substrate scope, commercially available free sugar and sugar derivatives with oxygen- and sulfur-containing substituents at the anomeric position were further examined under the optimized reaction conditions and, in all cases, the reaction gave excellent yields (Table [2], entries 8–12). This methodology was also applicable to a large-scale preparation in which d-glucose (10 g) was reacted with DMP (3 equiv) or acetone and 500 mg catalyst under the same reaction conditions to give the corresponding isopropylidene product (13.87 g, 96% yield); thus, the process can be effortlessly scaled up, simplifying the expansion procedure. Further, the efficiency of the GR-SO3H catalyst was compared with different reported catalysts as shown in Table [3]. All O-isopropylidene products were characterized by FT-IR, 1H and 13C NMR spectroscopic and ESI-MS spectrometric analyses. The NMR spectra of all known compounds were in good agreement with the reported data.

Table 3 O-Isopropylidenation of d-Glucose and d-Mannose Using Different Catalysts and Loadings

Entry

Starting material

Catalyst

Amount (mol%)

Time (h)

Yield (%)a

Ref.

1

d-glucose

FeCl3

>10

 6

83

[20]

iodine

>10

 4

80

[17]

)-Ph2P-I2 b

200

30 min

95

[26]

VO(OTf)2

  5

10

89

[27]

TBATB

  2

 8

88

[28]

BDMS

  5

10

84

[29]

CAT600

100 mg

10

74

[39]

H2SO4-SiO2

 20 mg

 3

89

[25]

GR-SO3H

 10 mg

 1

95

present work

2

d-mannose

FeCl3

>10

 1

90

[20]

iodine

>10

25 min

85

[17]

)-Ph2P-I2 b

200

30 min

95

[26]

VO(OTf)2

  5

 3

92

[27]

TBATB

  2

 2

96

[28]

BDMS

  5

 2

90

[29]

CAT600

100 mg

 3

89

[39]

H2SO4-SiO2

 20 mg

 3

82

[25]

GR-SO3H

 10 mg

 1

96

present work

a Isolated yield.

bPolymer bound triphenyl phosphine iodine complex.

To explore the possibility of recycling the GR-SO3H catalyst system, the catalyst was recovered by simple filtration after completion of the reaction and then was washed with DCM, ethanol and acetone several times to eliminate the adsorbed reagents before drying under vacuum. The recyclability test of GR-SO3H for the formation of O-isopropylidenation of d-glucose with DMP (3 equiv) was explored in six consecutive runs (Figure [2]). The reaction was performed with the recovered catalyst under the same reaction conditions and the catalyst showed high stability and remained active up to several runs, as shown in Figure [2]. After each reaction run the filtrate was analyzed by IR spectroscopy and showed no peaks corresponding to the catalyst, which confirmed that there was no loss of catalyst. Further, the weight of the recovered catalyst after each reaction run was the same as the initial weight, which also confirmed that there was no loss of catalyst.

Zoom Image
Figure 2 Recycling of catalyst

In summary, a simple and efficient method has been developed for the preparation of mono- and/or di-O-isopropylidene derivatives from free sugars and their derivatives by using GR-SO3H as a sustainable catalyst. The methodology offers several key advantages, including excellent yields, mild reaction conditions, and short reaction times, and it offers catalyst recyclability, which enhances its sustainability and contributes to its cost-effectiveness. Being operationally simple, versatile and effective, this strategy is applicable to large-scale synthesis of O-isopropylidene derivatives of a wide range of sugars.

All reactions were monitored by thin-layer chromatography over silica gel-coated TLC plates. The spots on TLC were visualized by warming plates sprayed with (2% Ce(SO4)2 in 2N H2SO4) on hot-plates. Silica gel 100–200 mesh was used for column chromatography. 1H and 13C NMR spectra were recorded with a Bruker Avance DRX 400 MHz using TMS as an internal reference. The chemical shift values are expressed in δ ppm. Graphene oxide (GO), graphene (GR) and sulfonated graphene (GR-SO3H) were prepared by following the reported methods.


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Preparation of Graphene (GR)

Graphite flakes (1 g) were mixed with an acid mixture (H2SO4/H3PO4 = 9:1, 160 mL) at 0–5 °C in an ice bath. The resulting mixture was stirred for 10 min, then KMnO4 (3.8 g, 3.5 wt. equiv.) was added portion-wise and the mixture and allowed to stir at 40 °C for 7 h. The temperature of the reaction was then increased to 50 °C and the mixture was stirred overnight. The obtained brown paste was collected at r.t. and poured into 30% H2O2 (3 mL) containing ice-cold water (150 mL) to generate a yellow precipitate. The solid was centrifuged to eliminate the liquid phase. Distilled water (50 mL) was added to the solid and centrifugation was performed. This process was repeated three times. Then the resulting solid was washed with 10% HCl (3 × 50 mL) and the resulting brown solid graphene oxide (1.59 g, 148% in mass) was washed with distilled EtOH and dried under vacuum overnight.[38]

GO (500 mg) was sonicated in distilled water (500 mL) for 2 h, then a 5% aqueous solution of Na2CO3 (15 mL) was added to the reaction mixture to increase the pH to 9–10. Then, 64% hydrazine hydrate (41.2 wt. equiv., 20 mL) was added to the reaction suspension and the reaction mixture was heated at reflux for 24 h. The resulting mixture was cooled to r.t., filtered, and the resulting solid was washed with 1 N HCl (100 mL) and acetone (300). GR (black powder, 293 mg, 59% in mass) was dried at 40 °C under vacuum overnight.[32]


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Preparation of Sulfonated Graphene (GR-SO3H)

Deionized water (50 mL) was added to GR (250 mg) and sonicated for 3 h. Sodium nitrite (3.50 wt. equiv., 875 mg) and sulfanilic acid (2.90 wt. equiv., 725 mg) were added to the suspension of GR, and the reaction mixture was stirred at r.t. for 24 h. The solution was filtered and the solid was washed with 1N HCl (100 mL) and acetone (250 mL). The resulting black powder of GR-SO3H (320 mg) was dried at 40 °C under vacuum overnight.[32]


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Preparation of O-Isopropylidene of Carbohydrate Derivatives; General Procedure

Anhydrous acetone (5 mL) or DMP (3 mmol) was added to the substrate (1.0 mmol), followed by GR-SO3H (10 mg) and the reaction mixture was stirred for the appropriate time at r.t. (Table [2]). The progress of reactions was monitored by TLC. After completion of the reaction, the reaction mixture was diluted with DCM and filtered to remove the solid catalyst. The organic layer was dried (Na2SO4) and evaporated to dryness to result in the crude product. Finally, the crude product was crystallized from EtOH or DCM–hexane or purified over a small silica gel column (100–200 mesh) using hexane–EtOAc (1:1) as the eluent to furnish the O-isopropylidene-protected derivatives in excellent yield.


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1,2:5,6-Di-O-isopropylidene-α-d-glucofuranose (1a)[15]

Prepared by the General Procedure using d-glucose 1 (180 mg, 1 mmol) to give the corresponding product 1a.

Yield: (247 mg, 95%) and (250 mg, 96%); colourless syrup.

IR (neat): 3431, 2985, 2935, 1456, 1374, 1218, 1158, 1057, 942, 846, 786 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 5.89 (d, J = 3.6 Hz, 1 H, H-1), 4.48 (d, J = 3.6 Hz, 1 H, H-6a), 4.31–4.28 (m, 1 H, H-5), 4.26 (d, J = 3.2 Hz, 1 H, H-6b), 4.13 (dd, J = 6.4 Hz, 6 Hz, 1 H, H-2), 4.02 (dd, J = 2.8, 2.8 Hz, 1 H, H-3), 3.97 (dd, J = 5.2, 5.2 Hz, 1 H, H-4), 1.45 (s, 3 H, CH 3), 1.39 (s, 3 H, CH 3), 1.31 (s, 3 H, CH 3), 1.27 (s, 3 H, CH 3).

13C NMR (CDCl3, 100 MHz): δ = 111.9 (1 C, C(CH3)2), 111.1 (1 C, C(CH3)2), 106.9 (1 C, C-1), 76.9 (1 C, C-4), 71.7 (1 C, C-2), 68.6 (1 C, C-3), 57.5 (1 C, C-5), 54.8 (1 C, C-6), 28.9 (1 C, CH3), 28.7 (1 C, CH3), 28.6 (1 C, CH3), 27.2 (1 C, CH3).

ESI MS: m/z = 283.30 [M + Na]+.

Anal. Calcd. for C12H20O6: C, 55.37; H, 7.74. Found: C, 55.31; H, 7.76.


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1,2;3,4-Di-O-isopropylidene-α-d-galactopyranose (2a)[15]

Prepared by the General Procedure using d-galactose 2 (180 mg, 1 mmol) to give the corresponding product 2a.

Yield: (240 mg, 92%) and (247 mg, 95%); colourless syrup.

IR (neat): 3495, 2985, 2925, 1456, 1374, 1254, 1208, 1167, 1061, 997, 896, 855, 768 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 5.58 (d, J = 5.2 Hz, 1 H, H-1), 4.62 (dd, J = 2.4, 2.4 Hz, 1 H, H-2), 4.34 (dd, J = 2.4, 2.4 Hz, 1 H, H-3), 4.28 (dd, J =1.2, 1.2 Hz, 1 H, H-4), 3.89–3.82 (m, 2 H, H-6ab), 3.77 (dd, J = 7.6, 8 Hz, 1 H, H-5), 1.53 (s, 3 H, CH 3), 1.45 (s, 3 H, CH 3), 1.33 (s, 6 H, CH 3).

13C NMR (CDCl3, 100 MHz): δ = 109.3–108.6 (2 C, C(CH3)2), 96.2 (1 C, C-1), 71.5 (1 C, C-5), 70.6 (1 C, C-4), 70.4 (1 C, C-3), 67.9 (1 C, C-2), 62.2 (1 C, C-6), 25.9–24.2 (4 C, CH3).

ESI MS: m/z = 283.16 [M + Na]+.

Anal. Calcd. for C12H20O6: C, 55.37; H, 7.74. Found: C, 55.35; H, 7.78.


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2,3:4,6-Di-O-isopropylidene-α-d-mannopyranose (3a)[40]

Prepared by the General Procedure using d-mannose 3 (180 mg, 1 mmol) to give the corresponding product 3a.

Yield: (250 mg, 96%); white solid; mp 120 °C.

IR (neat): 3431, 2985, 2949, 1456, 1374, 1204, 1158, 1057, 974, 887, 836, 685 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 5.37 (d, J = 2.8 Hz, 1 H, H-1), 4.81 (dd, J = 4 Hz, 3.6 Hz, 1 H, H-4), 4.61 (d, J = 6 Hz, 1 H, H-2), 4.42–4.38 (m, 1 H, H-3), 4.19 (dd, J= 3.6, 3.6 Hz, 1 H, H-5), 4.07 (dd, J = 4, 2.8 Hz, 2 H, H-6ab), 1.46 (s, 3 H, CH 3), 1.45 (s, 3 H, CH 3), 1.37 (s, 3 H, CH 3), 1.32 (s, 3 H, CH 3).

13C NMR (CDCl3, 100 MHz): δ = 112.5–109.0 (2 C, C(CH3)2), 101.0 (1 C, C-1), 85.3 (1 C, C-4), 79.9 (1 C, C-5), 79.4 (1 C, C-2), 73.1 (1 C, C-3), 66.3 (1 C, C-6), 26.7–24.3 (4 C, CH3).

ESI MS: m/z = 283.41 [M + Na]+.

Anal. Calcd. for C12H20O6: C, 55.37; H, 7.74. Found: C, 55.39; H, 7.75.


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1,2:3,4-Di-O-isopropylidene-α-l-arabinopyranose (4a)[15]

Prepared by the General Procedure using l-arabinose 4 (150 mg, 1 mmol) to give the corresponding product 4a.

Yield: (207 mg, 90%) and (212 mg, 92%); colourless syrup.

IR (neat): 2985, 2935, 1452, 1374, 1250, 1208, 1163, 1112, 1048, 993, 910, 873, 759 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 5.51 (d, J = 5.2 Hz, 1 H, H-1), 4.57 (dd, J = 2, 2.4 Hz, 1 H, H-2), 4.31 (dd, J = 2.4, 2 Hz, 1 H, H-3), 4.23 (dd, J = 1.2, 1.2 Hz, 1 H, H-4), 3.85 (dd, J =2, 2 Hz, 1 H, H-5a), 3.68 (dd, J = 0.8, 1.2 Hz, 1 H, H-5b), 1.53 (s, 3 H, CH 3), 1.48 (s, 3 H, CH 3), 1.35 (s, 3 H, CH 3), 1.33 (s, 3 H, CH 3).

13C NMR (CDCl3, 100 MHz): δ = 108.8–108.3 (2 C, C(CH3)2), 95.7 (1 C, C-1), 70.6 (1 C, C-4), 70.4 (1 C, C-3), 69.7 (1 C, C-2), 60.0 (1 C, C-5), 25.9–24.1 (4 C, CH3).

ESI MS: m/z = 253.13 [M + Na]+.

Anal. Calcd. for C11H18O5: C, 57.38; H, 7.88. Found: C, 57.35; H, 7.85.


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1,2:3,5-Di-O-isopropylidene-α-d-xylofuranose (5a)[15]

Prepared by the General Procedure using d-xylose 5 (150 mg, 1 mmol) to give the corresponding product 5a.

Yield: (207 mg, 90%) and (214 mg, 93%); colourless syrup.

IR (neat): 2990, 2935, 1452, 1374, 1199, 1163, 1076, 1011, 970, 823, 763, 634 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 6.00 (d, J = 3.6 Hz, 1 H, H-1), 4.52 (d, J = 3.6 Hz, 1 H, H-5a), 4.29 (d, J = 2.4 Hz, 1 H, H-5b), 4.09 (t, J = 2.4, 6 Hz, 2 H, H-2, H-3), 4.03 (t, J = 2.4, 1.6 Hz, 1 H, H-4), 1.49 (s, 3 H, CH 3), 1.44 (s, 3 H, CH 3), 1.38 (s, 3 H, CH 3), 1.32 (s, 3 H, CH 3).

13C NMR (CDCl3, 100 MHz): δ = 111.5–105.1 (2 C, C(CH3)2), 97.4 (1 C, C-1), 84.5 (1 C, C-4), 73.1 (1 C, C-2), 71.5 (1 C, C-3), 60.0 (1 C, C-5), 28.8–18.5 (4 C, CH3).

ESI MS: m/z = 253.69 [M + Na]+.

Anal. Calcd. for C11H18O5: C, 57.38; H, 7.88. Found: C, 57.36; H, 7.87.


#

2,3-O-Isopropylidene-α-l-rhamnofuranose (6a)[41]

Prepared by the General Procedure using l-rhamnose 6 (164 mg, 1 mmol) to give the corresponding product 6a.

Yield: (182 mg, 89%) and (184 mg, 90%); colourless syrup.

IR (neat): 3490, 2990, 2935, 1456, 1369, 1213, 1158, 1066, 1021, 851 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 5.43 (s, 1 H, H-1), 4.91 (dd, J = 3.2, 3.2 Hz, 1 H, H-2), 4.64 (d, J = 4.8 Hz, 1 H, H-4), 4.10–4.05 (m, 1 H, H-3), 3.97 (dd, J = 3.2, 2.8 Hz, 1 H, H-5), 1.50 (s, 3 H, CH 3), 1.35 (s, 6 H, CH 3).

13C NMR (CDCl3, 100 MHz): δ = 112.7 (1 C, C(CH3)2), 100.9 (1 C, C-1), 85.4 (1 C, C-2), 83.5 (1 C, C-4), 80.1 (1 C, C-3), 66.6 (1 C, C-5), 30.8 (1 C, CH3), 24.5 (1 C, CH3), 20.3 (1 C, CH3).

ESI MS: m/z = 227.52 [M + Na]+.

Anal. Calcd. for C9H16O5: C, 52.93; H, 7.90. Found: C, 52.95; H, 7.88.


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1,2:3,4:5,6-Tri-O-isopropylidene-d-mannitol (7a)[29]

Prepared by the General Procedure using d-mannitol 7 (182 mg, 1 mmol) to give the corresponding product 7a.

Yield: (278 mg, 92%) and (288 mg, 95%); white solid; mp 70 °C.

IR (neat): 3270, 2990, 2880, 1456, 1369, 1213, 1144, 1061, 966, 841, 786 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 4.22 (m, 2 H, H-2, H-5), 4.11 (t, J =8.4, 6.4 Hz, 2 H, H-3, H-4), 4.01 (s, 1 H, H-1a), 3.99 (d, J = 2.4 Hz, 1 H, H-6a), 3.97 (m, 2 H, H-1b, H-6b), 1.44 (s, 6 H, CH 3), 1.40 (s, 6 H, CH 3), 1.36 (s, 6 H, CH 3).

13C NMR (CDCl3, 100 MHz): δ = 110.1–109.5 (3 C, C(CH3)2), 79.4 (2 C, C-2, C-5), 76.3 (2 C, C-3, C-4), 66.2 (2 C, C-1, C-6), 27.4–25.3 (6 C, CH3).

ESI MS: m/z = 325.61 [M + Na]+.

Anal. Calcd. for C15H26O6: C, 59.58; H, 8.67. Found: C, 59.51; H, 8.63.


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Allyl 3,4-O-Isopropylidene-α-d-galactopyranose (8a)

Prepared by the General Procedure using allyl-α-d-galactose 8 (220 mg, 1 mmol) to give the corresponding product 8a.

Yield: (232 mg, 89%) and (242 mg, 93%); colourless syrup; [α]D 25 +82 (c 1.0, CHCl3).

IR (neat): 3421, 2985, 2939, 1649, 1456, 1218, 1158, 1025, 924, 873, 804 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 5.96–5.88 (m, 1 H, CH=CH2), 5.34–5.29 (m, 1 H, CH=CH 2), 5.25 (dd, J = 1.6, 1.6 Hz, 1 H, CH=CH 2), 4.96 (d, J = 3.6 Hz, 1 H, H-1), 4.30–4.28 (m, 1 H, H-2), 4.27 (dd, J = 1.6, 1.6 Hz, 2 H, CH 2-CH=CH2), 4.12–4.06 (m, 2 H, H-4, H-5), 3.96 (dd, J = 6, 6.4 Hz, 1 H, H-3), 3.84 (dd, J = 4, 2 H, H-6a, H-6b), 1.52 (s, 3 H, CH 3), 1.36 (s, 3 H, CH 3).

13C NMR (CDCl3, 100 MHz): δ = 133.5 (1 C, CH=CH2), 117.9 (1 C, C(CH3)2), 109.8 (1 C, CH=CH2), 96.7 (1 C, C-1), 76.2 (1 C, C-3), 73.9 (1 C, C-5), 69.4 (1 C, C-4), 68.7 (1 C, C-2), 68.2 (1 C, CH2-CH=CH2), 62.7 (1 C, C-6), 27.6–25.9 (2 C, CH3).

HRMS-ESI: m/z calcd. for [M + Na]+: 283.2860; found: 283.2857.

Anal. Calcd. for C12H20O6: C, 55.37; H, 7.75. Found: C, 55.34; H, 7.72.


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Methyl 4,6-O-Isopropylidene-α-d-glucopyranoside (9a)[42]

Prepared by the General Procedure using methyl-α-d-glucopyranoside 9 (194 mg, 1 mmol) to give the corresponding product 9a.

Yield: (209 mg, 89%) and (216 mg, 92%); colourless syrup.

IR (neat): 3384, 2925, 1709, 1566, 1388, 1264, 1195, 1061, 1029, 938, 841 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 4.74 (d, J = 4 Hz, 1 H, H-1), 3.87 (dd, J = 5.2, 5.2 Hz, 1 H, H-3), 3.79–3.70 (m, 2 H, H-4, H-5), 3.64–3.55 (m, 2 H, H-6a, H-6b), 3.53 (t, J = 9.2, 9.2 Hz, 1 H, H-2), 3.41 (s, 3 H, OCH 3), 1.50 (s, 3 H, CH 3), 1.42 (s, 3 H, CH 3).

13C NMR (CDCl3, 100 MHz): δ = 99.9 (1 C, C(CH3)2), 99.7 (1 C, C-1), 73.5 (1 C, C-4), 72.9 (1 C, C-2), 71.7 (1 C, C-5), 63.2 (1 C, C-3), 62.3 (1 C, C-6), 55.3 (1 C, OCH3), 29.0 (1 C, CH3), 19.0 (1 C, CH3).

ESI MS: m/z = 257.52 [M + Na]+.

Anal. Calcd. for C10H18O6: C, 51.27; H, 7.75. Found: C, 51.21; H, 7.70.


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p-Methoxyphenyl 3,4-O-Isopropylidene-β-d-galactopyranose (10a)

Prepared by the General Procedure using p-methoxyphenyl-β-d-galactose 10 (286 mg, 1 mmol) to give the corresponding product 10a.

Yield: (284 mg, 87%) and (297 mg, 91%); white solid; mp 117 °C; [α]D 25 +102 (c 1.0, CHCl3).

IR (neat): 3381, 2988, 2938, 1505, 1440, 1375, 1215, 1062, 867, 829, 733 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 6.95 (d, J = 9.2 Hz, 2 H, Ar-H), 6.80 (d, J = 9.2 Hz, 2 H, Ar-H), 4.68 (d, J = 8 Hz, 1 H, H-1), 4.17 (t, J = 6.4 Hz, 4 Hz, 2 H, H-2, H-4), 4.00–3.91 (m, 2 H, H-3, H-5), 3.83–3.76 (m, 2 H, H-6a, H-6b), 3.74 (s, 3 H, OCH 3), 1.53 (s, 3 H, CH 3), 1.34 (s, 3 H, CH 3).

13C NMR (CDCl3, 100 MHz): δ = 155.3–114.5 (6 C, Ar-C), 110.6 (1 C, C(CH3)2), 101.2 (1 C, C-1), 78.7 (1 C, C-3), 73.67 (1 C, C-5), 73.64 (1 C, C-4), 73.3 (1 C, C-2), 62.2 (1 C, C-6), 55.5 (1 C, OCH3), 28.0 (1 C, CH3), 26.2 (1 C, CH3).

HRMS-ESI: m/z calcd for [M + Na]+: 349.3450; found: 349.3421.

Anal. Calcd. for C16H22O7: C, 58.89; H, 6.80. Found: C, 58.85; H, 6.78.


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Ethyl 4,6-O-Isopropylidene-1-thio-β-d-glucopyranoside (11a)

Prepared by the General Procedure using thioethyl-β-d-glucose 11 (224 mg, 1 mmol) to give the corresponding product 11a.

Yield: (230 mg, 87%) and (243 mg, 92%); colourless syrup; [α]D 25 +90 (c 1.0, CHCl3).

IR (neat): 3431, 2972, 2875, 1631, 1452, 1374, 1259, 1199, 1066, 933, 855, 736 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 4.38 (d, J = 10 Hz, 1 H, H-1), 3.89 (dd, J = 5.2, 5.2 Hz, 1 H, H-6a), 3.74 (t, J = 10.8, 10.4 Hz, 1 H, H-2), 3.64 (t, J = 8.8, 8.4 Hz, 1 H, H-3), 3.56 (t, J = 9.6, 9.2 Hz, 1 H, H-4), 3.42 (dd, J = 8.4, 8.4 Hz, 1 H, H-6b), 3.30–3.24 (m, 1 H, H-5), 2.72 (dd, J = 2.4, 2 Hz, 1 H, S-CH 2-CH3), 2.68 (dd, J = 2, 2 Hz, 1 H, S-CH 2CH3), 1.46 (s, 3 H, CH 3), 1.39 (s, 3 H, CH 3), 1.27 (t, J = 7.2, 7.6 Hz, 3 H, S-CH2-CH 3).

13C NMR (CDCl3, 100 MHz): δ = 99.7 (1 C, C(CH3)2), 86.3 (1 C, C-1), 74.7 (1 C, C-5), 73.2 (1 C, C-4), 72.8 (1 C, C-3), 71.3 (1 C, C-2), 61.8 (1 C, C-6), 28.8 (1 C, CH3), 24.6 (1 C, CH3), 18.9 (1 C, S-CH2-CH3), 15.1 (1 C, S-CH2 CH3).

HRMS-ESI: m/z calcd for [M + Na]+: 287.3360; found: 287.3329.

Anal. Calcd. for C11H20O5S: C, 49.98; H, 7.63. Found: C, 49.95; H, 7.60.


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p-Methoxybenzyl 3,4-O-Isopropylidene-α-d-galactopyranose (12a)

Prepared by the General Procedure using p-methoxybenzyl-α-d-galactose 12 (300 mg, 1 mmol) to give the corresponding product 12a.

Yield: (303 mg, 89%) and (306 mg, 90%); colourless syrup; [α]D 25 +88 (c 1.0, CHCl3).

IR (neat): 3394, 2985, 2925, 1709, 1562, 1383, 1250, 1158, 1039, 883 cm–1.

1H NMR (CDCl3, 400 MHz): δ = 7.26–6.81 (m, 4 H, Ar-H), 4.86 (d, J = 11.6 Hz, 1 H, CH 2), 4.49 (d, J = 11.6 Hz, 1 H, CH 2), 4.24 (d, J = 7.6 Hz, 1 H, H-1), 4.11–4.02 (m, 2 H, H-6ab), 3.95 (dd, J = 1.6, 1.6 Hz, 1 H, H-4), 3.74 (s, 3 H, OCH 3), 3.70 (dd, J = 7.6, 7.6 Hz, 1 H, H-3), 3.55 (dd, J = 3.6, 4 Hz, 1 H, H-2), 3.27 (d, J = 1.2 Hz, 1 H, H-5), 1.2 (s, 6 H, CH 3).

13C NMR (CDCl3, 100 MHz): δ = 159.2–113.6 (6 C, Ar-C), 101.1 (1 C, C-1), 98.9 (1 C, C(CH3)2), 72.3 (1 C, C-3), 71.2 (1 C, C-5), 70.4 (1 C, C-4), 67.9 (1 C, C-2), 62.4 (1 C, CH2), 55.1 (1 C, C-6), 44.9 (1 C, OCH3), 22.0–18.4 (2 C, CH3).

HRMS-ESI: m/z calcd for [M + Na]+: 363.3720; found: 363.3714.

Anal. Calcd. for C17H24O7: C, 59.99; H, 7.11. Found: C, 59.95; H, 7.09.


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Conflict of Interest

The authors declare no conflict of interest.

Acknowledgment

We are grateful to the Department of Chemistry, Assam University, Silchar; Bose Institute, Kolkata; NECBH IIT Guwahati for providing instrumentation facilities.

Supporting Information

    Supporting information for this article is available online at https://doi-org.accesdistant.sorbonne-universite.fr/10.1055/a-2218-7604.
  • Supporting Information

Corresponding Author

Rajib Panchadhayee
Department of Chemistry, Assam University
Silchar, Assam-788011
India   

Publication History

Received: 04 October 2023

Accepted after revision: 28 November 2023

Accepted Manuscript online:
28 November 2023

Article published online:
18 December 2023

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