Synthesis of anti-inflammatory 2,3-unsaturated O-glycosides using conventional and microwave heating techniques

Adriana Cristina N. de Melo; Ronaldo N. de Oliveira; João R. de Freitas Filho; Teresinha G. da Silva; Rajendra M. Srivastava

doi:10.1515/hc-2016-0226

Article Open Access

Synthesis of anti-inflammatory 2,3-unsaturated O-glycosides using conventional and microwave heating techniques

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Published/Copyright: May 24, 2017

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From the journal Heterocyclic Communications Volume 23 Issue 3

Abstract

The preparation of eight 2,3-unsaturated O-glycosides from D-glycals and alcohols, using montmorillonite K-10 as an acid catalyst, is described. The Ferrier rearrangement products were obtained in good yields using conventional heating and microwave irradiation but the reaction time was substantially reduced employing the latter procedure. The yields were slightly lower under microwave exposure. Five of the di-O-acetylated products were deacetylated to the glycosides in excellent yields. The acetylated products possess good anti-inflammatory property suggesting that the acetyl group plays an important role in reducing the inflammation. Among the compounds tested, glycosides containing thiophene as an aglycone present much better inflammation reducing characteristics than the analogues without this function.

Keywords: anti-inflammatory glycosides; Ferrier rearrangement; tri-O-acetyl-D-galactal; tri-O-acetyl-D-glucal; 2,3-unsaturated glycosides

Introduction

The Ferrier rearrangement involves the reaction between a glycal and a nucleophile in the presence of a mild Lewis acid causing an allylic shift in the glycal [1], [2], [3]. This protocol furnishes a variety of glycosides as potential building blocks for the synthesis of natural products with promising biological activities [4]. In recent years, diverse conditions have been applied to facilitate this kind of synthesis with enhanced yields and often providing predominantly α-anomers of the glycosides. Examples are the use of montmorillonite K-10 [5], montmorillonite K-10 clay doped with FeCl₃·6H₂O [6], microwave-irradiation under solventless conditions [7], metal-free Ferrier reaction [8], ZnCl₂-alumina-impregnated catalysts [9], Mitsunobu reaction [10] and other reported protocols [11], [12], [13] furnishing the desired products with satisfactory results.

The literature cites the Ferrier type of strategy for the synthesis of a variety of sugar molecules for biological assays including glycosides containing phthalimido moiety as aglycones [14]. Such glycosides are interesting because phtalimides themselves are known to possess biological activities. For example, some phthalimide derivatives are antitumor [15], anticonvulsant [16] and anti-inflammatory agents [17]. A phthalimidomethyl-4,6-di-O-benzoyl-α-D-mannopyranoside shows significant reduction of plasma triglyceride concentration when tested in mice [14]. Recently, alkyl-substituted phthalimido-1,2,3-triazoles linked to 2,3-unsaturated O-glycoside have been synthesized and shown to decrease carrageenan-induced edema in mice [18]. In 2007, glycosides containing a phthalimido group were synthesized in an attempt to improve their biological activity [19].

In this work, we describe the synthesis of 9 new 2,3-unsaturated O-glycosides 3b,c, 5b,c, 6b,c and 7a–c from D-glucal and D-galactal and evaluation their anti-inflammatory activity.

Results and discussion

In order to synthesize 2,3-unsaturated-O-glycoside from glycals and alcohols, we decided to use montmorillonite K-10 clay as an acidic catalyst since it is inexpensive, reusable and eco-friendly. In this context, tri-O-acetyl-D-glucal 1 was initially used to react with some alcohols, namely benzyl alcohol (2a), 2-(thiophene-3-yl)ethanol (2b), 2-(thiophene-2-yl)ethanol (2c) and (1R,2S,5R)-(-)-menthol (2d) using two different methods. In method A, a mixture of montmorillonite K-10 and the reactants was heated under reflux in CH₂Cl₂ [5] and in method B, montmorillonite K-10 was mixed with the reactants and irradiated in a microwave oven [7]. These two methodologies [5], [7] were revisited in this work to afford O-glycosides 3a–d from D-glucal and alcohols. Procedure A yielded 70–85% of the desired glucosides after 2–3 h of heating, while in procedure B the microwave irradiation was completed in 1.5–4.0 min with 60–80% yields (Scheme 1). A similar synthesis with D-galactal gave 2,3-unsaturated O-galactosides 5a–d in moderate to good yields (Scheme 2).

Scheme 1

Synthesis of 2,3-unsaturated O-glucosides 3a–d.

Scheme 2

Synthesis of 2,3-unsaturated O-galactosides 5a–d.

Two main features were observed. First, 4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranosides 3a–d were obtained in better yields compared to 4,6-di-O-acetyl-2,3-dideoxy-α-D-threo-hex-2-enopyranosides 5a–d under similar conditions. Second, only the α-anomers were isolated in all cases, except for 3b where the α:β ratio was 85:15 in both A and B methods as determined by ¹HNMR spectroscopy. Initially, the difference in yields in the two sets of reactions appeared difficult to explain, but eventually the following reasonable interpretation emerged.

When tri-O-acetyl-D-glucal is treated with K-10, it is logical to assume that the metal combines with the oxygen atom of the C-3 O-acetyl group forming a metal-oxygen complex as shown in Scheme 3. This causes the weakening of C₃-OAc bond accompanied with anchimeric assistance from C₄-OAc group facilitating the elimination of the OAc group from C-3 and forming an intermediate product B. The restoration of the C-4-OAc moiety occurs when the carbonyl oxygen of C-6 approaches C-1 shifting the double bond to C₂–C₃ as depicted by C (Scheme 3). In this intermediate, the positive charge at carbon atom is stabilized by two oxygen atoms. In this case, the alcohol can attack C-1 only from below giving the protonated form of the molecule represented by D which after losing proton is transformed to 3a–d.

Scheme 3

Proposed mechanism to obtain glucosides 3a–d.

In the case of 4,6-di-O-acetyl-2,3-dideoxy-α-D-threo-hex-2-enopyranosides 5a–d, the lack of anchimeric assistance from C₄-acetoxy function would account for the slower removal of C₃-OAc group, thus furnishing the products in lower yields under similar conditions. The suggested mechanism of formation of α-anomers only is shown in Scheme 4. The attack of carbonyl oxygen of C₆-OAc at C-1 (structure B) causes the allylic rearrangement to generate C.

Scheme 4

Proposed mechanism to obtain galactosides 5a–d.

Since there is no anchimeric assistance of C₄-acetyl group in galactal 4, the exit of C₃-OAc becomes slower in these compounds, hence smaller yields under similar reaction conditions. Again, only α-anomers were isolated. Subsequently, five of the unsaturated glycosides, 3b,c and 5a–c, were hydrolyzed under Fraser Reid’s protocol [20] with good to excellent yields (Scheme 5).

Scheme 5

Synthesis of compounds 6b–c and 7a–c.

The structures of all compounds 3a–d, 5a–d, 6b,c and 7a–c were assigned by ¹H and ¹³C NMR spectral and elemental analyses. The configuration at C-4 in 2,3-unsaturated compounds was assigned by analysis of the coupling constant between H-4 and H-5. The vicinal constant ³J_4,5 is approximately 9.6 Hz for 3a–d and 6b,c indicative of erythro structure. The coupling constant in compounds 5a–d and 7a–c is in a range between 4.2 Hz and 6.6 Hz indicative of threo configuration. A 1D NOE-DIFF spectral investigation for compounds 3b and 5b showed the correct spatial interactions between the protons in the saccharide portion, demonstrating the correct relationships. During the preparation of this manuscript, we came across a very recent publication [21] where the authors described the preparation of (1R,2S,5R)-menthyl 4,6-di-O-acetyl-2,3-didesoxy-α-D-threo-hex-2-enopyranoside 5d, but did not provide adequate characterization of this compound. Full characterization of 5d is given in the Experimental section.

There are reports in the literature that 2,3-unsaturated glycosides possess anti-inflammatory property [19]. In particular, thiophene derivatives containing acetylenic subsituents are effective in reducing inflammation [22]. More recently, another thiophene-comprising product has been found to exhibit inflammation-reducing action [23]. Therefore, it was decided to explore the possible anti-inflammatory activity of compounds 3a, 5a and 6b. Compound 3a has a significant anti-inflammatory activity while 5a with threo configuration and 6b (deacetylated glycoside) have no anti-inflammatory activity at all. On the basis of on these results, it was decided to assay the activity of other 4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranosides 3b–d. These products show moderate to good inflammation-reducing property ranging from 41% to 62% at a dose of 100 mg/kg of the animal weight (Table 1). Compound 3c is the most active in reducing the inflammation by 62% at the dose of 100 mg/kg, while indomethacin shows 56% decrease in the cellular migration at a dose of 10 mg/kg, and acetylsalisylic acid, the most common anti-inflammatory agent in the market, exhibits 74% inflammation reduction at a dose of 200 mg/kg of the body weight. It is obvious that the acetyl group plays an important role in these unsaturated sugars to reduce the inflammation. The well known example of aspirin is instructive [24].

Table 1

Anti-inflammatory activity of compounds 3a–d and their comparison to indomethacin and ASA as references.

Treated	Dose (mg/kg)	No. of PMNL/mL (×10⁶) (n=6, after 6 h)^a	Inhibition (%)
Carregenan control		4.13±0.07	–
3a	100	1.96±0.16^a	52.0
3b	100	2.40± 0.20^a	41.3
3c	100	1.57±0.20^a	62.0
3d	100	2.17±0.30^a	46.7
Indomethacin	10	1.75±0.20^a	55.5
ASA	200	1.32±0.06^a	73.7

All data are expressed as mean±SD (n=6). Statistically significant ^ap<0.05 vs. control. Significance was determined with ANOVA one way followed by Bonferroni’s post hoc test when compared with carrageenan control group. PMNL, polymorphonuclear leukocyte; ASA, acetylsalycilic acid. N=6 animals per group.

Conclusions

Eight 4,6-di-O-acetyl-2,3-unsaturated glycosides were synthesized by Ferrier’s rearrangement from D-glucal or D-galactal under ordinary heating and microwave irradiation. Four thiophene derivatives 3b,c and 5b,c exhibit potent anti-inflammatory activity. Their deacylated analogues are devoid of anti-inflamatory activity.

Experimental

Melting points were determined using a MEL-TEMP Electro-Thermal instrument, model 1002D and are uncorrected. All commercially available reagents were used without purification (Sigma-Aldrich or Acros). All organic solvents used for the synthesis were of analytical grade (Vetec). Column chromatography was performed on Merck silica gel 60 (70–230 mesh). The reactions were monitored by TLC analysis with the plates containing GF₂₅₄ from Merck and using UV fluorescence, or 5% H₂SO₄/EtOH for visualization. ¹H NMR (300 MHz) and ¹³C NMR (75 MHz) spectra were obtained on a Varian unity plus-300 spectrometer. Optical rotations were measured using a Perkin-Elmer 241 at 20°C. Elemental analyses were carried out on an EA1110 CHNS-O analyzer. Microwave irradiation was performed in the domestic multimode oven SANYO, EM-804 TGR (2450 MHz, 700W). Tri-O-acetyl-D-glucal 1 and D-galactal 4 were prepared according to the literature procedures [25].

General procedure for the synthesis of 4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro and threo-hex-2 enopyranosides

Method A (conventional heating)

A mixture of tri-O-acetyl-D-glucal 1 or tri-O-acetyl-D-galactal 4 (1 mmol), an alcohol 2a–d (1.5 mmol) and dried CH₂Cl₂ (30 mL) was heated under reflux for 120 min (for 3d and 5d), 150 min (for 3b), 180 min (3a, 3c and 5c) or 240 min (for 5a and 5b). Then the mixture was cooled at 0–5°C, treated with montmorillonite K-10 (50% w/w of 1) or (100% w/w of 4) and heating was continued for several hours. Removal of montmorillonite K-10 by filtration followed by concentration under reduced pressure afforded the desired product which was purified by column chromatography on silica gel using hexane/ethyl acetate (6:4) as eluent.

Method B (microwave irradiation)

A mixture of tri-O-acetyl-D-glycal 1 or 4 (1 mmol), an alcohol 2a–d (1.5 mmol), and montmorillonite K-10 (50% w/w of 1) or (100% w/w of 4) in an open glass test tube was irradiated in the domestic microwave oven for 1 min (for 3b,c and 5b,c), 1.5 min (for 3d and 5d) or 4 min (for 3a and 5a). After cooling, the mixture was treated with dichloromethane. Filtration followed by concentration under reduced pressure furnished an oil that was subjected to silica gel column chromatography eluting with a mixture of 5% ethyl acetate in hexane (v/v) as eluent.

Benzyl 4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranoside (3a)

Yield 85% (method A); Yield 80% (method B); colorless oil; [α]_D²⁰+125° (c 1, CHCl₃); [α]_D²⁰+75° (c 0.44, CHCl₃) [12]. The ¹H NMR spectrum of this compound is virtually identical with the previously reported data [12].

2-(Thiophene-3-yl)ethyl 4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranoside (3b)

Yield 70% (method A, α:β=85:15); yield 60% (method B, α:β=85:15); colorless oil. R_f 0.6 (5% EtOAc/CH₂Cl₂); [α]_D²⁰+79° (c 0.85, CHCl₃); ¹H NMR (acetone-d₆): δ 2.01 (s, 3H, CH₃CO), 2.05 (s, 3H, CH₃CO), 2.97 (t, 2H, J=6.9 Hz, CH₂-Het), 3.76 (dt, 1H, J=9.6 Hz and 6.6 Hz, OCH₂), 3.97–4.05 (m, 2H, H-5, OCH₂), 4.12 (s, 1H, H-6 or H-6′), 4.13 (d, 1H, J=1.8 Hz, H-6 or H-6′), 5.07 (br s, 1H, H-1), 5.25 (dd, 1H, J=9.6 Hz and 1.2 Hz, H-4), 5.87 (s, 2H, H-2, H-3), 7.07 (dd, 1H, J=4.8 Hz and 1.5 Hz, Ar-H_a), 7.18–7.20 (m, 1H, Ar-H_c), 7.37 (dd, 1H, J=4.8 Hz and 3.0 Hz, Ar-H_b); ¹³C NMR (acetone-d₆): δ 21.3, 21.5, 32.0, 64.4, 66.7, 68.5, 70.0, 95.7, 122.6, 126.7, 129.8, 130.0, 130.2, 141.0, 171.2, 171.4. Anal. Calcd for C₁₆H₂₀O₆S: C, 56.46; H, 5.92. Found: C, 56.66; H, 5.77.

2-(Thiophene-2-yl)ethyl 4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranoside (3c)

Yield 85% (method A); yield 70% (method B); colorless oil. R_f==0.7 (5% EtOAc/CH₂Cl₂). [α]_D²⁰+44° (c 0.5, CHCl₃). ¹H NMR (acetone-d₆): δ 1.99 (s, 3H, CH₃CO), 2.05 (s, 3H, CH₃CO), 3.12 (dd, 2H, J=13.2 Hz and 6.8 Hz, CH₂-Het), 3.70–3.79 (dt, 1H, J=9.9 Hz and 6.6 Hz, OCH₂), 3.96–4.07 (m, 2H, H-5, OCH₂), 4.14 (d, 1H, J=4.2 Hz, H-6 or H-6′), 4.20 (d, 1H, J=5.4 Hz, H-6 or H-6′), 5.08 (br s, 1H, H-1), 5.20 (dd, 1H, J=9.6 Hz and 1.2 Hz, H-4), 5.87, 5.96 (2s, 2H, H-2 and H-3), 6.90–6.95 (m, 2H, Ar-H_a and Ar-H_b), 7.26 (ddd, 1H, J=5.1 Hz, 5.1 Hz and 1.2 Hz, Ar-H_c); ¹³C NMR (acetone-d₆): δ 21.3, 21.5, 30.8, 64.3, 66.6, 68.6, 70.6, 95.8, 125.2, 126.7, 128.1, 129.6, 130.4, 142.9, 171.3, 171.5. Anal. Calcd for C₁₆H₂₀O₆S: C, 56.46; H, 5.92. Found: C, 56.57; H, 6.01.

(1R,2S,5R)-Menthyl 4,6-di-O-acetyl-2,3-didesoxy-α-D-erythro-hex-2-enopyranoside (3d)

Yield 82% (method A); yield 71% (method B); colorless oil; R_f 0.6 (5% EtOAc/CH₂Cl₂); [α]_D²⁰+44° (c 1, CH₂Cl₂); [α]_D²⁰+46° (c 0.75, CH₂Cl₂) [23]. The ¹H NMR spectrum is virtually identical with previously reported data [26].

Benzyl 4,6-di-O-acetyl-2,3-didesoxy-α-D-threo-hex-2-enopyranoside (5a)

Yield 82% (method A); yield 78% (method B); colorless oil. R_f 0.8 (10% EtOAc/CH₂Cl₂); [α]_D²⁰−134° (c 2, CHCl₃); [α]_D²⁰−83° (c 0.27, CHCl₃). The ¹H NMR spectrum is virtually identical with previously reported details [12].

2-(Thiophene-3-yl)ethyl 4,6-di-O-acetyl-2,3-dideoxy-α-D-threo-hex-2-enopyranoside (5b)

Yield 60% (method A); yield 54% (method B); colorless oil. R_f 0.7 (5% EtOAc/CH₂Cl₂); [α]_D²⁰−101° (c 2, CHCl₃). ¹H NMR (acetone-d₆): δ 1.98 (s, 3H, CH₃CO), 2.02 (s, 3H, CH₃CO), 2.94 (t, 2H, J=6.9 Hz, CH₂-Het), 3.74 (dt, 1H, J=9.6, 6.9 Hz, OCH₂), 3.99 (dt, 1H, J=9.6, 6.9 Hz, OCH₂), 4.13 (dd, 1H, J=11.4 Hz and 7.8 Hz, H-6 or H6′), 4.20 (dd, 1H, J=11.4 Hz and 4.8 Hz, H-6 or H6′), 4.29 (ddd, 1H, J=7.8 Hz, 4.8 Hz and 2.4 Hz, H-5), 5.00 (dd, 1H, J=4.8 Hz and 2.4 Hz, H-4), 5.08 (brd, 1H, J=1.5 Hz, H-1), 6.04 (dd, 1H, J=11.1 Hz and 0.9 Hz, H-2 or H-3), 6.05 (d, J=11.1, 1H, H-2 or H-3), 7.05 (dd, 1H, J=5.1 Hz and 1.2 Hz, Ar-H_a), 7.17–7.19 (m, 1H, Ar-H_c), 7.38 (dd, 1H, J=5.1 Hz and 2.7 Hz, Ar-H_c); ¹³C NMR (acetone-d₆): δ 21.3 (2C), 32.0, 64.1 (2C), 68.4, 69.6, 95.4, 122.6, 126.4, 126.7, 130.0, 132.3, 141.0, 171.2, 171.4. Anal. Calcd for C₁₆H₂₀O₆S: C, 56.46; H, 5.92. Found: C, 56.36; H, 5.73.

2-(Thiophene-2-yl)ethyl 4,6-di-O-acetyl-2,3-dideoxy-α-D-threo-hex-2-enopyranoside (5c)

Yield 53% (method A); yield 50% (method B); colorless oil. R_f 0.7 (5% EtOAc/CH₂Cl₂); [α]_D²⁰−121° (c 1, CHCl₃); ¹H NMR (acetone-d₆): δ 1.98 (s, 3H, CH₃CO), 2.02 (s, 3H, CH₃CO), 3.14 (t, 2H, J=6.9 Hz, CH₂-Het), 3.74 (dt, 1H, J=9.9 Hz and 6.9 Hz, OCH₂), 4.00 (dt, 1H, J=9.9 Hz and 6.9 Hz, OCH₂), 4.15 (dd, 1H, J=11.4 Hz and 7.8 Hz, H-6 or H-6′), 4.21 (dd, 1H, J=11.4 Hz and 4.8 Hz, H-6 or H-6′), 4.32 (ddd, 1H, J=7.8 Hz, 4.8 Hz and 2.7 Hz, H-5), 5.02 (brdd, 1H, J=4.4 Hz and 2.7 Hz, H-4), 5.10 (br d, 1H, J=1.5 Hz, H-1)), 6.06 (s, 1H, H-2 or H-3), 6.07 (d, J=1.2, 1H, H-2 or H-3), 6.91–6.95 (m, 2H, Ar-H_a and Ar-H_b), 7.25 (dd, 1H, J=5.1 Hz and 1.2 Hz, Ar-H_c); ¹³C NMR (acetone-d₆): δ 20.6, 20.7, 31.1, 63.4, 63.5, 67.8, 69.5, 94.8, 124.5, 125.8, 126.0, 127.5, 131.5, 142.1, 170.6, 170.7. Anal. Calcd for C₁₆H₂₀O₆S: C, 56.46; H, 5.92. Found: C, 56.49; H, 6.18.

(1R,2S,5R)-Menthyl 4,6-di-O-acetyl-2,3-dideoxy-α-D-threo-hex-2-enopyranoside (5d)

Yield 72% (method A); yield 65% (method B); colorless solid from EtOAc/hexane; mp 65–67°C; [α]_D²⁵−200° (c 1, CH₂Cl₂); [α]_D²⁰−159° (c 0.16, CH₂Cl₂) [21]; ¹H NMR (CDCl₃): δ 0.77 (d, 3H, J=7.1 Hz, CH₃, menthyl), 0.90 (2d, 6H, J=7.0 and 6.5 Hz, 2CH₃, menthyl), 0.80–1.65 (m, 8H, menthyl), 2.06 (s, 3H, CH₃CO), 2.07 (s, 3H, CH₃CO), 2.20 (bd, 1H, J=12.3 Hz, menthyl), 3.43 (ddd, pseudo-td, 1H, J=10.6 Hz, 10.6 Hz and 4.1 Hz, menthyl), 4.18 (dd, 1H, J=11.5 Hz and 7.6 Hz, H-6 or H-6′), 4.23 (dd, 1H, J=11.5 Hz and 5.0 Hz, H-6 or H-6′), 4.40 (ddd, 1H, J=7.6 Hz, 5.0 Hz and 2.6 Hz, H-5), 5.00 (dd, 1H, J=4.7 Hz and 2.6 Hz, H-4), 5.13 (br d, 1H, J=2.4 Hz, H-1), 6.03 (dd, 1H, J=10.0 Hz and 2.4 Hz, H-2), 6.09 (dd, 1H, J=10.0 Hz and 4.7 Hz, H-3); ¹³C NMR (CDCl₃): δ 16.2, 20.8, 21.1, 22.4, 23.1, 25.6, 31.7, 34.3, 43.2, 48.9, 63.0, 63.2, 66.6, 80.7, 95.6, 124.7, 130.7, 170.3, 170.6.

General procedure for synthesis of 2,3-dideoxy-hex-2-enopyranosides

A mixture of the acetylated compound 3b,c or 5b,c in a mixed solvent of MeOH/H₂O/Et₃N (9:6:1) was stirred at room temperature for 2 h (for 6b,c) or 3 h (for 7b) or 4 h (for 7a and 7c). TLC plates were developed using methanol/CHCl₃ (1:9). The solvent was removed under reduced pressure and the residue was subjected to silica gel column chromatography eluting with a mixed solvent of ethyl acetate/hexane (4:5).

2-(Thiophene-3-yl)ethyl 2,3-dideoxy-α-D-erythro-hex-2-enopyranoside (6b)

Yield 87%; colorless oil; R_f 0.5 (10% EtOAc/CHCl₃); [α]_D²⁰+29° (c 0.7, CHCl₃); ¹H NMR (acetone-d₆): δ 2.91 (t, 2H, J=6.9 Hz, CH₂-Het), 3.59–3.80 (m, 5H, 2xOH, OCH₂, H-4, H-5), 3.94–4.05 (m, 3H, OCH₂, H-6, H-6′), 4.96 (br dd, 1H, J=2.7 Hz and 1.2 Hz, H-1), 5.67 (ddd, 1H, J=10.2 Hz, 2.7 Hz and 1.8 Hz, H-2), 5.88 (ddd, 1H, J=10.2 Hz, 1.8 Hz and 1.8 Hz, H-3), 7.04 (dd, 1H, J=5.1 Hz and 1.2 Hz, Ar-H_a), 7.15–7.18 (m, 1H, Ar-H_c), 7.54 (dd, 1H, J=5.1 Hz and 3.0 Hz, Ar-H_b); ¹³C NMR (acetone-d₆): δ 30.8, 61.9, 63.4, 68.5, 72.8, 94.5, 121.4, 125.5, 125.9, 129.0, 134.4, 139.9. Anal. Calcd for C₁₂H₁₆O₄S (1/4H₂O): C, 55.26; H, 6.38. Found: C, 55.25; H, 6.56.

2-(Thiophene-2-yl)ethyl 2,3-dideoxy-α-D-erythro-hex-2-enopyranoside (6c)

Yield 75%; colorless solid; mp 68–69°C. R_f 0.5 (EtOAc/CHCl_3, 1;9); [α]_D²⁰+51° (c 1, CHCl₃); ¹H NMR (acetone-d₆): δ 3.10 (td, 2H, J=6.6 Hz and 1.2 Hz, CH₂-Het), 3.62–3.73 (m, 4H, 2xOH, OCH₂, H-4), 3.80 (ddd, 1H, J=11.4 Hz, 4.8 Hz and 2.1 Hz, H-5), 3.97–4.08 (m, 2H, OCH₂, H-6 or H-6′), 4.98 (br d, 1H, J=2.7 Hz, H-1), 5.68 (ddd, 1H, J=10.2 Hz, 4.8 Hz and 2.7 Hz, H-2), 5.90 (dd, 1H, J=10.2 Hz and 2.7 Hz, H-3), 6.89–6.94 (m, 2H, Ar-H_a and H_b), 7.23 (dd, 1H, J=5.4 Hz and 1.5 Hz, Ar-H_c); ¹³C NMR (acetone-d₆): δ 31.2, 63.0, 64.5, 69.5, 73.4, 95.2, 124.4, 126.0, 126.5, 127.4, 134.9, 142.4. Anal. Calcd for C₁₂H₁₆O₄S: C, 56.23; H, 6.29. Found: C, 56.03; H, 5.92.

Benzyl 2,3-didesoxy-α-D-threo-hex-2-enopyranoside (7a)

Yield 60%; colorless crystals; mp 102–103^oC. R_f 0.5 (EtOAc/CHCl₃, 1:9); [α]_D²⁰−106^o (c 1, CHCl₃); ¹H NMR (acetone-d₆): δ 2.85 (brs, 2H, OH), 3.68–3.81 (m, 2H, H-6 and H-6′), 3.85 (ddd, 1H, J=5.4 Hz, 2.4 Hz and 2.4 Hz, H-5), 4.04 (dd, 1H, J=6.0 Hz and 2.4 Hz, H-4), 4.55 (d, 1H, J=11.8 Hz, OCH₂Ph), 4.82 (d, 1H, J=11.8 Hz, OCH₂Ph), 5.07 (brd, 1H, J=3.0 Hz, H-1), 5.86 (dd, 1H, J=9.9 Hz and 3.0 Hz, H-2), 6.09 (dd, 1H, J=9.9 Hz and 6.0 Hz, H-3), 7.25–7.40 (m, 5H, Ar-H); ¹³ C NMR (acetone-d₆): δ 62.1, 62.6; 69.7, 72.6, 94.2, 128.2, 128.7, 128.8 (2C), 129.0 (2C), 130.8, 139.5. Anal. Calcd for C₁₃H₁₆O₄: C, 66.09; H, 6.83. Found: C, 65.56; H, 6.76.

2-(Thiophene-3-yl)ethyl 2,3-dideoxy-α-D-threo-hex-2-enopyranoside (7b)

Yield 62%; colorless oil; R_f 0.5 (10% EtOAc/CHCl₃); [α]_D²⁰−91^o (c 0.7, CHCl₃); ¹H NMR (acetone-d₆): δ 2.89 (t, 2H, J=6.9 Hz, CH₂-Het), 3.63–3.83 (m, 6H, 2xOH, OCH₂, H-5, H-6, H-6′), 3.91–4.04 (m, 2H, OCH₂, H-4), 4.97 (br d, 1H, J=3.0 Hz, H-1), 5.81 (ddd, 1H, J=10.2 Hz, 3.0 Hz and 0.6 Hz, H-2), 6.05 (ddd, 1H, J=10.2 Hz, 5.4 Hz and 1.2 Hz, H-3), 7.04 (dd, 1H, J=4.8 Hz and 1.2 Hz, Ar-H_a), 7.17 (m, 1H, Ar-H_c), 7.35 (dd, 1H, J=4.8 Hz and 3.0 Hz, Ar-H_b); ¹³C NMR (CDCl₃): δ 32.1, 64.5, 64.7, 68.2, 73.2, 95.8, 122.5, 126.9, 129.5, 130.0, 131.5, 141.1. Anal. Calcd for C₁₂H₁₆O₄S: C, 56.23; H, 6.29. Found: C, 55.77; H, 6.02.

2-(Thiophene-2-yl)ethyl 2,3-dideoxy-α-D-threo-hex-2-enopyranoside (7c)

Yield 53%; colorless oil; R_f 0.5 (10% EtOAc/CHCl₃); [α]_D²⁰−144^o (c 0.8, CHCl₃); ¹H NMR (acetone-d₆): δ 3.10 (td, 2H, J=6.6, 2.1 Hz, CH₂-Het), 3.63–3.84 (m, 6H, 2×OH, OCH₂, H-5, H-6, H-6′), 3.94–4.04 (m, 2H, OCH₂, H-4), 4.99 (br d, 1H, J=2.7 Hz, H-1), 5.81 (dd, 1H, J=10.1 Hz and 2.7 Hz, H-2), 6.06 (dd, 1H, J=10.2 Hz and 5.3 Hz, H-3), 6.89–6.94 (m, 2H, Ar-H_a and Ar-H_b), 7.23 (dd, 1H, J=5.1 Hz and 1.5 Hz, Ar-H_c); ¹³C NMR (CDCl₃): δ 31.5, 62.8, 63.4, 69.9, 73.2, 95.9, 125.2, 126.8, 128.2, 129.4, 131.4, 143.2. Anal. Calcd for C₁₂H₁₆O₄S: C, 56.23; H, 6.29. Found: C, 56.62; H, 6.37.

Determination of anti-inflammatory activity

Experimental animals

Male Mus musculus mice (N=6), provided by the animal facilities of UFPE, Recife, Brazil, were used for the evaluation of anti-inflammatory activity of the compounds. The mice weighed between 25 g and 30 g and were kept in a room with controlled temperature (22±2°C) and humidity (50–60%) under a 12 h/12 h light/dark cycle. Water and food were made available to the animals without restriction. Before beginning the experiments, animals were acclimated to the laboratory environment for at least 30 min. All animals were fasted for 8 h prior to experimentation.

The Animal Studies Committee of the Federal University of Pernambuco approved the experimental protocols. The animals were treated according to the ethical principles of animal experimentation of COBEA (Brazilian College of Animal Experiments) and the norms of the National Institute of Health Guide for Care and Use of Laboratory Animals.

Carrageenan-induced air pouch

This assay was performed according to the methodology described previously [27], [28]. The anti-inflammatory activities of the compounds were tested by the formation of air pouches on the dorsal cervical region of mice via a subcutaneous injection of 2.5 mL of sterile air on day 0, followed by a second injection of 2.5 mL of sterile air 3 days later. On day six, the mice received vehicle, (saline solution 0.9%) indomethacin (10 mg/kg), acetylsalicylic acid (ASA, 200 mg/kg) or the compounds test (100 mg/kg) orally. The doses were chosen according to the results of a pilot experiment. One hour after drug administration, inflammation was induced by injecting 1 mL of carrageenan suspension (1% in saline solution) into the air pouch. After 6 h, the mice were euthanized in a CO₂ chamber and the pouches were flushed with 3 mL of phosphate-buffered solution (PBS) with heparin (10 IU/mL). Samples were diluted with Turk’s solution and leucocytes were counted in a Neubauer Chamber under a microscope. The average numbers of leucocytes from treated groups were compared with the number of leucocytes of the control group, assumed to be 100%. Statistical analysis between the groups was performed by one-way analysis of variance (ANOVA), followed by the Bonferroni’s test for a confidence interval of 95%, P values less than 0.05 (P<0.05) determined using Origin 7.0 graphical sofware.

Acknowledgments

This work was supported by CAPES, CNPq and FACEPE. R.M.S. extends his thanks to Dr. R. N. de Oliveira for (i) rendering assistance to A. C. N. de Melo in the laboratory and (ii) participating in the initial preparation of the manuscript.

References

[1] Ferrier, R. J.; Prasad, N. Unsaturated carbohydrates. Part IX. Synthesis of 2,3-dideoxy-α-D-erythro-hex-2-enopyranosides from tri-O-acetyl-D-glucal. J. Chem. Soc. Sect. C1969, 4, 570–575.10.1039/J39690000570Search in Google Scholar

[2] Ferrier, R. J. Substitution with Allylic Rearrangement Reactions of Glycal Derivatives. Top. Curr. Chem. 2001, 215, 153–175.10.1007/3-540-44422-X_7Search in Google Scholar

[3] Gómez, A. M.; Lobo, F.; Uriel, C.; López, J. C. Recent Developments in the Ferrier Rearrangement. Eur. J. Org. Chem.2013, 7221–7267.10.1002/ejoc.201300798Search in Google Scholar

[4] Panarese, J. D.; Waters, S. P. Enantioselective formal total synthesis of (+)-aspergillide. Org. Lett. 2009, 11, 5086–5088.10.1021/ol902154pSearch in Google Scholar

[5] Toshima, K.; Ishizuka, T.; Matsuo, G.; Nakata, M. Practical glycosidation method of glycals using montmorillonite K-10 as an environmentally acceptable and inexpensive industrial material. Synlett1995, 4, 306–308.10.1055/s-1995-4973Search in Google Scholar

[6] Melo, V. N.; Dantas, W. M.; Camara, C. A.; de Oliveira, R. N. Synthesis of 2,3-unsaturated alkynyl O-glucosides from tri-O-acetyl-D-glucal by using montmorillonite K-10/iron(III) chloride hexahydrate with subsequent copper(I)- catalyzed 1,3-dipolar cycloaddition. Synthesis2015, 47, 3529–3541.10.1055/s-0034-1378829Search in Google Scholar

[7] De Oliveira, R. N.; De Freitas Filho, J. R.; Srivastava, R. M. Microwave-induced synthesis of 2,3-unsaturated O-glycosides under solvent-free conditions. Tetrahedron Lett.2002, 64, 2141–2143.10.1016/S0040-4039(02)00156-9Search in Google Scholar

[8] De, K.; Legros, J.; Crousse, B.; Bonnet-Delpon, D. Synthesis of 2,3-unsaturated glycosides via metal-free Ferrier reaction. Tetrahedron2008, 64, 10497–10500.10.1016/j.tet.2008.09.005Search in Google Scholar

[9] Gorityala, B. K.; Lorpitthaya, R.; Bai, Y.; Liu, X-W. ZnCl2/alumina impregnation Catalyzed Ferrier rearrangement: an expedient synthesis of pseudoglycosides. Tetrahedron2009, 65, 5844–5848.10.1016/j.tet.2009.04.099Search in Google Scholar

[10] Michigami, K.; Hayashi, M. O- and N-Glycosidation of D-glycals using Ferrier rearrangement under Mitsunobu reaction conditions. Tetrahedron. 2012, 68, 1092–1096.10.1016/j.tet.2011.11.084Search in Google Scholar

[11] Zhang, G.; Liu, Q.; Shi, L.; Wang, J. Ferric sulfate hydrate-catalyzed O-glycosylation using glycals with or without microwave irradiation. Tetrahedron.2008, 64, 339–344.10.1016/j.tet.2007.10.097Search in Google Scholar

[12] Mukherjee, A.; Jayaraman, N. Reactivity switching and selective activation of C-1 or C-3 in 2,3-unsaturated thioglycosides. Carbohydr. Res. 2011, 346, 1569–1575.10.1016/j.carres.2011.04.039Search in Google Scholar

[13] Drew, M. D.; Wall, M. C.; Kim, J. T. Stereoselective propargylation of glycals with allenyltributyltin(IV) via a Ferrier type reaction. Tetrahedron Lett. 2012, 53, 2833–2836.10.1016/j.tetlet.2012.03.115Search in Google Scholar

[14] Srivastava, R. M.; Oliveira, F. J. S.; da Silva, L. P.; de Freitas-Filho, J. R.; Oliveira, S. P.; Lima, V. L. M. Synthesis and hypolipidemic activity of N-phthalimidomethyl tetra-O-acyl-α-D-mannopyranosides. Carbohydr. Res.2001, 332, 335–340.10.1016/S0008-6215(01)00088-XSearch in Google Scholar

[15] Chan, C. L.; Lien, E. J.; Tokes, Z. A. Synthesis, biological evaluation, and quantitative structure-activity relationship analysis of 2-hydroxy-1H-isoindolediones as new cytostatic agents J. Med. Chem. 1987, 30, 509–514.10.1021/jm00386a012Search in Google Scholar

[16] Bailleux, V.; Vallee, L.; Nuyts, J. P.; Vamecq, J. Anticonvulsant activity of some 4-amino-N-phenylphthalimydes and N-(3-amino-2-methylphenyl)phthalimides. Biomed. Pharmacother.1994, 48, 95–101.10.1016/0753-3322(94)90083-3Search in Google Scholar

[17] Sharma, U.; Kumar, P.; Kumar, N.; Singh, B. Recent advances in the chemistry of phthalimide analogues and their therapeutic potential. Mini-Rev. Med. Chem. 2010, 10, 678–704.10.2174/138955710791572442Search in Google Scholar PubMed

[18] Assis, S. P. O.; Silva, M. T.; de Oliveira, R. N.; Lima, V. L. M. Synthesis and anti-inflammatory activity of New alkyl-substituted phthalimide 1H-1,2,3-triazole derivatives. Sci. World J.2012, Article ID 925925, Doi: 10.1100/2012/925925.10.1100/2012/925925.Search in Google Scholar

[19] Meng, X. B.; Han, D.; Zhang, S. N.; Guo, W.; Cui, J. R.; Li, Z. J. Synthesis and anti-inflammatory activity of N-phthalimidomethyl 2,3-dideoxy- and 2,3-unsaturated glycosides. Carbohydr. Res.2007, 342, 1169–1174.10.1016/j.carres.2007.03.009Search in Google Scholar PubMed

[20] Fraser-Reid, B.; Mclean, A.; Usherwood, E.W.; Yunker, M. Pyranosiduloses. II. The synthesis and properties of some alkyl 2,3-dideoxy-2-enopyranosid-4-uloses. Can. J. Chem.1970, 48, 2877–2884.10.1139/v70-484Search in Google Scholar

[21] Zhou, J.; Chen, H.; Shan, J.; Li, J; Yang, G.; Chen, X.; Xin, K.; Zhang, J.; Tang. J. FeCl3·6H2O/C: An Efficient and Recyclable Catalyst for the Synthesis of 2,3-Unsaturated O- and S-Glycosides. J. Carbohydr. Chem.2014, 33, 313–325.10.1002/chin.201509278Search in Google Scholar

[22] Zeni, G.; Nogueira, C. W.; Panatieri, R. B.; Silva, D. O.; Menezes, P. H.; Braga, A. L.; Silveira, C. C.; Stefani, H. A.; Rocha, J. B. T. Synthesis and anti-inflammatory activity of acetylenic thiophenes. Tetrahedron Lett.2001, 42, 7921–7923.10.1016/S0040-4039(01)01703-8Search in Google Scholar

[23] Mishra, R.; Jha, K. K.; Kumar, S.; Tomer, I. Synthesis, properties and biological activity of thiophene: a review. Der Pharma Chim.2011, 3, 38–54.Search in Google Scholar

[24] Vane, J. R.; Botting, R. M. The mechanism of action of aspirin. Thromb. Res.2003, 110, 255–258.10.1016/S0049-3848(03)00379-7Search in Google Scholar

[25] Shull, B. K.; Wu, Z.; Koreeda, M. A convenient, highly efficient one-pot preparation of peracetylated glycals from reducing sugars. J. Carbohydr. Chem.1996, 15, 955–964.10.1080/07328309608005701Search in Google Scholar

[26] de Oliveira, R. N.; de Melo, A. C. N.; Srivastava, R. M.; Sinou, D. Exclusive formation of α-anomers in NbCl₅ promoted Ferrier rearrangement for the synthesis of 2,3 unsaturated glycosides. Heterocycles2006, 68, 2607–2613.10.1002/chin.200715188Search in Google Scholar

[27] Romano, M.; Faggioni, R.; Sironi, M.; Sacco, S.; Echtenacher, B.; Di Santo, E.; Salmona, M.; Ghezzi, P. Carrageenan-induced acute inflammation in the mouse air pouch synovial model. Role of tumour necrosis factor. Mediators Inflamm. 1997, 6, 32–38.10.1080/09629359791901Search in Google Scholar PubMed PubMed Central

[28] Guerra, A. S. H. S.; Malta, D. J. N.; Laranjeira, L. P. M.; Maia, M. B. S.; Colaço, N. C.; Lima, M. C. A.; Galdino, S. L.; Pitta, I. R.; Gonçalves-Silva, T. Anti-inflammatory and antinociceptive activities of indole–imidazolidine derivatives. Int. Immunopharmacol. 2011, 11, 1816–1822.10.1016/j.intimp.2011.07.010Search in Google Scholar PubMed

Received: 2016-12-3

Accepted: 2017-1-24

Published Online: 2017-5-24

Published in Print: 2017-6-27

This article is distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Articles in the same Issue

https://doi.org/10.1515/hc-2016-0226

Keywords for this article

anti-inflammatory glycosides; Ferrier rearrangement; tri-O-acetyl-D-galactal; tri-O-acetyl-D-glucal; 2,3-unsaturated glycosides

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