Synthesis, characterization, antibacterial and antifungal evaluation of novel monosaccharide esters

Article abstract of DOI:10.3390/molecules17078661

A novel series of 3-(2-furyl)acrylate monosaccharide esters Ia-f and menthyloxycarbonyl monosaccharide esters IIa-f were designed and synthesized. The chemical structures of the target compounds were confirmed by IR, 1H- and 13C-NMR and ESI-MS, and the target compounds were investigated for their in vitro antibacterial and antifungal activities. The antibacterial screening results showed that the 3-(2-furyl)acrylate monosaccharide ester derivatives Ia-f were either inactive or only weakly active against the three Gram-positive bacterial strains tested, whereas the menthyloxycarbonyl monosaccharide ester derivatives IIa-f exhibited higher levels of activity, with compound IIe being especially potent. The results of the antifungal screening revealed that compounds Ib, Ie, IIb and IIc displayed potent in vitro activities, whereas If and IIf showed promising activities against all of the microorganisms tested, with If exhibiting levels of activity deserving of further investigation.

Full text of DOI:10.3390/molecules17078661

Molecules 2012, 17, 8661-8673; doi:10.3390/molecules17078661
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis, Characterization, Antibacterial and Antifungal
Evaluation of Novel Monosaccharide Esters
Yi Shen 1,2, Yufeng Sun 2, Zhipei Sang 3, Chengjun Sun 1, Ya Dai 2,* and Yong Deng 3,*
1
West China School of Public Health, Sichuan University, Chengdu 610041, China
2
Harmful Components and Tar Reduction in Cigarette, Sichuan Key Laboratory. No. 56, Section 1,
Chenglong Road, Chengdu 610066, China
3
Key Laboratory of Drug Targeting and Drug Delivery System of the Education Ministry,
Department of Medicinal Chemistry, West China School of Pharmacy, Sichuan University,
Chengdu 610041, China
* Authors to whom correspondence should be addressed; E-Mails: dycy@263.net (Y.D.);
dengyong@scu.edu.cn (Y.D.); Tel./Fax: +86-28-8600-5092 (Y.D.);
Tel./Fax: +86-28-8550-3790 (Y.D.).
Received: 13 April 2012; in revised form: 5 July 2012 / Accepted: 16 July 2012 /
Published: 23 July 2012
Abstract: A novel series of 3-(2-furyl)acrylate monosaccharide esters Ia–f and
menthyloxycarbonyl monosaccharide esters IIa–f were designed and synthesized. The
chemical structures of the target compounds were confirmed by IR, 1H- and 13C-NMR and
ESI-MS, and the target compounds were investigated for their in vitro antibacterial and
antifungal activities. The antibacterial screening results showed that the 3-(2-furyl)acrylate
monosaccharide ester derivatives Ia–f were either inactive or only weakly active against the
three Gram-positive bacterial strains tested, whereas the menthyloxycarbonyl monosaccharide
ester derivatives IIa–f exhibited higher levels of activity, with compound IIe being
especially potent. The results of the antifungal screening revealed that compounds Ib, Ie, IIb
and IIc displayed potent in vitro activities, whereas If and IIf showed promising activities
against all of the microorganisms tested, with If exhibiting levels of activity deserving of
further investigation.
Keywords: carbohydrate-acetonides; 3-(2-furyl)acrylate monosaccharide esters;
menthyloxycarbonyl monosaccharide esters; antibacterial activities; antifungal activities

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1. Introduction
Microbial food contamination problems have been the cause of much public concern over the last
few decades because of an increase in the number of infections and diseases originating from the
consumption of spoiled food [1]. Antibacterial and antifungal agents are necessary for food preservation,
especially for food processors, because bacterial and fungal growth are important causes of food
spoilage. For this reason, many investigators have focused their research efforts on finding new
efficient, low toxicity and environmentally friendly antibacterial and antifungal agents.
Sugar esters have been widely used as cosmetic and pharmaceutical industries for many years
because they are considered biocompatible, biodegradable, and nontoxic and can be synthesized from
renewable resources [2–7]. Furthermore, sugar esters have attracted considerable research interest in
recent years because they have exhibited a variety of biological activities, including insecticidal [8],
antitumor [9–13], antimicrobial and antifungal properties [14–18]. These results prompted us to design
and synthesize a novel series of sugar esters in the hope that we might find some promising
antimicrobial or antifungal agents. From a review of the literature, there have been many reports concerning
propyl 3-(2-furanyl)acrylate ester and (−)-menthol and their applications in the food, beverage and
cosmetics industries. Furthermore, 3-(2-furyl)acrylic acid and its ester derivatives and (−)-menthol
have also been reported as antimicrobial agents [19–23]. But these compounds have poor solubility
in water and thus result in low bioactivity. Inspired by these observations, we planned to couple
3-(2-furyl) acrylic acid or (−)-menthol with monosaccharides to obtain the corresponding water-soluble
monosaccharide esters, as it was envisaged that these novel compounds would combine the favorable
properties of sugars with either the 3-(2-furyl)acrylic acid esters or (−)-menthol and will be more
bioavailable.
Based upon the aforementioned considerations, herein we describe the synthesis of two novel series,
including a series of 3-(2-furyl) acrylate monosaccharide esters Ia–f and a series of menthyloxycarbonyl
monosaccharide esters IIa–f (Scheme 1).
Scheme 1. Synthesis of compounds Ia–f and IIa–f.

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Scheme 1. Cont.
Reagents and conditions: (i) morpholine, AcOH, reflux 5 h (85%); (ii) SOCl2, cat. DMF, CH2Cl2,
r.t. 5 h (99.0%); (iii) Carbohydrate-acetonides (5a–f = R1OH), Et3N, CH2Cl2, r.t., 12–15 h;
(iv) 50% CF3COOH-H2O, r.t., 3–5 h (42.2–65.5% for 2 steps); (v) triphosgene, toluene, pyridine,
r.t. 15 h (quantitative yield); (vi) Carbohydrate-acetonides (5a–f = R1OH), Et3N, CH2Cl2, r.t.,
12–15 h; (vii) 50% TFA-H2O, r.t., 3–5 h (31.5–65.0% over the 2 steps).
Furthermore, their in vitro antibacterial activities against Bacillus subtilis, Staphylococcus aureus,
Staphylococcus epidermidis, Escherichia coli and Pseudomonas aeruginosa, and antifungal activities
against Aspergillus flavus, Aspergillus niger, Aspergillus fumigatus and Geotrichum candidum were
investigated.
2. Results and Discussion
2.1. Chemical Synthesis
The target compounds Ia–f and IIa–f were synthesized according to conventional procedures as
outlined in Scheme 1. Compound 3 [24] was prepared by a modified procedure which provided the
product more conveniently and in higher yield, and was subsequently reacted with thionyl chloride to
afford α-furanacryloyl chloride 4. Compounds 6a–f were obtained via the esterification of intermediate
4 with the corresponding one anomer of O-isopropylidene-protected monosaccharides 5a–f in dry
dichloromethane in the presence of Et3N at room temperature. Subsequent deprotection of the
O-isopropylidenes with a 50% TFA-H2O solution at room temperature gave the desired 3-(2-furyl)acrylate
monosaccharide esters Ia–f as a mixture of anomers for Ia, Ib, Ie and If due to mutarotation [25]. The
menthyloxycarbonyl monosaccharide esters IIa–f were synthesized from the readily available alcohol
(−)-menthol (7), which was reacted with triphosgene and pyridine in toluene to give menthyl
chloroformate 8 in quantitative yield [26]. Chloroformate 8 was taken into the next step without
purification and reacted with the one anomer of O-isopropylidene protected monosaccharides 5a–f in
dry dichloromethane in the presence of Et3N at room temperature to afford the corresponding menthol
carbonates 9a–f in high yields. Subsequent deprotection of the O-isopropylidenes with a 50%
TFA-H2O solution at room temperature gave the desired anomeric mixture of menthyloxycarbonyl

Molecules 2012, 17
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monosaccharide esters IIa–f. Among them, IIa, IIb, IIe and IIf were obtained as a mixture of
anomers due to mutarotation. All of the target compounds were purified by silica gel flash column
chromatography, and their chemical structures were confirmed by IR, 1H- and 13C-NMR and ESI-MS.
To the best of our knowledge, none of these monosaccharide esters have been reported in the literature,
and therefore represent novel compounds.
2.2. Antibacterial and Antifungal Activities
2.2.1. Antibacterial Activities
The in vitro antibacterial activities of the monosaccharide esters Ia–f and IIa–f were tested against
five bacterial strains, including the three Gram-positive organisms, B. subtilis, S. aureus, and
S. epidermidis, and the two Gram-negative organisms E. coli and P. aeruginosa. The antibacterial
assays were conducted according to the NCCLS (National Committee for Clinical Laboratory
Standards) document M100-S12 method [27]. Standard antibacterial agents, including penicillin and
streptomycin, were also screened under identical conditions for the sake of comparison. The minimum
inhibitory concentrations (MIC) values of the tested compounds are shown in Table 1.
Table 1. MIC values (µg/mL) of the tested compounds against selected bacterial strains.
MIC (µg/mL)
Compound
Gram-positive
Gram-negative
E. coli P. aeruginosa
B. subtilis
S. aureus
S. epidermidis
Ia
32
32
>64
>64
32
32
32
8
32
32
32
32
32
>64
16
32
32
32
2
32
32
>64
>64
>64
>64
32
32
16
32
8
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
8
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
4
Ib
Ic
Id
Ie
If
IIa
IIb
IIc
32
32
2
IId
IIe
IIf
8
16
32
16
1
16
16
8
3
8
(−)-Menthol
Penicillin
Streptomycin
8
1
4
32
16
8
8
16
4
2
Negative control 5% DMSO---no activity.
The compounds tested clearly exhibited varying degrees of antibacterial activity. The 3-(2-furyl)acrylate
monosaccharide ester derivatives Ia–f were either inactive or only weakly active against the three
Gram-positive bacterial strains tested, whereas the menthyloxycarbonyl monosaccharide ester
derivatives IIa–f showed greater levels of activity, with compound IIe exhibiting remarkably high

Molecules 2012, 17
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levels of antibacterial activities against all three bacterial strains. It was also shown that all of the target
compounds were inactive against the gram-negative bacterial strains tested.
2.2.2. Antifungal Activities
The in vitro antifungal activities of the monosaccharide esters Ia–f and IIa–f were determined
against four fungal strains, including A. flavus, A. niger, A. fumigatus, and G. candidum, using
clotrimazole as a reference standard. The antifungal activity assays were conducted according to the
NCCLS standard M27-A method [28]. The MIC data of the tested compounds are presented in Table 2.
Table 2. MIC data (µg/mL) of the tested compounds against selected fungal strains.
MIC (µg/mL)
Compound
A. flavus
32
A. niger
32
A. fumigatus
G. candidum
Ia
32
8
32
32
Ib
16
16
Ic
32
>64
>64
16
>64
32
8
>64
>64
32
Id
>64
16
Ie
If
2
2
2
4
IIa
>64
16
>64
16
>64
8
>64
32
IIb
IIc
16
32
8
16
IId
>64
32
>64
>64
4
>64
>64
4
>64
32
IIe
IIf
3
4
8
32
>64
32
>64
32
4
>64
>64
16
(−)-Menthol
Clotrimazole
32
8
8
Negative control 5% DMSO---no activity.
The in vitro antifungal activity results showed that compounds If and IIf exhibited potent activities
against all of the microorganisms tested. Furthermore, both of these compounds, especially If,
exhibited activities comparable to those of the standard fungicide, clotrimazole, indicating that these
compounds are worthy of further investigation. It was also found that compounds Ib, Ie, IIb and IIc
showed potent in vitro antifungal activities, and that their activities were superior to those of the
corresponding 3-(2-furyl)acrylic acid (3) and (−)-menthol. The other monosaccharide esters Ia, Ic, Id,
IIa, IId and IIe showed no activity against the antifungal strains tested.
3. Experimental
3.1. Materials and Reagents
Melting points were determined in open glass capillaries using a paraffin bath and are uncorrected.
13
1H- and C-NMR spectra were measured on a Varian INOVA-400 instrument at 400 and 100 MHz,
respectively, using TMS as an internal standard in CDCl3 or D2O solvents. IR spectra were obtained on

Molecules 2012, 17
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a Thermo Nicolet AVATAR 370 FT-IR instrument using KBr plates. Mass spectra were recorded on a
Waters Q-TOF Premier mass spectrometer. Optical rotation data were collected after mutarotation
equilibration in about 10 min on a Perkin-Elmer 341 Polarimeter using HPLC grade anhydrous
MeOH. All commercially available reagents and anhydrous solvents were purchased at the highest
commercial quality and were used without further purification. The bacterial and fungal strains
were obtained from Sichuan Industrial Institute of Antibiotics, Sinopharm Group Co. Ltd.,
(SINOPHARM-SIIA, Chengdu, China).
3.2. Chemical Synthesis
3.2.1. Preparation of 3-(2-furyl)acrylic acid (3)
Furfural (28.8 g, 0.30 mol) was dissolved in AcOH (120 mL) and morpholine (26.1 g, 0.30 mol)
was slowly added to the stirred mixture at 25 °C over a period of 10 min. Malonic acid (31.2 g,
0.30 mol) was then added to the reaction mixture and the resulting mixture was heated at reflux for
5.0 h. The mixture was then cooled to 25 °C and poured into cold water (400 mL). The resulting
precipitate was collected by filtration, washed with water, and dried under vacuum at 40 °C in a vacuum
oven to give the desired product. Yield: 35.2 g (85%), mp 140–141 °C (lit. m.p. 140–141 °C [24]).
3.2.2. Preparation of 3-(2-furyl)acryloyl chloride (4)
Thionyl chloride (17.85 g, 0.15 mol) was added to a stirred solution of 3-(2-furyl)acrylic acid
(3, 13.8 g, 0.1 mol) in CH2Cl2 (70 mL) at room temperature and the resulting mixture was heated at
reflux for 3 h. The mixture was then cooled and concentrated in vacuo to afford 3-(2-furyl)acryloyl
chloride quantitatively, which was used directly without further purification in the following reaction.
3.2.3. A general procedure for the synthesis of compounds Ia–f
A solution of 3-(2-furyl)acryloyl chloride (4, 0.024 mol or 0.048 mol in the synthesis of 6f) in dry
CH2Cl2 (15 mL) was added in a dropwise manner to a solution of carbohydrate-acetonide 5a–f (only
one anomer was used, 0.02 mol) and Et3N (0.05 mol) in dry CH2Cl2 (60 mL) at 0 °C in an ice bath.
The resulting solution was allowed to warm to room temperature and stirred for 12–15 h. The reaction
mixture was then diluted with CH2Cl2 (40 mL) and washed sequentially with H2O (2 × 25 mL),
saturated aqueous sodium bicarbonate (25 mL) and saturated aqueous sodium chloride (25 mL)
and dried (Na2SO4). The solvent was then removed in vacuo and to give the crude products 6a–f
(only one anomer was obtained), which were used directly in the next steps without further purification.
A 50% TFA-H2O solution (30 mL) was added to each of the compounds 6a–f and the mixture was
continuously stirred at room temperature for 3–5 h. Upon completion of the reaction (TLC, developing
solvent: CHCl3/CH3OH = 15:1), the solvents were removed in vacuo and residue was purified by silica
gel flash column chromatography (eluent: CHCl3/CH3OH = 10:1) to give the compounds Ia–f as light
yellow foams.
3-O-[3-(2-Furyl)acryloyl]-α/β-D-glucopyranose (Ia): yield 48.5%, (α:β isomer = 2:3 based on
1H-NMR); [α] 2D0 = +30.1 (c = 0.5, CH3OH); IR (KBr, cm−1): 3405.65, 2936.51, 1688.63, 1635.15,

Molecules 2012, 17
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1
1390.73, 1312.25, 1282.29, 1264.77, 1211.67, 1174.19, 1080.92, 1020.63, 751.60; H-NMR (D2O): δ
7.71 (s, 1H, Ar-H), 7.65 (d, J = 16 Hz, 1H, =CH), 6.90 (s, 1H, Ar-H), 6.66 (s, 1H, Ar-H), 6.46 (d,
J = 16 Hz, 1H, =CH), 5.34 (d, J = 4.0 Hz, 0.4H, 1'-Hα), 5.31 (d, J = 10.0 Hz, 0.6H, 1'-Hβ), 5.13 (t,
J = 9.6 Hz, 0.6H, 3'-Hβ), 4.82 (t, J = 8.6 Hz, 0.6H, 3'-Hα), 4.00–3.92 (m, 1H, 2'-H), 3.89–3.78 (m, 2H,
13
6'-H), 3.75–3.70 (m, 1H, 5'-H), 3.66–3.50 (m, 1H, 4'-H); C-NMR (D2O): δ 166.49, 166.30, 147.86,
143.49, 130.44, 130.33, 114.13, 111.38, 111.24, 110.27, 93.36, 89.59, 74.93, 73.26, 72.85, 70.03,
69.97, 68.74, 67.43, 65.47, 58.07, 57.90; ESI-MS (m/z): 623.5 [2M+Na]+, 339.05 [M+K]+, 323.10
[M+Na]+.
6-O-[3-(2-Furyl)acryloyl]-α/β-D-galactopyranose (Ib): yield 65.5%, (α:β isomer = 1:3 based on
1H-NMR); [α] 2D0 = +33.2 (c = 0.5, CH3OH); IR (KBr, cm−1): 3421.48, 2921.46, 1689.56, 1646.43,
1
1484.23, 1311.05, 1287.52, 1267.55, 1219.03, 1178.91, 1068.70, 1028.97, 766.04; H-NMR (D2O): δ
7.70 (s, 1H, Ar-H), 7.60 (d, J = 16 Hz, 1H, =CH), 6.90 (s, 1H, Ar-H), 6.65 (s, 1H, Ar-H), 6.42 (d,
J = 16 Hz, 1H, =CH), 5.33 (d, J = 4.0 Hz, 0.33H, 1'-Hα), 4.65 (d, J = 8.0 Hz, 0.67H, 1'-Hβ), 4.47–4.36
(m, 2H, 2'-H, 3'-H), 4.10–4.01 (m, 2H, 6'-H), 3.95–3.86 (m, 1H, 5'-H), 3.73–3.54 (m, 1H, 4'-H);
13C-NMR (D2O): δ 171.05, 152.68, 148.31, 135.04, 118.96, 116.04, 115.16, 98.90, 94.83, 78.0, 74.97,
74.90, 74.12, 71.40, 71.19, 70.66, 66.23, 63.2, 62.5; ESI-MS (m/z): 623.18 [2M+Na]+, 339.06 [M+K]+,
323.10 [M+Na]+.
1-O-[3-(2-Furyl)acryloyl]-β-D-fructopyranose (Ic): yield 51.5%; [α] 2D0 = −16.8 (c = 0.5, CH3OH); IR
(KBr, cm−1): 3425.36, 2919.49, 1689.56, 1633.87, 1392.49, 1309.13, 1280.21, 1268.82, 1212.08,
1
1165.22, 1079.39, 751.26; H-NMR (D2O): δ 7.69 (s, 1H, Ar-H), 7.62 (d, J = 16 Hz, 1H, =CH), 6.90
(s, 1H, Ar-H), 6.64 (s, 1H, Ar-H), 6.43 (d, J = 16 Hz, 1H, =CH), 4.35(d, J = 11.6 Hz, 1H, 1'-H), 4.33
(d, J = 11.6 Hz, 1H, 1'-H), 4.12–4.06 (m, 2H, 4'-H+3'-H), 3.99–3.96 (m, 1H, 5'-H), 3.88–3.86 (m, 1H,
13
6'-H), 3.77–3.74 (m, 1H, 6'-H); C-NMR (D2O): δ 171.12, 152.79, 148.44, 135.40, 119.14, 115.94,
115.20, 99.62, 71.83, 71.46, 70.51, 68.19, 66.10; ESI-MS (m/z): 623.58 [2M+Na]+, 339.28 [M+K]+,
323.34 [M+Na]+.
3-O-[3-(2-Furyl)acryloyl]-β-D-fructopyranose (Id): yield 42.2%; [α] 2D0 = −15.0 (c = 0.5, CH3OH); IR
(KBr, cm−1): 3423.50, 2919.06, 1690.32, 1639.41, 1390.12, 1311.75, 1285.37, 1267.76, 1216.13,
1175.78, 1075.620, 1048.93, 750.55; 1H-NMR (D2O): δ 7.71 (s, 1H, Ar-H), 7.66 (d, J = 16 Hz, 1H, =CH),
6.92 (s, 1H, Ar-H), 6.65 (s, 1H, Ar-H), 6.42 (d, J = 16 Hz, 1H, =CH), 5.34 (d, J = 10.0 Hz, 1H, 3'-H),
4.18 (d, J = 10.8 Hz, 2H, 6'-H), 4.13 (s, 2H, 1'-H), 3.91–3.78 (m, 1H, 4'-H), 3.65–3.49 (m, 1H, 3'-H);
13C-NMR (D2O): δ 170.93, 152.77, 148.52, 135.64, 119.29, 115.79, 115.22, 99.64, 72.23, 71.69,
70.63, 66.43, 65.99; ESI-MS (m/z): 339.28 [M+K]+, 323.34 [M+Na]+.
5-O-[3-(2-Furyl)acryloyl]-α/β-D-xylofuranose (Ie): yield 54.8%, (α:β isomer = 3:1 based on
1H-NMR); [α] 2D0 = +15.6 (c = 0.5, CH3OH); IR (KBr, cm−1): 3418.32, 2921.25, 1695.67, 1482.55,
1348.08, 1304.12, 1266.78, 1209.46, 1068.42, 1033.91, 752.10; 1H-NMR (D2O): δ 7.69 (s, 1H, Ar-H),
7.63 (d, J = 16 Hz, 1H, =CH), 6.89 (s, 1H, Ar-H), 6.64 (s, 1H, Ar-H), 6.43 (d, J = 16 Hz, 1H, =CH),
5.29 (d, J = 2.8 Hz, 0.75H, 1'-Hα), 5.26–5.03 (m, 1H, 4'-H), 4.74 (d, J = 8.0 Hz, 0.25H, 1'-Hβ),
4.06–3.86 (m, 2H, 5'-H), 3.84–3.80 (m, 1H, 3'-H), 3.53–3.45 (m, 1H, 2'-H); 13C-NMR (D2O): δ

Molecules 2012, 17
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169.35, 151.66, 147.22, 132.54, 116.26, 114.84, 112.45, 99.72, 96.68, 77.66, 77.05, 76.12, 75.39,
73.96, 73.80, 65.55, 63.23; ESI-MS (m/z): 563.48 [2M+Na]+, 309.30 [M+K]+, 293.28 [M+Na]+.
3,5-Bi-O-[3-(2-furyl)acryloyl]-α/β-D-xylofuranose (If): yield 63.6%, (α:β isomer = 6:1 based on
1H-NMR); [α] 2D0 = −15.4 (c = 0.5, CH3OH); IR (KBr, cm−1): 3417.95, 2921.02, 1703.85, 1638.68,
1479.26, 1351.47, 1308.86, 1264.24, 1210.32, 1168.12, 1077.95, 1045.66, 748.99; 1H-NMR (CDCl3): δ
7.50 (d, J = 2.0 Hz, 1H, Ar-H), 7.47 (d, J = 1.6 Hz, 1H, Ar-H), 7.44 (d, J = 16.0 Hz, 1H, =CH), 7.43
(d, J = 16.0 Hz, 1H, =CH), 6.65 (d, J = 3.2 Hz, 1H, Ar-H), 6.61 (d, J = 3.2 Hz, 1H, Ar-H), 6.48 (dd,
J = 3.2, 1.6 Hz, 1H, Ar-H), 6.46 (dd, J = 3.2, 2.0 Hz, 1H, Ar-H), 6.32 (d, J = 16.0 Hz, 1H, =CH), 6.30
(d, J = 16.0 Hz, 1H, =CH), 5.57 (d, J = 4.4 Hz, 0.85H, 1'-Hα), 5.37 (d, J = 8.4 Hz, 0.15H, 1'-Hβ),
5.35–5.28 (m, 1H, 2'-H), 4.76–4.70 (m, 1H, 4'-H), 4.40–4.35 (m, 2H, 5'-H), 4.34–4.29 (m, 1H,
13
3'-H); C-NMR (CDCl3): δ 166.84, 166.75, 150.66, 150.44, 145.27, 144.92, 132.69, 132.61, 131.88,
131.78, 115.98, 115.30, 115.24, 114.86, 113.97, 112.45, 112.29, 102.98, 96.08, 78.66, 77.35, 77.03,
76.72, 75.39, 74.98, 63.80, 62.47; ESI-MS (m/z): 803.25 [2M+Na]+, 429.12 [M+K]+, 413.14 [M+Na]+.
3.2.4. Preparation of Menthyl Chloroformate 8
A solution of pyridine (21.9 mL, 0.27 mmol) in toluene (150 mL) was added in a dropwise manner
to a stirred solution of triphosgene (21.96 g, 0.074 mol) in toluene (260 mL) at 0 °C under an argon
atmosphere. Stirring was continued for 15 min at 0 °C and a solution of (−)-menthol (7, 28.12 g,
0.18 mol) in toluene (100 mL) was then slowly added through a dropping funnel. The reaction mixture
was allowed to warm to ambient temperature and stirred for 15 h. The reaction mixture was then
diluted with water (300 mL) and extracted with toluene (2 × 200 mL). The combined organics were
washed sequentially with water (200 mL) and brine (200 mL) and dried (Na2SO4). The solvent was
removed in vacuo to give the title compound 8 as colorless oil (39.3 g, quant.), which was used
directly in the next step without further purification.
3.2.5. A General Procedure for the Synthesis of Compounds IIa–f
A solution of menthyl chloroformate 8 (0.024 mol or 0.05 mol for the synthesis of 9f) in dry
CH2Cl2 (15 mL) was added in a drop-wise manner to a solution of carbohydrate-acetonide 5a–f (only
one anomer was used, 0.02 mol) and Et3N (0.05 mol) in dry CH2Cl2 (60 mL) at 0 °C in an ice bath.
The resulting solution was allowed to warm to room temperature and stirred for 12–15 h. The reaction
mixture was then diluted with CH2Cl2 (40 mL) and washed sequentially with H2O (2 × 25 mL),
saturated aqueous sodium bicarbonate (25 mL) and saturated aqueous sodium chloride (25 mL) before
being dried (Na2SO4). The solvent was removed in vacuo to give a crude product from 9a–f (only one
anomer was obtained), which was used directly in the next step without further purification. A 50%
TFA-H2O solution (30 mL) was added to one of the compounds 9a–f and the resulting mixture
continuously stirred at room temperature for 3–5 h. Upon completion of the reaction (TLC, developing
solvent: CHCl3/CH3OH = 20:1), the solvents were removed in vacuo and the crude residue was
purified by silica gel flash column chromatography (eluent: CHCl3/CH3OH = 30:1) to give the
compounds IIa–f as a colorless foam.

Molecules 2012, 17
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3-O-Menthyloxycarbonyl-α/β-D-glucopyranose (IIa): yield 60.0%, (α:β isomer = 1:1 based on
1H-NMR); [α] 2D0 = +5.6 (c = 1.0, CH3OH); 1H-NMR (CDCl3): δ 5.36–5.30 (m, 0.5H, 1'-Hβ), 5.00–4.90
(m, 0.5H, 1'-Hα), 4.82–4.72 (m, 1H, 3'-H), 4.58–4.48 (m, 1H, 5'-H), 4.05–3.92 (m, 2H, 4'-H+CHO),
3.83–3.72 (m, 1H, 6'-H), 3.70–3.44 (m, 2H, 6'-H+2'-H), 2.10–2.02 (m, 1H, CH), 2.01–1.92 (m, 1H,
CH), 1.72–1.62 (m, 2H, CH2), 1.54–1.38 (m, 2H, CH+CH2), 1.12–0.99 (m, 2H, CH2), 0.91 (d, J = 6.4 Hz,
3H, CH3), 0.88 (d, J = 6.4 Hz, 3H, CH3), 0.88–0.84 (m, 1H, CH2), 0.76 (d, J = 4.4 Hz, 3H, CH3);
13C-NMR (CDCl3): δ 156.10, 92.30, 88.45, 79.52, 73.55, 73.08, 72.80, 71.05, 70.66, 69.25, 68.82,
62.02, 58.40, 57.96, 47.02, 40.48, 34.02, 31.35, 25.94, 23.24, 22.00, 20.68, 16.21; ESI-MS (m/z):
401.28 [M+K]+, 385.30 [M+Na]+.
6-O-Menthyloxycarbonyl-α/β-D-galactopyranose (IIb): yield 65.0%, (α:β isomer = 1:4 based on
1H-NMR), [α] 2D0 = −9.9 (c = 1.0, CH3OH); 1H-NMR (CDCl3): δ 5.38 (d, J = 3.6 Hz, 0.2H, 1'-Hα), 4.64
(d, J = 8.4 Hz, 0.8H, 1'-Hβ), 4.63–4.47 (m, 1H, 6'-H), 4.38–4.06 (m, 2H, 2'-H+6'-H), 4.05–3.95 (m, 2H,
3'-H+CHO), 3.82–3.75 (m, 1H, 5'-H), 3.73–3.62 (m, 1H, 4'-H), 2.07–2.04 (m, 1H, CH), 2.01–1.92 (m,
1H, CH), 1.72–1.63 (m, 2H, CH2), 1.52–1.34 (m, 2H, CH+CH2), 1.10–0.99 (m, 2H, CH2), 0.91 (d,
J = 6.0 Hz, 3H, CH3), 0.88 (d, J = 6.8 Hz, 3H, CH3), 0.86–0.84 (m, 1H, CH2), 0.76 (d, J = 6.8 Hz, 3H,
13
CH3); C-NMR (CDCl3): δ 154.89, 96.88, 92.52, 78.97, 73.10, 72.74, 72.28, 69.60, 69.06, 68.78,
67.30, 66.90, 66.23, 66.02, 46.90, 40.60, 34.02, 31.34, 25.84, 23.14, 21.97, 20.76, 16.16; ESI-MS
(m/z): 401.31 [M+K]+, 385.29 [M+Na]+.
1-O-Menthyloxycarbonyl-β-D-fructopyranose (IIc): yield 60.0%; [α] 2D0 = −44.8 (c = 1.0, CH3OH);
1H-NMR (CDCl3): δ 4.54 (d, J = 11.2 Hz, 1H, 1'-H), 4.52 (d, J = 11.6 Hz, 1H, 1'-H), 4.34–4.25
(m, 2H, 4'-H+3'-H), 4.14–4.06 (m, 1H, 5'-H), 4.05–4.00 (m, 1H, CHO), 3.92–3.82 (m, 1H, 6'-H),
3.80–3.73 (m, 1H, 6'-H), 2.07–2.03 (m, 1H, CH), 2.00–1.90 (m, 1H, CH), 1.72–1.64 (m, 2H, CH2),
1.52–1.36 (m, 2H, CH+CH2), 1.10–0.99 (m, 2H, CH2), 0.91 (d, J = 7.2 Hz, 3H, CH3), 0.88 (d, J = 7.2 Hz,
3H, CH3), 0.86–0.84 (m, 1H, CH2), 0.76 (d, J = 7.2 Hz, 3H, CH3); 13C-NMR (CDCl3): δ 155.03, 96.81,
79.32, 73.39, 70.31, 69.25, 67.51, 63.57, 46.92, 40.54, 33.99, 31.34, 25.86, 23.13, 21.96, 20.73, 16.13;
ESI-MS (m/z): 401.29 [M+K]+, 385.29 [M+Na]+.
3-O-Menthyloxycarbonyl-β-D-fructopyranose (IId): yield 53.4%; [ ] 2D0 = −61.3 (c = 1.0, CH3OH);
1H-NMR (CDCl3): δ 4.89 (d, J = 9.6 Hz, 1H, 3'-H), 4.59–4.51 (m, 1H, 6'-H), 4.15–4.10 (m, 1H, 6'-H),
4.06 (s, 2H, 1'-H), 3.88–3.82 (m, 1H, CHO), 3.67–3.63 (m, 1H, 4'-H), 3.52–3.45 (m, 1H, 3'-H),
2.10–2.03 (m, 1H, CH), 1.98–1.88 (m, 1H, CH), 1.70–1.67 (m, 2H, CH2), 1.54–1.36 (m, 2H,
CH+CH2), 1.14–0.99 (m, 2H, CH2), 0.91 (d, J = 7.2 Hz, 3H, CH3), 0.88 (d, J = 7.2 Hz, 3H, CH3),
13
0.87–0.85 (m, 1H, CH2), 0.76 (d, J = 7.8 Hz, 3H, CH3); C-NMR (CDCl3): δ 155.67, 97.06, 79.59,
73.90, 69.79, 68.67, 64.74, 63.16, 46.90, 40.46, 33.97, 31.35, 26.12, 23.23, 21.95, 20.66, 16.18;
ESI-MS (m/z): 401.30 [M+K]+, 385.31 [M+Na]+.
5-O-Menthyloxycarbonyl-α/β-D-xylofuranose (IIe): yield 42.0%, (α:β isomer = 4:1 based on
1
1H-NMR); [α] 2D0 = −29.7 (c = 1.0, CH3OH); H-NMR (CDCl3): δ 5.53 (d, J = 2.0 Hz, 0.8H, 1'-Hα),
4.58–4.48 (m, 1.2H, 1'-Hβ+4'-H), 4.46–4.38 (m, 2H, 3'-H+5'-H), 4.36–4.24 (m, 2H, 2'-H+5'-H), 4.20–4.13
(m, 1H, CHO), 2.10–2.03 (m, 1H, CH), 1.98–1.90 (m, 1H, CH), 1.72–1.64 (m, 2H, CH2), 1.53–1.36

Molecules 2012, 17
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(m, 2H, CH+CH2), 1.10–0.99 (m, 2H, CH2), 0.92 (d, J = 7.2 Hz, 3H, CH3), 0.89 (d, J = 6.8 Hz, 3H,
13
CH3), 0.87–0.85 (m, 1H, CH2), 0.77 (d, J = 6.8 Hz, 3H, CH3); C-NMR (CDCl3): δ 155.21, 155.06,
102.80, 96.09, 80.15, 79.83, 79.19, 79.10, 76.36, 75.70, 75.47, 69.85, 67.40, 66.45, 65.96, 46.83, 40.54,
33.94, 31.31, 25.86, 23.12, 21.92, 20.68, 16.13; ESI-MS (m/z): 371.27 [M+K]+, 355.31 [M+Na]+.
3,5-Di-O-menthyloxycarbonyl-α/β-D-xylofuranose (IIf): yield 31.5%, (α:β isomer = 3:1 based on
1
1H-NMR); [α] 2D0 = −40.2 (c = 1.0, CH3OH); H-NMR (CDCl3): δ 5.21 (d, J = 3.6 Hz, 0.75H, 1'-Hα),
5.02 (d, J = 8.4 Hz, 0.25H, 1'-Hβ), 4.61–4.47 (m, 3H, 4'-H+5'-H+3'-H), 4.38–4.29 (m, 1H, 2'-H),
4.29–4.14 (m, 2H, 5'-H+CHO), 4.14–3.96 (m, 1H, CHO), 2.09–2.03 (m, 2H, 2CH), 1.98–1.91 (m, 2H,
2CH), 1.72–1.57 (m, 4H, 2CH2), 1.53–1.36 (m, 4H, 2CH+2CH2), 1.16–0.99 (m, 4H, 2CH2), 0.96–0.85
(m, 16H, 4CH3+2CH2), 0.84–0.75 (m, 6H, 2CH3); 13C-NMR (CDCl3) δ: 155.66, 155.62, 101.45, 96.35,
79.75, 79.60, 79.12, 78.03, 77.16, 76.58, 75.30, 73.67, 63.72, 63.25, 46.85, 40.58, 33.92, 31.38, 26.32,
23.20, 21.95, 20.67, 16.20; ESI-MS (m/z): 553.21 [M+K]+, 537.44 [M+Na]+, 493.49 [M-CO2+Na]+.
3.3. Antibacterial and Antifungal Activity Assays
For each tested compound, 1.28 mg sample was put in a 25 mL flask and dissolved in 10 mL 5%
DMSO. The drug was filtered into autoclaving centrifuge tubes in super clean bench. Penicillin,
streptomycin and clotrimazole solutions were prepared to the same concentration as the positive
control drug. After all bacteria and fungi were recovered, each single colony was picked and
inoculated in 3 mL of either a sterilized Mueller-Hinton (MH) broth cultured at 37 °C for 18–24 h (for
bacteria) or a Sabouraud Dextrose (SD) broth cultured at 28 °C for 48 h (for fungi). The
microorganism solution was corrected to 0.5 McFarland standard turbidity using either the MH or SD
broths, and subsequently diluted by 1:100 (amount of microorganism approximately 106 colony
forming units/mL) with either the MH or SD broth and inoculated immediately. Blank broth (100 µL)
was added into all the wells of rows 2–12 of a 96-well plate. Broth (180 µL) and dispensed drug liquor
(20 µL) where added to the first row of the 96-well plate and the mixture was well mixed. A sample of
the resulting mixture (100 µL) was inhaled and added into the corresponding wells of the second row.
The same mixing and transferring operations were repeated until the wells in the 12th row were filled.
The concentrations of drug in the wells of rows 1–12 were 128, 64, 32, 16, 8, 4, 2, 1, 0.5, 0.25, 0.125,
0.0625 µg/mL, respectively. The seventh and eighth rows of the 96-well plate were used for the positive
and negative controls, respectively. A diluted microorganism solution (100 µL) was added to each well of
the 96-well plate and the plate was shaken on a shaker instrument and subsequently stored in an incubator
for 24–48 h at 37 °C (for bacteria) and at 28 °C (for fungi). Each experiment was performed in triplicate.
4. Conclusions
In summary, the design and synthesis of two novel series of 3-(2-furyl) acrylate monosaccharide
esters Ia–f and menthyloxycarbonyl monosaccharide esters IIa–f from simple starting materials and
under mild reaction conditions has been reported. The antibacterial and antifungal properties of these
novel compounds were evaluated. The results revealed that the 3-(2-furyl)acrylate monosaccharide
ester derivatives Ia–f were either inactive or only weakly active against the three Gram-positive bacterial
strains tested (B. subtilis, S. aureus, S. epidermidis), whereas the menthyloxy carbonyl monosaccharide

Molecules 2012, 17
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ester derivatives IIa–f exhibited greater degrees of activity, with compound IIe showing remarkably high
antibacterial activity. Compound Ib, Ie, IIb and IIc displayed potent in vitro antifungal activities, whereas
If and IIf showed promising antifungal activities against all of the microorganisms tested, with
compound If exhibiting significantly high activities, which are worthy of further investigation.
Acknowledgments
This work was financially supported by the National Science and Technology Major Project on
“Key New Drug Creation and Manufacturing Program” (2009ZX09103-037), the Chinese National
Natural Science Foundation (20872099), the Research Program of Sichuan Science and Technology
Agency (2008JY0142), and the related Post-Doctoral Research Program.
Conflict of Interest
The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds Ia–f and IIa–f are available from the authors.
© 2012 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).