Synthesis of inulin esters of phenylcarboxylic acids

Article abstract of DOI:10.1134/S1070428013050114

Inulin esters were synthesized containing residues of ferulic, p-hydroxycinnamic, and vanillic acids with a maximum degree of substitution of 1.1. The inulin acylation was carried out with chlorides of 4-acetoxy derivatives of the corresponding hydroxyphenylcarboxylic acids in a heterogenic water-organic environment. The removal of the protecting acetyl group at the phenol hydroxyl was carried out by treating with pyrrolidine or ammonium acetate. The solubility of the esters obtained was evaluated.

Full text of DOI:10.1134/S1070428013050114

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 5, pp. 702−706. © Pleiades Publishing, Ltd., 2013.
Original English Text © M.A. Torlopov, E.V. Udoratina, A.V. Kuchin, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49, No. 5, pp. 719−723.
Dedicated to Full Member of the Russian Academy of Sciences
I.P. Beletskaya on occasion of her jubilee
Synthesis of Inulin Esters of Phenylcarboxylic Acids
M. A. Torlopov, E. V. Udoratina, and A. V. Kuchin
Institute of Chemistry, Komi Scientific Center, Ural Branch, Russian Academy of Sciences,
Syktyvkar, 16798 Russia
е-mail: torlopov-ma@chemi.komisc.ru
Received December 26, 2012
Abstract—Inulin esters were synthesized containing residues of ferulic, p-hydroxycinnamic, and vanillic acids
with a maximum degree of substitution of 1.1. The inulin acylation was carried out with chlorides of 4-acetoxy
derivatives of the corresponding hydroxyphenylcarboxylic acids in a heterogenic water-organic environment.
The removal of the protecting acetyl group at the phenol hydroxyl was carried out by treating with pyrrolidine or
ammonium acetate. The solubility of the esters obtained was evaluated.
DOI: 10.1134/S1070428013050114
Inulin is contained in various types of plants, but it
is most common obtained from succory (Сichoriumin
tybus) or Jerusalem potato (Helianthus tuberosus). This
polysaccharide of relatively low molecular weight is
built commonly of several tens of fructose fragments
connected by bonds β(2 → 1) and in some cases it may
include glucose units. Various esters of this biopolymer
were synthesized [1] and diverse applications were
suggested for them in many fields, but the special
attention is attracted by inulin as a promising component
of the functional nutrition [2–4]. In this connection
the most rational way of the chemical modification of
inulin would be the synthesis of derivatives suitable for
application in the food industry and in biomedical field,
for instance, the preparation of derivatives possessing the
antioxidant activity. It would be favorable to introduce
into the inulin structure of vegetable phenols fragments,
especially of those commonly present in the food and in
the herbs. These phenol compounds are widely spread
in the groups of hydroxycinnamic and hydroxybenzoic
acids. Ferulic, caffeic, p-hydroxycinnamic, gallic acids
exhibit a large antioxidant activity [5], are contained
in the natural physiologically active compounds, in
particular, in glycosides and poysaccaride–phenol
compexes [6, 7]. Lately different researchers carried
out the synthesis of esters of similar phenolic acids and
polysaccarides. Publications are known on the synthesis
of esters of xylane, starch, chitosan, dextran, and other
polysaccharides with hydroxyphenylcinnamic acids, with
the gallic acid through the acylation with the carboxylic
acid chlorides or by the use of carbodiimide method in
organic solvents [8–11].
The goal of our work was the preparation of inulin
derivatives including the residues of ferulic (Ia),
p-hydroxycinnamic (IIa), and also vanillic (IIIa) acids.
The synthesisofthe corresponding inulinesterswas carried
out by its acylation with 4-acetoxybenzenecarboxylic
acids chlorides in a water-organic environment followed
by the removal of the protective acetyl group from the
phenol hydroxyl.
The preliminary synthesis of the acyl chlorides
included the stage of the phenol hydroxyl acylation by
treating with acetic anhydride solutions of acids Ia–IIIa
in aqueous NaOH. Further the 4-acetoxy derivatives Ib–
IIIb were treated with thionyl chloride and the obtained
acyl chlorides Ic–IIIc without additional purification
were used for inulin acylation (Scheme 1, synthesis of
ferulic acid derivatives).
The acylation of inulin (IV) with the obtained
702

SYNTHESIS OF INULIN ESTERS OF PHENYLCARBOXYLIC ACIDS
703
Scheme 1.
5
7
b
a
AcO
H3CO
Cl
O
HO
OH
O
AcO
H3CO
OH
O
1
3
H3CO
Iа
Ib
Ib
(a)– Ac2O, NaOH, H2O, 2 h, 0 → 25°C; (b) SOCl2 in CHCl3, boiling, 4 h.
Scheme 2.
OCH3
OAc
OCH3
OH
O
O
O
O
HO
O
6'
O
O
O
O
O
b
a
RO
2'
RO
HO
5'
CH2
CH2
CH2
4'
3'
n
n
1'
n
RO
OR
Vа_Vc
OH
VIа_VIc
IV
(a) 4-acetoxyferulic acid chloride, NaOH, H2O, 6 h, 0 → 25°C; (b) pyrrolidine or СH3COONН4 in DMAA–Н2O; R is the
residue of ferulicой acid (a); in positions 2О, 3О, 5О is the residue of p-hydroxycinnamic acid (b), the residue of vanillic acid (c)
chlorides of 4-acetoxy derivatives of the acids was carried
out in a heterogenic environment water–CHCl3 at room
temperature for 6 h using NaOH as base (Scheme 2). The
obtained acylated inulin derivatives Vа–Vc contained
from 5 to 56 wt% of the fragments of 4-acetoxy
derivatives of phenolic acids. At the final stage of the
synthesis (b) the protecting acetyl group was removed
from the phenol hydroxyl.
the band with the maximum at 2930 cm–1 belonged to the
stretching vibrations of the С–H bond.
In the 13С NMR spectrum of inulin derivatives Vа–Vc
signals located at 162 ppm belong to the carbonyl of the
ester group. In the region 115–151 ppm signals appear
corresponding to the carbon atoms of the aromatic ring. In
the spectra of polysaccarides Vb,Vc, VIb, VIc containing
the residues of the vanillin and the ferulic acids the signals
at δ 56 ppm belong to the methoxy group at the atom С4
of the phenolic acid. The signals of carbon atoms of the
polysaccaride part of compounds V, VI are located in
the region of 60–100 ppm. In the spectra of inulin esters
Vа–Vc signals are additionally observed of the acetyl
group at 168 (С=О) and 20 ppm (СН3).
The IR spectra of inulin esters Vа–Vc contain an ab-
sorption band in the region 1760 cm–1 corresponding to
the acetyl groups of the acetylated phenolic acids, which
is absent in the spectra of compounds VIа–VIc obtained
after the removal of the acetyl protection. In the region
1710–1730 cm–1 the bands characteristic of esters are
observed, and at 1630 and 1510 cm–1 the bands appear
corresponding to the skeletal vibrations of the aromatic
ring. In the spectra of compounds VIа–VIc strong ab-
sorption bands in the region of 3400 cm–1 were assigned
to the stretching vibrations of the “free” hydroxy groups
and the hydroxy groups involved in hydrogen bonds, and
The data on the inulin acylation with the chlorides
of 4-acetoxy derivatives of acid Ia–IIIa are compiled
in the table. The degree of substitution was determined
before the removal of the acetyl protection of the phenol
hydroxy group. The esterification of inulin with acid
chlorides Ia–IIIa in the developed system results in the
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 5 2013

TORLOPOV et al.
704
Conditions and results of inulin acylation with chlorides of
4-acetoxy derivatives of acids Ia–IIIа
both containing the fragments of 4-acetoxy derivatives of
the phenolic acids and the deacetylated fragments of these
acids, are insoluble in water. The samples of obtained
esters VIа–VIc of ferulic, p-hydroxycinnamic, and
vanillic acids with the degree of substitution γ from 0.1 to
0.2 partially dissolve in water giving opalescent solutions,
but, unlike the initial inulin, they are completely soluble
in DMSO and DMF only at heating. Inulin esters Vа–Vc
containing the 4-acetoxy derivatives of the phenolic acids
are well soluble in these organic solvents. The samples
of acylated inulin with γ 0.08–0.1 are soluble in water at
heating, and with lower content of the phenol residues
are well soluble in water. Although these data show that
the introduction of the residues of the phenolic acids
make the polysaccaride molecule more hydrophobic, we
have found inulin esters VIа–VIc with a high content of
the phenolic acid residues, insoluble in water and water
solutions with a neutral pH, to be well soluble in water
at its cautious alkalization to рН 8–9. The esters can be
precipitated from these solutions at their acidification to
рН 2–3. These observations indicate the formation of
intra- and intermolecular “cross-linking” resulting from
the formation of the hydrogen bonds involving the phenol
hydroxy groups which is the main cause of the decreased
solubility of the obtained esters. These hydrogen bonds
can be destroyed by adding bases resulting in the
formation of the corresponding phenolates and in the
dissolution of the obtained phenolic polysaccarides.
Molar ratio phenolcarboxylic
acid–monomer unit of insulin
Degree of
substitution
Acid
Ia
1 : 2
1 : 1
2 : 1
1 : 2
1 : 1
2 : 1
1 : 2
1 : 1
2 : 1
1.02
0.61
0.42
1.13
0.57
0.37
0.98
0.55
0.38
IIa
IIIa
formation of heteropolysaccarides containing fractions
of phenolic acids with the substitution degree γ from 0.1
to 1.1. In the table results are presented corresponding
to the inulin acylation at the relatively high ratios
acetoxyphenylcarboxylic acid chloride–monomer unit of
inulin. At all studied ratios it was found that in the main
reaction about a half of the acyl chloride brought into the
process was consumed.
The acetyl deprotection was carried out under the
action of pyrrolidine or CH3COONH4. These both
compounds are known to be deacetylating agents in the
syntheses of phenol derivatives [12, 13]. However at the
use of pyrrolidine beside the removal of the acetyl group
at the phenol hydroxyl the hydrolysis was observed of
the ester bonds with the carbon leading to a significant
(up to 20%) decrease in the substitution in inulin. The
reduction of the temperature at the acetyl group removal
with pyrrolidine from 25 to 0°C (at the same process
duration) only sightly decreased the hydrolysis of the ester
bond polysaccaride–p-hydroxyphenylcarboxylic acid.
Thus we obtained for the first time inulin esters with
the ferulic, p-hydroxycinnamic, and vanillic acids with a
high substitution degree. The efficient synthesis of these
esters was developed in a heterogenic system CHCl3–
H2O. The developed method can be used in the synthesis
of similar esters of the other water-soluble polysaccarides.
The modified method of removal of the acetyl protection
from the phenol hydroxy group using ammonium acetate
is simple, efficient, and does not affect the ester bonds in
the acylated polysaccaride.
At the use for the deacylation of CH3COONH4 no
decrease was observed in the degree of substitution in the
inulin. Taking into account also the easier procedure of
the deacylation at the use of this salt [13] the application
of CH3COONH4 can be recommended in the preparation
of the other polysaccaride-phenol compounds.
EXPERIMENTAL
13С NMR spectra were registered on a spectrometer
Bruker Avance II 300 (operating frequency 75 МHz) in
DMSO-d6. IR spectra were recorded on an IR Fourier
spectrophotometer Shimadzu IR Prestige 21. Inulin (MP
Biomedicals, LLS, М 5 × 103); ferulic [3-(4-hydroxy-
3-methoxyphenyl)prop-2-enoic], p-hydroxy-cinnamic
[3-(4-hydroxyphenyl)prop-2-enoic], and vanillic
(4-hydroxy-3-methoxybenzoicую) acids purchased from
The solubility of the obtained esters in water decreases
with the growing fraction of the residues of the phenolic
acids in the polysaccaride and does not depend on the
nature of the introduced fragments. The majority of inulin
esters obtained having the substitution degree over 0.1,
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SYNTHESIS OF INULIN ESTERS OF PHENYLCARBOXYLIC ACIDS
705
Sigma-Aldrich were before use recrystallized from aque-
ous ethanol and dried in a vacuum at 80°С. The solvents
before use were purified by standard procedures [14].
of NaOH. To the water solution of inulin cooled to 1–2°С
was added at vigorous stirring 3.1 mmol acyl chloride Ic
in 10 ml of СHCl3. Then within 1 h the temperature of
the reaction mixture was raised to 25°С, and the mixture
was stirred at this temperature for 5 h. In order to isolate
the inulin ester the reaction mixture was poured into 200
ml of 2-propanol, the formed precipitate was separated by
centrifuge, washed with ethanol, and dried in a vacuum
at 60°С. Yield 78%, γ 0.61. IR spectrum, ν, cm–1: 3363
(ОН), 2933 (СН), 1765 (СООН), 1726 (С=О), 1633,
1510 (С–Н, aromatic ring), 1033 (С–О, carbohydrate
skeleton). 13С NMR spectrum, δ, ppm: 20.78, 56.43
(OCH3), 62.60–62.00 (С6',1'), 74.57 (С4'), 77.13 (C3'),
82.00 (С5'), 103.63 (С2'), 112.90, 117.50, 119.73, 121.71,
122.78, 123.92, 132.98, 133.64, 141.29, 142.21, 143.97,
148.41, 151.71, 168.03, 169.09.
The content of phenolic acid in a polysaccaride
(ω, wt%) was determined by spectrophotometry using
Folin–Ciocalteu reagent by the method [10]. With inulin
esters containing fragments of phenolic acids acetoxy
derivatives this analysis was performed after preliminary
hydrolysis of the ester bond and the extraction of phenolic
acids with ethyl acetate by the method [7]. The degree
of substitution γ in the esterified polysaccaride was
calculated by formula (1).
Мmu ωpa
γ = –––––––––––––––––––––
(1)
Мfpa × 100 – (Mfpa – 1)ωpa
Inulin ester with 4-acetoxycinnamic acid (Vb).
γ 0.57. IR spectrum, ν, cm–1: 3408, 2899, 1765, 1707,
1598, 1514, 1066. 13С NMR spectrum, δ, ppm: 21.34,
62.51–62.00 (С6' 1'), 74.82 (С4'), 77.24 (C3'), 89.11 (С5'),
104.14 (С2'), 117.44, 119.78, 122.82, 122.97, 129.29,
130.49, 130.83, 131.96, 132.39, 143.43, 144.15, 146.23,
146.37, 148.13, 152.30, 152.87, 153.22, 163.16, 165.10,
166.18, 167.99, 169.48.
Here Мmu is the molecular weight of thrr monomer
unit of the polysaccaride; ωpa is the content of the
corresponding phenolic acid, wt%; Мfpa is the molecular
weight of the fragment of the phenolic acid (177 for
ferulic, 147 for p-hydroxycinnamic, 151 g/mol for vanillic
acid).
Acetylation of phenolic acids Ia–IIIa was carried ot
by procedure [15].
Inulin ester with 4О-acetylvanillic acid (Vc). γ 0.60.
IR spectrum, ν, cm–1: 3361, 2933, 1764, 1708, 1653,
1514, 1031. 13С, δ, ppm: 20.86, 56.63, 62.16–62.54
(С6',1'), 74.32 (С4'), 77.67 (C3'), 82.53 (С5'), 103.65 (С2'),
113.77, 114.12, 122.33, 122.79, 123.53, 124.14, 127.37,
127.73, 128.07, 141.87, 144.42, 144.58, 150.77, 151.73,
163.45, 168.65.
4О-Acetylferulic acid [3-(4-acetoxy-3-methoxy-
phenyl)prop-2-enoic acid] (Ib). Yield 73%. 13С NMR
spectrum, δ, ppm: 20.84 (OAc), 56.44 (OCH3), 112.32
(C2), 120.00 (C8), 121.79 (C6), 123.66 (C5), 133.73 (C1),
141.29 (C4), 143.80 (C7), 151.62 (C3), 168.06 (C=O),
168.48 (COOH).
4-Acetoxycinnamic acid [3-(4-acetoxy-phenyl)
prop-2-enoic acidа] (IIb). Yield 78%. 13С NMR
spectrum, δ, ppm: 21.32 (OAc), 119.77 (C8), 122.82
(C3,6), 129.89 (C2,6), 132.39 (C1), 143.42 (C7), 152.29
(C4), 167.99 (C=O), 169.48 (СOOH).
Removal of protecting acetyl group. а. In 3 ml of
DMAA was dissolved 200 mg of inulin ester V, 0.1 ml of
water and 3 mol-equiv of pyrrolidine per 1 mol-equiv of
acetyl group was added. The obtained mixture was stirred
for 5 min at 22°С, acidified with 0.25 N water solution of
hydrochloric acid to рН 4.0, and the polysaccaride was
precipitated by adding 20 ml of 2-propanol. The obtained
polymer was separated, washed with ethanol, and the
solvent and moisture were removed by lyophilic drying.
4О-Аcetylvanillic acid (4-acetoxy-3-methoxy-
benzoic acidа) (IIIb). Yield 75%. 13С NMR spectrum,
δ, ppm: 20.83 (OAc), 56.35 (OCH3), 113.62 (C2), 122.60
(C6), 123.52 (C5), 130.02 (C1), 143.42 (C4), 151.27 (C3),
167.11 (COOH), 168.67 (C=O).
b. In 3 ml of DMAA was dissolved 200 mg of inulin
ester V, 3.0 ml of water solution of CH3COONH4 was
added (8 mol-equiv of CH3COONH4 per 1 mol-equiv of
acetyl group). The mixture was stirred for 2 h at 22°С, and
afterwards the polysaccaride was precipitated by adding
20 ml of 2-propanol. The obtained polymer was separated,
washed with ethanol, and the solvent and moisture were
removed by lyophilic drying. Yield 78–86%.
The synthesis of acetoxyphenylcarboxylic acids
chlorides was performed by the method [15]. The
obtained acyl chlorides Ic–IIIc were used in subsequent
syntheses without additional purification.
Inulin ester with 4О-acetylferulic acid (Va). In 12 ml
of water was dissolved 500 mg (3.1 mmol) of inulin, and
at stirring under nitrogen atmosphere was added 3.2 mmol
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 5 2013

TORLOPOV et al.
(Jerusalem Potato for Life Prolonging), St. Petersburg:
706
Inulin ester with ferulic acid (VIa). γ 0.55. IR
Dilya, 2003, 128.
3. Borneo, R. and Leon, A.E., Food Funct., 2012, vol. 3,
p. 110.
4. Cecilia, D., Garcia, M.A., and Vina, S.Z., Food Funct.,
2012, vol. 3, p. 606.
spectrum (KBr), ν, cm–1: 3472 (ОН), 2941 (СН), 1717
(С=О), 1633, 1510 (С–Н, aromatic ring), 1032 (С–О, car-
bohydrate skeleton). 13С NMR spectrum, δ, ppm: 56.60,
63.24–62.88 (С6',1'), 75.64–72.02 (С4'), 80.67–79.54 (C3'),
82.59–82.13 (С5'), 105.34–102.54 (С2'), 116.70, 117.55,
125.81, 127.43, 146.30, 147.77, 166.25.
5. Men’shikova, E.B., Lankin, V.Z., Zenkov, N.K.,
Bondar’, I.A., Krugovykh, N.F., and Trufakin, V.A.,
Okislitel’nyi stress. Prooksidanty i antioksidanty (Oxidative
stress. Prooxydant and antioxydant), Moscow: Slovo, 2006,
p. 554.
6. Kikuzaki, H., Hisamoto, M., Hirose, K., Akiyama, K.,
and Taniguchi, H., J. Agric. Food, Chem., 2002, vol. 50,
p. 2161.
7. Mathew, S. andAbraham, T.E., Food Chem., 2007, vol. 105,
p. 579.
8. Wrigsted, P., Kylli, P., Pitcanen, L. Nousiaine, P.,
Tenkanen, M., and Sipil, J., J. Agric. Food, Chem., 2010,
vol. 58, p. 6937.
Inulin ester with 4-hydroxycinnamic acid (VIb).
γ 0.63. IR spectrum, ν, cm–1: 3494, 2949, 1710, 1602,
1510, 1166. 13С NMR spectrum, δ, ppm: 66.50–60.88
(С6',1'), 76.10–75.64 (C4'), 80.67 (С3'), 82.59–82.15 (С5'),
104.43–102.54 (С2'), 116.30, 117.32, 127.51, 133.75,
146.03, 160.39, 166.34.
Inulin ester with vanillic acid (VIc). γ 0.60. IR
spectrum, ν, cm–1: 3361, 2933, 1716, 1653, 1514, 1031.
13С NMR spectrum, δ, ppm: 56.11, 62.51–60.9 (С6',1'),
74.72–73.34 (С4'), 78.98–77.16 (C3'), 82.74–82.13 (С5'),
103.70–104.43 (С2'), 113.10, 115.65, 121.06, 124.11,
147.79, 151.94, 166.13.
9. Cassano, R., Trombino, S., Muzzalupo, R., Tavano, L., and
Picci, N., Eur. J. Pharm. Biopharm., 2009, vol. 72, p. 232.
10. Cho, Y., Kim, S., Ahn, C., and Je, J., Carb. Pol., 2011, vol.
83, p. 1617.
ACKNOWLEDGMENTS
11. Curcio, M., Puoci, F., Iemma, F., Parisi, O.I., Cirillo, G.,
Spizziri, U.G., and Picci, N., J. Agric. Food, Chem., 2009,
vol. 57, p. 5933.
12. Kylli, P., Nousiainen, P., Biely, P., Sipila, J., Tenkanen, M.,
and Heinonen, M., J. Agric. Food, Chem., 2008, vol. 56,
p. 4797.
The study was carried out under the financial support
of the Council for grants at the President of the Russian
Federation for the support of young Russian scientists
(grant MK 171.2012.3).
13. Ramesh, C., Mahender, G., Ravindranath, N. as B.A.,
Tetrahedron, 2003, vol. 59, p. 1049.
REFERENCES
14. Gordon, A.J. and Ford, R.A., The Chemist’s Companion,
New York: Wiley, 1972.
15. Hosoda, A., Nomura, E., Mizuno, K., and Taniguchi, H.,
J. Org. Chem., 2001, vol. 66, p. 7199.
1. Stevens, C.V., Meriggi,A., and Booten, K., Biomacromol.,
2001, vol. 2, no. 1, p. 1.
2. Artemova, A., Topinambur prodlevayushchii zhizn’
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