Lipase-Catalyzed Solvent-Free Amidation of Phenolic Acids

Article abstract of DOI:10.1080/00397911.2014.974611

A series of N-alkyl-substituted amides, based on various phenolic acids, have been synthesized by the condensation of equimolar amounts of phenolic acids with different alkyl amines in the presence of Candida antarctica lipase at 60-90 °C in 16-20 h. The reactions were carried out in a solvent-free system without the use of any activating agents. All the products were obtained in appreciable amounts and the yields for different compounds varied between 75.6% and 83.5%. The synthesized compounds were characterized using spectroscopy techniques, namely infrared and NMR (¹H and ¹³C). GRAPHICAL ABSTRACT.

Full text of DOI:10.1080/00397911.2014.974611

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Lipase Catalyzed Solvent-Free Amidation of Phenolic
Acids
Parshant Kaushika, Najam Akhtar Shakila, Jitendra Kumara & Braj Bhushan Singha
a Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi, India
Accepted author version posted online: 03 Nov 2014.
To cite this article: Parshant Kaushik, Najam Akhtar Shakil, Jitendra Kumar & Braj Bhushan Singh (2014): Lipase Catalyzed
Solvent-Free Amidation of Phenolic Acids, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, DOI: 10.1080/00397911.2014.974611
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LIPASE CATALYZED SOLVENT-FREE AMIDATION OF PHENOLIC ACIDS
Parshant Kaushik1, Najam Akhtar Shakil1, Jitendra Kumar1, Braj Bhushan Singh1
1Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi,
India
Corresponding author- Najam Akhtar Shakil, Division of Agricultural Chemicals, Indian
Agricultural Research Institute, New Delhi 110012. India E-mail: iamshakil@gmail.com
Abstract
A series of N-alkyl substituted amides, based on various phenolic acids, have been
synthesized by the condensation of equimolar amounts of phenolic acids with different
alkyl amines in presence of Candida antarctica lipase at 60-90°C in 16-20 h. The
reactions were carried out in a non - solvent system without the use of any activating
agents. All the products were obtained in appreciable amounts and the yields for different
compounds varied between 75.6 - 83.5%. The synthesized compounds were characterized
using spectroscopy techniques namely IR and NMR (1H and 13C).
KEYWORDS: Phenolic acids, N-substituted amides, Candida antarctica lipase, Non–
solvent system
INTRODUCTION
Cinnamic acids and their synthetic esters, amides and glycosides exhibit a wide range of
activities, including the anti-oxidative effect on low density lipoprotein (LDL),[1] the
1

peroxyl radical scavenging effect,[2] anti-inflammatory[3] and anti-mutagenic effect.[4] The
cholesterol lowering effect of several hydroxylated cinnamic acid derivatives of amino
acids has been evaluated in mice fed with high cholesterol diets.[5] The presence of double
bond in hydroxylated cinnamide derivatives decreases the cholesterol-lowering activities
and the number of free phenolic hydroxyl groups greatly affects the biological activity.
Amides of phenolic acids having hydrophobic side chains exhibit potent cholesterol
lowering effect.[6] The amides of cinnamic and hydroxycinnamic acids with aliphatic
monoamines have been synthesized and their radical scavenging activity against DPPH
tests have been reported.[7,8] Substituted amides and amines are also important because of
the presence of these functional groups in many compounds having both medicinal as
well as pesticidal activity. They are reported to have antibacterial, antifungal, antiviral,
insecticidal, nematicidal and herbicidal properties.[9-21] Synthesis of these compounds
have mainly been achieved by classical chemical reactions, which generally involve the
generation of a reactive carboxy derivative, either an acid chloride or anhydride, followed
by aminolysis with amine. Also, the conversion of esters to amides has some limitations
as the commonly used reagents, that is, sodium methoxide, sodium hydride, sodium metal
or butyl lithium often interfere with other functional groups present in the reacting
species. Among the many significant advances in organic chemistry, attempts for
environmentally benign processes in organic synthesis have highlighted the importance
of enzyme catalyzed reactions, particularly for large-scale industrial applications.[22]
Enzyme-catalyzed organic reactions have provided a great impetus to organic synthesis
during the last two decades. Enzymes, especially lipases are known for their low cost and
great tolerance towards their substrates. Environmentally benign character of the
2

enzymatic processes is desirable for large scale industrial applications. Even though some
enzyme catalyzed reactions for the synthesis of amides were reported, most of them
involved the use of activating agents or solvents and the bioactivity of these synthesized
compounds was hardly studied.[23-31]
Considering these facts, we got interested in search of new phenolic acids analogues. We
envisaged developing a one-pot biocatalytic amidation procedure by using lipase as
catalyst. In this report, we have carried out C. anatrctica lipase (CAL-B) catalysed
amidation of phenolic acids by different aliphatic amines in bulk (without solvent) at 60-
90 °C.
RESULTS AND DISCUSSION
The condensation of equimolar amount of different phenolic acids namely salicylic acid
(1), 3-hydroxy cinnamic acid (2), p-coumaric acid (3), caffeic acid (4), ferulic acid (5), o-
coumaric acid (6) and cinnamic acid (7) with amines viz propyl amine (8a), hexyl amine
(8b), heptyl amine (8c), undecyl amine (8d), hexadecyl amine (8e) and octadecyl amine
(8f), catalyzed by Candida antarctica lipase (CAL-B) in a non solvent system at 60–90
°C in 16–20 h resulted in the formation of N-propyl-salicylamide (9a), N-hexyl-
salicylamide (9b), N-heptyl-salicylamide (9c), N-undecyl-salicylamide (9d), N-
hexadecyl-salicylamide (9e), N-octadecyl-salicylamide (9f), N-propyl-3-
hydroxycinnamamide (10a), N-hexyl-3-hydroxycinnamamide (10b), N-heptyl-3-
hydroxycinnamamide (10c), N-undecyl-3-hydroxycinnamamide (10d), N-hexadecyl-3-
hydroxycinnamamide (10e), N-octadecyl-3-hydroxycinnamamide (10f), N-propyl-4-
3

hydroxycinnamamide (11a), N-hexyl-4-hydroxycinnamamide (11b), N-heptyl-4-
hydroxycinnamamide (11c), N-undecyl-4-hydroxycinnamamide (11d), N-hexadecyl-4-
hydroxycinnamamide (11e), N-octadecyl-4-hydroxycinnamamide (11f), N-propyl-3,4-
dihydroxycinnamamide (12a), N-hexyl-3,4-dihydroxycinnamamide (12b), N-heptyl-3,4-
dihydroxycinnamamide (12c), N-undecyl-3,4-dihydroxycinnamamide (12d), N-
hexadecyl-3,4-dihydroxycinnamamide (12e), N-octadecyl-3,4-dihydroxycinnamamide
(12f), N-propyl-4-hydroxy-3-methoxycinnamamide (13a), N-hexyl-4-hydroxy-3-
methoxycinnamamide (13b), N-heptyl-4-hydroxy-3-methoxycinnamamide (13c), N-
undecyl-4-hydroxy-3-methoxycinnamamide (13d), N-hexadecyl-4-hydroxy-3-
methoxycinnamamide (13e), N-octadecyl-4-hydroxy-3-methoxycinnamamide (13f), N-
propyl-2-hydroxycinnamamide (14a), N-hexyl-2-hydroxycinnamamide (14b), N-heptyl-
2-hydroxycinnamamide (14c), N-undecyl-2-hydroxycinnamamide (14d), N-hexadecyl-2-
hydroxycinnamamide (14e) N-octadecyl-2-hydroxycinnamamide (14f), N-propyl-
cinnamamide (15a), N-hexyl-cinnamamide (15b), N-heptyl-cinnamamide (15c), N-
undecyl-cinnamamide (15d), N-hexadecyl-cinnamamide (15e), N-octadecyl-
cinnamamide (15f).
The feasibility of non-solvent system was investigated. The reactions with equimolar
amounts of amines 8a-8f and phenolic acids 1-7 were performed (Scheme 1). The
reaction mixture was very viscous and the reaction temperature had to be raised up to 90
°C in order to achieve an efficient stirring in the system. There was a report in
literature[50] where the reaction temperature was maintained at 55 °C for the lipase
catalyzed amidation. In that case, the reaction did not go to completion as some unreacted
4

acid and amine remained in the reaction mixture in salt form even after incubating the
mixture for longer times. Such a situation did not arise in our study as the reaction
temperature was kept between 60-90 °C under reduced pressure. The conversion of acids
to amides was found to be 100% in 75.6-83.5% yields. The synthesized amides were
fully characterized from their spectral data.
In IR spectra, Amide I band due to CO stretching appeared at approximately 1645 cm-1,
Amide II band due to N-H bending appeared at approximately 1560 cm-1 and Amide III
band due to C-N stretching appeared at approximately 1250 cm-1, in all the products
confirmed the condensation of carbonyl group with amino group. In 1HNMR spectra,
quartet at δ 3.15–3.3 for CONH-CH2 and a singlet at δ 7.97-8.31 for the N-H proton were
characteristic of all the synthesized amides. In 13C NMR, the peaks at δ 41.4 – 43.1 for
CONHCH2 and at δ 168–172.4 for CONH were prominent for all the compounds.
In addition to the above mentioned characteristics, bands at approximately 3425 cm-1
(broad multiplet due to N-H stretching), 2932 cm-1 (strong) and 783 cm-1 (strong) were
also present for all the test compounds in IR spectra. In 1HNMR spectra, the signals in δ
range 6.6–7.4 are of aromatic protons (Ar-H), a singlet at δ 4.80-5.29 for Ar-OH, a
singlet at δ 3.7-3.8 for Ar-OCH3 and doublets at δ 6.2-7.7 for vinylic protons were
observed for the synthesized phenolic acid amides.
In 1H NMR spectral analysis, the H-2’ protons of all the propyl derivatives of phenolic
acid amides appear as a multiplet in δ range 1.19-1.68, whereas the aliphatic protons of
5

the side chain of other amides appear in δ range 1.16-1.84. The 1H and 13C NMR of one
representative amide from salicylic acid and phenolic acids is discussed here.
To the best of our knowledge, the results presented in this study demonstrate for the first
time the phenolic acid amide synthesis in non solvent system by the direct lipase
catalyzed reaction of amines with phenolic acids. The present enzymatic procedure offers
some important advantages over the chemical one for the application in industrial
processes.
EXPERIMENTAL
Laboratory grade reagents and solvents were procured from Qualigens. Different amines
were procured from M/S Sigma Aldrich and used as received. Candida antarctica lipase,
an immobilized enzyme, was a gift from Novozymes, Denmark. Thin Layer
Chromatography (TLC) was performed on 200 µm thick aluminium sheets with silica gel
as adsorbent. The solvent system used for developing the TLC plate was ethyl acetate:
hexane, 2:8. Spots were visualized in UV/ iodine chamber. The Infra Red (IR) spectra
were recorded on either a Perkin-Elmer 2000 Fourier Transform Infra Red (FT-IR). The
1HNMR and 13CNMR spectra were recorded on a Bruker AC-300 Avance
spectrophotometer at 400 and 100 MHz, respectively using Tetramethylsilane (TMS) as
an internal standard. The chemical shift (δ) values are expressed in ppm and the coupling
constants (J) values are in Hertz (Hz). The elemental analysis was done on a Eurovector
Elemental analyzer 3000 using sulphanilamide as standard with linear calibration.
6

General Procedure For The Preparation Of N-Alkyl Substituted Phenolic Acid
Amides
A total of forty two phenolic acids based amides were synthesized by the biocatalytic
condensation of different phenolic acids with amines in vacuum, out of which twenty,
that is, 9a, 10a, 10b, 10d, 10e, 10f, 11c, 11d, 11e, 12e, 13d, 13e, 13f, 14b, 14c, 14d, 14e,
14f, 15d and 15e, were reported for the first time in literature (Sch. 1). For the same,
equimolar amounts of different chain length amines and phenolic acids, along with
Candida antarctica lipase enzyme (10% of the total amount of the reactants) were taken
in a 250 mL, two necked round-bottom flask with a magnetic bar (to facilitate stirring)
and was then heated in an oil bath at 60–90 °C. One neck of the round bottom flask was
attached to a pump under vacuum and the other was punctured with a needle to regulate
the pressure inside the round-bottom flask. The different reactions were allowed to
proceed for 16–20 hours. The formation of products was confirmed by Thin Layer
Chromatography (TLC) in ethyl acetate: hexane (2:8) solvent system. After completion,
the reaction was quenched by adding dichloromethane (DCM), followed by filtration to
remove the enzyme. The solvent DCM was then evaporated off in a rotary evaporator.
The different phenolic acids based amides synthesized were purified by column
chromatography to afford the pure amides in 75.6-83.5 % yield. Compounds 9b, 9c, 9d,
9e, 9f, 10c, 11a, 11b, 11f, 12a, 12b, 12c, 12d, 12f, 13a, 13b, 13c, 14a, 15a, 15b, 15c, and
15f) were earlier reported in literature.[32-49]
Spectral Analysis Of Individual Amides Selected Data: N-Propyl-Salicylamide (9a)
7

It was obtained as a reddish brown coloured viscous liquid, after purification by column
chromatography by eluting with 2% ethyl acetate in hexane in 81.4% yield, Rf : 0.46
(ethyl acetate: hexane, 2:8). IR (Nujol) cm-1: 1643 (CO stretching, amide I band), 1557
(N-H bending, amide II band), 1261 (C-N stretching, amide III band), 3403 (N-H
stretching). 1HNMR (400 MHz, DMSO): δ 0.93 (3H, t, J=7.6, H-3’), 1.59–1.68 (2H, m,
H-2’), 2.81 (2H, t, J=7.6, H-1’), 6.71 (1H, d, J=8.4, H-3”), 7.20-7.22 ( 2H, dd, J=8.8 &
2.1 and J= 8.4 & 2.1 each, H-4” & H-5”), 7.74 (1H, d, J=7.6, H-6”) and 8.31 (1H, s, N-
H). 13C NMR (75.5 MHz, DMSO): δ11.1 (C-3’), 24.5 (C-2’), 42.7 (C-1’), 116.5 (C-1’’),
119.0 (C-3’’), 119.3 (C-5’’), 129.6 (C-6’’), 131.7 (C-4”), 161.7 (C-2”) and 172.7 (C-1).
Analyzed for molecular formula C10H13NO2: C, 67.02; H, 7.31; N, 7.82. Found: C, 67.23;
H, 7.26; N, 7.69.
Selected Data: N-Propyl-3-Hydroxycinnamamide (10a)
It was obtained as a dark brown coloured solid, after purification by column
chromatography by eluting with 2% ethyl acetate in hexane in 81.2% yield, Rf : 0.47
(ethyl acetate: hexane, 2:8). IR (Nujol) cm-1: 1650 (CO stretching, amide I band), 1572
(N-H bending, amide II band), 1243 (C-N stretching, amide III band), 3258 (N-H
stretching). 1HNMR (400 MHz, DMSO): δ 0.81 (3H, t, J=6.8, H-3’), 1.56–1.67 (2H, m,
H-2’), 3.19 (2H, t, H-1’), 4.80 (1H, s, Ar-OH); 6.35 (1H, d, J=15.6, H-2), 6.68 (1H, s, H-
2”), 6.75 (1H, dd, J=7.6 & 2.0, H-5” ), 6.94 (1H, d, J=8.0, H-4”), 7.16 (1H, d, J=7.6, H-
6”), 7.24 (1H, d, J=15.6, H-3) and 8.17 (1H, s, N-H). 13C NMR (75.5 MHz, DMSO):
δ14.3 (C-3’), 23.5 (C-2’), 42.5 (C-1’), 114.2(C-4”), 115.7 (C-2”), 118.7 (C-2), 119.1 (C-
6”), 129.0 (C-5”), 136.0 (C-1”), 139.6 (C-3), 158.7 (C-3”) and 170.7 (C-1). Analyzed for
8

molecular formula C12H15NO2: C, 70.22; H, 7.37; N, 6.82. Found: C, 70.15; H, 7.42; N,
6.97.
Selected Data: N-Propyl-4-Hydroxycinnamamide (11a)[36]
It was obtained as a light brown coloured solid, after purification by column
chromatography by eluting with 2% ethyl acetate in hexane in 77.2% yield, Rf : 0.49
(ethyl acetate: hexane, 2:8). IR (Nujol) cm-1: 1654 (CO stretching, amide I band), 1523
(N-H bending, amide II band), 1254 (C-N stretching, amide III band), 3422 (N-H
stretching). 1HNMR (400 MHz, DMSO): δ 0.90 (3H, t, J=8, H-3’), 1.58–1.64 (2H, m, H-
2’), 2.74 (2H, t, J=7.6, H-1’), 4.80 (1H, s, Ar-OH); 6.26 (1H, d, J=16, H-2), 6.78 (2H, d,
J=7.6, H-3” & H-5”), 7.33 (1H, d, J=16, H-3), 7.42 (2H, d, J=8.8,H-2” & H-6”) and 8.17
(1H, s, N-H). 13C NMR (75.5 MHz, DMSO): δ 14.2 (C-3’), 27.5 (C-2’), 43.5 (C-1’),
115.9 (C-3” & C-5”), 119.1 (C-2), 127.6 (C-1”), 130.0 (C-6” & C-2”), 143.1 (C-3), 159.9
(C-4”) and 169.7 (C-1). Analyzed for molecular formula C12H15NO2: C, 70.22; H, 7.37;
N, 6.82. Found: C, 70.35; H, 7.27; N, 7.54.
Selected Data: N-Propyl-3,4-Dihydroxycinnamamide (12a)[36]
It was obtained as a dark brown coloured viscous liquid, after purification by column
chromatography by eluting with 2% ethyl acetate in hexane in 80.4% yield, Rf : 0.46
(ethyl acetate: hexane, 2:8). IR (Nujol) cm-1: 1640 (CO stretching, amide I band), 1559
(N-H bending, amide II band), 1258 (C-N stretching, amide III band), 3423 (N-H
stretching). 1HNMR (400 MHz, DMSO): δ 0.79 (3H, t, J=7.6, H-3’), 1.19–1.39 (2H, m,
H-2’), 3.5 (2H, t, H-1’), 5.05 (1H, s, Ar-OH); 6.42 (1H, d, J=14.8, H-2), 6.52-654( 2H,
9

dd, J=8.0 & 2.0 and J= 8.0 & 2.0 each, H-5” & H-6”), 6.63 (1H, s, H-2”), 7.14 (1H, d,
J=14.8, H-3) and 8.19 (1H, s, N-H). 13C NMR (75.5 MHz, DMSO): δ 11.4 (C-3’), 27.4
(C-2’), 43.1 (C-1’), 113.5 (C-2”), 115.4 (C-5”), 121.0 (C-2), 123.7 (C-6”), 129.6 (C-1”),
139.6 (C-3), 144.8 (C-3”), 145.5 (C-4”) and 170.7 (C-1). Analyzed for molecular formula
C12H15NO3: C, 65.14; H, 6.83; N, 6.33. Found: C, 65.21; H, 6.74; N, 6.52.
Selected Data: N-Propyl-4-Hydroxy-3-Methoxycinnamamide (13a)[43]
It was obtained as a dark red colored solid, after purification by column chromatography
by eluting with 2% ethyl acetate in hexane in 83.6% yield, Rf : 0.49 (ethyl acetate:
hexane, 2:8). IR (Nujol) cm-1: 1645 (CO stretching, amide I band), 1571 (N-H bending,
amide II band), 1254 (C-N stretching, amide III band), 3426 (N-H stretching). 1HNMR
(400 MHz, DMSO): δ 0.82 (3H, t, J=7.2, H-3’), 1.20–1.50 (2H, m, H-2’), 2.70 (2H, t,
J=7.4, H-1’), 3.7 (3H, s, Ar-OCH3) 5.04 (1H, s, Ar-OH); 6.29 (1H, d, J=16, H-2), 6.74
(1H, d, J=8.0, H-6”), 7.01 (1H, d, J=7.6, H-5”) 7.15 (1H, s, H-2”), 7.24 (1H, d, J=16, H-
3) and 7.97 (1H, s, N-H). 13C NMR (75.5 MHz, DMSO): δ 14.2 (C-3’), 27.2 (C-2’), 42.6
(C-1’), 56.0 ( Ar-OCH3), 111.1 (C-2”), 115.9 (C-5”), 119.4 (C-2), 122.9 (C-6”), 127.0
(C-1”), 139.5 (C-3), 144.7 ( C-4”), 148.8 (C-3”) and 170.0 (C-1). Analyzed for molecular
formula C13H17NO3: C, 66.36; H, 7.28; N, 5.95. Found: C, 66.42; H, 7.26; N, 5.89.
Selected Data: N-Propyl-2-Hydroxycinnamamide (14a)[45]
It was obtained as a dark brown coloured solid, after purification by column
chromatography by eluting with 2% ethyl acetate in hexane in 78.7% yield, Rf : 0.49
(ethyl acetate: hexane, 2:8). IR (Nujol) cm-1: 1646 (C O stretching, amide I band), 1567
10

(N-H bending, amide II band), 1223 (C-N stretching, amide III band), 3249 (N-H
stretching). 1HNMR (400 MHz, DMSO): δ 0.91 (3H, t, J=7.2, H-3’), 1.36–1.64 (2H, m,
H-2’), 2.92 (2H, t, J=7.8, H-1’), 5.12(1H, s, Ar-OH), 6.50 (1H, d, J=16, H-2), 6.74 (1H,
d, J=7.6, H-3”), 6.88 (1H, dd, J=8.0 & 1.2, H-5” ), 7.10-7.14 ( 2H, dd, J=8.4 & 1.6, H-4”
), 7.46 (1H, d, J=7.6, H-6”), 7.74 (1H, d, J=16, H-3) and 8.21 (1H, s, N-H). 13C NMR
(75.5 MHz, DMSO): δ 11.9 (C-3’), 26.3 (C-2’), 42.7 (C-1’), 116.6 (C-3”), 119.3 (C-2),
121.2 (C-5”), 122.4 (C-1”), 128.3 (C-6”), 129.1 (C-4”) 140.2 (C-3), 156.9 (C-2”) and
170.5 (C-1). Analyzed for molecular formula C12H15NO2: C, 70.22; H, 7.37; N, 6.82.
Found: C, 7.19; H, 7.33; N, 6.89.
Selected Data: N-Propyl-Cinnamamide (15a)[46]
It was obtained as a dark brown colored viscous liquid, after purification by column
chromatography by eluting with 2% ethyl acetate in hexane in 81.1% yield, Rf : 0.49
(ethyl acetate: hexane, 2:8). IR (Nujol) cm-1: 1642 (CO stretching, amide I band), 1563
(N-H bending, amide II band), 1256 (C-N stretching, amide III band), 3448 (N-H
stretching). 1HNMR (400 MHz, DMSO): δ 0.88 (3H, t, J=7.2, H-3’), 1.37–1.65 (2H, m,
H-2’), 2.75 (2H, t, J=7.6, H-1’), 6.53 (1H, d, J=16, H-2), 7.42 (1H, d, J=16, H-3), 7.3-7.5
(5H, m, Ar-H), 8.04 (1H, s, N-H). 13C NMR (75.5 MHz, DMSO): δ 13.9 (C-3’), 26.5 (C-
2’), 41.9 (C-1’), 119.2 (C-2), 126.3 (C-4”) 127.5 (C-2” & C-6”), 128.6 (C-3” & C-5”),
135.3 (C-1”) 140.1(C-3) and 171.4 (C-1). Analyzed for molecular formula C12H15NO: C,
76.16; H, 7.99; N, 7.40. Found: C, 76.23; H, 7.96; N, 7.45.
CONCLUSION
11

A novel, efficient and environmentally benign method for the synthesis of phenolic acid
amides has been developed, which can be utilized for the synthesis of analogous
compounds as this method avoids the use of activating agents for the conversion of acids
to amides, which is otherwise not possible chemically.
SUPPORTING INFORMATION
Supplemental data for this article can be accessed on the publisher’s website. Please
make the words “publisher’s website” a live DOI link.
ACKNOWLEDGMENT
PK and BBS are grateful to the Department of Science and Technology, New Delhi and
Indian Council of Agricultural Research, New Delhi, respectively for financial assistance.
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16

Scheme 1. Synthesis of phenolic acid amides
17