CAL-B-mediated efficient synthesis of a set of valuable amides by direct amidation of phenoxy- and aryl-propionic acids

Article abstract of DOI:10.1007/s11696-021-01636-5

An efficient, easy and sustainable amidation of a set of non-activated carboxylic acids with anilines, assisted by CAL-B, as biodegradable catalyst, is reported. The enzymatic amidation reactions are performed on set of nonsteroidal anti-inflammatory drugs (NSAIDs), phenoxypropionic acid and protected-prolines by direct condensation of one equivalent of carboxylic acids and two equivalents of anilines derivatives in heptane after 72?h of reaction at 80?°C. The obtained carboxylic amides are recovered with isolated chemical yields varied between moderate and excellent. Fourteen from them are reported for the first time, and an X-ray crystal is obtained for: N-(4-iodophenyl)-2-(4-isobutylphenyl)propanamide 1d.

Full text of DOI:10.1007/s11696-021-01636-5

Chemical Papers
https://doi.org/10.1007/s11696-021-01636-5
ORIGINAL PAPER
CAL‑B‑mediated efcient synthesis of a set of valuable amides
by direct amidation of phenoxy‑ and aryl‑propionic acids
Nourelhouda Benamara1 · Mounia Merabet‑Khelassi1 · Louisa Aribi‑Zouioueche1 · Olivier Riant2
Received: 7 November 2020 / Accepted: 31 March 2021
© Institute of Chemistry, Slovak Academy of Sciences 2021
Abstract
An efcient, easy and sustainable amidation of a set of non-activated carboxylic acids with anilines, assisted by CAL-B, as
biodegradable catalyst, is reported. The enzymatic amidation reactions are performed on set of nonsteroidal anti-infammatory
drugs (NSAIDs), phenoxypropionic acid and protected-prolines by direct condensation of one equivalent of carboxylic acids
and two equivalents of anilines derivatives in heptane after 72 h of reaction at 80 °C. The obtained carboxylic amides are
recovered with isolated chemical yields varied between moderate and excellent. Fourteen from them are reported for the frst
time, and an X-ray crystal is obtained for: N-(4-iodophenyl)-2-(4-isobutylphenyl)propanamide 1d.
Keywords CAL-B · NSAIDs prodrugs · Boc-proline · Direct amidation
Introduction
Hence, catalytic pathways were highlighted as a reaction
of importance from a “green chemistry” perspective (Mon-
talbetti and Falque 2005). On these lights, several works
have been published, using various types of catalysts, for the
direct condensation of a carboxylic acid and amine as envi-
ronmentally benign solution with water as the unique side
product (Zheng and Xu 2011; Lanigan and Sheppard 2013;
De Figueiredo et al. 2016). Since biocatalysis fts very well
with the principles of green chemistry and sustainability, it
seems one of the most attractive, clean, sustainable and more
eco-friendly pathways to the amide structures, especially for
the production of active pharmaceutical ingredients (APIs)
(Lundberg et al. 2012, 2017; Cheng et al. 2018; Chandra
et al. 2020; Sheldon et al. 2020). Among that, hydrolytic
enzymes, and especially lipases (triacylglycerol acyl hydro-
lases, EC.3.1.1.3) as biocatalysts, dominate the synthesis of
amides from carboxylic acids and amines for their ease of
use under mild conditions, recyclability, biodegradability
and for their remarkable chemo-, regio- and enantioselec-
tivity (Sheldon 2016; Arroyo et al. 2017). More recently,
the use of lipases was extended to promiscuous reactions
(Hult and Berglund 2007; Guezane-Lakoud et al. 2017;
Aissa et al. 2019). The most commonly exploited lipases for
the synthesis of primary, secondary and tertiary amides are
the Candida antarctica lipase immobilized on acrylic resin
(CAL-B) (Busto et al. 2010; Lima et al. 2019). This lipase is
robust, highly active, thermostable, biodegradable, a facile
recovery and recyclable, tolerance for polar and non-polar
Amide bonds are a pivot unit in the elaboration and com-
position of biological systems, such peptides and proteins.
Amides as high valuable molecules constitute versatile
synthetic intermediates used in the manufacture of several
pharmacological and biological active products, polymers,
detergents, lubricants, food additives, favors, nutrients and
drug stabilizers (Greenberg et al. 2000; Lundberg et al.
2014; Lima and Porto 2017; Annunziata et al. 2020). The
majority of industrial amidation are based on an activation
of a carboxylic acid by a stoichiometric reagent followed
by nucleophilic displacement with a free amine. This great
importance leads to the American Chemical Society Green
Chemistry Institute to identify amide formation avoiding
poor atom economy process as a priority area of research
for the pharmaceutical industry (Constable et al. 2007).
* Mounia Merabet-Khelassi
mounia.merabet@gmail.com;
mounia.merabet@univ-annaba.dz
1
Ecocompatible Asymmetric Catalysis Laboratory (L.C.A.E),
Badji Mokhtar Annaba-University, B.P. 12, 23000 Annaba,
Algeria
2
Institute of Condensed Matter and Nanosciences Molecules,
Solids and reactiviTy (IMCN/MOST), Université Catholique
de Louvain, Bâtiment Lavoisier. Pl. Louis Pasteur, 1, bte
3. 1348, Louvain La Neuve, Belgium
Vol.:(0123456789)
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Chemical Papers
solvents and broad range of substrates accommodation. It is
also environmentally benign making it attractive for wide
applications in several domains (Kourist et al. 2011; José
et al. 2016; Alalla et al. 2016; Belkacemi et al. 2017; Braia
et al. 2018). Under various reaction conditions, respect-
ing some green chemistry criteria’s, the CAL-B-catalyzed
amidation has been reported for the synthesis of achiral or
enantiopure amides and amines widely used as biopolymers,
building block compounds and drugs (Nechab et al. 2007;
Kaushik et al. 2015; Mouad et al. 2016; Lima et al. 2017;
Manova et al. 2018).
by a chiral stationary phase HPLC on Chiralcel®OJ-H
(4.6 × 250 mm), Chiralpak®OD-H 4.6 × 250 mm,
Chiralpak®IC (4.6 × 250 mm), Chiralpak®IA
(4.6 × 250 mm) and Chiralpak ®IB 4.6 × 250 mm column.
Retention times are reported in minutes. Optical rotations
were determined using a MCP100 polarimeter at room
temperature using a cell of 1‐dm length and λ = 589 nm.
Enzymatic amidation of non‑activated carboxylic
acids
Previously, we have reported a clean and eco-compatible
pathway for both N-benzoylation and N-acetylation of ani-
lines, amines, diamines and aminoalcohols using activated
enol-esters, under free catalyst conditions (Alalla et al.
2014).
To a solution of 2 mmol amine and the 1 mmol carboxylic
acid dissolved in 1 mL of heptane, 50 mg of the molecular
sieves 4 Å and 50 mg of the immobilized CAL-B are intro-
duced. The reaction mixture is stirred at 80 °C for 72 h.
After cooling, the solvent is evaporated and the crude resi-
due was exposed to a standard acido-basic treatment (HCl,
3 M/3 M NaOH). The solvent was removed in vacuo, and
the residue was crystallized in hexane, or purifed by fash
chromatography if necessary. As a control reaction, the
same procedure is followed without introducing lipase. All
In the present paper, we describe our study on the enzy-
matic amidation of some 2-aryl-propionic acids (profens)
with aniline as the nitrogen source. This family of mole-
cules considered as one of the most important non-steroi-
dal anti-infammatory drugs (NSAIDs). The amidation of
a phenoxypropionic acid and some protected-prolines is
also reported. At the best of our knowledge, the applica-
tion of this approach for the amidation of profens has never
described yet by others.
the synthesized amides are characterized by 1H NMR, 13
C
NMR spectra and HRMS. Melting points were determined.
Separation conditions on chiral HPLC were established.
Optical rotations of proline amides 4a–5e were measured.
Materials and methods
2‑(4‑Isobutylphenyl)‑N‑phenylpropanamide (1a)
General information
White solid. mp: 151 °C. Yield: 40%. Rf = 0.52 (CH2Cl2).
1H NMR (300 MHz, CDCl3) δ 7.35–7.33 (d, J = 7.7 Hz,
2H), 7.22–7.15 (m, 4H), 7.08–6.95 (m, 4 H), 3.65–3.5 (q,
J = 7.2 Hz, 1H), 2.41–2.38 (d, J = 7.2 Hz, 2H), 1.83–1.72
(m, 1H), 1.52–1.5 (d, J = 7.2 Hz, 3H), 0.84–0.82 (d,
J = 6.6 Hz, 6H). 13C NMR (75 MHz, CDCl3) δ 172.6
(C=O amide), 141.1, 138.0, 137.9, 129.8, 128.9, 127.4,
124.1, 119.6, 47.7, 45.0, 30.2, 22.4, 18.5. HRMS (ESI+)
m/z (found): 304.1675, Calculated: 304.16718.
All starting materials and reagents used in this study were
obtained commercially from Sigma-Aldrich, Acros, TCI or
Alfa Aesar and were used as received. The Candida antarc-
tica lipase immobilized on acrylic resin CAL-B was pur-
chased from Sigma-Aldrich. Specifc activity >10,000 U/g
was used without any pre-treatment. All reactions were
monitored by thin-layer chromatography (TLC)carried out
on 0.25 mmE. Merck silica gel plates (60F-254) use UV
light (254 nm) as the visualizing agent and ninhydrine solu-
tion and heat as developing agents.
NMR spectra were recorded on Brucker spectrometers
2‑(4‑Isobutylphenyl)‑N‑(p‑tolyl)propanamide (1b)
1
(300 MHz for H, 75 MHz for 13C). Chemical shifts are
reported in δ ppm from tetramethylsilane with the sol-
White solid. mp: 115 °C. Yield: 90%. Rf = 0.41(CH2Cl2).
1H NMR (300 MHz, CDCl3) δ 7.23–7.16 (m, 4H), 7.16
(bs, 1H), 7.07–7.04 (d, J = 8.1 Hz, 2H), 6.98–6.96 (d,
J = 8.3 Hz, 2H), 3.63–3.56 (q, J = 7.1 Hz, 1H), 2.39–2.37
(d, J = 7.2 Hz, 2H), 2.19 (s, 3H); 1.82–1.69 (m, 1H),
1.50–1.48 (d, J = 7.1 Hz, 3H), 0.83–0.81 (d, J = 6.6 Hz,
6H).13C NMR (75 MHz, CDCl3) δ 172.5 (C=O amide),
140.9, 138.2, 135.4, 133.7, 129.8, 129.3, 127.4, 119.7,
47.6, 45, 33.9, 30.2, 25.6, 25, 22.4, 20.8, 18.5. HRMS
(ESI+)m/z (found): 296.20071, Calculated: 296.20089.
1
vent resonance as the internal standard for H NMR and
chloroform-d (δ 77.0 ppm) for 13CNMR. Coupling con-
stants (J) are given in hertz. The following abbreviations
classify the multiplicity: s=singlet, d=doublet, t=triplet,
q = quartet, m = multiplet, br = broad signal. The mass
spectra were obtained from the mass-service at Univer-
sité catholique de Louvain (FINNIGAN-MAT TSQ 7000
and FINNIGAN-MAT LQC spectrometers). Conversions
were evaluated by measuring of enantiomeric excesses
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2‑(4‑Isobutylphenyl)‑N‑(4‑(trifuoromethyl)phenyl)
propanamide (1c)
2‑(4‑Isobutylphenyl)‑N‑(4‑methoxyphenyl)propanamide
(1g)
White crystalline solid. mp: 140 °C. Yield: 72%. Rf =0.37
White crystalline solid. mp: 100 °C. Yield: 60%. Rf =0.64
1
1
(CH2Cl2). H NMR (300 MHz, CDCl3) δ 7.48–7.41
(CH2Cl2). H NMR (300 MHz, CDCl3) δ 7.28–7.20
(q, J = 9 Hz, 4H), 7.32 (bs, 1H), 7.19–7.03 (m, 4 H),
3.68–3.61 (q, J = 7.1 Hz, 1H), 2.41–2.39 (d, J = 7.2 Hz,
2H), 1.84–1.75 (m, 1H), 1.53–1.50 (d, J = 7.2 Hz, 3H),
0.85–0.82 (d, J=6.6 Hz, 6H). 13C NMR (75 MHz, CDCl3)
δ 171.9 (C=O amide), 140.9, 139.9, 136.5, 128.9, 128.2,
126.3, 126, 125.1, 125, 121.2, 118.1, 124.6, 59.6, 46.7,
43.9, 29.1, 21.3, 17.4, 13. HRMS (ESI+)m/z (found):
350.17251, Calculated: 350.17263.
(m, 4H), 7.11–7.09 (d, J = 8.1 Hz, 2H), 6.94 (bs, 1H),
6.77–6.74 (m, 2H), 3.71 (s, 3H), 3.66–3.59 (q, J = 7.2 Hz,
1H), 2.43–2.41 (d, J = 7.2 Hz, 2H), 1.86–1.77 (m, 1H),
1.55–1.52 (d, J = 7.2 Hz, 3H), 0.87–0.85 (d, J = 6.6 Hz,
6H).13C NMR (75 MHz, CDCl3) δ 172.4 (C=O amide),
156.2, 141, 138.1, 131, 129.8, 127.4, 121.4, 114, 55.4,
47.5, 45, 30.2, 22.4, 18.5. HRMS (ESI+) m/z (found):
312.19586, Calculated: 312.19581.
N‑(4‑Iodophenyl)‑2‑(4‑isobutylphenyl)propanamide (1d)
N‑Benzyl‑2‑(4‑isobutylphenyl)propanamide (1 h)
White crystalline solid. mp: 131 °C. Yield: 55%. Rf =0.82
White powder. mp: 49 °C. Yield: 34%. Rf =0.21 (CH2Cl2).
1H NMR (300 MHz, CDCl3) δ 7.29–7.12 (m, 9H), 5.66
(bs, 1H), 4.43–4.41(d, J = 5.8 Hz, 2H), 3.64–3.57(q,
J = 7.2 Hz, 1H), 2.49–2.46 (d, J = 7.2 Hz, 2H), 1.91–1.82
(m, 1H), 1.59–1.56 (d, J = 7.2 Hz, 3H), 0.93–0.91 (d,
J = 6.6 Hz, 6H). 13C NMR (75 MHz, CDCl3) δ 174.3
(C=O amide), 140.8, 138.4, 129.6, 128.5, 127.3, 127.3,
46.8, 45, 43.5, 30.2, 22.3, 18.4. HRMS (ESI+) m/z
(found): 318.1828, Calculated: 318.18283 [M + Na]+
(C20 H25 NONa).
1
(CH2Cl2). H NMR (300 MHz, CDCl3) δ 7.49–7.46
(d, J = 8.8 Hz, 2H), 7.24–6.93 (m, 7H), 3.63–3.56 (q,
J = 7.1 Hz, 1H), 2.41–2.38 (d, J = 7.2 Hz, 2H), 1.83–1.48
(m, 1H), 1.53–1.50 (d, J = 7.2 Hz, 3H), 0.84–0.82 (d,
J = 6.6 Hz, 6H).13C NMR (75 MHz, CDCl3) δ 171.9
(C=O amide), 140.5, 137, 136.9, 129.2, 126.6, 120.7, 86.1,
47, 44.2, 29.4, 21.6, 17.7. HRMS (ESI+) m/z (found):
408.08187, Calculated: 408.08188.
N‑(4‑Bromophenyl)‑2‑(4‑isobutylphenyl)propanamide (1e)
2‑(3‑Benzoylphenyl)‑N‑phenylpropanamide (2a)
White crystalline solid. mp: 124 °C. Yield: 50%. Rf =0.85
1
(CH2Cl2). H NMR (300 MHz, CDCl3) δ 7.51–7.10
White solid. mp: 90 °C. Yield: 30%. Rf = 0.11 (CH2Cl2).
1H NMR (300 MHz, CDCl3) δ 7.82–7.06 (ma, 15H),
3.78(q, J=7.1 Hz, 1H), 1.60 (d, J=7.1 Hz, 3H). 13C NMR
(75 MHz, CDCl3) δ 196.6 (C=O Benzoyl-), 171.7(C=O
amide), 153.8, 141.8, 141.6, 138.1, 137.8, 137.3, 132.6,
132.5, 131.4, 131.3, 130.08, 130.03, 129.3, 129.2, 129.1,
128.9, 128.8, 128.7, 128.3, 128.3, 124.3, 119.8, 50.1, 47.9,
45.2, 32.7, 32.5, 31.1, 30.6, 26.1, 26.1, 25.4, 25.2, 24.7,
20.5, 18.8. HRMS (ESI+) m/z (found): 330.148, Calcu-
lated: 330.14886.
(m, 8H), 7.06 (bs,1H), 3.74–3.67 (q, J = 7.2 Hz, 1H),
2.51–2.49 (d, J = 7.2 Hz, 2H), 1.93–1.84 (m, 1H),
1.62–1.59 (d, J = 7.1 Hz, 3H), 0.94–0.92 (d, J = 6.6 Hz,
6H). 13C NMR (75 MHz, CDCl3) δ172.5 (C=O amide),
141.2, 137.7, 136.9, 131.8, 129.9, 127.4, 121.1, 47.7, 45,
30.1, 22.3, 18.4. HRMS (ESI+) m/z (found): 360.09582,
Calculated: 360.09575.
N‑(4‑Chlorophenyl)‑2‑(4‑isobutylphenyl)propanamide (1f)
White crystalline solid. mp: 113 °C. Yield: 45%. Rf =0.84
2‑(3‑Benzoylphenyl)‑N‑(p‑tolyl)propanamide (2b)
1
(CH2Cl2). H NMR (300 MHz, CDCl3) δ 7.31–7.28
(d, J = 8.8 Hz, 2H), 7.24–6.93 (ddd,, J = 19.2, 13.8,
8.2 Hz,7H), 3.65–3.58 (q, J = 7.1 Hz, 1H), 2.42–2.39
(d, J = 7.2 Hz, 2H), 1.84–1.75 (m, 1H), 1.52–1.50 (d,
J = 7.1 Hz, 3H), 0.85–0.83 (d, J = 6.6 Hz, 6H).13C NMR
(75 MHz, CDCl3) δ 172.7 (C=O amide), 141.2, 137.8,
129.9, 129.1, 128.8, 127.4, 120.9, 136.4, 47.7, 45, 30.2,
22.4, 18.4. HRMS (ESI+) m/z (found): 316.14623, Cal-
culated: 316.14627.
White solid. mp: 118 °C. Yield: 25%. Rf =0.11 (CH2Cl2). 1H
NMR (300 MHz, CDCl3) δ 7.75–7.71 (m, 3H), 7.64–7.50
(m, 3H), 7.43–7.38 (m, 3H), 7.27–7.24 (d, J=8.4 Hz, 2H),
7.03–7.00 (d, J = 8.2 Hz, 3H), 3.72–3.65 (q, J = 7.1 Hz,
1H), 2.22 (s, 3H), 1.55–1.53 (d, J=7.1 Hz, 3H). 13C NMR
(75 MHz, CDCl3) δ 196.6 (C=O Benzoyl-), 171.6 (C=O
amide), 156.8, 141.6, 138, 137.3, 135.2, 133.9, 132.6, 131.5,
130, 129.4, 129.3, 129.2, 128.9, 128.3, 119.9, 47.8, 25.5,
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24.9, 18.8. HRMS (ESI+) m/z (found):247.1783, Calcu-
lated: 247.17808.
2H), 7.02–6.90 (m, 3H), 4.78–4.71(q, J=6.8 Hz, 1H), 2.24
(s, 3H), 1.61–1.59 (d, J=6.8 Hz, 3H). 13C NMR (75 MHz,
CDCl3) δ 170.6 (C=O amide), 156.5, 140.1, 130, 126.3,
126.2, 122.7, 119.5, 115.8, 75.4, 18.6. HRMS (ESI+) m/z
(found): 332.0869, Calculated: 332.08688 [M+Na]+(C16
H14 N O2 F3 Na).
2‑(2‑Fluoro‑[1,1′‑biphenyl]‑4‑yl)‑N‑phenylpropanamide
(3a)
White solid. mp: 177 °C. Yield: 60%. Rf =0.48 (CH2Cl2).
1H NMR (300 MHz, CDCl3) δ 7.50–7.03 (ma, 14H),
3.70–3.63 (q, J = 7.1 Hz, 1H), 1.57–1.55 (d, J = 7.1 Hz,
3H). 13C NMR (75 MHz, CDCl3) δ 170.6 (C=O amide),
141.4, 136.8, 134.4, 130.4, 128.1, 128.09, 128.05, 127.6,
126.9, 123.6, 122.7, 118.9, 114.6, 114.3, 46.7, 17.8. HRMS
(ESI+) m/z (found): 320.14450, Calculated: 320.14452.
N‑(4‑Methoxyphenyl)‑2‑phenoxypropanamide (4d)
White crystalline solid. mp: 127 °C. Yield: 90%. Rf =0.50
1
(CH2Cl2). H NMR (300 MHz, CDCl3) δ 8.04 (bs, 1H),
7.37–7.34 (m, 2H), 7.27–7.18 (m, 2H), 6.98–6.88 (m, 3H),
6.79–6.76 (m, 2H), 4.73–4.67 (q, J=6.7 Hz), 3.70 (s, 3H),
1.59–1.57 (d, J=6.2 Hz, 3H). 13C NMR (75 MHz, CDCl3)
δ 170.6 (C=O amide), 156.7, 156.6, 130.1, 129.9, 122.4,
121.7, 115.7, 114.1, 75.4, 55.4, 18.7.
2‑(2‑Fluoro‑[1, 1′‑biphenyl]‑4‑yl)‑N‑(p‑tolyl)propanamide
(3b)
White crystalline solid. mp: 128 °C. Yield: 66%. Rf =0.47
(CH2Cl2).1H NMR (300 MHz, CDCl3) δ 749–7.01 (ma,
13H), 3.69–3.61 (q, J=7.1 Hz, 1H), 2.22 (s, 3H), 1.56–1.54
(d, J = 7.1 Hz, 3H). 13C NMR (75 MHz, CDCl3) δ 171.5
(C=O amide), 142.4, 142.3, 135.3, 135.14, 134.13, 131.2,
129.4, 128.96, 128.92, 128.5, 127.7, 123.6, 119.9, 115.5,
115.2, 47.5, 20.8, 18.6. HRMS (ESI+) m/z (found):
334.16004, Calculated: 334.16017.
N‑(4‑Iodophenyl)‑2‑phenoxypropanamide (4e)
White crystalline solid. mp: 147 °C. Yield: 98%. Rf =0.92
1
(CH2Cl2). H NMR (300 MHz, CDCl3) δ 8.16 (bs, 1H),
7.56–7.53 (m, 2H), 7.28–7.23 (m, 4H), 7.08–6.88 (m, 3H),
4.74–4.67(q, J = 6.8 Hz, 1H), 1.59–1.56 (d, J = 6.8 Hz,
3H). 13C NMR (75 MHz, CDCl3) δ 170.3 (C=O amide),
156.5, 137.9, 136.8, 129.9, 122.6, 121.8, 115.7, 88, 75.4,
18.6. HRMS (ESI+) m/z (found): 368.01409, Calculated:
368.01420.
2‑Phenoxy‑N‑phenylpropanamide (4a)
White solid. mp: 120 °C. Yield: 89%. Rf =0.48 (CH2Cl2).
1H NMR (300 MHz, CDCl3) δ 8.13 (bs, 1H), 7.48–7.45
(m, 2H), 7.28–7.23 (t, J=7.8 Hz, 4H), 7.08–6.90 (m, 4H),
4.75–4.68 (q, J = 6.8 Hz, 1H), 1.60–1.58 (d, J = 6.8 Hz,
3H). 13C NMR (75 MHz, CDCl3) δ 170.2 (C=O amide),
156.7, 137, 129.9, 129, 124.7, 122.4, 119.96, 115.7, 76.6,
18.7. HRMS (ESI+) m/z (found):264.0996, Calculated:
264.0995.
N‑(4‑Bromophenyl)‑2‑phenoxypropanamide (4f)
White crystalline solid. mp: 132 °C. Yield: 80%. Rf =0.88
1
(CH2Cl2). H NMR (300 MHz, CDCl3) δ 8.16 (bs, 1H),
7.39–7.17 (m, 6H), 6.99–6.87 (m, 3H), 4.73–4.66(q,
J = 6.8 Hz, 1H), 1.58–1.55 (d, J = 6.8 Hz, 3H). 13C NMR
(75 MHz, CDCl3) δ 169.1 (C=O amide), 155.3, 134.9,
130.7, 121.3, 120.3, 116.1, 114.5, 128.7, 74.2, 17.4. HRMS
(ESI+) m/z (found): 320.02809, Calculated: 320.02807.
2‑Phenoxy‑N‑(p‑tolyl) propanamide (4b)
N‑(4‑Chlorophenyl)‑2‑phenoxypropanamide (4g)
White solid. mp: 117 °C. Yield: 85%. Rf =0.41 (CH2Cl2).
1H NMR (300 MHz, CDCl3) δ 8.09 (bs, 1H), 7.36–7.18 (m,
4H), 7.06–6.89 (m, 5H), 4.74–4.67 (q, J=6.8 Hz, 1H), 2.24
(s, 3H), 1.59–1.57 (d, J=6.8 Hz, 3H). 13C NMR (75 MHz,
CDCl3) δ 170.1 (C=O amide), 156.7, 134.5, 134.3, 129.9,
129.5, 122.4, 120, 115.7, 75.4, 20.9, 18.7. HRMS (ESI+)
m/z (found):278.1154, Calculated: 279.11515 [M+Na]+
(C16 H17 N O2 Na).
White crystalline solid. mp: 137 °C. Yield: 87%. Rf =0.83
1
(CH2Cl2). H NMR (300 MHz, CDCl3) δ 8.17 (bs, 1H),
7.43–7.40 (m, 1H), 7.27–7.18(m, 4H), 6.99–6.87 (m, 3H),
4.73–4.66(q, J=6.8 Hz, 1H), 1.57–1.55 (d, J=6.8 Hz, 3H).
13C NMR (75 MHz, CDCl3) δ 170.3 (C=O amide), 156.6,
135.6, 129.9, 129.6, 129, 122.5, 121.2, 115.7, 135.6, 75.4,
18.6. HRMS (ESI+) m/z (found): 276.07867, Calculated:
276.07858.
2‑Phenoxy‑N‑(4‑(trifuoromethyl)phenyl)propanamide (4c)
N‑Benzyl‑2‑phenoxypropanamide (4h)
White solid. mp: 123 °C. Yield: 92%. Rf =0.11 (CH2Cl2). 1H
NMR (300 MHz, CDCl3) δ 8.31 (bs, 1H), 7.63–7-50 (dd,
J=32.2 & 8.6 Hz, 4H), 7.30–7.19 (dt, J=18.8 & 12.1 Hz,
White solid. mp: 220 °C. Yield: 64%. Rf =0.16 (CH2Cl2).
1H NMR (300 MHz, CDCl3) δ 8.17 (bs, 1H), 7.43–7.40 (m,
1 3

Chemical Papers
1H), 7.27–7.18 (m, 4H), 6.99–6.87 (m, 3H), 4.73–4.66 (q,
J = 6.8 Hz, 1H), 1.57–1.55 (d, J = 6.8 Hz, 3H). 13C NMR
(75 MHz, CDCl3) δ 170.3 (C=O amide), 156.6, 135.6,
129.9, 129.6, 129, 122.5, 121.2, 115.7, 135.6, 75.4, 18.65.
HRMS (ESI+) m/z (found): 279.20659, Calculated:
279.20635.
128.7, 120.6, 137, 80.9, 60.4, 47.2, 28.4, 27.6, 24.5. HRMS
(ESI+) m/z (found):325.13137, Calculated: 325.13135.
[α]20D (c 1,CH2Cl2) -101.9
Tert‑butyl (S)‑2‑((4‑bromophenyl)carbamoyl)
pyrrolidine‑1‑carboxylate (5e)
Tert‑butyl (S)‑2‑(phenylcarbamoyl)
pyrrolidine‑1‑carboxylate (5a)
Brown crystalline solid. mp: 193 °C. Yield: 60%. Rf =0.28
1
(AcOEt/Petroleum Ether: 2/8). H NMR (300 MHz,
CDCl3) δ 9.68 (bs, 1H), 7.39–7.28 (m, 4H), 4.48 (bs, 1H),
3.49–3.40 (m, 2H), 2.37–1.89 (m, 4H), 1.50 (s, 9H). 13C
NMR (75 MHz, CDCl3) δ 170.2 (C=O amide), 156.3,
137.5, 131.7, 121, 116.1, 121.4, 80.9, 60.5, 47.2, 28.4, 27.6,
24.5. HRMS (ESI+) m/z (found): 391.06272, Calculated:
White crystalline solid. mp: 187 °C. Yield: 52%. Rf =0.28
1
(AcOEt/Petroleum Ether: 2/8). H NMR (300 MHz,
CDCl3) δ 9.49 (bs, 1H), 7.54–7.51 (dd, J=8.6, 1.0 Hz, 2H),
7.30–7.28 (m, 2H), 7.08 (bs, 1H), 4.48 (bs, 1H), 3.46 (bs,
2H), 2.52–1.80 (m, 4H), 1.50 (s, 9H).13C NMR (75 MHz,
CDCl3) δ 169.9 (C=O amide), 156.56, 138.3, 128.9, 123.8,
119.65, 80.9, 60.5, 47.2, 28.3, 27.1, 24.5. HRMS (ESI+)
m/z (found): 291.17023 Calculated: 291.17032. [α]20D (c
1,CH2Cl2) − 147.3 (− 147.3; Litt: − 140.9 (Doherty et al.
2008; Kanemitsu et al. 2012)).
391.06278 [M + Na]+ (C16 H21 N2 79Br 23Na). [α]20 (c 1,
D
CH2Cl2) -92.1
Results and discussion
Firstly, we have examined the efciency of the amidation
reaction conditions. For thus, we have selected four carbox-
ylic acids: ibuprofen 1, ketoprofen 2, furbiprofen 3, and the
phenoxypropionic acid 4 and diverse anilines derivatives,
having diferent electronic efects, as well as benzylamine.
All condensation experiments were performed on one
equivalent of carboxylic acids or ester, two equivalents of
aniline and 50 mg of CAL-B (>10,000 U/g) diluted in 1 mL
of heptane. 50 mg of molecular sieves 4 Å are added. The
suspensions were stirred at 80 °C for 72 h. The reactions
mixtures were diluted in ethyl acetate and fltered. The
amides formed were recovered by acido-basic liquid–liquid
extraction. The structures of the formed amides were char-
acterized by usual spectroscopic analyses (NMR 1H, NMR
13C and HRMS). The conversions were determined by chiral
HPLC (Scheme 1).
Tert‑butyl (S)‑2‑(p‑tolylcarbamoyl)
pyrrolidine‑1‑carboxylate (5b)
White crystalline solid. mp: 181 °C. Yield: 72%. Rf =0.28
1
(AcOEt/Petroleum Ether: 2/8). H NMR (300 MHz,
CDCl3) δ 9.37 (bs, 1H), 7.42–7.10 (m, 4H arm), 4.46 (bs,
1H), 3.46 (bs, 2H), 2.52–1.94 (m, 4H), 2.32 (s, 3H), 1.50
(s, 9H).13C NMR (75 MHz, CDCl3) δ 169.7 (C=O amide),
135.7, 134.9, 129.4, 119.6, 80.8, 60.4, 47.1, 28.3, 24.3,
20.8. HRMS (ESI+) m/z (found):305.18571, Calculated:
305.18597. [α]20D (c 1, CH2Cl2) −111.7
Tert‑butyl(S)‑2‑((4‑(trifuoromethyl)phenyl)carbamoyl)
pyrrolidine‑1‑carboxylate (5c)
White crystalline solid. mp: 185 °C. Yield: 72%. Rf =0.35
(AcOEt/Petroleum Ether: 2/8). 1H NMR (300 MHz, CDCl3)
δ 9.92 (bs, 1H), 7.59–7.46 (m, 4H), 4.53 (bs, 1H), 3.53–3.42
(m, 2H), 2.42–1.96 (m, 4H), 1.52 (s, 9H). 13C NMR
(75 MHz, CDCl3) δ 170.7 (C=O amide), 156.3, 166.7,
141.5, 129.5, 122.3, 118.9, 100.2, 125.9, 81, 60.5, 47.3,
28.4, 27.6, 24.5. HRMS (ESI+) m/z (found):359.15763,
Calculated: 359.15770. [α]20D (c 1,CH2Cl2) − 127.5
The enzymatic amidation displays a broad variety of
results and ofers the synthesized amides with variable yields
between 25%≤ Yield≤ 98%. These diferences depend on
the structure of the carboxylic acid and the electronic and
steric efects of the primary amines.
The enzymatic amidation of the ibuprofen 1 with ani-
lines possessing diferent substituents on para- position,
from strong electro-donating to strong electron-withdraw-
ing efects (–CH3, –CF3, –OMe, I, Br, –Cl), gave the cor-
responding amides in good-to-excellent yields. The use of
p-toluidine increases signifcantly the conversion rates and
the isolated yields compared to the aniline. The recorded
yields are 90% and 40%, respectively; the same efect was
notifed with the p-CF3-aniline. The amidoprofen 1c was
isolated with 72% of yield. The use of the p-Cl-aniline, p-Br-
aniline, p-I-aniline and the p-OMe-aniline gave the amido-
profens (1d–1g) with acceptable yields varying from 45 to
Tert‑butyl (S)‑2‑((4‑chlorophenyl)carbamoyl)
pyrrolidine‑1‑carboxylate (5d)
White crystalline solid. mp: 185 °C. Yield: 58%. Rf =0.28
1
(AcOEt/Petroleum Ether: 2/8). H NMR (300 MHz,
CDCl3) δ 9.66 (bs, 1H), 7.45–7.21(m, 4H), 4.48 (bs, 1H),
3.50–3.40 (m, 2H), 2.43–1.80 (m, 4H), 1.50 (s, 9H). 13C
NMR (75 MHz, CDCl3) δ 170.2 (C=O amide), 156.3,
1 3

Chemical Papers
Scheme 1 Enzymatic amidation of carboxylic acids (1–4) by means
of anilines. Reaction Conditions: 1 mmol of carboxylic acid, 2 mmol
of aniline derivatives, 50 mg of molecular sieves 4 Å and 50 mg of
CAL-B in 1 mL of heptane at 80 °C for 72hours. (a) Isolated yield. (b)
(c)
Conversion: C=eeS/eeP +ees. Monitored by TLC. ND: Not deter-
mined
60%. The use of benzylamine instead of anilines decreases
signifcantly the yield of the formed amidoprofen to 34%. On
the same lines, the enzymatic amidation of the ketoprofen
2 and the furbiprofen 3 using aniline and p-toluidine as the
amidation partners is very diferent. While the amidation of
the ketoprofen 2 was hardly performed (25–30% of isolated
yields), those of the furbiprofen 3 were reached 60–66% of
isolated yields.
arylpropionic acids (profens) 1–3. The carboxylic amides
(4a–4g) are recovered with good-to-excellent isolated yields
(89% to 98%), with total conversions. The same observa-
tion is recorded when benzylamine is used instead anilines;
the corresponding amide is obtained with 64% yield. The
amide structures (4c–4g) are reported for the frst one. Using
the p-CF3-aniline, as the amidation partner, the reaction is
widely improved by the presence of the CAL-B as catalyst;
the corresponding amide is isolated with 92% yield. From all
the synthesized amidoprofens, the structures 1c, 1d, 1e, 2b
Moreover, the enzymatic amidation of the phenoxypro-
pionic acid 4 was performed very smoothly compared to the
1 3

Chemical Papers
and 3b are reported for the frst time. The 1d is demonstrated
by X-ray data (CCDC deposition number: 1943833).
The reported conditions of the CAL-B catalyzed direct
amidation allow easily to potent carboxylic amides with
a high atom economy and chemical yields depend to the
acid structure. Since the CAL-B is recyclable and biode-
gradable, the unique considered waste is water. At the best
of our knowledge, the enzymatic amidation of those acid
structures, especially, the NSAIDs ones, is described for the
frst time. It is a cleaner and safer approach with low envi-
ronmental impact process.
the aminolysis using aniline and benzylamine by means of
coupling agents was described for the synthesis of the cor-
responding amides which were used as a potential organo-
catalysts in the aldolization and imine hydrogenation reac-
tions and exploited without Boc-moiety cleavage (Galanakis
et al. 2004). It is well known that several described ways for
amidation of aminoacids sufer of serious problem of the
loss of the enantiopurity or racemization. In our case, we
have applied the optimal enzymatic amidation on the L-Boc-
proline, commercially available, with aniline derivatives
(Scheme 3). All the obtained amide structures are confrmed
by the usual spectroscopic data. Their enantiomeric purity
was examined by the measurement of the optical rotations
and compared to the literature data for the known structures.
The amidation of the L-Boc-proline without lipase is
performed smoothly by the fve anilines. The amides are
furnished with various yields from 52 to 72% and that
depending on the electronic efects due to the substituent
on para- position of aniline. It is to be underlined that the
thermal amidation, without the use of lipase, is possible but
with less yields and longer reaction time. The presence of
a hydrolytic enzyme improves signifcantly the amidation,
especially in the case of p-CF3-aniline, and no cleavage of
In order to valorize this simple and easy approach, we
have done a gram scale reaction. We have applied the opti-
mal conditions on 6 mmol (1 g) of phenoxypropionic acid 4
with 6 mmol (0.193 g) of p-CF3-aniline and 300 mg of CAL-
B. The enzymatic amidation is reproducible, and the amide
is isolated with 93% yields. We have recovered and reused
the CAL-B lipase in second and third times. The amides are
obtained with 92% and 88% yields (Scheme 2), showing that
until the third use the lipase keeps its performance.
To further extend this enzymatic approach, we have envis-
aged to applying it for the amidation of a protected amino
acid, the Boc-proline. At the best of our knowledge, only
Scheme 2 Gram-scale CAL-B
catalyzed amidation of 4 with
p-CF3-aniline
Scheme 3 Enzymatic amidation
of Boc-proline by means of ani-
lines. 1 mmol of Boc-proline,
2 mmol of aniline derivatives,
50 mg of molecular sieves 4 Å
and 50 mg of CAL-B in 1 mL
of heptane at 80 °C for 72 h. (a)
Isolated yield
1 3

Chemical Papers
Arroyo M, De Le Mata I, García JL, Barredo JL (2017) Biocatalysis
for industrial production of active pharmaceutical ingredients
(APIs). In: Biotechnology of microbial enzymes, Chap 17. Aca-
demic Press, pp 451–473
the protected group (-Boc) was observed. So, this enzy-
matic approach for the amidation of N-protected aminoac-
ids constitutes a new path promising, more safe, clean and
sustainable.
Belkacemi FZ, Merabet-Khelassi M, Aribi-Zouioueche L, Riant
O (2017) Diastereoselective and enantioselective alkaline-
hydrolysis of 2-aryl-1-cyclohexyl acetate: a CAL-B catalyzed
deacylation/acylation tandem process. Tetrahedron Asymmetry
28:1644. https://doi.org/10.1016/j.tetasy.2017.09.010
Braia N, Merabet-Khelassi M, Aribi-Zouioueche L (2018) Efcient
access to both enantiomers of 3-(1-hydroxyethyl) phenol by
regioselective and enantioselective CAL-B-catalyzed hydroly-
sis of diacetate in organic media by sodium carbonate. Chirality
30:1312. https://doi.org/10.1002/chir.23025
Conclusions
In summary, we have developed an efcient direct amidation
of a set of non-activated carboxylic acids with anilines and
benzylamine, catalyzed by CAL-B as biodegradable biotool.
A set of nonsteroidal anti-infammatory drugs (NSAIDs),
phenoxypropionic acid and protected-proline are selected to
examine the efciency of the enzymatic pathway. This direct
enzymatic amidation system is examined for the frst time.
The obtained carboxylic amides are recovered with isolated
chemical yields varied between moderate and excellent.
Of the twenty fve carboxylic amides synthesized, at least
fourteen from them are reported for the frst time and one
from them: N-(4-iodophenyl)-2-(4-isobutylphenyl)propana-
mide 1d is characterized by X-ray difraction.
Busto E, Gotor-Fernandez V, Gotor V (2010) Hydrolases: catalyti-
cally promiscuous enzymes for non-conventional reactions in
organic synthesis. Chem Soc Rev 39:4504. https://doi.org/10.
1039/C003811C
Chandra P, Singh R, Arora PK (2020) Microbial lipases and their
industrial applications: a comprehensive review. Microb Cell
Fact 19:169. https://doi.org/10.1186/s12934-020-01428-8
Cheng L, Ge X, Huang L (2018) Direct amidation of non-activated
phenylacetic acid and benzylamine derivatives catalysed by
NiCl
2. Royal Soc Open Sci 5:171870. https://doi.org/10.1098/
rsos.171870
Constable DJC, Dunn PJ, Hayler JD, Humphrey GR, Leazer JL, Lin-
derman RJ, Lorenz K, Manley J, Pearlman BA, Wells A, Zaks
A, Zhang TY (2007) Key green chemistry research areas—a
perspective from pharmaceutical manufacturers. Green Chem
9:411–420. https://doi.org/10.1039/B703488C
The reported conditions of the CAL-B-catalyzed direct
amidation allow easily to potent carboxylic amides with a
high atom economy, minimal waste production and chemical
yields depending on the acid structure. This new sustainable
and eco-friendly route opens up very interesting perspectives
for easily recoverable applications.
De Figueiredo RM, Suppo JS, Campagne JM (2016) Nonclassical
routes for amide bond formation. Chem Rev 116:12029–12122.
https://doi.org/10.1021/acs.chemrev.6b00237
Doherty S, Knight JG, McRae A, Harrington RW, Clegg W (2008)
Oxazoline-substituted prolinamide-based organocatalysts for the
direct intermolecular aldol reaction between cyclohexanone and
aromatic aldehydes. Eur J Org Chem 10:1759. https://doi.org/
10.1002/ejoc.200700922
Supplementary Information The online version contains supplemen-
tary material available at https://doi.org/10.1007/s11696-021-01636-5.
Galanakis D, Kourounakis AP, Tsiakitzis KC, Doulgkeris C, Rekka
EA, Gavalas A, Kravaritou C, Christos C, Kourounakis PN
(2004) Synthesis and pharmacological evaluation of amide
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potent antiinfammatory and antioxidant properties with signif-
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Acknowledgements Algerian Ministry of Higher Education and Sci-
entifc Research (MESRS, FNR 2000) and ANDRU (PNR) are grate-
fully acknowledged for the fnancial support of this work. Prof. Olivier
RIANT (IMCN/UCL-Louvain-La-Neuve, Belgium) is acknowledged
for his assistance and the welcome of NourElhouda BENAMARA and
Mounia MERABET-KHELASSI to perform specifc analyses.
Greenberg A, Breneman CM, Liebman JF (2000) The amide linkage:
structural signifcance in chemistry, biochemistry and materials
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