Lipase-catalyzed amidation of carboxylic acid and amines

Article abstract of DOI:10.1016/j.tetlet.2018.04.049

The amidation reaction is of a very particular interest, especially in the pharmaceutical industry and always requires the activation of the acid with a large excess of reactants. Therefore, a large amount of waste is generated. In order to reduce the environmental impact of such reaction, we have developed enzymatic amidation conditions which are compatible with a wide range of amines and acids, in particular with the biologically relevant lipoic acid. Water is the only by-product generated during this reaction thus a very high atom economy is obtained. In addition, we have shown that the lipase can be recovered and reused several times without a significant loss of activity.

Full text of DOI:10.1016/j.tetlet.2018.04.049

Accepted Manuscript
Lipase-Catalyzed Amidation of Carboxylic Acid and Amines
Daniela Manova, Florian Gallier, Lotfi Tak-Tak, Lyubov Yotava, Nadège
Lubin-Germain
PII:
S0040-4039(18)30522-7
https://doi.org/10.1016/j.tetlet.2018.04.049
TETL 49912
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
19 March 2018
17 April 2018
19 April 2018
Please cite this article as: Manova, D., Gallier, F., Tak-Tak, L., Yotava, L., Lubin-Germain, N., Lipase-Catalyzed
Amidation of Carboxylic Acid and Amines, Tetrahedron Letters (2018), doi: https://doi.org/10.1016/j.tetlet.
2018.04.049
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphical Abstract
To create your abstract, type over the instructions in the template box below.
Fonts or abstract dimensions should not be changed or altered.
Lipase-Catalyzed Amidation of Carboxylic
acid and amines
Leave this area blank for abstract info.
Daniela Manova, Florian Gallier, Lotfi Tak-Tak, Lyubov Yotova, Nadège Lubin-Germain

1
Tetrahedron Letters
journal homepage: www.els evier.com
Lipase-Catalyzed Amidation of Carboxylic Acid and Amines
Daniela Manova,a,b Florian Gallier,a* Lotfi Tak-Tak,a Lyubov Yotava,b† and Nadège Lubin-Germaina,*
a Laboratoire de Chimie Biologique, EA 4505, University of Cergy-Pontoise, F-95000 Cergy-Pontoise cedex, France
b University of Chemical Technology and Metallurgy Sofia 1754, blv. st K. Ohridski,8 Sofia Bulgaria
† Deceased (08.11.2016 ?)
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
The amidation reaction is of a very particular interest, especially in the pharmaceutical industry
and always requires the activation of the acid with a large excess of reactants. Therefore, a large
amount of waste is generated. In order to reduce the environmental impact of such reaction, we
have developed enzymatic amidation conditions which are compatible with a wide range of
amines and acids, in particular with the biologically relevant lipoic acid. Water is the only by-
product generated during this reaction thus a very high atom economy is obtained. In addition,
we have shown that the lipase can be recovered and reused several times without a significant
loss of activity.
Available online
Keywords:
amidation
lipases
lipoic acid
solvents
2009 Elsevier Ltd. All rights reserved
.
recycling
Transition metal catalysts, especially elements from group IV
(Ti, Zr, Hf), have been used on several occurrence since the
simultaneous seminal work of Williams and Adolfsson.5,1c The
same drawbacks (water removal and high temperature) can also
be pointed out. Very recently, diphenylsilane has been used
stoichiometrically for the direct coupling of carboxylic acid and
amines in refluxing acetonitrile.6
1. Introduction
The amide bond is one of the most widespread bonds since it
is the core structure of peptides and proteins. Nature assembles
enzymatically the free aminoacids in the ribosome. However,
synthetic chemists have devised the use of alternative methods
since the reaction of a free carboxylic acid and a free amine (as in
the case of free aminoacids) will solely results in the formation of
the ammonium carboxylate salt, obtained from the acid-base
reaction, unless elevated temperature is applied.1
Enzymes, especially lipases, have been used for a long time to
perform esterification reactions using the alcohol as solvent to
draw the equilibrium towards the formation of the ester. When
both a primary or secondary amine and an alcohol (which is
typically used as solvent) are present in the reaction medium, the
ester formed is ultimately converted to the corresponding amide.7
The direct conversion of a carboxylic acid and an amine remains
scarce in the literature,8 or limited to specific substrates such as
the formation of primary amides from various sources of
ammonia.9
For peptides and proteins formation, the use of protected
aminoacids and
a
rather expensive activator or the
immobilization on a resin, allowing the use of large excess of
reagents, are key parameters for a successful synthesis and are
routinely applied.2 However, the amide bond formation avoiding
poor atom economy or large excess of reagents has been
identified as a priority by the ACS Green Chemistry Institute and
by pharmaceutical companies.3 Therefore, new sustainable
methods for the formation of amide bonds are of high concern. In
the recent years several methods have been developed for the
acylation of amines with free carboxylic acids.1 Probably one of
the most versatile methods rely on the use of boronic acids which
transiently generates an activated acid.4 These Lewis acids,
which activity can be finely tuned by modifying the substituents
at the boron atom, usually have a high functional group tolerance
and are stable in the presence of water. However, the water
generated in the course of the reaction has to be removed and
usually elevated temperatures are required to achieve good
yields, which conditions can also lead to racemization.
2. Discussion
We wish to report here a simple and convenient method for
the direct amidation of free carboxylic acids and amines without
the transient formation of an active ester, generating therefore
water as the sole, non-toxic, by-product.
2.1. Solvent Screening
We initially started our investigations of the lipase catalyzed
amidation reaction in various solvents with octanoic acid and
benzyl amine.10 Immobilized Candida Antarctica Lipase B
(CAL-B) was chosen for its ability to perform several kinds of

2
Tetrahedron
organic reaction and for its compatibility with organic
used for the synthesis of amides (including N-benzyloctylamide
3) by amidation of the corresponding benzyl esters.18 More
interestingly, the free Candida Antarctica Lipase B afforded the
desired product in a very low yield (Table 2, Entry 6) compared
to the immobilized one. If the role of the acrylic resin cannot be
excluded by specific interactions or a specific conformation of
the lipase, the immobilization itself does not seem responsible for
the yield since the Amano Lipase PS is immobilized on diatomite
and was inefficient for the amidation reaction.
solvents.11 The reaction was carried out at 50°C with molecular
sieves to avoid the reversible hydrolysis reaction. For all the
reactions described throughout this paper a control reaction
without lipase was performed in order to assess the lipase
amidation activity under various conditions. It is well-known that
the solvent can have a dramatic influence on the outcome of a
biocatalyzed reaction.12 Indeed, the solvent should be able to
solubilize the reactants as well as the product and stabilize the
intermediates involved, but it can also change the conformation
of the active site or drain out the water molecules from it, thus
modifying the catalytic properties of the enzymes.
Table 1: Lipase screening
Although lipases are known to perform better in apolar
solvents,13 we have screened usual organic solvents such as
toluene or well tolerated ethereal solvent like 1,4-dioxane,
MTBE, diglyme and cyclopentyl methyl ether CPME14 in order
to ensure solubilization of the reactants or the product and to
avoid heterogeneous conditions.
Entry
Lipase
Yield
2%
5%
5%
5%
3%
9%
94%
1
2
3
4
5
6
7
Candida Rugosa lipase type VII
Aspergillus NigerLipase
Amano Lipase PS
Pseudomonas CepaciaLipase
Mucor Javanicus lipase
Candida Antarctica Lipase B free
Candida Antarctica Lipase B immobilized
We have also screened greener or safer alternatives (MeTHF,
propylene carbonate, PEG200) and the ionic liquid BMP(NTf2).15
These different types of solvents allow us to screen various
polarities and proticities thus selecting the best solvent. In most
of the solvents the yields were very satisfactory (Table 1: entries
1-7), above 80%, which proves the versatility of this enzyme in
organic solvents. Interestingly, the reaction performed in Butyl
Methyl Pyrrolidinium Triflimide (BMP(NTf2)) only afford the
desired compound in 28 % yield. This result is rather surprising
since CAL-B has been for amidation with ammonia in ionic
liquids,16 or used in a Baeyer-Villiger oxidation in BMP(NTf2)17
with good results.
2.3. Exemplification
Having in hand the optimized conditions for the amidation
reaction we then undertook a screening of both carboxylic acid
and amine in order to define the scope of this reaction.
2.3.1.1. Amine screening
We thus focused our attention on the screening of different
amines using octanoic acid and CAL-B at 50°C in 1,4-dioxane.
The amidation reaction was stopped for all the amines after 3
days and the yield was checked after washing off the starting
materials with basic and acidic aqueous solutions and the purity
of the product was assessed by NMR analysis.
In order to rationalize the influence of the solvent we have
initially examined the dielectric constant (ε, Table 1) and the
dipole moment (µ, Table) of these solventsIt turns out that the
solvents with a dielectric constant below 12.5 (except pyridine)
afford yields above 80 %. A similar trend can be drawn with the
dipole moment, which best yields are obtained with the less polar
Table 3. Amines screening
solvents (<
2
Debye). We have then examined the
solvatochromic parameters of these solvents and another trend
can be drawn. Yields over 80 % are achieved with solvents
having hydrogen-bond acidity (α) of 0 (pyridine excluded)
whereas the hydrogen-bond basicity (β) doesn’t seem to have an
influence. However the polarity/polarizability parameter (π*)
needs to remain below 0.65. Similar observation has been made
for the ETN parameter which has to be under 0.25 to give the best
yields (t-BuOH excluded).
Considering other criterions such as the ability to dissolve a
wider range of substrates or the price we have decided to use the
1,4-dioxane as the solvent of choice despite its relative toxicity.
However less acute solvents can be used albeit with a slight
decrease in yield.
We noticed that the amidation is efficient (Table 3) with
aliphatic (propyl 83% yield, compound 6 or benzyl 94% yield,
compound 3) amines and tolerates also functionalized amines
such allylic (60% yield, compound 7), propargylic (94%,
compound 10) or bearing a functionalization such as a silyl ether
protecting group. However, this protecting group is partially
As the reactivity of the lipase is known to be reversible we
have also explored the influence of the water amount in these
conditions (Table 1: entries 14, 15). Anhydrous conditions are
not mandatory since only a small decrease in yield is observed
when molecular sieve is absent. However, the presence of larger
amounts of water (10 % v/v) inhibits partially the conversion.
1
deprotected during the acidic washing step (as observed by H-
NMR). Therefore, the compound 8 is obtained in a good overall
yield, after full deprotection of the TBDMS ether using standard
TBAF procedure. The low yield observed in the case of
octadecylamine (6%, compound 9) is explained by the very low
solubility of the product impeding the extraction step. Steric
hindrance at the carbon bearing the amine function leads to a
dramatic decrease in the lipase activity (22%, compound 4).
Moreover CAL-B was inefficient with secondary amines
(compounds 11 and 12) as well as hydrophilic amines
(compound 8). In the case of aminoethanol no conversion was
observed, whereas in the case of glycine methyl ester no product
2.2. Lipase Screening
Since lipases are specific for either a transformation or for
some substrates, we have then investigated the role of the
biocatalyst on the amidation reaction in the conditions
determined previously.
It turns out that the lipases from Candida Rugosa, Aspergillus
Niger, Pseudomonas Cepacia, Mucor Javanicus or the Amano
Lipase were almost inactive (Table 2, Entry 1-5). The case of
Pseudomonas Cepacia is rather surprising since this lipase was

3
Table 1. Solvent screening
Entry
N
Solvent
Yield
94%
92%
89%
89%
83%
83%
80%
73%
33%
23%
28%
50%
4%
ε
µ (D)
0,45
0,31
1,38
1,27
1,66
1,32
1,92
4,94
2,69
3,44
-
π*
0.55
0.54
0.48
0.42
0.41
-
0.64
0.83
0.71
0.75
0.95
-
α
β
ET
0.164
0.099
0.179
-
1
1,4-dioxane
2,21
2,38
7,53
4,76
12,5
2,6
0
0
0
0
0.37
0.11
0.45
0.53
0.93
-
2
Toluene
MeTHF
CPME
3
4
5
t-BuOH
0.68
0.389
0.124
0.244
0.472
0.355
0.460
0.540
-
6
MTBE
0
0
0
7
Diglyme
7,3
-
0.4
8
Propylene Carbonate
65,5
20,7
37,5
-
18,35
12,4
9
10
Acetone
0.08
0.19
0.41
-
0.48
0.31
0.723
Acetonitrile
BMP(NTf)2
PEG 200
11
12
-
-
13
Pyridine
2,37
0.87
0
0.64
0.302
14
15
1,4-dioxane*
1,4-dioxane/H2O (10 :1)* 25%
87%
* No MS 3Å was used
was observed probably due to self-oligomerization (amidation of
the methyl ester).
2.3.1. 2. Carboxylic acid screening
TBAF treatment, with a low overall yield due to solubility
problems (of both the TBDMS ether intermediate and the
compound 31). Finally, amidation of the side-chain of a suitably
protected L-lysine has been carried out in order to prepare a
building block for the peptide synthesis.20 Unfortunately, all the
attempts to prepare compound 31 failed.
We then explored the scope concerning the other partner of
the reaction by testing different carboxylic acids. The amidation
reactions were carried out in 1,4-dioxane at 50°C during 3 days
in the presence of CAL-B. We heve noted that the lipase was less
tolerant with the carboxylic acids since no reaction occurred with
diphenylethanoic acid, hydroxyphenyl ethanoic acid or 4-
oxopentanoic acid (compounds 16, 17 and 18). Nevertheless we
succeeded to obtain the amide compounds with benzoic acid,
with a low yield explained by solubility problems (compound 15,
19%) and N-protected glycine (compounds 20 and 21: 27% and
44% respectively). The reaction was very efficient with but-3-
enoic acid (compound 22, 83%).
Table 5. Lipoic acid amidation
Table 4: Acids screening
Lipoic acid is also an interesting substrate for lipase-catalzyed
reactions owing to its chiral center. Indeed, lipases have a chiral
active pocket which can discriminate a racemic mixture.
Therefore, we have measured the optical rotation of some of the
amides obtained previously (Table 5). The optical rotation of the
amide 19 obtained from the lipase-catalyzed reaction between
racemic lipoic acid and benzyl amine has been found to be +15.
The major enantiomer has been attributed to be (R) configured
(with an enantiomeric excess of 28 %) after having recorded that
the pure (S)-lipoamide 29 has an optical rotation of ‒54. This
proves that the lipase is able to partially discriminate the 2
enantiomers of lipoic acid even though the chiral center is rather
remote from the reactive site. This behavior has also been
observed for the lipoamide 29. Using aqueous ammonia solution,
the enantiomeric excess remains moderate whatever the reaction
time (16 % ee after 1 day and 18 % ee after 3 days). Although the
yields obtained with dry ammonia solution in 1,4-dioxane are
significantly lower (11 % yield), the enantiomeric excess is
improved, reaching 38 % ee after 3 days. Under these conditions,
the reaction can favorably be stopped after only 1 day (14 %
yield, 42 % ee).
One of our best result was obtained using lipoic acid as
substrate (compound 19, 66%). This constitutes an interesting
opportunity to further explore the reactivity of this specific acid
as the amidation of lipoic acid provides compounds with unique
antioxidant and cytoprotective properties.19 Furthermore,
lipoylated peptides have been recently described as potential
immunological probes for the diagnosis of primary biliary
cirrhosis.20 Similarly to the use of octanoic acid (Table 5), best
results were obtained with aliphatic amines such as propyl (68%,
compound 24), benzyl (66%, compound 19), allyl (72%,
compound 26) or propargyl (64%, compound 27). Interestingly,
the octadecylamide of lipoic acid 25 is obtained in a better yield
than the compound 9 owing to a better solubility of the product.
Lipoamide 28 can be prepared with different ammonia donors.
Aqueous ammonia solution yields the product 28 with a low
yield of 34 % explained by the large amount of water present.
Dry ammonia solution, obtained by bubbling gaseous ammonia
in 1,4-dioxane, gives an unexpectedly worse yield. The
amidation of lipoic acid with 2-(2-(2-tert-butyldimethyl-
silyloxyethoxy)ethoxy)ethylamine gives the desired product with
partial deprotection. The compound 30 can then be isolated after
2.4. Sustainability

4
Tetrahedron
The amidation reaction usually requires an excess of one
including lipoic acid. However, as often observed with lipases
the scope of substrates is limited by steric constraints. In
addition, we have studied the solvent dependence, by means of
different parameters, and demonstrated that the lipase can be
efficiently recovered and reuse for several runs.
reactant and thus generates large amounts of wastes. Our
methodology intends to respect the sustainability criterion and we
have decided to set the reaction conditions in order to limit the
wastes generated or to be able to recover the biocatalyst.
2.4.1. Stoichiometry
Therefore, the stoichiometric ratio of carboxylic acid and
amine was initially defined for the optimization of the reaction
conditions (Table 6). However, we have still checked the
influence of an excess of either the amine or the carboxylic acid
with immobilized CAL-B in 1,4-dioxane. In both cases, the
yields obtained were significantly lower than the yield of the
stoichiometric ratio.
H
CAL-B immobilized
NH2
OH
N
+
1,4-dioxane
50°C, 3d, MS 3Å
O
O
3
1
2
(94 % yield after run# 1)
(88 % yield after run# 2)
(83 % yield after run# 3)
(78 % yield after run# 4)
(62 % yield after run# 5)
(1 eq.)
(1 eq.)
Yield
100
Table 6. Amidation stoichiometry
80
60
40
20
0
H
CAL-B immobilized
NH2
OH
N
+
1,4-dioxane
50°C, 3d, MS 3Å
O
O
1
2
3
1
2
3
4
Eq.
Eq.
1
1
Yield
94 %
62 %
75 %
5
Runs
1
5
1
Scheme 2. Lipase recycling
5
Acknowledgments
This observation can be quantified by measuring the atom
economy of this reaction. The atom economy is one the 12
principles of green chemistry21 and has been defined as the
amount of atoms from the reactants and the reagents that are
present in the product. In our conditions, AE has been calculated
to be 0.93, which is close to the value of an ideal reaction (AE =
1). This direct amidation reaction can be compared with other
classical amide synthesis. The use of acyl chlorides (32) also
requires a base such as triethylamine (33) thus reducing the atom
economy.22 The aminolysis of an ester (34) gives an even worse
atom economy due to the ester itself and the need of an excess of
amine.18
Marine Pietri is gratefully acknowledged for performing
several test reactions. The french “Ministère des Affaires
Etrangères” is gratefully acknowledged for funding a scholarship
for D.M.
Supplementary data
Supplementary data (experimental data, NMR spectra)
associated with this article can be found in the online version.
References and notes
1. (a) De Figueiredo, R. M.; Suppo, J.-S.; Campagne, J.-M.; Chem.
Rev. 2016, 116, 12029-12122. (b) Pattairaman, V. R.; Bode, J. W.;
Nature, 2011, 480, 471-479. (c) Lundberg, H.; Tinnis F.; Selander
N.; Adolfsson, H.; Chem. Soc. Rev. 2014, 43, 2714–2742.
2. Behrendt, R.; White, P.; Offer, J.; J. Pept. Sci. 2016, 22, 4-27.
3. Bandichlor, R.; Bhattacharya, A.; Cosbie, A.; Diorazio, L.; Dunn,
P.; Fraunhoffer, K.; Gallou, F.; Hayler, J.; Hinkley,
B.;Humphreys, L.; Kaptein, B.; Oh, L.; Ridcharson, P.; White, T.;
Wuyts, S.; Yin, J.; Org. Process. Res. Dev. 2015, 19, 1924-1935.
4. (a) Ishihara, K.; Ohara, S.; Yamamoto, H.; J. Org. Chem. 1996,
61, 4196–4197 (b) Al-Zoubi, R. M.; Marion, O.; Hall, D. G.;
Angew. Chem. Int. Ed. 2008, 47, 2876–2879. (c) Noda, H.;
Furutachi, M.; Asada, Y.; Shibasaki, M.; Kumagai, N.; Nat. Chem.
2017, 9, 571–577. (d) El Dine, T. M.; Rouden, J.; Blanchet, J.;
Chem. Commun. 2015, 51, 16084-16087.
Scheme 1. Atom economy
2.4.2. Recycling
5. Allen, C. L.; Chhatwal, A. R.; Williams, J. M. J.; Chem. Commun.
2012, 48, 666–668.
The next parameter we were interested in was the recyclability
of the biocatalyst (Scheme 2). The reactions were performed in
the optimized conditions as described above (50 mg of lipase,
1,4-dioxane, 50°C, 3 days). After the first run, the immobilized
lipase was filtered off and reused for the next reaction with only a
slight decrease in yield (from 94 % to 88 % yield). The activity
of the lipase remains stable until the run #4 (78 % yield). The
overall decrease in yield, which is significant in the 5th run (62 %
yield), is imputed to the loss of the biocatalyst in each filtration
step. Indeed, a loss of 15 mg of lipase has been observed after the
4th run. The 5th experiment was performed using only 25 mg,
which is half of the amount required in the optimized conditions,
hence explaining the drop in yield.
6. Sayes, L. M.; Charette, A. B.; Green Chem. 2017, 19, 5060-5064.
7. de Zoete, M. C.; Kock-van Dalen, A. C.; van Rantwijk, F.;
Sheldon, R. A.; J. Mol. Catal. B: Enzym. 1996, 2, 19-25.
8. Tuccio, B.; Ferré, E.; Comeau, L.; Tetrahedron Lett. 1991, 32,
2763-2764.
9. Čeřovský, V.; Kula, M. R.; Angew. Chem. Int. Ed. 1998, 37, 1885-
1887.
10. Typical procedure: in
a screw-capped tube are successively
introduced the amine (0.915 mmol, 1 eq), the acid (0.915 mmol, 1
eq) in a suitable solvent (usually 1,4-dioxane, 2 mL). The 3Å
molecular sieve (50 mg) and the immobilized CAL-B (50 mg) are
finally introduced. The reaction mixture is heated to 50°C for 3
days. After cooling, the solvent is evaporated the crude residue is
partionned between water and EtOAc. The aqueous layer is
extracted with EtOAc (2 x 2 mL) and the combined organic
phases are washed with 3 M HCl (2 x 2 mL) and 10 % aqueous
K2CO3 (2 x 2 mL). The solvent is finally evaporated under
reduced pressure giving the pure amide (assessed by NMR).
3. Conclusion
In conclusion we have developed a direct amidation reaction

5
11. a) Anderson, E. M.; Larsson, K. M.; Kirk, O.; Biocatal.
Biotransform. 1998, 16, 181–204. (b) Gotor-Fernández, V.; Busto,
E.; Gotor, V.; Adv. Synth. Catal. 2006, 348, 797–812.
12. Organic Synthesis with enzymes in Non-Aqueous Media; Carrea,
A., Riva, S., Eds; Wiley-VCH, 2008.
16. Madeira Lau, R.; van Rantwijk, F.; Seddon, K. R.; Sheldon, R.
A.; Org. Lett. 2000, 2, 4189-4191.
17. Drożdż, A.; Erfurt, K.; Bielas, R.; Chrobok, A.; New J. Chem.
2015, 39, 1315-1321.
18. Adamczyk, M.; Grote, J.; Tetrahedron Lett. 1996, 37, 7913-7916.
19. Kates, S. A.; Casale, R. A.; Baguisi, A.; Beeuwkes, R.; Bioorg.
Med. Chem. 2014, 22, 505-512.
13. Laane, C.; Boeren, S.; Vos, K.; Veeger, C.; Biotechnol. Bioeng.
1987, 30, 81-87.
14. Watanabe, K.; Yamagiwa, N.; Torisawa, Y.; Org. Process Res.
Dev. 2007, 11, 251-258.
20. Rentier, C.; Pacini, G.; Nuti, F.; Peroni, E.; Rovero, P.; Papini, A.-
M.; J. Pept. Sci. 2015, 21, 408-414.
15. (a) Kim, S. H.; Park, S.; Yu, H.; Kim, J. H.; Kim, H. J.; Yang, Y.-
H.; Kim, Y. H.; Kim, K. J.; Kan, E.; Lee, S. H.; J. Mol. Catal. B:
Enzym. 2016, 128, 65-72. (b) Irimescu, R.; Kato K.; J. Mol. Catal.
B: Enzym. 2004, 30, 189-194.
21. (a) Trost, B. M.; Angew. Chem. Int. Ed. 1995, 34, 259-281. (b)
Sheldon, R. A.; Pure Appl. Chem. 2000, 72, 1233-1246.
22. Oda, Y.; Sato, T.; Chida, N.; Org. Lett. 2012, 14, 950-953.

6
Tetrahedron
Enzymatic amidation reaction
No activation needed
Wide range of substrates
Lipoîc acid amide derivatives