Michael additions of primary and secondary amines to acrylonitrile catalyzed by lipases

Article abstract of DOI:10.1016/j.tetlet.2009.02.100

The present Letter details our findings on the lipase-catalyzed Michael reactions between primary or secondary amines and acrylonitrile. Several lipases were evaluated, and good results were obtained leading to the formation of Michael adducts in shorter reaction times than the uncatalyzed reactions.

Full text of DOI:10.1016/j.tetlet.2009.02.100

Tetrahedron Letters 50 (2009) 2017–2018
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Michael additions of primary and secondary amines to acrylonitrile catalyzed
by lipases
a
a
a
b
Rodrigo O. M. A. de Souza a, , Lilian M. C. Matos , Karen M. Gonçalves , Ingrid C. R. Costa , Ivelize Babics ,
*
Selma G. F. Leite b, E. G. Oestreicher a, O. A. C. Antunes a
a Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Bloco A 641, RJ 21941-909, Brazil
b Escola de Química, Laboratório de Microbiologia Industrial, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Bloco E, Lab-113, RJ 21941-909, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
The present Letter details our findings on the lipase-catalyzed Michael reactions between primary or sec-
ondary amines and acrylonitrile. Several lipases were evaluated, and good results were obtained leading
to the formation of Michael adducts in shorter reaction times than the uncatalyzed reactions.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 22 September 2008
Revised 11 February 2009
Accepted 12 February 2009
Available online 20 February 2009
Keywords:
Lipases
Michael additions
Enzyme promiscuity
Catalysis
1. Introduction
petitive processes, the aminolysis (the expected lipase-catalyzed
reaction), the uncatalyzed Michael reaction and the unexpected
The use of enzymes for organic synthesis has become an emerg-
ing area for organic chemists. During the recent years, many
enzymes have demonstrated high activity against nonnatural
substrates in organic media and have become widely used for syn-
thetic transformations such as reductions, oxidations, epoxidations,
and aldol reactions, among others.1–5 Lipases are the most used and
well-known enzymes, which have high stability and activity, and
can be used for different kinds of transformations.
In connection with our continuous work on synthetic applica-
tions of enzymes,6 we start evaluating lipase catalytic activities
of commercial enzymes on Michael addition reactions between
secondary and primary amines and acrylonitrile (Scheme 1).
The literature points out that lipases are able to catalyze
aminolysis and ammonolysis reactions7–9, and the use of these en-
zymes on Michael addition reactions has been reported.10
Gotor reviewed the non-conventional hydrolase chemistry, and
disclosed some undesired Michael reactions that could occur
competitively to aminolysis of esters. Ishida and Kato proposed a
general mechanism to serine protease reactions11 that act similarly
to lipases.
catalyzed Michael reaction.
In the case of acrylonitriles, only two processes are possible, the
catalyzed and the uncatalyzed Michael reactions which we choose
to investigate.
Our group is studying the mechanism of the hydrolysis reaction
and the geometry of the oxyanion hole that stabilizes the interme-
diate,12 considering a late transition state.
Taking into account the model that was proposed early11 and
our own12, in the latter step after the conjugated addition of the
nucleophile, the zwiterionic intermediate is formed and is stabi-
lized by both the oxyanion hole and the His–Asp pair.11 We
hypothesized, however, that this kind of mechanism in the Michael
reaction based on a late transition state would not play a role to
justify rate acceleration effects (in Michael additions),13 that is, in
the case of esters, the transition states would be very similar in
both Michael and aminolysis, considering the oxyanion formation,
so not justifying a rate acceleration effect toward the desired
Michael product.
In the case of the reaction of amines with alpha, beta-unsatu-
rated esters, the competitive aminolysis would play a role and
the final product selectivity pattern will be the result of three com-
R1
N
CN
Lipase
R1
R2
+
N
H
R2
CN
Toluene, 250 r.p.m.
30 ºC
* Corresponding author. Tel.: +55 2125627248.
E-mail address: souzarod21@yahoo.com.br (R.O.M.A. de Souza).
Scheme 1. Michael addition reaction.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.02.100

2018
R. O. M. A. de Souza et al. / Tetrahedron Letters 50 (2009) 2017–2018
Table 2
δ
H N
Michael reaction between primary and secondary amines and acrylonitrile in the
presence of a lipase catalyst
R2
N
Coxyanion hole
δ
N
δ
R1
H N
Conversiona
H
Entry
Amine
Lipase
Time (h)
active site
O
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
1
1
1
2
2
2
2
3
3
3
3
4
4
4
4
Novozyme 435
Lipozyme TL IM
Lipozyme RM IM
PS Amano
Novozyme 435
Lipozyme TL IM
Lipozyme RM IM
PS Amano
Novozyme 435
Lipozyme TL IM
Lipozyme RM IM
PS Amano
Novozyme 435
Lipozyme TL IM
Lipozyme RM IM
PS Amano
0.8
1
1
6, 90%
6, 88%
6, 92%
6, 85%
7, 80%
7, 85%
7, 71%
7, 77%
8, 70%
8, 71%
8, 65%
8, 68%
9, 71%
9, 66%
9, 61%
9, 70%
H
O
N
Asp
N
H
O
1
Ser
His
1.2
1.2
1.2
0.8
1.2
1.4
1.4
1.2
1.4
1.6
2
Figure 1. Hypothesized mechanism for the lipase-catalyzed Michael addition.
Table 1
Michael reaction between primary and secondary amines and acrylonitrile without
the use of lipase catalyst
Entry
Amine
Time (h)
Conversiona
1.5
1
2
3
4
Benzylamine (1)
Diethylamine (2)
Diisopropylamine (3)
Pyrrolidine (4)
2
3
3
2.5
6, 92%
7, 83%
8, 74%
9, 72%
a
Based on GC analysis.
a
Based on GC analysis.
substances were confirmed by comparison with NMR data and
GC-MS analysis, and are included in the supplementary data.
So we envisaged that in the lipases’-catalyzed Michael reac-
tions, substrate activation would occur via protonation (or high
energy hydrogen bonding) of the nitrile so implying in a substrate
activation that would result in a rate acceleration effect (Fig. 1).
Based on this expectation, we undertook the present investiga-
tion on the Michael reaction between primary and secondary
amines (1–4) and acrylonitrile (5) envisaging a kind of substrate
activation.
To compare such expectation, we carried out Michael reaction
without the use of lipase as catalyst. The results displayed in
Table 1 show that all amines lead to the formation of Michael
addition product in 2–3 h.
Acknowledgment
The authors thank CNPq, CAPES, FAPERJ, and FINEP for the
financial support.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2009.02.100.
To investigate the effect of lipase catalyst on this type of reac-
tion, we decided to perform the same reaction in the presence of
different types of lipases, and the results are summarized in Table 2.
As shown in Table 2, all lipases evaluated led to a consistent
shorter reaction time tendency (about 50% time reduction) when
compared to the same reaction without the use of the lipase cata-
lyst. Novozyme 435 (Table 2, entries 1, 5, 9, and 13) gave the best
results, but the other systems were also effective.
In conclusion, it has been demonstrated that different lipases
that share in general the same active site are capable to catalyze
the Michael reaction between primary or secondary amines and
acrylonitrile. In comparison with the non-catalyzed reaction, this
methodology leads to a great improvement in the reaction time.
Studies are in progress to observe if enantioselectivity can be
achieved with beta-substituted acrylates or acrylonitriles and also
on the kinetics of these reactions.
References and notes
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Reactions were carried out using amine (1 mmol), acrylonitrile
(1 mmol), and 2% w/w of Lipase, in toluene (5 mL). The reaction
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