Reduction of substituted benzaldehydes, acetophenone and 2-acetylpyridine using bean seeds as crude reductase enzymes

Article abstract of DOI:10.1080/10242422.2018.1510492

The reduction of substituted benzaldehydes, benzaldehyde, acetophenone and 2-acetylpyridine to the corresponding alcohols was conducted under mild reaction conditions using plant enzyme systems as biocatalysts. A screening of 28 edible plants, all of which have reductase activity, led to the selection of pinto, Flor de Mayo, ayocote, black and bayo beans because these enabled the quantitative biocatalytic reduction of benzaldehyde to benzyl alcohol. The biocatalyzed reduction of substituted benzaldehydes was dependent on the electronic and steric nature of the substituent. Pinto beans were the most active reductase source, reduced 2-Cl, 4-Cl, 4-Me and 4-OMe-benzaldehyde with a conversion between 70% and 100%. All the beans reduced 2- and 4-fluorobenzaldehyde at a conversion between 83% and 100%. The reduction of the ketones was low, but bayo and black beans yielded (R)-1-(pyridin-2-yl)ethanol in enantiopure form.

Full text of DOI:10.1080/10242422.2018.1510492

Biocatalysis and Biotransformation
ISSN: 1024-2422 (Print) 1029-2446 (Online) Journal homepage: http://www.tandfonline.com/loi/ibab20
Reduction of substituted benzaldehydes,
acetophenone and 2-acetylpyridine using bean
seeds as crude reductase enzymes
Aida Solís, Rosa María Martínez, Fadia Cervantes, Herminia I. Pérez,
Norberto Manjarrez & Myrna Solís
To cite this article: Aida Solís, Rosa María Martínez, Fadia Cervantes, Herminia I. Pérez, Norberto
Manjarrez & Myrna Solís (2018): Reduction of substituted benzaldehydes, acetophenone and 2-
acetylpyridine using bean seeds as crude reductase enzymes, Biocatalysis and Biotransformation,
DOI: 10.1080/10242422.2018.1510492
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BIOCATALYSIS AND BIOTRANSFORMATION
https://doi.org/10.1080/10242422.2018.1510492
RESEARCH ARTICLE
Reduction of substituted benzaldehydes, acetophenone and 2-acetylpyridine
using bean seeds as crude reductase enzymes
a
a
a
a
a
Aida So lꢀı s , Rosa Mar ꢀı a Mart ꢀı nez , Fadia Cervantes , Herminia I. P ꢀe rez , Norberto Manjarrez and
b
Myrna So lꢀı s
a
b
Departmento de Sistemas Biol ꢀo gicos, Universidad Aut ꢀo noma Metropolitana, Ciudad de M ꢀe xico, M ꢀe xico; Centro de Investigaci ꢀo n en
Biotecnolog ꢀı a Aplicada, Instituto Polit ꢀe cnico Nacional, Tlaxcala, M ꢀe xico
ABSTRACT
ARTICLE HISTORY
The reduction of substituted benzaldehydes, benzaldehyde, acetophenone and 2-acetylpyridine
to the corresponding alcohols was conducted under mild reaction conditions using plant enzyme
systems as biocatalysts. A screening of 28 edible plants, all of which have reductase activity, led
to the selection of pinto, Flor de Mayo, ayocote, black and bayo beans because these enabled the
quantitative biocatalytic reduction of benzaldehyde to benzyl alcohol. The biocatalyzed reduction
of substituted benzaldehydes was dependent on the electronic and steric nature of the substitu-
ent. Pinto beans were the most active reductase source, reduced 2-Cl, 4-Cl, 4-Me and 4-OMe-ben-
zaldehyde with a conversion between 70% and 100%. All the beans reduced 2- and
Received 6 July 2018
Accepted 4 August 2018
KEYWORDS
Bean; benzyl alcohols;
biocatalysis; plant
reductase; enzyme
4
-fluorobenzaldehyde at a conversion between 83% and 100%. The reduction of the ketones was
low, but bayo and black beans yielded (R)-1-(pyridin-2-yl)ethanol in enantiopure form.
Introduction
metals and hydride reducing agents. The biocatalytic
reduction of carbonyl groups such as aldehydes and
ketones can be conducted using nicotinamide-
dependent dehydrogenases (E.C. 1.1.1) as the catalysts
of choice (Hollmann et al. 2011). Aldo–keto reductases
The reduction of aldehydes and ketones constitutes
an important tool in organic chemistry for the prepar-
ation of alcohols, which can be used in the synthesis
of cosmetics, pharmaceuticals and agrochemicals.
Even though a wide range of reduction systems are
available and show high yields, most of these reaction
systems use heavy metals or their hydrides and
organic solvents as the reaction medium, which indi-
cates that they are not environmentally friendly.
For organic chemists, an attractive alternative is the
use of plant parts as biocatalysts because they are
inexpensive and easily available (Giri et al. 2001;
Cordell et al. 2007). The advantages of biocatalyzed
reactions are high chemo-, regio- and stereoselectivity,
diminished formation of by-products and waste,
reduced energy consumption and substantially
decreased negative environmental effects; therefore,
these reactions can be used on a sustainable basis
because they fit some of the principles of green chem-
istry (Clouthier and Pelletier 2012).
(AKRs) are enzymes that catalyse the biotransform-
ation of ketones/aldehydes to the corresponding alco-
hols and vice versa at the expense of a nicotinamide
cofactor [nicotinamide adenine dinucleotide (NADH) or
nicotinamide
adenine
dinucleotide
phosphate
(NADPH)] (Sengupta et al. 2015). It is well established
that crude preparations of parts of fresh plants, such
as roots, fruits, seeds or leaves, can be used as alterna-
tive high-yield reducing agents for the synthesis of
alcohols from aldehydes or ketones. Some recent
examples of reductase sources include the following:
fresh sugar cane (Saccharum officinarum) juice
(
Assun c¸ ~a o et al. 2008), Damask rose (Rosa damascena)
petals (Chen et al. 2011), mung bean (Vigna radiata)
seeds (Colrat et al. 1999), fresh passion fruit (Passiflora
edulis) (Machado et al. 2008), fresh vegetables, such as
broccoli (Brassica oleracea var. italica), cauliflower (B.
oleracea var. botrytis), spinach beet (Beta vulgaris var.
cicla) and spinach (Spinacia oleracea) (Su ꢀa rez-Franco
Reduction methodologies using enzymes avoid the
formation of toxic waste, which might pollute the
environment, and the use of non-sustainable heavy
CONTACT Aida So lꢀı s
asolis@correo.xoc.uam.mx
Departamento de Sistemas Biol ꢀo gicos, Universidad Aut ꢀo noma Metropolitana, Unidad Xochimilco,
Calzada del Hueso 1100, Col. Villa Quietud, Delegaci ꢀo n Coyoac ꢀa n, CDMX, C.P. 04960, M ꢀe xico
Supplemental data for this article can be accessed here.
ß 2018 Informa UK Limited, trading as Taylor & Francis Group

ꢀ
A. SOLIS ET AL.
2
et al. 2010), coconut (Cocos nucifera L.) and Asian pal-
myra palm (Borassus flabellifer L.) juices (Misra et al.
Table 1. Reduction of benzaldehyde (AH) to benzyl alcohol
(BH) with aqueous extracts from plants as enzyme sources.
Scientific name
BH (% conv.)
2012), Vietnamese coriander (Persicaria odorata Lour)
Seeds
leaves (Quynh et al. 2009), purple carrot (Daucus car-
ota) roots (Omori et al. 2016), cassava (Manihot escu-
lenta) (Machado et al. 2006), ginger (Zingiber officinale)
Pinto beans
Phaseolus vulgaris L.
Phaseolus vulgaris L.
Phaseolus coccineus L.
Phaseolus vulgaris L.
Phaseolus vulgaris L.
Phalaris canariensis
Hordeum vulgare
Lens culinaris
100
100
100
100
100
75
Flor de mayo beans
Ayocote beans
Black beans
Bayo beans
Canary grass
Barley
(Alves et al. 2015), Aloe vera (Leyva et al. 2012), hem-
lock (Conium maculatum) (Salvano et al. 2011) and flax
seeds (Linum usitatissimum) (Tavares et al. 2015).
64
53
Lentil
Oat
Squash
Wheat
Mamey
Pepper
Chili pepper
Avocado
Avena sativa
51
29
28
25
23
17
14
Plants have been demonstrated to be useful cata-
lysts for the specific reduction of aldehydes and
ketones to the corresponding alcohols. Furthermore,
because M ꢀe xico is a country with high biodiversity, a
screening of the natural diversity can lead to the dis-
covery of novel biocatalysts. The reduction of benzal-
dehyde to benzyl alcohol was used as a model
reaction to identify new sources of reductases in 28
different plants or their parts that are easily accessible
in local markets. The scope of the reduction reactions
with the novel biocatalysts was explored using
substituted benzaldehydes with electron-withdrawing
or electron-donating groups, acetophenone and
Cucurbita maxima
Triticum aestivum
Pouteria sapota
Capsicum annuum
Capsicum frutescens
Persea americana
Roots
Carrot
Radish
Turnip
Daucus carota
Raphanus sativus
Brassica rapa
63
20
18
Leaves
Lettuce
Coriander
Nopal
Fruit
Banana
Zucchini
Cucumber
Lactuca sativa
Coriandrum sativum
Opuntia ssp.
22
14
19
Coriandrum sativum
Cucurbita pepo
Cucumis sativus
60
30
18
Florets
Cauliflower
2-acetylpyridine.
Brassica oleracea var. botrytis
Brassica oleracea var. capitata
Brassica oleracea var. italic
Apium graveolens
25
24
19
33
Cabbage
Broccoli
Celery (Stalk)
Materials and methods
Materials
and then centrifuged at 5000 rpm. The seeds were
separately pulverized in a coffee grinder, and the pow-
der (10 g) was stirred in distilled water (30 mL) and
then centrifuged at 5000 rpm. The supernatants were
used as the enzyme source.
2
-,3- and 4-Chlorobenzaldehydes, 2- and 4-fluoroben-
zaldehyde, 2- and 3-bromobenzaldehyde, 2- and 4-tol-
ualdehyde, 4-methoxybenzaldehyde, benzaldehyde
and NaBH4 were purchased from Sigma-Aldrich. All
the solvents used were purchased from J.T. Baker or
Techrom and used without further purification.
Bioreduction of aldehydes and ketones
Preparation of the alcohols
The
corresponding
aldehyde
or
ketone
ꢂ5
(
1.484 ꢁ 10 mol) was added to the aqueous extract
The corresponding alcohols were prepared by reduc-
ing the substituted benzaldehydes and ketones with
of the selected bean (1 mL, Table 1). The reaction mix-
ꢀ
ture was incubated at 25 C, stirred magnetically for
24 h and then extracted with diethyl ether. The
organic phase was dried over anhydrous Na SO and
evaporated under reduced pressure. The conversion to
benzyl alcohol was determined by gas chromatog-
raphy, and the enantiomeric excess was determined
by HPLC using a Chiracel OD column. The experiments
were performed in triplicate.
NaBH following standard methods (Tae et al. 2006)
4
1
13
and were identified by H-NMR,
C-NMR and IR
2
4
(Supplementary material). NMR spectra were recorded
ꢀ
on an Agilent DD2-600 at 25 C using CDCl as the
solvent and TMS as the internal reference.
3
Reductase enzyme source
Fresh vegetables and seeds (Table 1) were purchased
from local markets. The biological material was disin-
fected with 5% sodium hypochlorite solution and
rinsed with sterile distilled water. The leaves, fruit
pulp, roots, florets and stalks (50 g) were cut into small
Analytical methods
Gas chromatographic analyses were performed using
an Agilent Technologies chromatograph (model 6890)
equipped with a flame ionization detector and a
3
pieces (0.5 cm ), blended with distilled water (50 mL),

BIOCATALYSIS AND BIOTRANSFORMATION
3
Supelcowax-10 (30 m ꢁ 25 mm ꢁ25 lm) column. The
O
OH
ꢀ
injector and detector temperature were set to 250 C,
H
H
reductase
and nitrogen was used as the carrier gas. The HPLC
analysis was performed on an Agilent 1100 liquid
chromatograph equipped with a diode array detector
using a Chiracel OD (25.0 cm ꢁ0.46 cm) column (Daicel
Chemical Industries, Ltd., Tokyo, Japan), and the
mobile phase was a mixture of hexane and isopro-
pyl alcohol.
3
1
3
1
R
R
R
R
2
2
R
R
(A)
(B)
1
2
3
1
2
3
R
R
R
R
R
R
H
H
F
H
H
H
H
Cl
H
H
H
F
2Br
3Br
Br
H
H
Br
H
H
H
2
F
F
4
H
Cl
H
H
2Me
4Me
4OMe
CH
H
3
H
2
3
Cl
Cl
H
H
Cl
H
CH
3
Results and discussion
H
H
OCH
3
Selection of the biological material with
reductase activity
4Cl
Figure 1. Reduction of benzaldehydes (A) to the correspond-
ing alcohols (B) using reductase enzymes from plants.
The reductase activity of 28 different parts of plants,
such as seeds, roots, fruits, leaves, florets or stalks, was
evaluated using benzaldehyde (AH) as the model sub-
strate to obtain benzyl alcohol (BH). As shown in
Table 1, all the tested biological materials showed
reductase activity; however, the seeds of plants of the
Phaseolus genus were identified as the source of the
most active reductases. The reduction of benzalde-
hyde to benzyl alcohol with seeds of pinto, Flor de
Mayo, ayocote, black and bayo beans was quantitative,
and these beans were thus selected for the reduction
of other carbonyl substrates. Daucus carota (carrot),
one of the most studied reductase sources (Omori
et al. 2016), yielded a moderate conversion to AH
Table 2. % Conversion of benzaldehydes (A) to the corre-
sponding alcohols (B) using Phaseolus seeds as reduc-
tase sources.
Entry Bean AH A2F A4F A2Cl A3Cl A4Cl A2Br A3Br A2Me A4Me A4OMe
1
2
3
4
5
Pinto
Bayo
Black
100 99 96 70 16 97 55 25 13
100 83 100 11 18 100 47 28 15
100 98 100 12 20 100 10 23 14
97
29
48
4
77
71
54
42
50
Ayocote 100 88 98 11 23 77 16 17
Flor de 100 89 100
Mayo
8
3
3
50 18
7
8
1
Nidetzky 2002; Pratihar 2014). The reduction was
improved in the presence of electron-withdrawing
substituents: the reduction of A4F showed between
(63%) under our reaction conditions.
9
6% and 100% conversion, and A4Cl was reduced at a
conversion between 50% and 100%. In contrast, the
presence of electron-donor groups diminished the
conversion: the reduction of A4Me ranged from 1% to
Bioreduction of substituted benzaldehydes
The catalytic specificity of the reduction using the
selected beans as biocatalyst sources was examined
with benzaldehydes substituted with electron-donating
groups (methoxy and methyl groups) and electron-
withdrawing groups (fluoride, chloride or bromide) in
the ortho, meta and para positions (Figure 1). As shown
in Table 2, both the reducing activity and the extent of
conversion to the corresponding alcohol depended on
the electrophilic activating/deactivating effects of the
substituents, the steric hindrance, the position with
respect to the carbonyl in the benzene ring and the
source of the biocatalyst (Figure 1).
The extent of the bioreduction of para-substituted
benzaldehydes was dependent on the electronic prop-
erties of the substituent and the biocatalyst source.
The presence of electron-withdrawing groups
decreased the electron density and subsequently
increased the nucleophilicity of the carbonyl, and the
electron-deficient aldehydes were reduced at a higher
extent than the electron-rich aldehydes (Mayr and
4
8%, but 97% conversion was obtained with pinto
beans, and A4OMe was reduced at a conversion
between 42% and 77%. The extent of the biocatalysed
reduction of A3Cl and A3Br was between 3% and 28%
with all the tested biocatalyst sources, the substituents
in the meta position relative to the carbonyl did not
favour the enzymatic reaction with the beans selected.
The chemical reactivity of ortho-substituted aro-
matic rings is not completely explained by the elec-
tronic properties of the substituent, because proximity
effects at the reaction centre like intramolecular
hydrogen bond formation, steric inhibition of reson-
ance, steric hindrance and short-range polar effects
are also involved in the reactivity of the compound
(Sedon and Zuman 1976; Sayyed and Suresh 2009;
Santiago et al. 2016). The extent of the reduction of
A2Me was very low (8%–15%, Table 2) with all
the tested biocatalyst sources, and this low reduction
was probably due to steric factors and the

ꢀ
A. SOLIS ET AL.
4
electron-donating nature of the methyl group, which
deactivates the carbonyl towards nucleophilic attack.
The extent of the reduction of A2F (99%), A2Cl (70%)
and A2Br (55%) using pinto beans as the reductase
source could be explained by the steric hindrance
effect and electronegativity of the halogen atoms F, Cl
and Br, because the fluorine is the smallest and the
most electronegative atom that favored the reduction
to a greater extent than the larger and less electro-
negative bromine atom. The other reductase sources
only yielded a high reduction of A2F (83%–98%),
whereas the conversion of A2Cl and A2Br was
between 3% and 11% and 10%–47%, respectively.
Pinto beans were the most active and versatile
reductase source because five (AH, A2F, A4F, A4Cl and
A4Me) of the 11 aldehydes were reduced to the corre-
sponding alcohols at a conversion higher than 90%
and A2Cl, A2Br and A4OMe were reduced at a conver-
sion between 55% and 77%. Bayo and black beans
reduced AH, A2F, A4F and A4Cl at a conversion higher
than 80%, whereas ayocote and Flor de Mayo beans
reduced AH, A2F and A4F at a conversion higher
than 80%.
Table 3. Reduction of ketones PhAc and PyAc to the corre-
sponding alcohols PhOH and PyOH using bean seeds as
reductase sources.
a,b
b,c
PhOH
PhOH
PyOH
PyOH
Beans
%conv
%ee
%conv
%ee
Pinto
Bayo
Black
Ayocote
Flor de Mayo
a
25
25
17
17
22
48
53
39
38
45
10
8
10
12
8
77
100
100
62
77
The configuration of PhOH was assigned as (R) by comparison of the
optical rotation in the literature (Basavaiah et al. 2004).
b
Determined by chiral HPLC.
c
The configuration of PyOH was assigned as (R) by comparison of the
optical rotation in the literature (Soai et al. 1987).
that the nitrogen in the pyridine ring possibly pro-
moted a better interaction between the active site of
the enzyme and the substrate, which would allow
enantioface-selective delivery of hydride from the
bound cofactor (Pal et al. 2012).
With D. carota the reduction of PhAc was 100%
and the ee was 99%; the same ee was obtained with
F. vulgare and C. pepo however conversions were
3
7% and 10% respectively in 72 h (Bruni et al. 2002).
The reduction of PhAc with the beans negro, bayo,
flor de mayo, ayocote and pinto was similar to that
with Ximenia americana (54% conv, 48% ee) (da Silva
et al. 2018) and Saccharum officinarum (39% conv,
There are reports on the reduction of benzaldehyde
using several plants, in this work the beans pinto, Flor
de Mayo, ayocote, black and bayo reduced 100% of
benzaldehyde in 24 h, similar to C. maculatum
5
7%ee) (Assun c¸ ~a o et al. 2008) in 72 h. Regarding the
(Salvano et al. 2011) whereas with M. esculenta and M.
chiral reduction of PyAc, the conversions with D. car-
ota and V. radiata were100% and the corresponding
ee was 99% and 100%, respectively (Lakshmi et al.
dulcis (Machado et al. 2006), Ximenia Americana (da
Silva et al. 2018) and Saccharum officinarum (Assun c¸ ~a o
et al. 2008) the conversion was also 100% but in 72 h.
2
011, the conversion was100% and the ee was 83%)
(Santhanam et al. 2017). In this work, the ee of PyOH
Bioreduction of acetophenone and
obtained with the bayo and black beans was 100%,
however the conversions were low (8% and
2-acetylpyridine
1
0%, 24 h)
The reduction of acetophenone (PhAc) and 2-acetyl-
pyridine (PyAc) to the corresponding alcohols, PhOH
and PyOH, respectively, with the beans selected seeds
was lower with respect to the reduction of the alde-
hydes, probably due to the steric factor, which
decreases the reactivity of the ketones (Table 3).
Conclusions
The seeds from plants of the Phaseolus genus, namely,
pinto, bayo, black, ayocote and Flor de Mayo beans,
are reductase sources that can reduce a variety of
benzaldehydes. The extent of conversion was influ-
enced by the reductase source and by the nature and
position of the substituents on the aromatic ring.
Pinto beans were identified as the most versatile bio-
catalyst source due to their tolerance of para- and
ortho-substituted benzaldehydes as substrates. With
regard to ketones, the interaction of a heteroaromatic
ketone with the enzyme was more efficient than that
of the other ketone, and the optical purity of the
resulting alcohol was higher.
However, the enantioselectivity of the reaction was
highly influenced by the nature of the aromatic ring
and the enzyme source: bayo and black beans gave
enantiopure (R)-1-(pyridin-2-yl)ethanol (PyOH), and
bayo beans provided the highest enantiomeric excess
(ee) for (R)-1-phenylethanol (PhOH), which was 53%.
These results are in agreement with those reported by
Pal et al. (2012), who compared the reduction of PhAc
and PyAc using three fungi as reductase source, the
ee of PyOH was 99%, whereas PhOH was obtained
with a lower enantiopurity. The researchers speculated

BIOCATALYSIS AND BIOTRANSFORMATION
5
Lakshmi CS, Reddy GR, Rao AB. 2011. Asymmetric reduction
of heteroaryl methyl ketones using Daucus carota. Green
Sust Chem. 1:117–122.
Acknowledgements
Rosa Mar ꢀı a Mart ꢀı nez extends her appreciation to the
Master’s Program in Pharmaceutical Sciences, Universidad
Aut oꢀ noma Metropolitana.
Leyva E, Moctezuma E, Santos-D ꢀı az M, Loredo-Carrillo S,
Hernandez-Gonzalez O. 2012. Fast microwave assisted bio-
reduction of aromatic aldehydes using aloe vera. A green
chemistry reaction. Rev Latinoam Qu ꢀı m. 40:140–147.
ꢀ
ꢀ
Disclosure statement
Machado LL, Monte FJQ, de Oliveira M.D., de Mattos MC,
Lemos TLG, Gotor-Fern ꢀa ndez V, de Gonzalo G, Gotor V.
No potential conflict of interest was reported by the authors.
2
008. Bioreduction of aromatic aldehydes and ketones by
fruits’ barks of Passiflora edulis. J Mol Catal B: Enzym. 54:
30–133.
1
Funding
Machado LL, Souza JSN, de Mattos MC, Sakata SK, Cordell G,
Lemos TLG. 2006. Bioreduction of aldehydes and ketones
using Manihot species. Phytochemistry. 67:1637–1643.
Mayr P, Nidetzky B. 2002. Catalytic reaction profile for
NADH-dependent reduction of aromatic aldehydes by
xylose reductase from Candida tenuis. Biochem J. 366:
The authors thank Consejo Nacional de Ciencia y Tecnolog ꢀı a,
CONACYT, M ꢀe xico for Scholarship Grant [578495].
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