Searching for local biocatalysts: Bioreduction of aldehydes using plant roots of the Province of Cordoba (Argentina)

Article abstract of DOI:10.1016/j.molcatb.2011.03.003

A screening for the capacity of wild plants growing in the Province of Cordoba to bioreduce benzaldehyde was carried out. From this study, thirteen species showed quantitative reduction yields to benzyl alcohol, with Conium maculatum showing the best reduction efficiency. This plant was also tested against different substituted benzaldehydes, and quantitative yields of substituted benzylic alcohols were obtained, except for vanillin, where only 27% of vanillic alcohol was formed (main product: 2-methoxyphenol at a 73% yield). A scaling study of the reaction using C. maculatum and benzaldehyde was carried out, and it was observed that high substrate-catalyst relationships reduced the efficiency of the reaction due to side reactions of oxidation. The bioreduction method presented here permits substituted benzylic alcohols to be obtained using an environmentally friendly methodology, with excellent yields produced on a laboratory scale.

Full text of DOI:10.1016/j.molcatb.2011.03.003

Journal of Molecular Catalysis B: Enzymatic 71 (2011) 16–21
Contents lists available at ScienceDirect
Journal of Molecular Catalysis B: Enzymatic
journal homepage: www.elsevier.com/locate/molcatb
Searching for local biocatalysts: Bioreduction of aldehydes using plant roots of
the Province of Córdoba (Argentina)
Mario S. Salvanoa, Juan J. Canterob, Ana M. Vázquezc, Stella M. Formicad, Mario L. Aimard,∗
a Subsecretaría Ceprocor, Ministerio de Ciencia y Tecnología de la Provincia de Córdoba, Álvarez de Arenales 230, Barrio Juniors (X5004AAP), Córdoba, Argentina
b Departamento de Biología Agrícola, Facultad de Agronomía y Veterinaria, Universidad Nacional de Río Cuarto, Ruta Nacional 36 Km 601 (X5804BYA), Río Cuarto, Córdoba, Argentina
c Laboratorio de Tecnología Química, Facultad de Ciencias Químicas, Universidad Católica de Córdoba, Camino a Alta Gracia Km 7.5 (5000), Córdoba, Argentina
d Departamento de Quìmica, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Vélez Sársfield 1611, Ciudad Universitaria (X5016CCA), Córdoba,
Argentina
a r t i c l e i n f o
a b s t r a c t
Article history:
A screening for the capacity of wild plants growing in the Province of Córdoba to bioreduce benzaldehyde
was carried out. From this study, thirteen species showed quantitative reduction yields to benzyl alcohol,
with Conium maculatum showing the best reduction efficiency. This plant was also tested against different
substituted benzaldehydes, and quantitative yields of substituted benzylic alcohols were obtained, except
for vanillin, where only 27% of vanillic alcohol was formed (main product: 2-methoxyphenol at a 73%
yield). A scaling study of the reaction using C. maculatum and benzaldehyde was carried out, and it was
observed that high substrate–catalyst relationships reduced the efficiency of the reaction due to side
reactions of oxidation. The bioreduction method presented here permits substituted benzylic alcohols
to be obtained using an environmentally friendly methodology, with excellent yields produced on a
laboratory scale.
Received 19 October 2010
Received in revised form 3 March 2011
Accepted 11 March 2011
Available online 21 March 2011
Keywords:
Biocatalysis
Bioreduction
Conium maculatum
Aromatic aldehydes
Benzylic alcohols
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
Many transformations of different substrates, such as hydrox-
ylation and oxidation reactions (Gynostemma pentaphyllum) [4],
The reduction of the carbonyl group is among the most impor-
tant reactions in organic chemistry, with today’s organic chemists
having a wide range of appropriate reduction systems at their dis-
posal. In general, most of these use heavy metals or their hydrides
and organic solvents as the reaction medium, which are able
to provide excellent yields of the desired alcohols [1]. However,
comparatively few reduction methodologies have been developed
taking into account the concept of green chemistry (environmen-
tally friendly reaction systems) in order to avoid the formation of
toxic waste that may pollute the environment [2].
In recent years, chemical reactions using plant parts and their
cell cultures as biocatalysts have received great attention due to
the large biotechnological potential of enzymatic reactions. Some
important characteristics of these biocatalysts are their low cost,
high versatility and efficiency, in addition to highly desirable
chemical aspects such as chemoselectivity, regioselectivity, and
enantioselectivity, with the combination of these factors having
made biocatalytic reactions very attractive to the industrial sector
[3].
hydrolysis of esters (Solanum tuberosum, Helianthus tuberosus) [5],
bioreduction of ketones and aldehydes (Daucus carota, Foeniculum
vulgare, Cucurbita pepo, Phaseolus aureus, Cocos nucifera, Saccharum
officinarum, Manihot dulcis, Manihot esculenta) [3,6–16], enzymatic
lactonization (Malus sylvestris, Helianthus tuberosus) [17], glycosy-
lation (Ipomoea batatas, Eucalyptus perriniana) [18], etc., have been
performed, and have produced very good results using plants and
their cultured cells.
The use of plants as biocatalysts has many advantages. First of
all, a large array of taxonomically different plants is available at a
very low cost. Another important aspect is that the separation of
the product from the reaction mixture can be carried out very eas-
ily by filtration/centrifugation and the remaining material is easily
disposed of. Moreover, these systems have the advantage of being
environmentally friendly, due to the reaction being carried out in
water as the solvent and the catalyst being biodegradable [19], as
opposed to the classic reactions of organic chemistry where heavy
metal disposal may be an issue.
In summary, it can be stated without equivocation that plants
represent an alternative source of “new” enzymes for use in organic
synthesis.
Recently, as a part of a major program on the study of the flora
in the Province of Córdoba, a project was commenced with the
∗
Corresponding author. Tel.: +54 351 4344983x7; fax: +54 351 4334139.
E-mail address: mlaimar@efn.uncor.edu (M.L. Aimar).
1381-1177/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcatb.2011.03.003

M.S. Salvano et al. / Journal of Molecular Catalysis B: Enzymatic 71 (2011) 16–21
17
aims of finding green alternatives and economically viable proce-
dures to synthesize chemical products of commercial interest using
biocatalytic processes.
aqueous solution for 20 min. Then, they were washed with ster-
ile deionized water and the external layer was removed, with the
remaining roots being cut into small thin slices (1 cm) with a ster-
ile cutter. Both the treated and cut plant roots (10 g) were added
to a sterile Erlenmeyer flask (250 mL) with sterile deionized water
(80 mL), and the corresponding aldehyde (50 mg) was added to this
suspension and the reaction carried out by stirring on an orbital
shaker at room temperature with the Erlenmeyer flask closed. The
reaction’s progress was monitored every 24 h for 7 days, and the
samples (5 mL, saturated with sodium chloride) were extracted by
shaking with ethyl acetate (2 mL). The organic layer was collected,
sodium sulfate was added to remove the dissolved water, and the
organic solution was filtered and analyzed (1 ␮L) by GC.
In the particular case of the benzylic alcohols, several of these are
considered to be key starting materials in the synthesis of scented
substances for cosmetics, fragrances and the flavour industry [20],
which in general are more expensive than the corresponding alde-
hydes from which they are obtained. However, the reduction of
benzaldehydes may be potentially carried out through biocatalytic
methodologies, if an efficient and affordable biocatalyst is available
which is also capable of generating the desired product in adequate
quantities. With this objective in mind, the screening of the native
flora was initiated to find plants that could be used as biocatalysts
in reduction reactions of aromatic aldehydes.
2.5. Scaling study
2. Experimental
This study was carried out using treated and cut roots (10 g),
sterile deionized water (80 mL) and an orbital shaker at room tem-
perature. In this system, the concentration of the substrate and the
reaction time were modified to optimize the conditions, with the
evolution of the reactions being periodically monitored by GC-FID
analysis. The crude reaction mixture described in Table 3 (entry
6) was filtered and the aqueous solution was extracted with ethyl
acetate (3× 20 mL). Then, the combined organic layer was dried
over calcium sulfate, and the solution was preconcentrated on a
rotary evaporator. The crude solution was filtered on a short col-
umn with silica gel (70–230 mesh) using ethyl acetate as eluent,
and benzyl alcohol was isolated (192 mg, 96% yield). The presence
of benzoic acid in the reactions (Table 3; entries 9 and 10) was
determined by GC, using a standard sample of benzoic acid and
through GC–MS analysis by comparing the obtained spectra with
library data.
2.1. General methods
Benzaldehyde, benzoic acid, 2-methoxyphenol and substituted
benzaldehydes were purchased from the Sigma–Aldrich Chem-
ical Company (Argentina). 4-(N,N-dimethylamino) benzaldehyde
was obtained from Fluka. Benzyl alcohol and substituted benzyl
alcohols were purchased from the Sigma–Aldrich Chemical Com-
pany. 4-(N,N-dimethylamino)benzyl alcohol, 2-methylthiobenzyl
alcohol and vanillic alcohol were synthesized by a methodology
described in the literature [21], and sterile deionized water was
used as the solvent in all experiments. The crude reaction products
were extracted with ethyl acetate, the organic solutions were evap-
orated, and the products were filtered on a short column with silica
gel (70–230 mesh) using ethyl acetate as the eluent. GC analyses
were made on a Shimadzu GC-14B instrument, with FID detector
and GC–MS analyses were carried out on a Shimadzu GC-17A/QP-
5000 instrument. 1H NMR spectra were recorded on a Bruker AC
200 MHz using CDCl3 as the solvent. All products were charac-
terized by comparison of their GC retention time (GC Rt) with
authentic samples, and by comparison of their MS and 1H NMR
spectra with literature data [21–26].
2.6. Spectroscopic and GC data
2.6.1. Benzyl alcohol
GC Rt: 13.5 min (benzaldehyde GC Rt: 10.7 min), MS m/z: 109
(M+ +1, 5%), 108 (M+, 60%), 107 (41%), 91 (13%), 79 (100%), 78 (13%),
77 (62%), 65 (10%), 63 (10%), 53 (14%), 52 (14%), 51 (50%), 50 (27%).
1H NMR ı (ppm): 2.30 (s, 1H), 4.61 (s, 2H), 7.20–7.40 (m, 5H).
2.2. GC-FID and GC–MS analyses
The GC separations were performed on a Hewlett Packard HP-5
fused silica capillary column (Crosslinked 5% PhMe Siloxane, 30 m,
0.32 mm, 0.25 ␮m film thickness) with GC conditions of: split 1/50,
injector 220 ◦C, detector FID: 220 ◦C, carrier gas: N2 to 1 mL/min,
temp: T1 = 50 ◦C (5 min), ꢀT = 5 ◦C/min, T2 = 150 ◦C (5 min). The
yields of the reactions were determined by GC using the normalized
peak areas without a correction factor. The GC–MS (70 eV) analyses
were performed using the same conditions as those used in the GC
analysis and the same capillary column.
2.6.2. Benzoic acid
GC Rt: 19.6 min, MS m/z: 277 (M+ +1, 9%), 276 (M+, 93%), 245
(100%), 217 (14%), 90 (24%), 89 (17%), 63 (8.5%).
2.6.3. 4-Chlorobenzyl alcohol
GC Rt: 18.9 min (4-chlorobenzaldehyde GC Rt: 14.9 min), MS
m/z: 143 (M+ +1, 17%), 142 (M+, 84%), 125 (24%), 113 (24%), 107
(52%), 89 (11%), 79 (53%), 77 (100%), 51 (25%). 1H NMR ı (ppm):
2.30 (s, 1H), 4.61 (s, 2H), 7.05–7.50 (m, 4H).
2.3. Biocatalysts
2.6.4. 4-Methoxybenzyl alcohol
Healthy and intact plants were collected in the Punilla Valley
(Province of Córdoba, Argentina) and identified by a botanist. To
carry out this study, plants were selected whose roots were similar
in form and texture to that of carrot. The aerial parts were discarded,
and the roots were washed with distilled water to remove traces
of soil.
GC conditions: T1 = 50 ◦C (2 min), ꢀT = 5 ◦C/min, T2 = 200 ◦C
(2 min), GC Rt: 17.5 min (4-methoxybenzaldehyde GC Rt: 16.3 min),
MS m/z: 139 (M+ +1, 10%), 138 (M+, 100%), 137 (67%), 121 (56%), 109
(71%), 107 (27%), 105 (22%), 94 (17%), 77 (36%), 65 (15%), 63 (16%),
51 (18%), 39 (16%). 1H NMR ı (ppm): 2.30–2.42 (s, 1H), 3.77 (s. 3H),
4.52 (s, 2H), 6.87 (d, 2H), 7.21 (d, 2H).
2.4. Bioreductions
2.6.5. 4-(N,N-Dimethylamino)benzyl alcohol
The reactions were conducted immediately after acquisition of
the plant to assure the integrity of the enzymatic system. A typical
reaction was conducted as follows: fresh plant roots were washed
with distilled water and maintained in a 5% sodium hypochlorite
GC
retention
time:
19.6 min
(4-(N,N-
dimethylamino)benzaldehyde GC Rt: 21.6 min), MS m/z: 152
(M+ +1, 5%), 151 (M+, 49%), 135 (100%), 134 (67%), 120 (34%), 119
(40%), 118 (42%), 105 (11%), 91 (45%), 89 (19%), 77 (22%), 65 (18%),

18
M.S. Salvano et al. / Journal of Molecular Catalysis B: Enzymatic 71 (2011) 16–21
Table 1
Screening for biocatalysts: reduction of benzaldehyde to benzyl alcohol carried out by roots of wild plants
O
H
OH
Roots of plants
water r.t.
.
Entry
Family
Alliaceae
Amaranthaceae
Apiaceae
Apiaceae
Apiaceae
Scientific name
Time (days)
% Benzyl alcohola
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Nothoscordum gracile (Dryand. ex Aiton) Steam var. gracile
Alternanthera pungens Kunth
Daucus carota L.
Pastinaca saliva L.
Conium maculatum L.
4
5
3
4
1
4
4
4
5
4
4
4
4
5
4
6
nrb
99
>99
>99
>99
>99
99
Apiaceae
Eryngium horridum Malme
Apocynaceae
Asteraceae
Bromeliaceae
Cannaceae
Euphorbiaceae
Fabaceae
Mandevilla petraea(A. St.-Hil.) Pichon
Trichocline reptans (Wedd.) Hieron.
Puya spathacea (Griseb.) Mez.
Canna indica L.
Euphorbia portulacoides L. var. portulacoides
Dalea elegans Gillies ex Hook. & Arn var. elegans.
Iris pseudacorus L.
Mirabilis jalapa L.
Oxalis articulata Savigny ssp. articulata
Talinum polygaloides Gillies ex Arn.
97
98
99
nrb
97
Iridaceae
99
Nyctaginaceae
Oxalidaceae
Talinaceae
98
nrb
98
a
Measured by GC analysis.
nr: No reaction.
b
63 (15%), 51 (20%), 42 (19%), 39 (15%). 1H NMR ı (ppm): 2.30 (s,
3. Results and discussion
1H), 2.98 (s, 6H), 4.54 (s, H), 6.78 (d, 2H), 7.21 (d, 2H).
3.1. Screening of plants for the bioreduction of benzaldehyde
2.6.6. Vanillic alcohol
GC conditions: T1 = 50 ◦C (2 min), ꢀT = 6 ◦C/min, T2 = 200 ◦C
(2 min), GC Rt: 19.6 min (vanillin GC Rt: 18.3 min), MS m/z: 155
(M+ +1, 9%), 154 (M+, 100%), 137 (32%), 135 (9%), 125 (31%), 123
(21%), 122 (28%), 107 (13%), 93 (31%), 77 (16%), 65 (42%), 63 (15%),
53 (19%), 51 (21%), 50 (17%), 39 (22%). 1H NMR ı (ppm): 3.74 (s,
3H), 4.38 (s, 2H), 5.03 (s, 1H), 6.71 (d, 2H), 6.89 (s, 1H), 8.79 (s, 1H).
With the dual purpose of firstly developing economically viable
and environmentally friendly reaction systems, and secondly, of
finding a use for the local flora, the study of the biocatalytic reduc-
tion of benzaldehyde was performed on roots of plants that grow
wild in Córdoba Province. Sixteen species of naturalized or native
plants from thirteen families were collected, and studies were car-
ried out using a methodology similar to one previously reported
[6], with benzaldehyde as the model substrate. Results are shown
in Table 1.
2.6.7. 2-Methylthiobenzyl alcohol
GC Rt: 24.4 min (2-methylthiobenzaldehyde GC Rt: 23.5 min),
MS m/z: 155 (M+ +1, 10%), 154 (M+, 100%), 139 (50%), 137 (34%),
136 (35%), 135 (34%), 111 (32%), 109 (25%), 105 (22%), 91 (8%), 77
(43%), 52 (11%), 51 (20%), 50 (12%), 45 (18%), 39. 1H NMR ı (ppm):
2.41 (s, 3H), 4.62 (s, 2H), 7.07–7.30 (m, 3H), 7.33–7.41(m, 1H).
Table 2
Ability of C. maculatum to reduce different substituted benzaldehydes
OH
O
H
2.6.8. 4-Methylthiobenzyl alcohol
GC Rt: 25.6 min (4-methylthiobenzaldehyde GC Rt: 24.3 min),
MS m/z: 155 (M+ +1, 12%), 154 (M+, 100%), 137 (22%), 125 (16%),
122 (11%), 109 (35%), 107 (24%), 91 (8%), 79 (25%), 77 (34%), 51
(13%), 45 (18%). 1H NMR ı (ppm): 2.21 (s, 1H), 2.47 (s, 3H), 4.60 (s,
2H), 7.23 (m, 4H).
R
R
Roots of C. maculatum
water r.t.
R`
R`
2.6.9. 3-Nitrobenzyl alcohol
R"
R"
.
GC Rt: 20.8 min (3-nitrobenzaldehyde GC Rt: 16.9 min), MS m/z:
154 (M+ +1, 26%), 153 (M+, 3%), 137 (29%), 136 (60%), 124 (9%), 108
(40%), 107 (100%), 105 (66%), 88 (30%), 77 (90%), 76 (78%), 74 (75%),
62 (28%), 51 (24%), 50 (46%), 49 (17%), 39 (11%). 1H NMR ı (ppm):
2.55 (s, 1 H), 4.8 (s, 2H), 7.40–7.65 (m, 2H), 8.00–8.20 (m, 2H).
Entry
R
Rꢀ
Rꢀꢀ
Time (days)
% Alcohola
1
2
3
4
5
6
7
8
H–
H–
H–
H–
HO–
H–
H–
NO2–
H–
H–
Cl–
1
1
1
2
1
1
1
7
>99
>99
>99
27
>99
>99
>99
>99
H–
H–
H–
CH3–S–
H–
CH3–O–
CH3–O–
H–
CH3–S–
H–
2.6.10. 2-Methoxyphenol
GC Rt: 11 min MS m/z: 125 (M+ +1, 10%), 124 (M+, 94%), 110
(20%), 109 (100%), 81 (80%), 63 (10%), 54 (15%), 53 (35%), 51 (23%).
1H NMR ı (ppm): 3.80 (s, 3H), 5.81 (s, 1H), 6.80–6.95 (m, 4H).
H–
H–
(CH3)2–N–
a
Measured by GC analysis.

M.S. Salvano et al. / Journal of Molecular Catalysis B: Enzymatic 71 (2011) 16–21
19
Table 3
As can be seen in Table 1, thirteen of the sixteen species studied
Scaling study: bioreduction of benzaldehyde by C. maculatum.
produced excellent results: Alternanthera pungens, Pastinaca sativa,
Conium maculatum, Mandevilla petraea, Trichocline reptans, Eryn-
gium horridum, Puya spathacea, Canna indica, Iris pseudacorus, Dalea
elegans, Mirabilis jalapa and Talinum polygaloides showed quantita-
tive yields for the formation of benzyl alcohol. The reaction using
D. carota as a model bioreducer of carbonyl compounds was con-
ducted as well, and as with other members of the family, this
reaction was also quantitative (Table 1, entry 3).
It can be observed in Table 1 (entries 3–6) that the Apiaceae
family was able to reduce benzaldehyde with a high efficiency,
which appears to be a common feature of this family. In contrast,
no reduction reaction was found using Euphorbia portulacoides,
Nothoscordum gracile or Oxalis articulata as catalysts (Table 1,
entries 1, 11 and 15).
Entry
Benzaldehyde (mg)
Time (days)
% Benzyl
alcohola
% Benzoic
acida
1
2
3
4
5
6
7
8
9
50
100
150
175
187.5
200
250
300
400
800
1
4
4
4
4
4
7
7
7
7
>99
–
–
–
–
–
–
–
–
19
15
>99
>99
>99
>99
>99
21
9
5
3
10
a
Measured by GC analysis.
3.2. Bioreduction of substituted benzaldehydes by C. maculatum:
advantages and scope
are studies on other plant species reporting the reduction of the
nitro group to an amine [10,31,32]. When vanillin, however, was
used as the substrate (Table 2, entry 5), the reaction produced only
27% of the corresponding vanillic alcohol. Here, it was observed that
the major reduction product was 2-methoxyphenol, at a 73% yield
(Fig. 1).
It is worth noting that in previous studies using Passiflora edulis
[15] and two species of Manihot [13] no reduction of vanillin was
observed, but vanillic alcohol, as well as the corresponding benzyl
methyl ether, were obtained when using sugar cane juice [14] and
coconut water [10].
The important increase in reaction time observed for 4-(N,N-
dimethylamino) benzaldehyde (Table 2, entry 8), may have been
due to steric factors or to stronger ␲-donating effects inherent to
the N,N-dimethylamino group [1], or to both, which could have
decreased the reactivity of the aldehyde group.
Although most of the species studied showed almost quantita-
tive yields for the reduction reaction, C. maculatum (Apiaceae) was
selected for the experiments because the reaction for the reduction
of benzaldehyde occurred in the shortest period of time (Table 1,
entry 5). In addition to this, C. maculatum, a weed that grows abun-
dantly in the Province of Córdoba and is available throughout most
of the year, is not used industrially and can be discarded as a live-
stock feed due to its toxicity. It is commonly known as hemlock, and
is an annual herb of 50–300 cm high which presents green stalks
with slightly violet specks and parsley-like leaves. Its thick vertical
root is like a carrot, with some branching, and is yellowish-white
in colour. It is highly toxic due to the presence of alkaloids, a neu-
rotoxin and coumarins [27–29]. Hemlock is in fact better known as
an active ingredient in the preparation of poisons [30].
With the aim of establishing the ability and the scope of C. mac-
ulatum to reduce substituted benzaldehydes to the corresponding
substituted benzyl alcohols, studies were conducted and the results
are listed in Table 2, where it can be seen that C. maculatum proved
to be a very efficient biocatalyst for the reduction of substituted
benzaldehydes. In this process, all of the aldehydes tested, except
vanillin, produced alcohols of excellent yield, better than the results
reported for coconut water [10] and comparable to those of M. escu-
lenta, M. dulcis [13], sugar cane juice [14], Brassica oleracea, Beta
vulgaris and Spinacia oleracea [20].
It is also noteworthy that, for these working conditions, there
were no limitations as concerning the position or nature of the sub-
stituent, with the reaction giving quantitative yields, regardless of
the relative position of the substituent with respect to the aldehyde
function, with the substituents being either electron withdrawing
or donating groups.
3.3. Scaling of the bioreduction of benzaldehyde using C.
maculatum
A scaling study of the reduction process was carried out using
hemlock as the biocatalyst and the results are summarized in
Table 3, where it can be seen (entry 6) that the reaction proceeded
quantitatively when a substrate ratio of 200 mg per 10 g of catalyst
was used in 80 mL of water. This reduction methodology permitted
the theoretical acquisition of 2.5 g of benzyl alcohol per liter of reac-
tion, but it should be noted that when a higher substrate/catalyst
ratio was used the performance of the reaction lapsed abruptly
(Table 3 entries 7–10), with substrate oxidation to the benzoic acid
beginning to occur unexpectedly as the main reaction (Table 3,
entries 9 and 10). In addition, when the concentration of the sub-
strate was increased, the reaction time was longer (Table 3, entries
1–6).
In the particular case of 3-nitrobenzaldehyde (Table 2, entry 8),
it was observed that C. maculatum produced the reduction of the
aldehyde group without reducing the nitro group, although there
OH
H
O
Roots of C. maculatum
water r.t.
+
OCH3
OCH3
OCH3
OH
OH
OH
73 %
27 %
Fig. 1. Bioreduction of vanillin to vanillic alcohol and 2-methoxyphenol catalyzed by C. maculatum.

20
M.S. Salvano et al. / Journal of Molecular Catalysis B: Enzymatic 71 (2011) 16–21
4. Conclusions
[12] W.K. Maczka, A. Mironowicz, Tetrahedron: Asymmetry 15 (2004) 1965–1967.
[13] L.L. Machado, J.S.N. Souza, M.C. de Mattos, S.K. Sakata, G.A. Cordell, T.L.G. Lemos,
Phytochemistry 67 (2006) 1637–1643.
The results demonstrate that most of the locally available
species studied have enzyme systems with the ability to reduce
aldehydes to the corresponding alcohols at high yields, with thir-
teen species (out of sixteen) showing an excellent ability to reduce
benzaldehyde to benzyl alcohol. Moreover, it is noteworthy that
C. maculatum showed the fastest reaction rate in carrying out this
transformation.
C. maculatum was also effective in reducing substituted ben-
zaldehydes and the yield was always quantitative, except for
the reaction using vanillin, where 2-methoxyphenol was the
main product. Nevertheless, based on the results observed
here, the reaction may not be efficient with disubstituted
aldehydes, with more extensive studies being required to inves-
tigate this hypothesis. Currently, we are conducting studies to
determine the ability of C. maculatum to produce the decar-
bonylation of aldehydes similar to vanillin, and to attempt to
identify if this type of reaction is common with disubstituted
benzaldehydes.
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In the study of the scaling reaction using benzaldehyde as a
model substrate and C. maculatum as a biocatalyst, it was observed
that a higher substrate–catalyst ratio reduced the efficiency of
the reaction, resulting in side reactions of oxidation to benzoic
acid.
The results obtained here using C. maculatum for biocatalysis
may offer new strategies for the reduction of selected substi-
tuted benzaldehydes as a critical step in a synthetic organic
pathway, thereby avoiding the use of costly and non-renewable
metal reducing agents and organic solvents commonly utilized
in organic synthesis. As a result of this study with wild plants,
it is clear that an unexpected opportunity has arisen to establish
new applications for the native flora, especially for those species
which do not have any other reported practical utility and are
branded weeds. The bioreduction method presented here allows
substituted benzylic alcohols to be obtained using a methodology
which is more environmentally friendly than classical reductions
of aldehydes, with excellent yields produced on a laboratory
scale.
Mario S. Salvano is a Pharmacist. He is currently working
on a research project to obtain new biocatalysts for the
bioreduction of carbonyl compounds.
Acknowledgments
These studies were supported by the Ministry of Science and
Technology of the Province of Córdoba, Argentina. This work is
dedicated to the teaching career of Dr. Rita H. de Rossi. Special
thanks are due to Dr Elba Buján for technical assistance in this
study, and to Dr. Paul Hobson, native speaker, for revision of the
manuscript.
Dr. Juan J. Cantero is an Associate Professor of Agricul-
tural Systematic Botany in the Faculty of Agronomy and
Veterinary at Universidad Nacional de Rio Cuarto, Córdoba
(Argentina) His research interests are focused on botany
and plant diversity. He currently holds the position of Sec-
retary for the Promotion of Science under the Ministry of
Science and Technology of the Province of Cordoba.
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M.S. Salvano et al. / Journal of Molecular Catalysis B: Enzymatic 71 (2011) 16–21
21
Dr. Stella M. Formica is a Titular Professor of Applied
Chemistry in the Faculty of Exact, Physical and Natural
Sciences at Universidad Nacional de Córdoba (Argentina).
Her research interests are focused on organic synthesis
and biocatalysis, particularly in the study of the reduction
of carbonyl compounds.
Dr. Mario L. Aimar is an Associate Professor of Applied
Chemistry in the Faculty of Exact, Physical and Natural
Sciences at Universidad Nacional de Córdoba (Argentina).
His research interests are focused on organic synthesis,
biocatalysis and the phytoremediation of contaminated
water. At present, he is leading a Biocatalysis Research
Group, which is particularly involved in the study of the
bioreduction of carbonyl compounds.