Chemoselective hydrolysis of ester bonds in the presence of Baker's yeast

Article abstract of DOI:10.1080/00397910903068196

The catalytic effect of baker's yeast on the hydrolysis of aliphatic esters in p-acetoxybenzoates is described. The chemoselective character of this reaction enables the selective protection of the hydroxyl group in p-hydroxybenzoic acid derivatives.

Full text of DOI:10.1080/00397910903068196

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Chemoselective Hydrolysis of Ester
Bonds in the Presence of Baker's Yeast
Ewa Białecka-Florjańczyk a & Ewa Majewska a
a Warsaw University of Life Sciences, Institute of Chemistry ,
Warsaw, Poland
Published online: 07 Apr 2010.
To cite this article: Ewa Białecka-Florjańczyk & Ewa Majewska (2010) Chemoselective Hydrolysis
of Ester Bonds in the Presence of Baker's Yeast, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 40:9, 1264-1269, DOI:
10.1080/00397910903068196
To link to this article: http://dx.doi.org/10.1080/00397910903068196
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Synthetic Communications1, 40: 1264–1269, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903068196
CHEMOSELECTIVE HYDROLYSIS OF ESTER BONDS
IN THE PRESENCE OF BAKER’S YEAST
´
Ewa Białecka-Florjanczyk and Ewa Majewska
Warsaw University of Life Sciences, Institute of Chemistry, Warsaw, Poland
The catalytic effect of baker’s yeast on the hydrolysis of aliphatic esters in p-acetoxybenzoates
is described. The chemoselective character of this reaction enables the selective protection of
the hydroxyl group in p-hydroxybenzoic acid derivatives.
Keywords: Baker’s yeast; ester hydrolysis; hydroxyl group protection
Biotransformations provide efficient procedures in organic synthesis because of the
high selectivity of enzymes. Thus, the use of enzymes’ labile protecting groups offers
viable alternatives to chemical methods.[1] In this way, protection and deprotection
can be carried out for polyfunctional molecules such as carbohydrates,[2] peptides,[3]
nucleosides,[4] steroids, alkaloids, and phenolic natural products.[5]
Hydroxyl groups protected as esters of carboxylic acids can be liberated enzy-
matically. Many biocatalysts are used in this field, among them hydrolytic enzymes
such as lipases, which are particularly suitable for the regioselective acylation and
deacylation of primary and secondary hydroxyl groups.[6] In the deprotection of
peracetylated phenols with broad spectrum of lipases in general, the sterically more
accessible ones are cleaved.[5]
To explore new sources of hydrolases that display wider activities than those
exhibited by commercially available enzymes, we screened microbial whole cells such
as baker’s yeast for hydrolytic activity.
The carbonyl group reduction is probably the most extensively studied baker’s
yeast–mediated biotransformation, but several hydrolytic enzymes (such as sterol
ester hydrolase, carboxylic ester hydrolase, and lipase) have been isolated from Sac-
charomyces cerevisiae.[7,8] Their hydrolytic abilities, first discovered as an undesired
side reaction,[9] were found to have an interesting application to the resolution of
enantiomers of amino acids by submitting to hydrolysis of the N-acetyl derivatives
of ethyl esters (Scheme 1).[6]
The hydrolysis reaction of racemic N-acetyl a-amino acids esters runs
selectively in the ester group, but only derivatives of natural (S)-amino acids are
subject to it. Enantiomer (R) can be regained in N-acetylamino ester form.[9]
Received February 9, 2009.
Address correspondence to Ewa Białecka-Florjanczyk, Warsaw University of Life Sciences
´
(SGGW), Institute of Chemistry, ul. Nowoursynowska 166, 02-787 Warsaw, Poland. E-mail:
Ewa_Bialecka_Florjanczyk@sggw.pl
1264

SELECTIVE HYDROLYSIS OF ESTERS BY BAKER’S YEAST
1265
Scheme 1. Enantiospecific hydrolysis of amino acid esters.
Also, hydrolysis of racemic 1-alkyn-3-ol acetates[10] (Scheme 2) has led to the
formation of the enantiomer, which is a major substrate in the synthesis of alkaloids,
prostaglandins, pyrethroids, and steroids.
The aim of this study was to investigate the chemoselectivity in baker’s yeast–
mediated hydrolysis of esters of different carboxylic acids, especially aromatic and
aliphatic esters. The comparison of the catalytic effect of baker’s yeast on hydrolysis
reaction of aliphatic and aromatic esters showed significant differences in the
reactivity. Phenyl acetate underwent a complete hydrolysis during a few or several
hours, depending on the reaction conditions (Scheme 3).
Interestingly, methyl benzoate did not exhibit any reactivity even after 3 days
(Scheme 4).
According to these observations, we have assumed that if a diester that
comprises both aliphatic and aromatic ester groups undergoes hydrolysis, for
example, methyl p-acetoxybenzoate, only hydrolysis of acetyl group will be possible,
according to Scheme 5.
This hydrolysis reaction of methyl p-acetoxybenzoate was carried out, and the
structures of the substrate and the obtained product were confirmed by infrared (IR)
spectra. In the IR spectrum of the substrate, two characteristic stretching
bands assigned to two ester groups were observed: 1731 cmꢀ1 (acetate) and
1756 cmꢀ1 (benzoate), whereas in the IR spectrum of the product only one band
corresponding to the C Oꢀ 1742 cmꢀ1 group can be seen (benzoate). In the IR spec-
=
trum of the product, another band at 3428 cmꢀ1 appears, which indicates the pres-
ence of an OH group formed in the course of the acetyl ester hydrolysis.
The kind of ester group of methyl p-acyloxybenzoate subjected to enzymatic
hydrolysis depends on the enzyme applied: in the experiments using hydrolysis
by commercially available pig liver esterase (PLE) and porcine pancreatic
lipase (PPL), different selectivity of each hydrolase was observed.[11] Methyl
p-acetoxybenzoate was hydrolyzed to hydroxyester in the presence of both
Scheme 2. Enantiospecific hydrolysis of 1-alkyn-3-ol acetates.
Scheme 3. Baker’s yeast–assisted hydrolysis of phenyl acetate.

´
E. BIAŁECKA-FLORJANCZYK AND E. MAJEWSKA
1266
Scheme 4. Baker’s yeast–assisted hydrolysis of methyl benzoate.
Scheme 5. Baker’s yeast–assisted hydrolysis of methyl 4-acetoxybenzoate.
PLE and PPL (the only difference was the reaction rate), and hydrolysis of methyl
p-benzoyloxybenzoate catalyzed by PLE gave only hydroxyester, whereas methyl
p-nonanoyloxybenzoate in the presence of PPL gave nonanoyloxybenzoic acid.
The chemoselective character of the hydrolysis of acetoxybenzoates in the pres-
ence of baker’s yeast means that it can be used in the selective protection of hydroxy
groups in the derivatives of p-hydroxybenzoic acid. p-Hydroxybenzoic acid contains
two functional groups, and to obtain its phenyl ester the hydroxy group should be
protected to avoid side reactions. Esterification of the hydroxy group by acetic acid
enables safe esterification of the carboxylic group into phenyl ester, and then after
selective hydrolysis of the acetyl group it is possible to obtain hydroxyester
(Scheme 6).
Phenyl 4,40-substituted benzoates make an important group of liquid crystal-
line compounds,[12] and the method described may facilitate their synthesis. The
described method was verified in the synthesis of 4-cyanophenyl 40-[400-(pentyl)
benzoyloxy]benzoate (10) and 4-methoxyphenyl 40-[400-(decyloxy)benzoyloxy]benzo-
ate (11), which is shown in Scheme 7.
Scheme 6. Synthesis of p-hydroxyphenyl benzoate.
Scheme 7. Synthesis of phenyl 4-benzoyloxybenzoates.

SELECTIVE HYDROLYSIS OF ESTERS BY BAKER’S YEAST
1267
Table 1. Progress of the hydrolysis of some aromatic and aliphatic esters
Substrate conversion (%)
No.
Ester
4 h
24 h
48 h
1
2
3
4
5
6
7
8
9
Phenyl acetate
Phenyl heptanoate
Benzyl acetate
26
15
28
27
47
0
75
52
62
50
88
0
100
100
100
100
100
0
Benzyl propanoate
Ethyl pentanoate
Methyl benzoate
Ethyl benzoate
Phenyl benzoate
Benzyl benzoate
0
0
0
0
0
0
0
0
0
To confirm these observations on a broader group of compounds, we
compared the catalytic effect of baker’s yeast on the hydrolysis reaction of several
different esters. The examined esters and the percentage out of them that underwent
the reaction (detected by chromatography method) are shown in Table 1.
The obtained results have completely confirmed the initial observations:
the progress of the reaction was in a strict correlation with the structure of the ester
molecule.
. Only the hydrolysis of aliphatic esters of phenols or aliphatic alcohols in the
presence of baker’s yeast is possible.
. Among the examined esters, the fastest reaction rate was observed for aliphatic
alcohol ester (ethyl pentanoate 5); the elongation of the aliphatic chains in the
carboxylic acid molecules inhibited the reaction rate.
. Benzoic acid esters did not show any reactivity under the applied conditions.
We compared our results with experiments performed without the addition of
baker’s yeast. After 2 days, the acetyl group was hydrolyzed about 15%; in the case
of phenyl benzoate, we observed only traces of phenol after 3 days.
These experiments led us to the introduction of a convenient and inexpensive
method for the protection of hydroxy groups in aromatic acids hydroxy esters.
EXPERIMENTAL
All the chemicals used were analytical-grade commercial products (Aldrich)
and were applied without further purification. Esters from Table 1 were commercial
products (Aldrich) or were synthesized according to known procedures.
The 4-methoxy- or 4-cyanophenyl esters of 4-acetoxybenzoic acid were pre-
pared from the appropriate acids and phenols in the presence of N,N0-dicyclohexyl-
carbodiimide and a catalytic amount of N,N0-dimethyl-4-aminopyridine.
The IR spectra (in CH2Cl2) were recorded on a Perkin-Elmer 2000 apparatus
equipped with Pegrams 2000 software, and the NMR spectra (in CDCl3) were
recorded using a Varian Gemini 200-MHz spectrometer. The structures were

´
E. BIAŁECKA-FLORJANCZYK AND E. MAJEWSKA
1268
confirmed also by elemental analysis (within ꢁ0.4% of theoretical values). A purity
of all compounds obtained was checked by means of thin-layer chromatography
(TLC) using SiO2 plates with ultraviolet (UV) indicator and chloroform as an eluent.
Hydrolysis reactions were carried out at room temperature in the presence of
lyophilized baker’s yeast (S. I. Lessafre) for 10 different esters. In the reaction, 3 g
of Baker’s yeast, 3 g of sucrose, 50 cm3 of distilled water, and 0.0015 mol of a suitable
ester dissolved in 0.5 cm3 of ethanol were used. The samples of the reaction mixtures
(chloroform extraction) were taken after 4, 24, and 48 h. The conversion percentage
was identified with the aid of a Shimadzu GC-171 gas chromatograph using a BPX
70 capillary column and flame ionization detector.
Synthesis of 4-Methoxyphenyl 4-Hydroxybenzoate and
4-Cyanophenyl 4-Hydroxybenzoate with Baker’s Yeast
A mixture of fresh baker’s yeast (100 g) and sucrose (100 g) in distilled water
(200 ml) was stirred for 15 min, after which an ethanolic solution (5 ml) of 4-methoxy-
phenyl 40-acetoxybenzoate (3.4 g, 11.8 mmol) or 4-cyanophenyl 40-acetoxybenzoate
(1.8 g, 8.72 mmol) was added to it. The mixtures were stirred at room temperature
for 5 days with TLC monitoring, and then 50 ml of chloroform were added to each
of them and stirring was continued for another 24 h, after which the reaction
mixtures were centrifuged. The supernatant was placed in a funnel, and the water
phases were extracted with chloroform (2 ꢂ 50 ml). The collected organic phases
were dried over MgSO4, CHCl3 was evaporated, and crude products were purified
by column chromatography (SiO2) using CHCl3 as eluent to afford 1.5 g of pure
4-methoxyphenyl 40-hydroxybenzoate (yield 52%) and 0.9 g of pure 4-cyanophenyl
40-hydroxybenzoate (yield 43%).
Synthesis of 4-Cyanophenyl 40-[400-(Pentyl)benzoyloxy]benzoate
(10) and 4-Methoxyphenyl 40-[400-(Decyloxy)benzoyloxy]-
benzoate (11)
To 512 mg of 4-decyloxybenzoic acid (1.8 mmol) or 345 mg of 4-pentylbenzoic
acid (1.8 mmol) dissolved in 30 ml of dry CH2Cl2, 450 mg of 4-methoxyphenyl
40-hydroxybenzoate (1.8 mmol) or 430 mg of 4-cyanophenyl 40-hydroxybenzoate
(1.8 mmol) were added respectively. Next, 420 mg of N,N0-dicyclohexylcarbodiimide
(DCC) (2 mmol) and a catalytic amount of N,N-dimethylaminopyridine (DMAP)
were added to both mixtures. The reaction mixtures were vigorously stirred at room
temperature for 24 h with TLC monitoring using CHCl3 as eluent. The side product
N,N0-dicyclohexylurea was filtered off and washed with CH2Cl2 (3 ꢂ 10 ml). Then,
20 ml of CH3OH were added to both filtrates, which caused the products to precipi-
tate from the mixture. The white solids were filtered off and washed with CH3OH to
afford 430 mg of pure 4-methoxyphenyl 40-[400-(decyloxy)benzoyloxy]benzoate (yield
48%; mps Cr 107 ꢃC SmC 140 ꢃC SmA 207 ꢃC I) and 350 mg of pure 4-cyanophenyl
40-[400-(pentyl)benzoyloxy]benzoate (yield 50%; mps Cr 115 ꢃC N 242 ꢃC I).
1H NMR data for 10 (200 MHz, CDCl3, ppm): 0.907 (t, 3H, CH3–, J ¼ 6.5 Hz),
1.37 (m, 6H, –CH2CH2CH2–), 2.71 (t, 2H, –CH2Ph–, J ¼ 7.6 Hz), aromatic protons:

SELECTIVE HYDROLYSIS OF ESTERS BY BAKER’S YEAST
1269
7.32 (d, 2H, J ¼ 8.4 Hz), 7.37 (d, 2H, J ¼ 8.6 Hz), 7.42 (d, 2H, J ¼ 8.8 Hz), 7.78 (d,
2H, J ¼ 8.8 Hz), 8.14 (d, 2H, J ¼ 8.3 Hz), 8.25 (d, 2H, J ¼ 8.8 Hz).
1H NMR data for 11 (200 MHz, CDCl3, ppm): 0.88 (t, 3H, CH3, J ¼ 6.8 Hz),
1.28 [m, 14H, –(CH2)7–], 1.82 (m, 2H, –CH2CH2O-), 3.83 (s, 3H, –OCH3), 4.05 (t,
2H, –CH2O, J ¼ 6.6 Hz), aromatic protons 6.94 (d, 2H, J ¼ 8.8 Hz), 6.99 (d, 2H,
J ¼ 8.4 Hz), 7.14 (d, 2H, J ¼ 8.8 Hz), 7.38 (d, 2H, J ¼ 8.8 Hz), 8.17 (d, 2H,
J ¼ 8.8 Hz), 8.29 (d, 2H, J ¼ 8.6 Hz).
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