Bioorganic & Medicinal Chemistry Letters
Donor specificity and regioselectivity in Lipolase mediated acylations
of methyl
a-D-glucopyranoside by vinyl esters of phenolic acids and
their analogues
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Mária Mastihubová , Vladimír Mastihuba
Institute of Chemistry, Center for Glycomics, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 38 Bratislava, Slovakia
a r t i c l e i n f o
a b s t r a c t
Article history:
Methyl
a-D-glucopyranoside as a model acceptor was acylated by several phenolic and non-phenolic
Received 10 June 2013
Revised 22 July 2013
Accepted 23 July 2013
Available online 31 July 2013
vinyl esters using immobilised Lipolase. Donor specificity and regioselectivity of reaction were investi-
gated. Conversion and rate of acylation by structurally varied donors indicates that the synthetic reactiv-
ity of Lipolase corresponds to the hydrolytic activity of feruloyl esterase type A. Lipolase exhibited
remarkable regioselectivity for primary position of methyl a-D-glucopyranoside. The acylation occurred
exclusively at 6-O primary position when vinyl esters of phenolic acids (hydroxybenzoates, hydrox-
yphenylalkanoates and hydroxycinnamates) served as acyl donors (5–77%). In addition to the major 6-
O-acyl products (52–79%), 2,6-di-O-acylated derivatives were isolated from reaction mixtures (2–13%)
when non-phenolic donors were used (vinyl esters of fully methoxylated derivatives of phenolic acids,
along with vinyl benzoates, cinnamates or some heterocyclic analogues).
Keywords:
Donor specificity
Feruloyl esterase activity
Glucopyranoside acylation
Lipolase
Ó 2013 Elsevier Ltd. All rights reserved.
Regioselectivity
Regioselective acylation of hydroxyls along the saccharide ring
is constantly a fundamental challenge for organic chemists. The
problem encountered in the chemical modification of sugar mole-
cules may be avoided by introduction of biocatalytic procedures
possessing high degree of regioselectivity in the acylation of poly-
hydroxylated substrates. Various hydrolases (lipases, esterases,
proteases) have been introduced as catalysts for this purpose.1–4
Feruloyl esterases (FAEs) [E.C. 3.1.1.73] represent a group of
carboxylic acid esterases catalysing hydrolysis of an ester bond
between p-hydroxycinnamic acids and saccharides present in plant
cell walls.5–9 The classification of FAEs into four sub-classes (A–D)
was proposed based on similarities in profiles of hydrolytic ester-
ase activity against methyl esters of partly substituted hydroxycin-
namic acids, their dimers, and protein sequence identities of the
enzymes.10 Recently, a new FAEs classification into 12 distinct
families was proposed according to their sequences by descrip-
tor-based computational analysis.11 Based on the classification in
terms of their substrate specificity, FAEs type A show a preference
for the phenolic moiety of the substrate that contains methoxy
substitutions. These enzymes appear to prefer hydrophobic
substrates with bulky substituents on the benzene ring. Their
protein sequences are more similar to sequences of lipases.10
Regarding specificity against the hydrolysis of synthetic substrates,
these FAEs hydrolyse methyl ferulate, methyl sinapate and methyl
p-coumarate, but not methyl caffeate.
Thermomyces lanuginosus lipase (TLL)12 possesses feruloyl ester-
ase activity and displays a high level of sequence identity with FAE
from Aspergillus niger13,14 which was classified as FAE type A. TLL is
the enzyme responsible for lipolytic activity of LipolaseÒ, a com-
mercial lipase preparation supplied by Novozymes. LipolaseÒ is
produced by a genetically modified strain of Aspergillus oryzae.12,15
Several reports describe enzymatic acylations of monosaccha-
rides and oligosacharides,16–21 as well as glycosides20,22–28 (mainly
flavonoids)24–26 by phenolic acids and their aryl or arylalkyl ana-
logues under action of lipases or FAEs to obtain substances with
stronger antioxidant activities. Only few reports however studied
regioselectivity23 or enzyme specificity for wider scale of
donors.18,20,25 Donor specificity or regioselectivity of FaEs and rel-
ative lipases in acylations of saccharides by phenolic acids and
their aromatic analogues is still not well understood. Some exper-
imental conclusions of regioselectivity are questionable due to
insufficient characterisation of products.
Most of reports describe use of the commercial lipase B from
Candida antarctica (CALB) for successful synthesis of saccharide
esters of phenolic acids.20,22,24–27 Lipases from Aspergillus niger,18
Penicillium expansum23 or feruloyl esterase from Sporotrichum ther-
mophile16,17 were also applied with satisfactory results. Another
commercial enzyme preparations with FAE activity were success-
fully applied in feruloylation of glycosides28 or monosaccharides.19
Generally, application of activated esters of phenolic acids in
⇑
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0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.