10.1002/ejoc.201701313
European Journal of Organic Chemistry
COMMUNICATION
A novel Chemoenzymatic route to a new class of Sucrose esters
Christian Possiel,[a], Alexandra Bäuerle and Jürgen Seibel*[a]
enzymatically with levansucrase from Bacillus megaterium
(SacB) in the presence of glycopyranose acceptors like
galactose or
-xylose up to 60 % yield. [10]
Abstract: Sucrose esters are the most developed carbohydrate
esters and applied in food, cosmetic and pharmaceutical industries.
Here we introduce a novel chemoenzymatic pathway for the synthesis
of β-D-fructofuranosyl-(2,1)-α-D-uronic acid derivatives, a new class of
sucrose esters.
D
-
D
We begin from the belief, supported by many experimental
studies, that glucuronic acid will be tolerated and fructosylated by
the levansucrase from B. megaterium.[10a, 11] The catalytic triad of
the B. megaterium levansucrase (Bm-Ls) consists the nucleophile
D95, the transition state stabilizer D257 and the acid/base catalyst
E352 (Fig. 1). The substitution of the glucopyranoside is initiated
by protonation of the glycosidic bond of sucrose with E352,
followed by a nucleophilic attack of D95 to form a covalent
fructosyl-enzyme intermediate (Fig. 1c) by inverting the
stereogenic center of C-2 (α-configuration). The mechanism
undergoes an oxocarbenium ion-like transition state (TS1, Fig. 1).
Then the acceptor substrate attacks in a SNi/SN2 mechanism to
finally yield the fructosylated acceptor substrate. [9b, 12]
Carbohydrates are an important source of renewable compounds.
The disaccharide sucrose (α-D-glucopyranosyl-(1,2)-β-D-
fructofuranoside) is produced in industrial scale of 170 x 106
MT/y.[1]
The development of chemical processes from
carbohydrates instead of fossil resources became a principal of
Green Chemistry. Sucrose esters are one of these examples.
They have many applications in food, cosmetics and
pharmaceutical industry.[2] Sucrose possesses 8 hydroxyl groups
that can be esterified with fatty acids with aliphatic tails of 1 to 18
carbons.[3] The chemical production of sucrose esters has been
investigated[4] but the selectivity in the synthesis of these esters
a
b
LG
OH
4E
remains
a
challenge. Lipases from i.e. Thermomyces
LG
HO
O
O
O
OH
HO
lanuginosus[5], Candida antarctica[6] and Rhizomucor miehei[7]
catalyze the transesterification to 2-O-acylsucrose or 6-O-
acylsucrose. All these sucrose esters derive from a carboxylic
acid (fatty acid) and sucrose equipped with hydroxyl-groups. We
envisaged that sucrose could function as a carboxylic acid and be
condensed with an alcohol to form sucrose ester of structure 2
and 3 (scheme 1).
E3
4T3
O
4C1
HO
O
HO
352Glu
HO
O
O
O
O
OH
OH
O
O
Asp95
H
H
O
OH
352Glu
HO
O
O
O
Asp95
Asp257
O
H
O
Asp257
transition state 1
OR
c
O
d
O
HO
HO
HO
O
OH
O
HO
OR
O
O
O
O
O
H
O
HO
HO
OH
O
OH
O
R
O
HO
Asp95
HO
HO
HO
O
R2
352Glu
R
O
O
O
O
H
O
O
Asp95
OH
O
OH
O
O
O
R1
HO
HO
HO
O
H
O
O
Asp257
Asp257
transition state 2
OH
HO
OH
HO
tetrahedral intermediate
E-S
O
O
complex
OH
OH
HO
1
HO
1
R2
H
=
=
=
2
R
OH,
3 R1
R2
LG
OR
=
OH
H,
e
O
O
HO
4T3
O
E3
Scheme 1. Structures of different esters with sucrose acting as an alcohol (1)
and sucrose derivative acting as carboxylic acid (2, 3).
4C1
HO
HO
O
H
OH
OH
O
O
OH
352Glu
HO
O
O
Asp95
O
H
The Bacillus subtilis sacB gene encodes the secreted
O
Asp257
enzyme levansucrase (sucrose: 2,6-β-D-fructan 6-β-D-
fructosyltransferase; EC 2.4.1.10) and belongs to the family
[8]
of glycoside hydrolases 68 (GH 68).
hydrolysis of sucrose although it also transfers fructosyl units
to sucrose resulting in
(2→6)-linked fructans.[9] In previous
(1→2)-linked sucrose analogues were synthesized
It catalyzes the
Figure 1. Proposed mechanism of the levenasucrase Bm-LS for the acceptor
reaction.
β
work
α
Unanticipated we observed the desactivation of the enzyme by
using D-glucuronic acid (500 mM) as acceptor substrate. The
observation can be rationalized if a pH-shift in the catalytic pocket
takes place and the nucleophile Asp95 is protonated. To avoid the
pH-shift the sodium salt of the glucuronic acid (500 mM) was used
in the enzymatic reaction as acceptor and indeed the desired
sucrose analogue β-D-fructofuranosyl-(2,1)-α-D-glucuronic acid
2a has been formed up to 43% (78 g/l, Fig. 2). Because galactose
[a]
C. Possiel, A. Bäuerle, Prof. Dr. J. Seibel*
Institut für Organische Chemie
Julius-Maximilians Universität Würzburg
Am Hubland
E-mail: seibel@chemie.uni-wuerzburg.de
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.
Possiel, Christian
