Chemistry Reference
In-Depth Information
AcO
HO
O
O
CAL B
45
o
C, 3h
ethanol
OMe
OMe
AcO
OAc
AcO
OAc
81%
HO
AcO
OMe
CAL B
45
o
C, 7 days
ethanol
O
O
OMe
OH
HO
quantitative
AcO
OAc
FIGURE 1.13
Highly regioselective and exhaustive deacetylation using lipases described
by Iglesias and coworkers [28].
exceptionally cautious when trying to expand the use of specific enzymes to other
categories of compounds. It applies particularly to reactions performed on small
molecules. It may not translate well to much larger (macro) molecules even when
the specific part of the molecule is the same. We can only hope that with time our
understanding of specific enzymatic processes will improve and there will be the
abundance of literature data enabling successful application of enzymatic decoupling
to specific situations. The following examples derive from small molecule chemistry,
but hopefully will find application in decoupling processes as well.
Iglesias and coworkers [28] studied alcoholysis of methyl 2,3,5-tri-
O
-acetyl-
-D-
ribofuranoside and methyl 2,3,5-tri-
O
-acetyl-
-D-ribofuranoside using the
Candida
antarctica lipase
B (CAL B). The reaction of the
-anomer lead to the isolation
of the monodeacetylated product. The reaction of the
-anomer lead to a variety of
partially deacetylated products but eventually provided the fully deacetylated product
in a quantitative yield (Fig. 1.13).
Italian and Spanish researchers [29] performed selective hydrolysis of peracety-
lated
-monosaccharides using immobilized lipases from different sources [
Ther-
momyces lanuginosa
(TLL),
Aspergillus niger
(ANL), and
Candida antarctica
B
(CAL B)]. Figure 1.14 shows some of the results. The shown yields represent iso-
lated yields. The results illustrate a crucial role played by the procedure applied to
the immobilization of enzymes. The paper is an example of a larger series of papers
devoted to studying regioselectivity of various enzymatic hydrolyses [30] and ref-
erences quoted therein. The acquired knowledge was employed to a very elegant
synthesis of linear oligosaccharides by a simple monoprotective, chemoenzymatic
approach.
Baba and Yoshioka [31] prepared 1-
-
O
-acyl glucuronides of three nonsteroidal,
anti-inflammatory drugs, diclofenac (DF), mefenamic acid (MF), and (
S
)-naproxen
(NP) (their structures are shown in Fig. 1.15). Next, after some screening, they
employed selected commercial enzymes—lipase AS Amano LAS: (from ANL),
and porcine liver esterase (PLE). LAS hydrolyses the
O
-acetyl groups with high
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