Chloroperoxidase-Catalyzed Achmatowicz Rearrangements

Article abstract of DOI:10.1002/ejoc.201800333

Chloroperoxidase from Caldariomyces fumago catalyzes the selective oxidation of furfuryl alcohols in an Achmatowicz-type ring expansion. In combination with glucose oxidase as oxygen-activating biocatalyst, a purely enzymatic, aerobic protocol for the synthesis of 6-hydroxypyranone building blocks is obtained. Thanks to an only modest stereochemical bias of the oxygenating heme protein, optically active alcohols of either configuration are converted without a significant mismatch opening up opportunities for enantioselective multienzymatic cascades. Balancing the oxidase-driven aerobic activation, extended enzyme half-lives and productive conversion of poorly soluble and slowly reacting substrates can be achieved with high yields of the six-membered O-heterocycles.

Full text of DOI:10.1002/ejoc.201800333

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Accepted Article
Title: Chloroperoxidase-catalyzed Achmatowicz Rearrangements
Authors: Daniel Thiel, Fabian Blume, Christina Jäger, and Jan Deska
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10.1002/ejoc.201800333
European Journal of Organic Chemistry
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Chloroperoxidase-catalyzed Achmatowicz Rearrangements
Daniel Thiel,[a,‡] Fabian Blume,[a] Christina Jäger,[a] and Jan Deska*[a]
Abstract: Chloroperoxidase from Caldariomyces fumago catalyzes the selective oxidation of furfuryl alcohols in an Achmatowicz-type
ring expansion. In combination with glucose oxidase as oxygen-activating biocatalyst, a purely enzymatic, aerobic protocol for the
synthesis of 6-hydroxypyranone building blocks is obtained. Thanks to an only modest stereochemical bias of the oxygenating heme
protein, optically active alcohols of either configuration are converted without a significant mismatch opening up opportunities for
enantioselective multienzymatic cascades. Balancing the oxidase-driven aerobic activation, extended enzyme half-lifes and productive
conversion of poorly soluble and slowly reacting substrates can be achieved with high yields of the six-membered O-heterocycles.
Achmatowicz, halonium species generated by the catalytic
Introduction
conversion of hydrogen peroxide as terminal oxidant and bromide
through a vanadium-dependent haloperoxidase promote the
Over the past decades, the Achmatowicz-type ring expansion[1]
–
oxidative furan cleavage that ultimately leads to the six-
membered heterocycles and its efficacy has been demonstrated
for the synthesis of both pyranones and piperidinones. In addition
to these mediated processes, in 2014 our group established a
novel protocol exploiting the oxygenating properties of heme-
dependent peroxidases in order to catalyze Achmatowicz-type
reactions in a truly biocatalytic manner exploiting a direct protein-
furan interaction.[11] In combination with an oxidase and a cheap
sacrificial reductant such as sugars or alcohols for the controlled
in situ generation of hydrogen peroxide, the aerobic
rearrangement of furfuryl alcohols is achieved.[12]
the oxidative conversion of a-heterosubstituted furfuryl
derivatives to six-membered O- or N-heterocyclic building blocks
– has become a valuable tool in modern synthetic organic
chemistry.[2-5] Both the easy access to suitable heteroaromatic
Achmatowicz substrates as well as the broad range of follow-up
chemistry offered by the pyranone or piperidinone products make
this transformation an attractive instrument in the synthesis of
complex natural products and biologically active agents. While the
original procedures by Achmatowicz [1,6] and Lefebvre [7] still relied
on the use of stoichiometric oxidants such as bromine or meta-
chloroperbenzoic acid, over the years multiple powerful variations
based on e.g. metal catalysis, photoactivation and
electrochemistry have been brought forward providing additional
selectivities and broader applicability.[8] In light of milder and
environmentally more benign approaches towards the oxidative
ring rearrangement of the furfuryl derivatives, recently the use of
enzymes as biological catalyst has been brought into the focus
R
air + laccase + TEMPO
R'
Beifuss, 2013
O
OH
1
H2O2 + haloperoxidase + bromide
Rutjes/Hollmann, 2016
(Scheme 1). Here, both the groups of Beifuss,[9] and of Rutjes and
O
O
[10]
air + oxidase + peroxidase
Hollmann
have been successful in the development of bio-
R
O
R
this work
induced protocols relying on the biocatalytic generation of
diffusible oxidizing species from the interaction of an
oxidoreductase with a suitable redox mediator. In the first
enzyme-driven report, laccases in combination with TEMPO-
based redox moderators act as catalytic principle in an aerobic
ring expansion to give substituted pyranones utilizing air as
terminal oxidant. Similarly to the original Br2-based method by
HO
O
R'
O
H
R'
2
Scheme 1. Biocatalytic approaches for the oxidative ring expansion of furfuryl
alcohols.
In this paper, we disclose the results of an in-depth study on the
initial development and the improvement of an enzyme-catalyzed
Achmatowicz protocol based on chloroperoxidase from
Caldariomyces fumago, including stereochemical investigations
on the enantioselectivity of the heme protein and an extended
substrate scope analysis. Additionally, a mediated protocol
exploiting biocatalytically generated peracetic acid is presented
as alternative to overcome the current structural limitations of the
wild-type chloroperoxidase.
[a]
Dr. D. Thiel, Dipl.-Chem. F. Blume, Christina Jäger, Prof. Dr. J.
Deska
Department of Chemistry and Materials Science, Aalto-yliopisto
Kemistintie 1, 02150 Espoo, Finland
E-mail: jan.deska@aalto.fi
www.deskalab.com
[‡]
Current affiliation: CAT Catalytic Center, RWTH Aachen University,
Worringerweg 2, 52074 Aachen, Germany
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejoc.201800333
European Journal of Organic Chemistry
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formed. Considering the structural similarities between the sugar
substrate of the glucose oxidase and the Achmatowicz pyranones,
it was first assumed that oxidase activity on the initially formed
lactol 2a might attribute to the discrepancy of conversion and
yields under the non-optimized reaction conditions. However,
spectroscopic analysis of the crude reaction mixtures did not
show any traces of the 2a-derived lactone as side product. Also,
a photospectrometric oxidase assay coincubating 2a and glucose
oxidase (with horseradish peroxidase and ABTS as reporter)
remained silent, thus ruling out any undesired cross-reactivity
between the sugar oxidase and the sugar-like hydroxypyranone
products. Nevertheless, also other oxidase/reductant systems
were tested and while both leucine/amino acid oxidase and
methanol/alcohol oxidase did not match the outcome of the
glucose oxidase-driven protocol, modification of oxidase loading
or the reaction environment might give rise to productive
Achmatowicz systems in those cases as well.
Results and Discussion
Methodological Studies
Our study towards an enzyme-catalyzed version of the well
established Achmatowicz rearrangement commenced with the
identification of biological systems that would resemble the key
step in the transformation, that is, the oxygenative cleavage of
furans to form ketoenal intermediates (Scheme 1).[13] Here,
investigations on the in vivo degradation of furans by cytochrome
P450 monooxygenases indicated that heme-dependent
oxygenation biocatalysts might provide the required reactivity to
be utilized in the title reaction.[14,15] As relatively cheap commercial
alternative to the P450s, we envisaged that heme peroxidases
could potentially serve this purpose, and initial studies aimed to
elucidate the oxygenating abilities of a set of peroxidases with
regard to the conversion of 1-furylethanol (1a). Owing to structural
differences in the active site, particularly the nature of the axial
heme ligand, only a few peroxidases actually behave in a
cytochrome P450-like manner and hence,[16,17] it was no surprise
that classical peroxidases such as soybean-, horseradish- or
lactoperoxidase, fueled by a glucose/glucose oxidase H2O2
production system,[18] did not exhibit major activity in the oxidation
of 1a and only in the case of horseradish peroxidase, traces of the
desired pyranone 2a were detected after 24 h (Scheme 2). On the
other hand, employing the same oxidase-based H2O2 delivery tool
Yet, considering the generally low cost of both glucose and
the glucose oxidase (GOx), subsequent optimization studies were
pursued on this most successful initial screening hit. Variation of
the pH of the reaction medium (aqueous citrate or phosphate
buffers) revealed a rather wide plateau between 4.5 and 6.5 with
greater 90% conversion of 1a with 2 h, and a sharp loss of
oxygenating power at neutral pH (Figure 1a, left). In the context
of pH optimization, it is important to pay attention not only to the
enzyme activity but also to the stability of the reaction substrates,
in particular with regard to their stereochemical integrity.
Therefore, enantiomerically pure (R)-1a was also incubated in
absence of any biocatalyst for 24 h after which the optical activity
of the recovered starting material was determined. Clearly, due to
the benzylic situation of the alcohol, racemization can become an
issue at pH values less than 5.5 where slow epimerization is
taking place (Figure 1a, right). Consequently, the optimal
operation window for the CPO-mediated ring expansion of furfuryl
alcohols can be set to pH 5.5 – 6.5.
but changing the peroxidase to
a chloroperoxidase from
Caldariomyces fumago (CPO) that acts as peroxidase-P450
functional hybrid,[19,20] almost full conversion was observed
already after 3 h with a significant amount of 2a (51%) being
Next, the influence of cosolvents was addressed in order to
identify
suitable
solubilizing
additives
enabling
high
concentrations of the more or less lipophilic furfuryl substrates
(Figure 1b). To our delight, addition of 10% tert-butanol to the
reaction medium did not affect the enzymes’ activity and full
conversion of 1a was achieved after 3 h. Yet, in contrast to the
purely aqueous medium, pyranone 2a was isolated in greatly
improved 82% yield after reaction in the buffer/tBuOH mixture, an
effect that could be later attributed to the improved stability of
Achmatowicz-type pyranones in the medium (pure buffer: t1/2 (2a)
= 11.9 h; buffer/tBuOH: t1/2 (2a) = 40.7 h). In this medium, the
reaction could also be significantly scaled to a total of 50 mmol of
1a at increased concentration (50 mM) and reduced CPO loading
(200 U/mmol) with a yield of 76%. Acetone as cosolvent exhibited
a similar effect although the activity was slightly reduced, reaching
conversion levels >90% only after 6 h. Addition of DMSO or
acetonitrile on the other hand resulted in modest inhibition of the
Scheme 2. Peroxidase and oxidase screening
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10.1002/ejoc.201800333
European Journal of Organic Chemistry
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reaction and in biphasic reaction media such as buffer/heptane
mixtures, no reaction was observed.
purities remain elusive. Hence, the production of enantioenriched
pyranones by enzymatic resolution must be considered
unpractical unless further optimization of the biocatalyst by
directed evolution could deliver more specific chloroperoxidase
variants.
Table 1. Enantiodiscrimination in the oxidative conversion of racemic furfuryl
alcohols.
chloroperoxidase (C. fumago)
glucose oxidase (A. niger)
O
R
R
+
O
O
D-glucose, tBuOH (10% v/v)
citrate buffer (pH 5.5)
30 °C, 10 min
HO
O
R
OH
OH
rac-1
(S)-1
(R)-2
Entry[a]
R
conversion
[%][b]
ee (1)
[%][b]
E
[c]
[k(R)/k(S)
]
1
2
3
4
5
6
7
8
9
10
methyl (1a)
16
16
13
11
12
18
12
8
6
2.3
3.0
4.4
6.9
10.4
3.3
7.2
2.8
4.2
1.5
ethyl (1b)
9
n-propyl (1c)
vinyl (1d)
9
9
allyl (1e)
11
11
10
4
i-propyl (1f)
i-butyl (1g)
t-butyl (1h)
phenyl (1i)
CH2CO2Et (1j)
12
17
8
Figure 1. Optimization of reaction parameters for the CPO-mediated oxidative
ring expansion of 1-(2-furyl)ethanol (1a).
4
[a] Reaction conditions: alcohol
1 (25 µmol), D-glucose (125 µmol),
chloroperoxidase (25 U), glucose oxidase (25 U), citrate buffer (2.25 mL, 0.1 M,
pH 5.5), tBuOH (0.25 mL), 30 °C. Yields determined after purification by column
chromatography. [b] Conversions and optical purities determined by chiral gas
Stereochemical Investigations
chromatography
using
bromobenzene
as
internal
standard.
[c]
Enantioselectivities calculated according to Sih et al.[21]
With an effective biocatalytic Achmatowicz system in hand, next
the stereoselectivity of the chloroperoxidase towards different
kinds of furans was studied. Starting from racemic 1-(2-
furyl)alkanols with varying chain length, branching, and
functionalization patterns, the extent of enantiodiscrimination in
kinetic resolutions of the furans was recorded at low conversion
rates (Table 1). In all cases, the tested furan were transformed to
the corresponding ring expanded heterocycles and a certain
enantioenrichment of the remaining alcohols was observed. Yet
the enantioselectivity E (k(R) vs k(S)) proved to be mediocre at best.
Moreover, there was no obvious trend with regard to steric bias of
the side chain as both the slim methyl-substituted furfuryl alcohol
1a as well as the bulky tert-butyl derivative 1h exhibited E values
of less than 3 (Table 1, entry 1 & 8). The most effective kinetic
resolution took place with the homoallylic alcohol 1e but with
relative rates of approximately 10:1 favoring the conversion of the
(R)-enantiomer (Table 1, entry 5), synthetically useful optical
Substrate Scope and Limitations
On the other hand, the lack of substantial
enantiodiscrimination by the chloroperoxidase can also be seen
as a positive feature of the biocatalytic method since limitations to
certain stereoisomers due to matched/mismatched situations
become less likely. Considering the general disadvantage of
kinetic resolution approaches to be yield-limited to a maximum of
50% of optically pure material, alternative pathways to address
enantioenriched pyranone products by combining the
stereoselective synthesis of furfuryl alcohols with the subsequent
aerobic rearrangement appear highly attractive. In particular, the
ketoreductase-mediated alcohol synthesis by reduction of the
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10.1002/ejoc.201800333
European Journal of Organic Chemistry
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corresponding furyl ketones opens up great opportunities for an
effective, fully enzymatic route to these synthetically valuable
building blocks. Based on a previously reported method utilizing
two commercial alcohol dehydrogenases (ADH200 & ADH 030
from evoCatal) as asymmetric reduction catalyst,[11] a set of
optically active furylcarbinols was prepared and tested under the
optimized conditions for the Achmatowicz-type ring expansion
(Table 2). Gratifyingly, both antipodes of the model substrate 1a
were converted smoothly and the enantiomeric pyranones (R)-2a
and (S)-2a were not only isolated in high yields but also with
complete conservation of the stereogenic information (Table 2,
entry 1 & 2). Also the homologues (R)-2b and (R)-2c could be
obtained in reasonable yields (Table 2, entry 3 & 4), and notably,
further improvement of optical purity was observed starting from
just moderately enantioenriched 1c (from 95% ee to 98% ee of
2c). Moreover, the CPO-mediated procedure exhibited a high
functional group tolerance, not only accepting ester- or chloro-
substituted furylcarbinols (Table 2, entry 6 & 7) but more
importantly, providing selectivity in the furan oxidation in presence
of oxidation-labile moieties such as olefins and primary
alcohols (Table 2, entry 5 & 8). The propargylic alcohol 1m,
however, could not be transformed to the corresponding
pyranone. Subsequent coincubation studies with 1a revealed that
1m, and other alkyne additives, exhibit inhibitory properties on the
CPO-catalyzed reaction. The core-substituted alcohol 1n on the
other hand did not affect the conversion of other substrates in a
negative way, yet, also here the CPO/GOx system failed to
provide the 2,6-dimethylpyranone 2n.
Despite the mostly convincing yields, optical purities and the
good functional group tolerance of the CPO-catalyzed
Achmatowicz protocol, the stereochemical investigations and
substrate scope studies also revealed some issues related to
conversion rates of highly lipophilic long-chain or branched
aliphatic furylalkanols in particular. Hereby, the decline in reaction
rates, and consequently in product yields, follows a very clear
trend along the homologous series from the rapidly reacting
furylethanol (1a) to the virtually non-reactive furylheptanol (1q)
(Scheme 3). Likewise, incorporation of branched aliphatics results
in severely diminished pyranone yields ranging from mediocre
34% for the isopropyl derivative (2f) to only trace amounts of the
butyl derivatives 2g and 2h. While unfavorable sterics might be a
reason for this effect, the observation that the similarly bulky
ester-functionalized substrate 1j performed well in the CPO-
mediated ring expansion points towards a different explanation
where the poor solubility of substrates such as 1g or 1q in the
aqueous medium could account for their sluggish conversion.
Unfortunately, increased concentrations of tBuOH, that would
improve the solubility of lipophilic substrates in the reaction
mixture, in turn resulted in rapid enzyme inhibition. Thus, further
studies targeting suitable solubilizing additives seem to be
necessary as one option to widen the scope of the reaction to
long-chain furylcarbinols.
Table 2. Oxidative ring expansion of optically active furfuryl alcohols.
chloroperoxidase (C. fumago)
O
glucose oxidase (A. niger)
R'
R
O
HO
D
-glucose, tBuOH (10% v/v)
citrate buffer (pH 5.5)
30 °C, 2 h
O
R'
OH
R
(R)-1
(R)-2
Entry[a]
R/R’
ee (1)
[%][b]
yield (2)
[%]
ee (2)
[%][c]
1
2
3
4
5
6
7
8
9
10
H / methyl (1a)
99
83
81
77
53
65
64
68
31
0
99
99
99
98
98
99
99
99
–
H / methyl (ent-1a)
H / ethyl (1b)
99
99
95
95
99
99
99
99
99
H / n-propyl (1c)
H / allyl (1e)
H / CH2CO2Et (1j)
H / CH2Cl (1k)
H / CH2OH (1l)
H / ethynyl (1m)
methyl / methyl (1n)
0
–
[a] Reaction conditions: alcohol
1 (0.5 mmol), D-glucose (2.5 mmol),
chloroperoxidase (0.5 kU), glucose oxidase (0.5 kU), citrate buffer (45 mL,
0.1 M, pH 5.5), tBuOH (5 mL), 30 °C. Yields determined after purification by
column chromatography. [b] Optical purities determined by chiral gas
chromatography.
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10.1002/ejoc.201800333
European Journal of Organic Chemistry
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proceeds slowly and after 24 h, 84 % conversion is reached. A
subtle balancing of the oxygen-activating and the oxygen-transfer
biocatalyst should thus allow for productive enzymatic
Achmatowicz rearrangements even of slowly reacting furfuryl
substrates.
Scheme 3. Influence of chain length and branching on the CPO-mediated
Scheme 4. Balancing of oxidase and peroxidase activity.
Achmatowicz rearrangement.
The modified CPO-based Achmatowicz system was
subsequently tested on a set of particularly challenging furans that
exhibited very low yields under the originally applied conditions
(Scheme 5). On a preparative scale, the yields of both the
isopropyl- (2f) and the isobutyl-substituted (2g) pyranone were
significantly increased by exploiting an aerobic ring expansion
protocol that was rate-limited by the reduced GOx loading
(GOx/CPO = 0.03). Utilizing enantioenriched 1f (97% ee), the
desired pyranone was obtained in optically pure form, clearly
indicating that despite the extended reaction times, racemization
of the furfuryl alcohols is not an issue. Notably, under identical
conditions, also highly problematic substrates such as the tertiary
alcohol 1r or the core-substituted 3-methylfurfuryl alcohol 1s were
oxidatively converted to the corresponding pyranones 2r and 2s,
respectively, achieving moderate to very high yields after a
reaction time of 18 h.
In addition to solubility issues, with a low rate of conversion
of the sterically more biased, challenging furfuryl alcohol
substrates by the chloroperoxidase, apparently the accumulation
of hydrogen peroxide produced by the glucose oxidase at
constant rates might become an issue as bleaching of the heme
protein at high concentrations of H2O2 could account for an
enzyme inhibition and the low overall turnover to the desired
pyranones.[22,23] In order to investigate this hypothesis, furan 1f
was incubated with the CPO/GOx enzyme mix, with the amount
of oxidase relative to the peroxidase (units of GOx vs units of
CPO) being systematically reduced (Scheme 4). The comparison
between conversion values after 3 h and 24 h indicates how
strongly the biocatalytic system is impaired by the different rates
of H2O2 production. At high peroxide generation rates (GOx/CPO
> 1), the peroxidase obviously suffers a rapid deactivation
resulting in low consumption of 1f. Since no additional turnover is
observed between the first and second measurements, it can be
assumed that complete CPO inhibition is taking place within the
first three hours. By lowering the oxidase loading, significantly
higher conversions up to greater 90% are achieved and the
lifetime of the peroxidase is considerably improved. Even at a
100-fold reduction of the GOx, oxidation of the furfuryl alcohol
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10.1002/ejoc.201800333
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R
Considering the relatively long reaction times and an
unfavorable pH profile of the aqueous perhydrolysis approach
with regard to furanol racemization issues, we envisaged that the
unique ability of lipases to perform in non-aqueous reaction media
might be of benefit in the further optimization process. Moving
away from an aerobic protocol based on the oxidase-mediated
activation of aerial oxygen, the robustness of the hydrolase
enzyme towards both high H2O2 concentrations and organic
solvents was expected to give rise to a simplified system.
Consequently, immobilized C. antarctica lipase B was used in
ethyl acetate providing good solubility for all tested furfuryl
alcohols. Upon addition of aqueous hydrogen peroxide, the
perhydrolysis activity of the lipase delivered the required peracid
and smooth conversion to the desired pyranones was observed
(Scheme 7a). Moderate to mainly good yields were achieved for
a series of furan substrates that proved to be inert to the
chloroperoxidase methodology.[24] In addition, the use of a
peracetic acid mediator system also allowed for a productive aza-
Achmatowicz rearrangement of the furyl carbamate 3 giving rise
to piperidinone 4 in 65% yield (Scheme 7b).
R
chloroperoxidase (C. fumago)
glucose oxidase (A. niger)
O
R'
R''
O
R''
R'
D
-glucose, tBuOH (10% v/v)
HO
O
OH
citrate buffer (pH 6.0), 18 h
1
2
ratio GOx/CPO: 1.0 = high GOx
0.03 = low GOx
O
O
HO
O
HO
O
2f
2g
high GOx: 34%
low GOx: 86%
high GOx: 14%
low GOx: 56%
O
O
HO
O
HO
O
2r
2s
high GOx: 6%
low GOx: 87%
high GOx: <5%
low GOx: 46%
Scheme 5. Optimization towards slowly reacting furfuryl substrates.
a
oxa-Achmatowicz
lipase B (C. antarctica)
aq. H2O2, ethyl acetate, 40 °C
O
R
R
Alternative Systems
R'
O
HO
O
R'
then catalase (C. glutamicum)
phosphate buffer (pH 7.0), r.t.
OH
While the peroxidase/oxidase system for the biocatalytic
ring expansion of furanols proved to be effective for a wide range
of substrates with little to no bias towards existing stereogenic
elements, the structural limitation regarding chain length and
furan core substitution prompted us to reconsider alternative
systems that would be independent on a productive active site
1
2
O
O
O
HO
O
HO
O
HO
O
2n, 74%
2t, 56%
2q, 75%
binding of the furans. Here, the original protocol by Lefebvre
[5]
utilizing peracids as oxidant for the rearrangement
reaction
served as the template for an enzyme cascade design providing
a pathway for the catalytic generation of peracetic acid as
diffusible redox mediator. Replacement of the peroxidase
biocatalyst by a lipase (from Candida antarctica type B) rendered
a system where glucose oxidase provided hydrogen peroxide to
be used by the lipase to catalyze the perhydrolysis of acetic acid
(from an acidic acetate buffer, pH 4.5).[11] To our delight, 1-(5-
methylfuryl)ethanol (1n), previously not affected by the
peroxidase/oxidase treatment, was converted smoothly under
these modified conditions and gave rise to the desired 2,6-
dimethylpyranone 2n in moderate yield (Scheme 6).
b
aza-Achmatowicz
O
lipase B (C. antarctica)
aq. H2O2, ethyl acetate, 40 °C
HO
N
O
Cbz
NHCbz
then catalase (C. glutamicum)
phosphate buffer (pH 7.0), r.t.
3
4, 65%
Scheme 7. Lipase-mediated oxa- and aza-Achmatowicz-type ring expansions.
lipase B (C. antarctica)
glucose oxidase (A. niger)
O
O
HO
Conclusions
D-glucose, tBuOH (10% v/v)
acetate buffer (pH 4.5)
37 °C, 67 h
O
OH
1n
2n, 41%
In
summary, the
commercial chloroperoxidase from
Caldariomyces fumago exhibits high activity and a broad
substrate scope in the oxidative ring expansion of furfuryl alcohols.
Thanks to the absence of significant enantiodiscrimination of the
Scheme 6. Aerobic ring expansion of the core-substituted furan 1x by a
oxidase/lipase couple.
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10.1002/ejoc.201800333
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heme protein, optically active substrates can be converted to the
corresponding enantioenriched pyranones with high effectivity
independent on their sense of chirality. An H2O2 generation
system based on glucose and glucose oxidase allows for an
accurate fine tuning of the aerobic protocol in order to adapt to the
efficacy of the heme enzyme on different furan derivatives
providing full conversions and high yields even for very slowly
reacting substrates.
GC System using a Macherey-Nagel FS-Lipodex E column (25 m
x 0.25 mm), N2, 1.0 ml/min: 50 °C (1 min) / 5 °C×min–1 (35 min) /
120 °C (15 min).
General procedure for the chloroperoxidase-mediated
oxidative ring expansion: In a 100 mL round bottom flask, the
furylcarbinol (10 mM, 0.5 mmol) was dissolved in a mixture of
citrate buffer (45 mL, 100 mM, pH 5.5) and tert-butanol (5 mL).
After addition of chloroperoxidase (500 U), glucose oxidase (500
U) and D-glucose (50 mM), the solution was incubated at 30 °C
(200 rpm) for 120 -180 min. L-Methionine (250 mg) was added
and the reaction mixture was extracted with ethyl acetate (3 x 15
mL). The combined organic layers were dried over MgSO4,
evaporated under reduced pressure and the pyranone was
obtained after column chromatographic purification (SiO2,
hexanes/ethyl acetate) as mixture of inseparable diastereomers.
Experimental Section
Commercially available reagents were used without further
purification. Furfuryl alcohols and furyl carbamates were
synthesized as previously described.[11,24] Catalysts and cofactors
were obtained from: NADH, Carbolution Chemicals GmbH;
lactoperoxidase from Bos taurus (LPO, 106 U/mg, Bio-Research
Products Inc.), peroxidase from Armoracia rusticana (HRP, 148
U/mg, Sigma); peroxidase from Glycine max (SBP, 17.5 kU/mL,
6-Hydroxy-2-methyl-2H-pyran-3(6H)-one (2a): Colorless solid
(53.4 mg, 0.417 mmol, 83% yield; a/b = 67/33). [a]20D: –79.6 (c
0.50, CHCl3), 99% ee, if starting from (R)-1a. M.p.: 61 °C. Rf
(cyclohexane/ethyl acetate, 2/1): 0.25. Major isomer: 1H NMR
(300 MHz, CDCl3): d [ppm] = 6.89 (dd, 3J = 10.2 Hz, 3J = 3.2 Hz,
1H), 6.10 (d, 3J = 10.2 Hz, 1H), 5.63 (m, 1H), 4.71 (q, 3J = 6.7 Hz,
1H), 3.53 (d, 3J = 5.0 Hz, 1H), 1.38 (d, 3J = 6.7 Hz, 3H); 13C NMR
(75 MHz, CDCl3): d [ppm] = 197.0, 144.5, 127.3, 87.7, 70.4, 15.3.
Minor isomer: 1H NMR (300 MHz, CDCl3): d [ppm] = 6.94 (d, 3J =
10.2 Hz, 1H), 6.15 (d, 3J = 10.2 Hz, 1H), 5.67 (d, 3J = 7.2 Hz, 1H),
4.23 (1H, m), 3.87 (d, 3J = 7.2 Hz, 1H), 1.45 (d, 3J = 6.7 Hz, 3H);
13C NMR (75 MHz, CDCl3): d [ppm] = 196.5, 148.1, 128.6, 91.0,
75.3, 16.2. FT-IR (neat, ATR): n [cm−1] = 3294 (br), 3051 (w), 2987
(w), 1676 (s), 1435 (m), 1371 (m), 1334 (w), 1273 (w), 1232 (m),
1143 (m), 1109 (m), 1091 (m), 1031 (s), 937 (m), 900 (m), 808
(m), 690 (m). GC: a-(2R)-2a = 37.0 min, a-(2S)-2a = 37.6 min.
This reaction was also successfully scaled up to a preparative
level: 1a (5.61 g, 50 mmol), D-glucose (10.8 g, 60 mmol), glucose
oxidase (5 kU), chloroperoxidase (10 kU) in citrate buffer (900 mL,
100 mM, pH 5.5) and tert-butanol (100 mL), 30 °C, 5 h, to yield 2a
(4.91 g (38.2 mmol) after chromatographic purification.
Bio-Research
Products
Inc.);
chloroperoxidase
from
Caldariomyces fumago (CPO, 10.0 kU/mL, Sigma), glucose
oxidase type II from Aspergillus niger (GOx, 19.3 U/mg, Sigma);
L-Amino acid oxidase from Crotalus atrox (0.1 U/mg, Sigma);
alcohol dehydrogenase recombinant from Escherichia coli (ADH
200, 17.6 U/mg evocatal GmbH); alcohol dehydrogenase,
recombinant from Escherichia coli (ADH 030, 18.8 U/mg, evocatal
GmbH); glucose dehydrogenase, recombinant from Escherichia
coli (GDH 060, 214 U/mg, evocatal GmbH); Lipase from Candida
sp., recombinant from Aspergillus niger, non-immobilized (7.3
kU/mL, Sigma); immobilized recombinant Lipase B from Candida
antarctica, (14.3 kU/g, c-LEcta GmbH); catalase from
Corynebacterium glutamicum (500 kU/mL, Sigma). Enzymatic
reactions were performed under non-inert conditions on an orbital
shaker in open glass vials or round bottom flasks. Column
chromatography was performed with silica gel from Merck
(Millipore 60, 40-60 μm, 240-400 mesh). Reactions were
monitored by thin layer chromatography (TLC) carried out on
Macherey-Nagel pre-coated silica gel plates (TLC Silica gel 60
F254). Visualisation of the TLC plates was done by using UV light
or staining with a basic potassium permanganate solution. 1H and
13C NMR spectra were recorded on Bruker instruments (Avance
300 or Avance 400) at 20 °C. Chemical shifts are reported in parts
per million (ppm) calibrated using residual non-deuterated solvent
as internal reference (CHCl3 at δ = 7.26 ppm (1H NMR) and
δ = 77.16 ppm (13C NMR)). Infrared spectra were recorded on a
Bruker ALPHA Eco-ATR spectrometer, absorption bands are
reported in wave numbers [cm−1]. High resolution mass
spectrometry was performed on an Agilent 6530 (Q-TOF) mass
spectrometer. Optical rotations were measured on an Autopol VI
polarimeter from Rudolph Research Analytical. Uncorrected
melting points were measured on a Stuart SMP30 melting point
apparatus using open glass capillaries. Gas chromatography
analysis was performed on a Hewlett Packard HP 6890 Series
6-Hydroxy-2-ethyl-2H-pyran-3(6H)-one (2b): Colorless oil
(54.9 mg, 386 µmol, 77% yield; a/b = 68/32). [a]20D: –24.9 (c 0.55,
CHCl3), 99% ee, if starting from (R)-1b. Rf (cyclohexane/ethyl
1
acetate, 2/1): 0.27. Major isomer: H NMR (300 MHz, CDCl3): d
3
3
[ppm] = 6.97-6.89 (dd, J = 10.4 Hz, J = 3.4 Hz, 1H), 6.18-6.10
(d, 3J = 10.3 Hz, 1H), 5.68 (m, 1H), 4.53 (dd, 3J = 7.4 Hz, 3J = 4.1
Hz, 1H), 3.37 (s, 1H), 2.06-1.71 (m, 2H), 1.06-0.97 (m, 3H); 13C
NMR (75 MHz, CDCl3): d [ppm] = 196.2, 144.4, 127.7, 87.7, 75.2,
23.0, 23.0, 9.32. Minor isomer (selected signals): 1H NMR (300
MHz, CDCl3): d [ppm] = 4.06-4.02 (m, 1H), 3.65 (dd, 3J = 7.3 Hz,
3J = 4.1 Hz, 1H); 13C NMR (75 MHz, CDCl3): d [ppm] = 147.8,
128.8, 90.9, 80.0, 23.9, 9.6. FT-IR (neat, ATR): n [cm−1] = 3307
(br), 2978 (w), 1666 (s), 1458 (w), 1377 (m), 1267 (m), 1234 (m),
1161 (m), 1112 (m), 1080 (m), 1026 (s), 960 (m), 889 (w), 777 (m),
750 (m), 692 (m).
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201800333
European Journal of Organic Chemistry
FULL PAPER
6-Hydroxy-2-propyl-2H-pyran-3(6H)-one (2c): Colorless oil
(41.4 mg, 265 µmol, 53% yield; a/b = 65/35). [a]20D: –17.9 (c 0.52,
CHCl3), 98% ee, if starting from (R)-1c. Rf (cyclohexane/ethyl
(m, 1H), 5.59 (s, 1H), 3.44 (d, 3J = 5.1 Hz, 1H); 13C NMR (75 MHz,
CDCl3): d [ppm] = 194.5, 144.8, 135.2, 128.6, 128.5, 128.0, 127.9,
1
88.0, 77.0. Minor isomer: H NMR (300 MHz, CDCl3): d [ppm] =
1
acetate, 2/1): 0.29. Major isomer: H NMR (300 MHz, CDCl3): d
7.41-7.33 (m, 5H), 7.01-6.97 (m, 1H), 6.26 (dd, 3J = 10.3 Hz, 4J =
1.6 Hz, 1H), 5.79-5.76 (m, 1H), 5.09 (d, 3J = 1.5 Hz, 1H), 3.64 (d,
3J = 7.2 Hz, 1H); 13C NMR (75 MHz, CDCl3): d [ppm] = 194.1,
148.2, 128.3, 91.5, 81.1. FT-IR (neat, ATR): n [cm−1] = 3392 (br),
1689 (s), 1629 (w), 1469 (w), 1454 (m), 1371 (w), 1290 (m), 1219
(m), 1089 (m), 1074 (m), 1024 (s), 1002 (s), 945 (m), 891 (m), 794
(w), 750 (s), 698 (s).
[ppm] = 6.92 (dd, 3J = 10.1 Hz, 3J = 3.2 Hz, 1H), 6.15 (d, 3J = 10.2
Hz, 1H), 5.68-5.64 (m, 1H), 4.58 (dd, 3J = 8.1 Hz, 3J = 3.9 Hz, 1H),
3
3.17 (br s, 1H), 2.10-1.39 (m, 4H), 0.96 (t, J = 7.4 Hz ,3H); 13C
NMR (75 MHz, CDCl3): d [ppm] = 194.8, 144.3, 127.6, 87.6, 74.0,
31.6, 18.2, 13.8. Minor isomer (selected signals): 1H NMR (300
3
MHz, CDCl3): d [ppm] = 4.10 (dd, 3J = 8.2 Hz, J = 4.1 Hz, 1H),
3
0.92 (t, J = 7.4 Hz, 3H); 13C NMR (75 MHz, CDCl3): d [ppm] =
6-Hydroxy-2-ethoxycarbonylmethyl-2H-pyran-3(6H)-one (2j):
147.7, 128.8, 91.1, 78.7, 32.6, 18.2, 13.8. FT-IR (neat, ATR): n
[cm−1] = 3394 (br), 2960 (m), 2873 (w), 1685 (s), 1458 (m), 1375
(m), 1265 (m), 1215 (w), 1157 (w), 1083 (m), 1020 (s), 914 (w),
759 (w). GC: a-(2R)-2c = 41.0 min, a-(2S)-2c = 41.9 min.
Colorless oil (68.1 mg, 340 µmol, 68% yield; a/b = 72/28). [a]20
:
D
+7.4 (c 1.00, CHCl3), 99% ee, if starting from (R)-1j. Rf
(cyclohexane/ethyl acetate, 2/1): 0.19. Major isomer: 1H NMR
(300 MHz, CDCl3): d [ppm] = 6.93 (dd, 3J = 10.3 Hz, 3J = 3.5 Hz,,
1H), 6.17 (d, 3J = 10.3 Hz, 1H), 5.75-5.53 (m, 1H), 5.03 (dd, 3J =
6-Hydroxy-2-allyl-2H-pyran-3(6H)-one (2e): Colorless oil
(50.1 mg, 325 µmol, 65% yield; a/b = 69/31). [a]20D: –33.6 (c 0.59,
CHCl3), 98% ee, if starting from (R)-1e. Rf (cyclohexane/ethyl
3
7.2 Hz, J = 4.0 Hz, 1H), 3.00-2.98 (m, 1H), 2.85-2.68 (m, 1H),
1.30-1.25 (m, 3H). 13C NMR (75 MHz, CDCl3): d [ppm] =195.0,
171.0, 144.6, 127.1, 87.4, 70.7, 61.0, 35.3, 14.1. Minor isomer
(selected signals):1H NMR (300 MHz, CDCl3): d [ppm] = 6.98 (dd,
3J = 10.3 Hz, 3J = 1.5 Hz, 1H), 6.13 (dd, 3J = 10.3 Hz, 3J = 1.5 Hz,
1
acetate, 2/1): 0.27. Major isomer: H NMR (300 MHz, CDCl3): d
[ppm] = 6.90 (dd, 3J = 10.3 Hz, 3J = 3.7 Hz, 1H), 6.11 (d, 3J = 10.3
Hz, 1H), 5.89-5.78 (m, 1H), 5.66 (m, 1H), 5.18-5.09 (m, 2H), 4.67
1H), 4.61-4.57 (m, 1H), 4.21-4.13 (m, 3H), 3.06-3.03 (m, 1H). 13
C
3
3
(dd, J = 8.0 Hz, J = 3.8 Hz, 1H), 2.73-2.71 (m, 1H), 2.58-2.46
(m, 1H); 13C NMR (75 MHz, CDCl3): d [ppm] = 195.9, 144.5, 133.7,
127.6, 118.1, 87.7, 73.7, 34.1. Minor isomer (selected signals): 1H
NMR (300 MHz, CDCl3): d [ppm] = 6.94 (dd, 3J = 10.2 Hz, 3J = 1.6
Hz, 1H), 6.16 (d, 3J = 10.2 Hz, 1H), 4.18-4.16 (dd, 3J = 8.2 Hz, 3J
= 3.9 Hz, 1H); 13C NMR (75 MHz, CDCl3): d = 195.8, 147.9, 133.6,
128.6, 117.8, 90.8, 78.5, 35.1. FT-IR (neat, ATR): n [cm−1] = 3381
(br), 2958 (w), 1685 (s), 1431 (w), 1373 (w), 1267 (w), 1211 (w),
1155 (w), 1087 (m), 1022 (s), 918 (m), 800 (w), 765 (w). GC: a-
(2R)-2e = 41.9 min, a-(2S)-2e = 43.1 min.
NMR (75 MHz, CDCl3): d [ppm] = 194.4, 171.0, 148.4, 128.4, 90.9,
75.3, 67.4, 36.2, 14.1. FT-IR (neat, ATR): n [cm−1] = 3420 (br),
2988 (w), 1732 (m), 1693 (m), 1375 (w), 1286 (w), 1178 (m), 1089
(m9 1020 (s), 931 (w), 846 (w), 759 (w).
6-Hydroxy-2-chloromethyl-2H-pyran-3(6H)-one
(2k):
Colorless solid (52.0 mg, 320 µmol, 64% yield; a/b = 64/36).
[a]20D: –2.8 (c 0.51, CHCl3), 99% ee, if starting from (S)-1k. M.p.:
75 °C. Rf (cyclohexane/ethyl acetate, 2/1): 0.23. Major isomer: 1H
NMR (300 MHz, CDCl3): d [ppm] = 7.00 (dd, 3J = 10.3 Hz, 3J = 3.6
Hz, 1H), 6.19 (d, 3J = 10.3 Hz, 1H), 5.79 (m, 1H), 4.90 (dd, 3J =
6-Hydroxy-2-tert-butyl-2H-pyran-3(6H)-one (2h): Colorless oil
(6.8 mg, 40 µmol, 4% yield; a/b = 70/30). Rf (cyclohexane/ethyl
3
5.5 Hz, J = 3.2 Hz, 1H), 3.98-3.92 (m, 2H), 3.62-3.58 (m, 1H).
13C NMR (75 MHz, CDCl3): d [ppm] = 193.0, 145.1, 127.5, 87.9,
74.0, 42.9. Minor isomer (selected signals): 1H NMR (300 MHz,
1
acetate, 2/1): 0.35. Major isomer: H NMR (300 MHz, CDCl3): d
[ppm] = 6.84 (dd,3J = 10.2 Hz, 3J = 3.2 Hz, 1H), 6.04 (d, 3J = 10.2
3
3
3
CDCl3): d ppm] = 7.03 (dd, J = 10.3 Hz, J = 1.6 Hz, 1H), 6.23
(dd, 3J = 1.5 Hz, 3J = 10.3 Hz, 1H), 4.43 (dd, 3J = 6.3 Hz, 3J = 3.8
Hz, 1H), 4.01-3.99 (m, 1H). 13C NMR (75 MHz, CDCl3): d [ppm] =
192.6, 148.2, 128.4, 90.4, 78.5, 43.7. FT-IR (neat, ATR): n [cm−1]
= 3329 (br), 1666 (s), 1631 (w), 1436 (w), 1371 (w), 1273 (m),
1232 (m), 1192 (w), 1153 (w), 1107 (m), 1080 (m), 1028 (s), 902
(m), 802 (m), 763(m), 731 (m), 690 (m).
Hz, 1H), 5.66 (d, J = 3.2 Hz, 1H), 4.21 (s, 1H), 3.48 (br s, 1H),
1.06 (s, 9H); 13C-NMR (75 MHz, CDCl3): d [ppm] = 196.8, 143.4,
128.8, 87.9, 80.2, 34.9, 26.3. Minor isomer (selected signals): 1H
NMR (300 MHz, CDCl3): d [ppm] = 6.89-6.85 (m, 1H), 6.10- 6.06
(m, 1H), 5.60 (m, 1H), 3.70 (s, 1H), 3.69 (d, 3J = 1.2 Hz, 1H), 1.09
(s, 9H); 13C-NMR (75 MHz, CDCl3): d [ppm] = 196.1, 147.1, 130.4,
91.8, 85.1. FT-IR (neat, ATR): n [cm−1] = 3371 (br), 2958 (m),
2872 (w), 1726 (m), 1681 (s), 1633 (w), 1463 (w), 1363 (m), 1300
(m), 1234 (m), 1182 (m), 1089 (m), 1026 (s), 1004 (s), 968 (m),
900 (m), 821 (w), 746 (m).
6-Hydroxy-2-hydroxymethyl-2H-pyran-3(6H)-one (2l): Yellow
oil (22.3 mg, 155 µmol, 31% yield; a/b = 55/44). [a]20D: +22.5 (c
0.55, CHCl3), 99% ee, if starting from (R)-1l. Rf (cyclohexane/ethyl
1
acetate, 1/1): 0.15. Major isomer: H NMR (300 MHz, CDCl3): d
6-Hydroxy-2-phenyl-2H-pyran-3(6H)-one (2i): Colorless oil
[ppm] = 6.98-6.93 (m, 1H), 6.15 (d, 3J = 10.3 Hz, 1H), 5.72 (d, 3J
= 3.4 Hz, 1H), 4.67 (t, J = 4.5 Hz, 1H), 4.10-3.88 (m, 2H); 13C
(25.2 mg, 132 µmol, 26% yield; a/b
=
75/25). Rf
3
(cyclohexane/ethyl acetate, 2/1): 0.30. Major isomer: 1H NMR
3
NMR (75 MHz, CDCl3): d = 145.0, 127.8, 87.5, 74.1, 61.8. Minor
isomer (selected signals): 1H NMR (300 MHz, CDCl3): d [ppm] =
(300 MHz, CDCl3): d [ppm] = 7.41-7.33 (m, 5H), 6.95 (dd, J =
3
3
10.2 Hz, J = 3.3 Hz, 1H), 6.21 (d, J = 10.3 Hz, 1H), 5.73-5.71
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201800333
European Journal of Organic Chemistry
FULL PAPER
6.22 (d, 3J = 10.4 Hz, 1H), 5.65 (d, 3J = 1.8 Hz, 1H), 4.53 (t, 3J =
3.5 Hz, 1H); 13C NMR (75 MHz, CDCl3): d =146.9, 128.5. FT-IR
(neat, ATR): n [cm−1] = 3392 (br), 2942 (m), 2854 (w), 2358 (s),
2331 (m), 1683 (m), 1465 (m), 1375 (w) 1103 (w), 1029 (m), 769
(w), 669 (m).
6-Hydroxy-2-isopropyl-2H-pyran-3(6H)-one (2f): Colorless oil
(26.9 mg, 172 µmol, 86% yield; a/b = 73/27). [a]20D: –8.6 (c 0.50,
CHCl3), 99% ee, if starting from (R)-1f. Rf (cyclohexane/ethyl
1
acetate, 2/1): 0.32. Major isomer: H-NMR (300 MHz, CDCl3): d
[ppm] = 6.93 (dd, 3J = 10.2 Hz, 3J = 3.4 Hz, 1H), 6.12 (d, 3J = 10.2
3
Hz, 1H), 5.71-5.65 (m, 1H), 4.43 (d, J = 3.4 Hz, 1H), 3.15-3.10
6-Hydroxy-2-butyl-2H-pyran-3(6H)-one (2o): Colorless oil (31.5
mg, 185 µmol, 37% yield; a/b = 76/24). Rf (cyclohexane/ethyl
(m, 1H), 2.52-2.41 (m, 1H), 1.05 (d, 3J = 7.1 Hz, 3H), 0.90 (d, 3J =
6.9 Hz, 3H); 13C-NMR (75 MHz, CDCl3): d [ppm] = 196.2, 144.2,
128.1, 87.7, 77.3, 28.6, 19.0, 16.2. Minor isomer (selected
signals):1H NMR (300 MHz, CDCl3): d [ppm] = 6.14 (dd, 3J = 10.3
Hz, 3J = 1.5 Hz, 1H), 3.93 (dd, 3J = 3.4 Hz, 3J = 1.3 Hz, 1H), 3.43-
3.37 (m, 1H), 0.96 (d, 3J = 6.8 Hz, 3H); 13C NMR (75 MHz, CDCl3):
d [ppm] = 148.0, 129.5, 91.2, 83.1, 28.9, 19.1, 16.5. FT-IR (neat,
ATR): n [cm−1] = 3385 (br), 2966 (w), 1681 (m), 1463 (w), 1369
(m), 1273 (w), 1230 (w), 1153 (w), 1082 (m), 1016 (s), 946 (m),
885 (w), 756 (m), 680 (w). GC: a-(2R)-2f = 38.7 min, a-(2S)-2f =
39.9 min.
1
acetate, 2/1): 0.33. Major isomer: H NMR (300 MHz, CDCl3): d
[ppm] = 6.80 (dd, 3J = 10.1 Hz, 3J = 3.3 Hz, 1H), 6.11 (d, 3J = 10.4
Hz, 1H), 5.66 (d, 3J = 3.1 Hz, 1H), 4.56 (q, 3J5,6 = 4.1 Hz, 1H, H-
5), 3.00 (br s, 1H, OH), 1.98-1.64 (m, 2H, H-6), 1.48-1.30 (m, 4H,
H-7, H-8), 0.91 (t, 3J = 7.1 Hz, 3H, H-9); 13C NMR (75 MHz,
CDCl3): d [ppm] = 196.8 (C-4), 144.1 (C-3), 127.7 (C-2), 87.7 (C-
1), 74.2 (C-5), 29.1 (C-6), 26.9, 22.2 (C-7, C- 8), 13.9 (C-9). Minor
isomer (selected signals): 1H NMR (300 MHz, CDCl3): d [ppm] =
6.94-6.90 (m, 1H), 6.16- 6.12 (m, 1H), 5.66 (d, 3J = 3.1 Hz, 1H),
4.09-4.05 (m, 1H), 3.24 (br s, 1H), 1.98-1.64 (m, 2H), 1.48-1.30
3
(m, 4H), 0.91 (t, J = 7.1 Hz, 3H); 13C NMR (75 MHz, CDCl3): d
6-Hydroxy-2-isobutyl-2H-pyran-3(6H)-one (2g): Colorless oil
[ppm] = 147.5, 128.8, 90.9, 79.0, 30.4. FT-IR (neat, ATR): n [cm−1]
= 3327 (br), 2949 (m), 2927 (w), 1672 (s), 1627 (w), 1467 (m),
1373 (m), 1309 (w), 1257 (m), 1157 (m), 1187 (w), 1087 (s), 1026
(s), 974 (m), 933 (w), 875 (m), 759 (m).
(30.3 mg,
178 µmol,
89%
yield;
a/b
=
70/30).
Rf (cyclohexane/ethyl acetate, 2/1): 0.48. Major isomer: 1H NMR
(400 MHz, CDCl3): d [ppm] = 6.90 (dd, 3J = 10.2 Hz, 3J = 3.4 Hz,
3
3
1 H), 6.12 (d, J = 10.2 Hz, 1 H), 5.66 (d, J = 3.4 Hz, 1 H), 4.63
3
3
(dd, J = 9.7 Hz, J = 3.3 Hz, 1 H), 1.77-1.91 (m, 2 H), 1.57-1.75
(m, 1 H), 0.92-1.02 (m, 6 H); 13C NMR (100 MHz, CDCl3): d [ppm]
= 193.1, 143.9, 127.8, 87.4, 72.5, 38.2, 24.2, 23.4, 21.2. Minor
isomer (selected signals): 1H NMR (400 MHz, CDCl3): d [ppm] =
6-Hydroxy-2-pentyl-2H-pyran-3(6H)-one (2p): Colorless oil (5.7
mg, 31 µmol, 6% yield; a/b = 74/26). Rf (cyclohexane/ethyl
1
acetate, 2/1): 0.34. Major isomer: H NMR (300 MHz, CDCl3): d
[ppm] = 6.88 (dd, 3J = 10.2 Hz, 3J = 3.3 Hz, 1H), 6.10 (d, 3J = 10.3
Hz, 1H), 5.65 (d, 3J = 3.0 Hz, 1H), 4.55 (q, 3J = 3.9 Hz, 1H), 3.03
(br s, 1H), 1.95-1.63 (m, 2H), 1.33-1.20 (m, 6H), 0.90-0.85 (m,
3H); 13C NMR (75 MHz, CDCl3): d [ppm] = 196.8, 144.1, 127.7,
87.7, 74.3, 31.7, 29.6, 24.9, 22.6, 14.0. Minor isomer (selected
signals): 1H NMR (300 MHz, CDCl3): d [ppm] = 6.94-6.90 (m, 1H),
3
3
3
6.94 (dd, J = 10.3 Hz, J = 1.6 Hz, 1 H), 6.17 (dd, J = 10.3 Hz,
4J = 1.6 Hz, 1 H), 5.67 (d, 3J = 1.6 Hz, 1 H), 4.15 (dddd,
3J = 9.6 Hz, J = 3.3 Hz, J = 1.2 Hz, J = 0.4 Hz, 1 H); 13C NMR
(100 MHz, CDCl3): d [ppm] = 147.1, 129.0, 90.9, 82.3, 39.3. FT-
IR (ATR): n [cm–1] = 3307 (br), 2954 (m), 1672 (m), 1629 (w), 1371
(m), 1276 (m), 1157 (m), 1091 (s), 1020 (s), 975 (m), 898 (m), 702
(m). HRMS (ESI): m/z [M–OH]+ calcd for C9H13O2: 153.0916;
found: 153.0910.
3
4
4
3
6.16- 6.12 (m, 1H), 5.65 (d, J = 3.0 Hz, 1H), 4.09-4.05 (m, 1H),
3.26 (br s, 1H), 1.95-1.63 (m, 2H), 1.33-1.20 (m, 6H), 0.90-0.85
(m, 3H); 13C NMR (75 MHz, CDCl3): d [ppm] = 147.5, 128.8, 90.9,
79.2, 30.7, 29.1, 25.1, 22.8. FT-IR (neat, ATR): n [cm−1] = 3317
(br), 2949 (m), 2873 (m), 1674 (s), 1627 (w), 1469 (m), 1375 (m),
1274 (m), 1242 (m), 1157 (m), 1093 (s), 1026 (s), 999 (m), 952
(m), 891 (m), 785 (m), 700 (m).
6-Hydroxy-2,2-dimethyl-2H-pyran-3(6H)-one (2r): Colorless
liquid (15.4 mg, 108 µmol, 54 % yield). Rf (cyclohexane/ethyl
acetate, 2/1): 0.33. 1H NMR (CDCl3, 400 MHz): d [ppm] = 6.87 (dd,
3J = 10.3 Hz, 3J = 2.2 Hz, 1 H), 6.07 (dd, 3J = 10.3 Hz, 4J = 1.3 Hz,
1 H), 5.70-5.68 (m, 1 H), 3.38 (br s, 1 H), 1.49 (s, 3 H), 1.39 (s,
3 H); 13C NMR (CDCl3, 100 MHz): d [ppm] = 198.9, 145.7, 126.6,
88.0, 79.5, 26.6, 23.9. FT-IR (neat, ATR): n [cm−1] = 3402 (br),
2982 (w), 1681 (s), 1380 (m), 1293 (m), 1238 (m), 1084 (m), 1036
(s), 924 (m).
General procedure for the oxidase-limited modification of the
biocatalytic Achmatowicz reaction: The furylcarbinol
(0.2 mmol) was dissolved in tert-Butanol (2 mL) and the solution
was added to a mixture of chloroperoxidase (200 U), glucose
oxidase (6 U) in citrate buffer (18 mL, 100 mM, pH 6.0). After
addition of D-glucose (50 mM), the reaction mixture was incubated
at 30 °C (200 rpm) overnight. L-Methionine (250 mg) was added
and the reaction mixture was extracted with ethyl acetate (3 x 5
mL). The combined organic layers were dried over MgSO4,
evaporated under reduced pressure and the pyranone was
obtained after purification by column chromatography (SiO2,
hexanes/ethyl acetate).
6-Hydroxy-4-methyl-2H-pyran-3(6H)-one (2s): Colorless solid
(12.3 mg,
96 µmol,
48 %
yield).
M.p.:
59 °C.
Rf
(cyclohexane/ethyl acetate, 2/1): 0.25. 1H NMR (400 MHz.
CDCl3): d [ppm] = 6.68 (dq, 3J = 3.1 Hz, 4J = 1.4 Hz, 1 H),
5.55-5.68 (m, 1 H), 4.56 (d, 2J = 16.9 Hz, 1 H), 4.12 (d,
2J = 16.9 Hz, 1 H), 3.32 (br s, 1 H), 1.84 (t, 4J = 1.4 Hz, 3 H);
13C NMR (100 MHz, CDCl3): d [ppm] = 195.3, 140.8, 135.4, 89.2,
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10.1002/ejoc.201800333
European Journal of Organic Chemistry
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1 H), 4.71 (q, 3J = 6.8 Hz, 1 H), 3.93 (br s, 1H), 1.83 (s, 3H), 1.39
(d, 3J = 6.8 Hz, 3H). 13C NMR (100 MHz, CDCl3): d [ppm] = 197.6,
66.6, 14.5. FT-IR (ATR): n [cm–1] = 3409 (br), 2963 (w), 1665 (s),
1434 (m), 1360 (m), 1236 (m), 1144 (m), 1102 (m), 990 (s), 859
(m), 788 (m), 656 (m).
1
139.7, 134.3, 88.1, 70.2, 15.6, 14.7. Minor isomer: H NMR
(400 MHz, CDCl3): d [ppm] = 6.67-6.69 (m, 1H), 5.61-5.63 (m, 1H),
General procedure for the lipase-catalyzed biocatalytic
Achmatowicz reaction: The furylcarbinol (5.0 mmol) was
dissolved in ethyl acetate (50 mL), and immobilized lipase B from
C. antarctica (105 mg, 1.5 kU) and aqueous H2O2 (50 % v/v,
858 µL, 1.02 g, 15.0 mmol) were added. The reaction mixture was
placed on an orbital shaker at 40 °C (200 rpm). After 24 h,
phosphate buffer (15 mL, 100 mM, pH 7.0) and catalase (5 µL)
were added and the mixture was shaken for additional 15 min.
The organic layer was separated and the aqueous layer was
extracted with ethyl acetate (10 mL). The combined organic layers
were dried over Na2SO4 and the volatiles were evaporated under
reduced pressure. The pyranone was obtained after purification
by column chromatography (SiO2, hexanes/ethyl acetate).
3
4.22-4.13 (m, 1H), 1.82 (s, 3H), 1.44 (d, J = 6.7 Hz, 3 H). 13C
NMR (100 MHz, CDCl3): d [ppm] = 197.2, 143.1, 135.7, 91.0, 74.8,
16.4. FT-IR (neat, ATR): n [cm−1] = 3427 (br), 2984 (w), 1651 (s),
1448 (m), 1367 (m), 1305 (w), 1130 (m), 1091 (s), 1024 (s), 995
(s). HRMS (ESI): m/z [M+Na]+ calcd for C7H10O3Na: 165.0527;
found: 165.0523.
Benzyl 6-ethyl-2-hydroxy-5-oxo-5,6-dihydropyridine-1(2H)-
carboxylate (4): Yellow oil (82 mg, 0.58 mmol, 65 %;
a/b = 80:20). Rf (cyclohexane/ethyl acetate, 3/2): 0.45. Major
isomer: 1H NMR (400 MHz, CDCl3): d [ppm] = 7.38 (m, 5 H), 6.91
(dd, 3J = 10.4 Hz, 3J = 3.9 Hz, 1 H), 6.13 (dd, 3J = 10.4 Hz,
4J = 1.2 Hz, 1 H), 6.02-6.09 (m, 1 H), 5.21-5.23 (m, 2 H), 4.51 (t,
3
3J = 7.3 Hz, 1 H), 1.80-1.92 (m, 2 H), 0.95 (t, J = 7.3 Hz, 3 H).
6-Hydroxy-2,6-dimethyl-2H-pyran-3(6H)-one (2n): Yellow oil
13C NMR (100 MHz, CDCl3): d [ppm] = 195.4, 151.5, 143.9, 135.5,
128.7,128.6, 128.3, 127.1, 72.2, 68.2, 61.6, 28.9, 10.4. Minor
isomer (selected signals): 1H NMR (400 MHz, CDCl3): d [ppm] =
6.80 (dd, 3J = 10.5 Hz, 3J = 3.2 Hz, 1 H). FT-IR (neat, ATR): n
[cm−1] = 3428 (br), 2969 (w) 1677 (s), 1426 (w), 1380 (m), 1316
(m), 1069 (m), 1028 (m), 980 (m), 907 (m), 809 (w), 726 (s), 695
(s). HRMS (ESI): m/z [M+Na]+ calcd for C15H17NO4: 298.1050;
found: 298.1049.
(528 mg,
3.71 mmol,
74 %
yield;
a/b = 84:16).
Rf
(cyclohexane/ethyl acetate, 2/1): 0.36. Major isomer: 1H NMR
(400 MHz, CDCl3): d [ppm] = 6.80 (d, 3J = 10.1 Hz, 1 H), 5.99 (d,
3J = 10.1 Hz, 1 H), 4.63 (q, J = 6.7 Hz, 1 H), 1.61 (s, 3 H), 1.34
(d, 3J = 6.7 Hz, 3 H);13C NMR (100 MHz, CDCl3): d [ppm] = 197.2,
147.9, 126.1, 92.9, 70.7, 28.9, 15.3. Minor isomer (selected
signals): 1H NMR (400 MHz, CDCl3):
3J = 10.2 Hz, 1 H), 4.30 (q, J = 6.8 Hz, 1 H), 1.59 (s, 3 H), 1.43
(d, 3J = 6.8 Hz, 3 H); 13C NMR (100 MHz, CDCl3): d [ppm] = 150.1,
126.0, 74.3, 24.3, 17.3. FT-IR (neat, ATR): n [cm−1] = 3302 (m),
2987 (w), 1676 (s), 1444 (m), 1371 (m), 1242 (m), 1145 (m), 1109
(m), 1070 (m), 1028 (s), 939 (m), 688 (m).
3
d [ppm] = 6.86 (d,
3
Acknowledgements
Financial support by the by the Suomen Akatemia (298250), the
Deutsche Forschungsgemeinschaft (DE1599/4-1), the Fonds der
Chemischen Industrie and the Dr.-Otto-Röhm-Gedächtnisstiftung
is gratefully acknowledged.
6-Hydroxy-2-hexyl-2H-pyran-3(6H)-one (2q): Colorless solid
(744 mg, 3.75 mmol, 75 %; a/b = 75:25.). M.p.: 70 °C.
Rf (cyclohexane/ethyl acetate, 2/1): 0.45. Major isomer: H NMR
1
(400 MHz, CDCl3): d [ppm] = 6.88 (dd, 3J = 10.2 Hz, 3J = 3.3 Hz,
3
3
1 H), 6.10 (d, J = 10.2 Hz, 1 H), 5.65 (d, J = 3.3 Hz, 1 H), 4.55
(dd, 3J = 8.1 Hz, 3J = 3.9 Hz, 1 H), 3.08 (br s, 1 H), 1.88-1.96 (m,
1 H), 1.65-1.80 (m, 1 H), 1.24-1.48 (m, 8 H), 0.82-0.92 (m, 3 H);
13C NMR (100 MHz, CDCl3): d [ppm] = 196.7, 144.3, 127.8, 87.8,
74.4, 31.8, 29.7, 29.2, 25.0, 22.7, 14.2. Minor isomer (selected
signals): 1H NMR (400 MHz, CDCl3): d [ppm] = 6.92 (dd,
3J = 10.2 Hz, 3J = 1.5 Hz, 1 H), 6.14 (dd, 3J = 10.2 Hz, 4J = 1.5 Hz,
Keywords: biocatalysis
• peroxidase • ring expansion •
heterocyclic chemistry • furan
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6-Hydroxy-2,4-dimethyl-2H-pyran-3(6H)-one (2t): Colorless
solid
(398 mg,
2.80 mmol,
56 %;
a/b = 88:12).
1
[9]
Rf (cyclohexane/ethyl acetate, 1/1): 0.54 Major isomer: H NMR
(400 MHz, CDCl3): d [ppm] = 6.86-6.89 (m, 1 H), 5.58-5.60 (m,
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Entry for the Table of Contents (Please choose one layout)
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Biocatalysis
air + glucose
O
R'
glucose oxidase
R
Daniel Thiel, Fabian Blume, Christina
Jäger, Jan Deska*
(A. niger)
R
HO
O
R'
chloroperoxidase
O
OH
(C. fumago)
gluconic acid
Page No. – Page No.
Chloroperoxidase-catalyzed
Achmatowicz Rearrangements
Chloroperoxidase from Caldariomyces fumago catalyzes the selective oxidation of
a variety of functionalized furfuryl alcohols in an Achmatowicz-type ring expansion.
In combination with glucose oxidase as oxygen-activating biocatalyst, a purely
enzymatic, aerobic protocol for the synthesis of 6-hydroxypyranone building blocks
is obtained.
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