Chloroperoxidase-catalyzed oxidation of conjugated dienoic esters

Article abstract of DOI:10.1016/S0040-4039(01)02127-X

The chloroperoxidase (CPO)-catalyzed oxidations of dienes conjugated to an ester group were studied using tert-butyl hydroperoxide as the terminal oxidant.

Full text of DOI:10.1016/S0040-4039(01)02127-X

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 339–342
Chloroperoxidase-catalyzed oxidation of conjugated dienoic
esters
Despina J. Bougioukou and Ioulia Smonou*
Department of Chemistry, University of Crete, Iraklio 71409, Crete, Greece
Received 4 October 2001; revised 29 October 2001; accepted 8 November 2001
Abstract—The chloroperoxidase (CPO)-catalyzed oxidations of dienes conjugated to an ester group were studied using tert-butyl
hydroperoxide as the terminal oxidant. © 2002 Elsevier Science Ltd. All rights reserved.
Chloroperoxidase first isolated in 1961 by Hager1,2 from
Caldariomyces fumago (CPO, EC 1.11.1.10), is one of the
OH
OH
HO
CPO
+
most versatile and promising of the heme enzymes for
synthetic applications.3–7 Various transformations typi-
cal of catalases and cytochrome P-450 like monooxyge-
nases are catalyzed by CPO.8 The enzyme shows broad
substrate specificity catalyzing various halide-dependent
as well as halide-independent reactions.9 In the halide-
independent oxidation reactions, CPO uses hydrogen
peroxide or other organic peroxides as the source of
oxygen without requiring cofactors.10 Substrate specific-
ity studies as well as mechanistic studies have shown that
CPO catalyzes the epoxidation of a number of function-
alized or unfunctionalized olefins with a high degree of
enantio- and diastereoselectivity.11–13 Epoxidation is
often accompanied by the formation of aldehydes as well
asbyallylichydroxylation.4 Thechainlengthofthealkene
as well as the size and type of substituents adjacent to
the double bond control the enantioselectivity of the
epoxidation.14–16
(2)
tBHP
OH
In this communication, we report the first examples of
CPO-catalyzed oxidations of dienes conjugated to an
ester group, and we discuss possible mechanisms for
these synthetically useful transformations.
The reactions of the isomeric conjugated dienoic esters
methyl (2E,4E) (1), methyl (2Z,4E) (2), methyl (2Z,4Z)
(3) and methyl-(2E,4Z)-hexadienoate (4) were investi-
gated. The stereoisomers 2, 3 and 4 were prepared by
photoisomerization19 of 1 by irradiation at 254 nm,
followed by separation by flash column chromatogra-
phy on silica gel enriched with 25% AgNO3. tert-Butyl
hydroperoxide (tBHP) was used as the terminal oxidant.
None of the substrates used in this study isomerize
under the enzymatic reaction conditions, as shown by
control experiments. The enzymatic oxidation of each
isomer was carried out in a phosphate buffer (100 mM,
pH 6), by using 25 mg of substrate, 1000 units of
commercially available CPO and 2 equiv. of 70% tBHP
which was added in two aliquots to a total volume of 5
ml. All the reactions were monitored by gas chromatog-
Although CPO-catalyzed oxidations of a wide variety of
simple and functionalized alkenes have been studied
extensively, only two examples of conjugated dienes have
been reported in the last few years. For example, Elfarra
and his co-workers17 reported the CPO-catalyzed epoxi-
dation of 1,3-butadiene, which gave butadiene monoxide
accompanied by the formation of a small amount of
crotonaldehyde (Eq. (1)). Recently, Nicolosi and his
co-workers reported18 the asymmetric oxidation of 1,3-
cyclohexadiene catalyzed by CPO (Eq. (2)).
1
raphy, the products were identified by H NMR and
GC–MS, and all product yields are reported after 6 h
reaction.
O
CPO
+
(1)
H
H2O2
O
The CPO-catalyzed oxidation of (E,E)-1, under aerobic
conditions gave the aldehydic ester 5 as the major product
(83%), accompanied by small amounts of the epoxide
7 (4%) and a second aldehydic ester 6 (13%), as
Keywords: chloroperoxidase; oxidation; dienoic esters.
* Corresponding author. Tel: +30-81-393610; fax: +30-81-393601.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)02127-X

340
D. J. Bougioukou, I. Smonou / Tetrahedron Letters 43 (2002) 339–342
shown in Scheme 1. When the reaction was run under
anaerobic conditions (nitrogen flow) only the aldehyde
5 and epoxide 7 were detected, in a 92:8 ratio.
Similarly, from the catalytic oxidation of (Z,E)-2,
(Scheme 2), under aerobic conditions, the aldehydic
ester 8 was the major product (78%), accompanied by
small amounts of 5 (7%) and 6 (15%).
The CPO-catalyzed oxidation of substrate (Z,Z)-3,
under aerobic conditions gave the three products shown
in Scheme 3; the aldehydic esters 6 (38%) and 8 (27%)
and the cis-epoxide 9 (35%) with high enantioselectivity
(96% ee).
Scheme 4. CPO-catalyzed oxidation of (E,Z)-4 and (E,E)-1
mixture.
epoxidation20 of their corresponding dienoic ester pre-
cursors. The absolute configuration of 9 and 10 was
assigned to be R,S in analogy to that of related com-
pounds.21 The same stereochemistry R,S is also pre-
dicted by the model proposed by Sheldon.22
The (E,Z)-4 dienoic ester was oxidized as a mixture
with the isomer (E,E)-1, in a ratio 48/52 because efforts
to separate the two were unsuccessful. As shown in
Scheme 4, under anaerobic conditions, the major prod-
ucts were the aldehyde 5 (60%) and the cis-epoxide 10
(40%) with high enantioselectivity (93% ee). The ee
values for epoxides 9 and 10 were determined by gas
chromatography with a chiral column (HP-Chiral 20%
permethylated-cyclodextrin, 30 m×0.25 mm). In a con-
trol experiment the racemic mixtures of the epoxides
The above results show that the reaction mode of
CPO-epoxidation versus allylic oxidation depends on
the stereochemistry at the C4ꢀC5 double bond. When
the alkyl terminal double bond has the trans configura-
tion, as in substrates 1 and 2, allylic oxidation predom-
inates over C4ꢀC5 double bond epoxidation. This
finding is consistent with previous results showing that
in cases of trans alkenes, only limited, if any, epoxida-
tion occurs.4,13
9
and 10 were prepared separately by mCPBA
In a control experiment, a mixture of alcohols 11, 12
and 13 was subjected to CPO oxidation (Scheme 5). We
wish to point out the following observations: the start-
ing ratio of alcohols 11, 12 and 13 remained constant
during the course of the reaction. In the absence of
enzyme, none of the alcohols isomerized. The ratio of 5,
14 and 8 remained constant in a phosphate buffer (pH
6) for 6 h. The relative ratio of the aldehydic esters
produced by the enzymatic oxidation was the same as
that of the reactant alcohols. Interpretation of these
results indicated that the aldehydes 5 and 8 formed in
the reactions of 1–4, arise from the oxidation of their
corresponding alcohols which are intermediates in these
enzymatic reactions. Although we did not detect these
alcohols during the course of the enzymatic reaction,
we were not surprised. It is well established that the
oxidation of alcohols to aldehydes is a much faster
reaction than the initial hydroxylation.23–27
Scheme 1. CPO-catalyzed oxidation of (E,E)-1.
CO2Me
CO2Me
Scheme 2. CPO-catalyzed oxidation of (Z,E)-2.
HO
HO
O
O
11
(89%)
5 (89%)
CO2Me
H
H
CO2Me
CPO/tBHP
12
13
(9%)
14 (8%)
CO2Me
(2%)
CO2Me
8 (3%)
HO
O
H
Scheme 3. CPO-catalyzed oxidation of (Z,Z)-3.
Scheme 5. CPO-catalyzed oxidation of alcoholic esters.

D. J. Bougioukou, I. Smonou / Tetrahedron Letters 43 (2002) 339–342
341
Scheme 6.
When the C4ꢀC5 double bond has the Z configuration,
as in substrates 3 and 4, enantioselective epoxidation
competes well with allylic oxidation, to give the epox-
ides 9 and 10 and the allylic aldehydes 8 and 5 in
comparable amounts. It is worth pointing out again the
high enantiomeric purity of the epoxides 9 (96% ee) and
10 (93% ee) which are of the highest observed in such
reactions.
5. van Deurzen, M. P. J.; van Rantwijk, F.; Sheldon, R. A.
Tetrahedron 1997, 53, 13183–13220.
6. Colonna, S.; Gaggero, C.; Richelmi, C.; Pasta, P.
TIBTECH 1999, 17, 163.
7. Miller, V. P.; Tschirret-Guth, R. A.; Ortiz de Montel-
lano, P. R. Arch. Biochem. Biophys. 1995, 319, 333.
8. Blanke, S. R.; Hager, L. P. J. Biol. Chem. 1988, 263,
18739.
9. Adam, W.; Lazarus, M.; Saha-Mo¨ller, C. R.; Weichold,
O.; Hoch, U.; Ha¨ring, D.; Schreier, P. In Biotransforma-
tions with peroxidases in Biotransformations; Faber, K.,
Ed.; Springer: Berlin, 1999; pp. 73–108.
10. (a) van Deurzen, M. P. J.; Seelbach, K.; van Rantwijk,
F.; Kragl, U.; Sheldon, R. A. Biocatal. Biotransform.
1997, 15, 1–16; (b) Manoj, M. K; Hager, L. P. Biochim.
Biophys. Acta 2001, 1547, 408–417.
11. Ortiz de Montellano, P. R.; Choe, Y. S.; DePillis, G.;
Catalano, C. E. J. Biol. Chem. 1987, 262, 11641–11646.
12. Geigert, J.; Lee, T. D.; Dalietos, D. J.; Hirano, D. S.;
Neidelman, S. L. Biochem. Biophys. Res. Commun. 1986,
136, 778–782.
A reasonable explanation for the formation of all prod-
ucts, including aldehyde 6, under aerobic but not anaer-
obic conditions, involves the intermediacy of the radical
cation I, Scheme 6. This intermediate can lead to
partial isomerization of the dienoic esters that competes
with the oxidation of the terminal methyl group, and
can react with oxygen to form the dioxetane intermedi-
ate that leads to the cleaved product aldehyde 6. Simi-
lar CꢀC bond cleavage products have been observed in
many cases.28 Further studies on the mechanism of
these reactions, including the competition between iso-
merization and hydrogen abstraction, are currently
under investigation in our laboratories.
13. Alain, E. J.; Hager, L. P.; Deng, L.; Jacobsen, E. N. J.
Am. Chem. Soc. 1993, 115, 4415–4416.
14. Lakner, F. J.; Cain, K. P.; Hager, L. P. J. Am. Chem.
Acknowledgements
Soc. 1997, 119, 443–444.
15. Dexter, A. F.; Lakner, F. J.; Campbell, R. A.; Hager, L.
P. J. Am. Chem. Soc. 1995, 117, 6412–6413.
16. Lakner, F. J.; Hager, L. P. Tetrahedron: Asymmetry 1997,
8, 3547–3550.
17. Elfarra, A. A.; Duescher, R. J.; Pasch, C. M. Arch.
Biochem. Biophys. 1991, 286, 244–251.
We thank Professor G. J. Karabatsos for his valuable
comments. This work was supported by the graduate
program EPEAEK.
18. Sanfilippo, C.; Patti, A.; Nicolosi, G. Tetrahedron: Asym-
References
metry 2000, 11, 3269–3272.
19. Lewis, F. D.; Howard, D. K.; Barancyk, S. V.; Oxman, J.
D. J. Am. Chem. Soc. 1986, 108, 3016.
20. (a) Bur, D.; Nikles, M.; Se´quin, U.; Neuburger, M.;
Zehnder, M. Helv. Chim. Acta 1993, 76, 1863; (b) Lee, A.
S.-Y.; Su, F.-Y; Liao, Y.-C. Tetrahedron Lett. 1999, 40,
1323; (c) Akita, H.; Saotome, C.; Ono, M. Tetrahedron:
Asymmetry 1996, 7, 2595.
1. Shaw, P. D.; Hager, L. P. J. Biol. Chem. 1961, 236,
1626–1630.
2. Hager, L. P.; Morris, D. R.; Brown, F. S.; Eberwein, H.
J. Biol. Chem. 1966, 241, 1769–1777.
3. Thomas, J. A.; Morris, D. R.; Hager, L. P. J. Biol. Chem.
1970, 245, 3129.
4. Zaks, A.; Dodds, D. R. J. Am. Chem. Soc. 1995, 117,
10419–10424.
21. Hu, S.; Hager, L. P. Tetrahedron Lett. 1999, 40, 1641–
1644.

342
D. J. Bougioukou, I. Smonou / Tetrahedron Letters 43 (2002) 339–342
22. van Rantwijk, F.; Sheldon, R. A. Curr. Opin. Biotech.
2000, 11, 554–564.
1999, 10, 3529–3535.
27. Baciocchi, E.; Lanzalunga, O.; Manduchi, L. Chem.
Commun. 1999, 1715–1716.
23. Hu, S.; Hager, L. P. Biochem. Biophys. Res. Commun.
28. (a) Tuynman, A.; Spelberg, J. L.; Kooter, M. I.; Schoe-
maker, H. E.; Wever, R. J. Biol. Chem. 2000, 275,
3025–3030; (b) Ortiz de Montellano, P. R.; Grab, L. A.
Biochemistry 1987, 26, 5310–5314; (c) Schoemaker, H. E.
Recl. Trav. Chim. Pays-Bas. 1990, 109, 255–272.
1998, 253, 544.
24. Hu, S.; Hager, L. P. J. Am. Chem. Soc. 1999, 121, 872.
25. Kiljunen, E.; Kanerva, L. T. J. Mol. Catal. B: Enzym.
2000, 9, 163–172.
26. Kiljunen, E.; Kanerva, L. T. Tetrahedron: Asymmetry