Selective oxidation and N-coupling by purified laccase of Xylaria polymorpha MTCC-1100

Article abstract of DOI:10.1134/S1068162014040025

The chemical route of oxidation of methyl group to its aldehyde is inconvenient because once a methyl group is attacked, it is likely to be oxidized to the carboxylic acid and it is very difficult to stop the reaction at the aldehyde stage. Fungal laccases can be used for such oxidation reaction and the reaction can be completed sharply within 1-2 h. Coupling of amines are another important reactions known for fungal laccases; coupling reactions generally take 3-7 h. We have used the purified laccase of molecular weight 63 kDa obtained from the fungal strain Xylaria polymorpha MTCC-1100 with activity of 1.95 IU/mL for selective oxidation of 2-fluorotoluene, 4-fluorotoluene, and 2-chlorotoluene to 2-fluorobenzaldehyde, 4-fluorobenzaldehyde, and 2-chlorobenzaldehyde, respectively, and syntheses of 3-(3, 4-dihydroxyphenyl)- propionic acid derivatives by N-coupling of amines. In each oxidation reactions, ABTS was used as mediator molecule. All the syntheses are ecofriendly and were performed at room temperature.

Full text of DOI:10.1134/S1068162014040025

ISSN 1068ꢀ1620, Russian Journal of Bioorganic Chemistry, 2014, Vol. 40, No. 4, pp. 455–460. © Pleiades Publishing, Ltd., 2014.
Selective Oxidation and NꢀCoupling by Purified Laccase of Xylaria
polymorpha MTCCꢀ11001
Pankaj Kumar Chaurasia2, Sudha Yadava, Shashi Lata Bharati, and Sunil Kumar Singh
Department of Chemistry, D.D.U. Gorakhpur University, Gorakhpur, UttarꢀPradesh, 273009 India
Received November 13, 2013; in final form, January 29, 2014
Abstract—The chemical route of oxidation of methyl group to its aldehyde is inconvenient because once a
methyl group is attacked, it is likely to be oxidized to the carboxylic acid and it is very difficult to stop the reacꢀ
tion at the aldehyde stage. Fungal laccases can be used for such oxidation reaction and the reaction can be
completed sharply within 1–2 h. Coupling of amines are another important reactions known for fungal lacꢀ
cases; coupling reactions generally take 3–7 h. We have used the purified laccase of molecular weight 63 kDa
obtained from the fungal strain Xylaria polymorpha MTCCꢀ1100 with activity of 1.95 IU/mL for selective
oxidation of 2ꢀfluorotoluene, 4ꢀfluorotoluene, and 2ꢀchlorotoluene to 2ꢀfluorobenzaldehyde, 4ꢀfluorobenꢀ
zaldehyde, and 2ꢀchlorobenzaldehyde, respectively, and syntheses of 3ꢀ(3, 4ꢀdihydroxyphenyl)ꢀpropionic
acid derivatives by Nꢀcoupling of amines. In each oxidation reactions, ABTS was used as mediator molecule.
All the syntheses are ecofriendly and were performed at room temperature.
Keywords: laccase, 2ꢀfluorotoluene, 4ꢀfluorotoluene, 2ꢀchlorotoluene, 3ꢀ(3,4ꢀdihydroxyphenyl)ꢀpropionic acid
derivatives
DOI: 10.1134/S1068162014040025
2 1
INTRODUCTION
makes it valuable from the point of view of their comꢀ
mercial applications [4, 8–10]. The biotechnological
importance of laccases have increased after the discovꢀ
ery that oxidizable reaction substrate range could be
further extended in the presence of small readily oxiꢀ
dizable molecules called mediators [11, 12]. During
the last two decades, laccases have turned out to be the
most promising enzymes for industrial uses [9, 10]
having applications in food, pulps, paper, textile, and
cosmetics industries and in synthetic organic chemisꢀ
try [13–16].
Laccase [benzenediol: oxygen oxidoreductase;
E.C. 1.10.3.2] is a polyphenol oxidase, which belongs
to the superfamily of multicopper oxidases [1, 2] and
catalyzes [3–5] the four electron reduction of molecꢀ
ular oxygen to water. Laccases are dimeric or tetꢀ
rameric glycoproteins. To perform their catalytic
functions, laccases depend on Cu atoms that are disꢀ
tributed at three different copper centers viz. typeꢀ1,
or blue copper center, typeꢀ2, or normal copper center
and typeꢀ3, or coupled binuclear copper center. The
center types differ in their characteristic electronic
paramagnetic resonance (EPR) signals [6, 7]. Organic
substrate is oxidized by one electron at the active site
of the laccase generating a reaction radical which furꢀ
ther reacts nonꢀenzymatically. The electron is received
at typeꢀ1 Cu and is shuttled to the trinuclear cluster
where oxygen is reduced to water.
Fungal laccases have been used for the selective
oxidation reactions [17–22] and Nꢀcoupling reactions
[16]. Nꢀcoupling reactions have been done by using
crude fungal laccases, previously. The objective of this
communication was to do the selective oxidations of
substituted toluenes, such as 2ꢀfluorotoluene, 4ꢀfluoꢀ
rotoluene, and 2ꢀchlorotoluene to corresponding 2ꢀ
fluorobenzaldehyde, 4ꢀfluorobenzaldehyde, and 2ꢀ
chlorobenzaldehyde in the presence of ABTS as mediꢀ
ator molecule, as well as synthesis of 3ꢀ(3,4ꢀdihydroxꢀ
yphenyl)ꢀpropionic acid derivatives by Nꢀcoupling
reactions, using purified laccase. For this purpose, we
used purified laccase from Xylaria polymorpha
MTCCꢀ1100 of molecular weight of 63 kDa having
activity 1.95 IU/mL, directly as reported by Pankaj
et al. [23].
Ortho and para diphenols, aminophenols,
polyphenols, polyamines, lignins, and arylamines and
some of the inorganic ions are the substrates for laccaꢀ
ses. The ability of laccases to catalyze the oxidation of
various phenolic, as well as nonꢀphenolic compounds,
coupled to the reduction of molecular oxygen to water
1
The article is published in the original.
Corresponding author: phone: +91 9648082044, +91 8896728759;
eꢀmail: pankaj.chaurasia31@gmail.com.
2
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456
0.6
PANKAJ KUMAR CHAURASIA et al.
ence of mediator molecules like 2,2'ꢀazinoꢀbisꢀ(3ꢀ
ethylbenzothiazolineꢀ6ꢀsulfonic acid) diammonium
salt (ABTS) [17]. The potentiality of the pure laccase
as a biocatalyst for the conversion of aromatic methyl
group to the corresponding aldehyde group in the
presence of the mediator molecule was tested using 2ꢀ
fluorotoluene, 4ꢀfluorotoluene, and 2ꢀchlorotoluene as
substrates for this fungal strain (Scheme 1).
T
= 115 minutes
T
= 0 minute
500 600
0
200
300
400
Wavelength (nm)
CH3
CHO
Y
X
X
Purified laccase
pH 4.5, 1–2 h, RT
(Yield >90%)
Fig. 1. UV–visible spectra of the biotransformation reacꢀ
tion of 2ꢀfluorotoluene to 2ꢀfluorobenzaldehyde. = 0
shows the spectrum of reaction solution after the addition of
laccase at zero time. = 115 shows the spectrum of reaction
T
Y
T
(i) X = F/Cl, Y = H
(ii) X = H, Y = F
solution after 115 min from the addition of laccase.
Scheme 1. Syntheses of substituted benzaldehydes from
substituted toluenes.
RESULTS AND DISCUSSION
One of the best applications of the laccases in orꢀ
ganic synthesis is the selective oxidation of the aromatꢀ
Other important reactions of laccases are the couꢀ
ic methyl group to the corresponding aldehyde. The pling reactions [16]. These coupling reactions have
chemical routes of this conversion are inconvenient been done by using crude laccase previously. In this
because methyl groups are preferably converted into communication, synthesis of 3ꢀ(3,4ꢀdihydroxypheꢀ
carboxylic acids and it becomes very difficult to stop nyl)ꢀpropionic acid derivatives have been done by Nꢀ
the reaction at aldehyde stage. Moreover, they require coupling reactions with purified laccase of molecular
drastic reaction conditions which pollutes the enviꢀ weight 63 kDa having activity 1.95 IU/mL purified by
ronment. The conversion done with pure laccase ocꢀ Pankaj et al. from the liquid culture growth medium of
curs under milder conditions, the yield is >90% and Xylaria polymorpha MTCCꢀ1100 [23] (Scheme 2). All
the process is ecofriendly. The use of purified laccases the above synthesized products were characterized and
for this purpose has been studied [17, 18] in the presꢀ identified by HPLC, IR, and NMR spectroscopy.
COOH
COOH
X
NH
Purified laccase
pH 4.5, 3–6 h, RT
75–90%
+
X
NH2
OH
OH
OH
OH
NH2
NH2
NH2
=
X
NH2
and
,
,
H3C
NH2
H3COOC
H3COC
HOOC
Scheme 2. Syntheses of 3ꢀ(3,4ꢀdihydroxyphenyl)ꢀpropionic acid derivatives by coupling reactions with purified laccase
of X. polymorpha MTCCꢀ1100.
UVꢀVisible Spectroscopy
and then measured after constant time interval and
changes in UVꢀspectrum were observed. Figure 1 preꢀ
sents an example of a UVꢀspectrum of an oxidation
reaction of 2ꢀfluorotoluene to 2ꢀfluorobenzaldehyde
by laccase in which time taken for reaction completion
Completions of the reactions were confirmed by
spectrophotometry measurements. In all the cases,
reaction solution was firstly measured by UVꢀvisible
spectrophotometry at zero time of laccase addition was 115 minutes.
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SELECTIVE OXIDATION AND NꢀCOUPLING
457
High Performance Liquid Chromatography (HPLC)
script do not include a study on side reactions of dihyꢀ
droxyphenylpropionic acid in the presence of laccase.
In the above mentioned selective enzyme catalyzed
biotransformations, all products formed are easily
available and simple. So, authors have used HPLC
technique to confirm the actual product formation by
comparing the HPLC profiles of standard aldehyde
compounds with the enzymatically transformed comꢀ
pounds. Retention times of the standard samples of
2ꢀfluorotoluene, 4ꢀfluorotoluene, 2ꢀchlorotoluene,
2ꢀfluorobenzaldehyde, 4ꢀfluorobenzaldehyde, and
2ꢀchlorobenzaldehyde were 7.17, 6.97, 7.33, 6.14,
6.11, and 6.25 min, respectively. Retention times of
the products of the enzyme catalyzed reaction (6.12,
6.1, and 6.24 min) revealed that they were 2ꢀfluoꢀ
robenzaldehyde, 4ꢀfluorobenzaldehyde, and 2ꢀchloꢀ
robenzaldehyde. Yields of the extracted 2ꢀfluorobenꢀ
zaldehyde, 4ꢀfluorobenzaldehyde, and 2ꢀchlorobenꢀ
zaldehyde were 94, 94, and 96%, respectively.
CONCLUSIONS
Thus, this communication reports the successful
involvement of a purified laccase in selective oxidation
of aromatic methyl group of substituted toluenes to
their respective aldehyde group in the presence of
ABTS as mediator molecule and synthesis of 3ꢀ(3,4ꢀ
dihydroxyphenyl)ꢀpropionic acid derivatives by
Nꢀcoupling of amines. These above syntheses, easily
done by laccase are novel because there is neither need
of drastic reaction conditions nor costly reagents and
each synthesis has been done at room temperature.
One more important thing is that these syntheses are
ecofriendly because purified laccase was used instead
of synthetic catalysts.
Retention time of major peak obtained for Nꢀcouꢀ
pling products of 3ꢀ(3,4ꢀdihydroxyphenyl)ꢀpropionic
acid with 4ꢀaminobenzoic acid, methyl 4ꢀaminobenꢀ
zoate, 4ꢀaminoacetophenone, and 1ꢀhexylamine were
5.21 (yield 89%), 5.16, (82%), 5.10 (86%) and
4.82 min (76%), respectively, while retention times for
3ꢀ(3,4ꢀdihydroxyphenyl)ꢀpropionic acid, 4ꢀaminobenꢀ
zoic acid, methyl 4ꢀaminobenzoate, and 4ꢀaminoaceꢀ
tophenone were 5.85, 6.21, 5.97, and 6.15, respectively,
which demonstrates the formation of coupling products
that have been identified and characterized by IR and
NMR spectroscopy. HPLC chromatograms of all the
coupling products are presented in Fig. 2.
EXPERIMENTAL
Materials
4ꢀFluorotoluene, 2ꢀfluorotoluene, 2ꢀchlorotoluꢀ
ene, 2,2'ꢀazinoꢀbis (3ꢀethylbenzthiazolineꢀ6ꢀsulꢀ
phonic acid) diammonium salt (ABTS), 3ꢀ(3,4ꢀdihyꢀ
droxyphenyl)ꢀpropionic acid, and 4ꢀaminobenzoic
acid were from Fluka, Chemi new Ulm (Switzerland).
All other chemicals used in these investigations were
either from Himedia laboratory Ltd. Mumbai (India)
or from E. Merck Ltd. Mumbai (India) and were used
without further purifications.
In IR spectra of biotransformed products, a band
near 815 cm–1 was due to C–Cl stretching. A band at
~1705 cm–1 was due to aldehydic carbonyl stretching
confirming formation of the products. In IR spectra of
coupling products, a single stretching band at ~3441 cm–1
was due to the N–H (2ꢀamino group) and showed that
these two reactants have been coupled and desired
products have been formed.
Selective Oxidation in the Presence of ABTS
The biotransformation [17, 18, 23] of 2ꢀfluorotolꢀ
uene to 2ꢀfluorobenzaldehyde was done in 7 mL of
100 mM sodium acetate buffer, pH 4.5, containing
20 mM 2ꢀfluorotoluene in 15 mL of dioxane, 0.1 mM
ABTS, and 300 L of purified laccase [23] in a 100 mL
µ
conical flask; the mixture was stirred vigorously for
115 minutes. The reaction solution was extracted
1
In H NMR spectra of different biotransformed
products, a peak at
δ
> 9.00 was due to the aldehydic
thrice with 20 mL of ethyl acetate. 20
acetate extract was injected in Waters HPLC Model
600E using spherisorb C18 5 UV, 4.5 250 mm colꢀ
µ
L of the ethyl
proton, confirming formation of expected benzaldeꢀ
hydes. In spectra of different coupling products, peak
between 3.73–3.85 ppm (s, 1H) was due to NH hydroꢀ
gen, which shows that reactants have been coupled to
form the product.
×
umn. The eluant phase was methanol at the flow rate
of 0.5 mL/min. The detection was made using Waters
UV detector model 2487 at = 254 nm. The oxidation
λ
1
of 2ꢀchlorotoluene and 4ꢀfluorotoluene to 2ꢀchloꢀ
robenzaldehyde and 4ꢀfluorobenzaldehyde were also
studied using the same method described above except
for time of stirring the reaction solutions were 90 and
110 min, respectively.
The results of HPLC, IR and H NMRꢀspectrosꢀ
copy demonstrate that oxidation products were 2ꢀfluꢀ
orobenzaldehyde, 4ꢀfluorobenzaldehyde, and 2ꢀchloꢀ
robenzaldehyde (Scheme 1), while coupling products
were 3ꢀ(3,4ꢀdihydroxyphenyl)ꢀpropionic acid derivaꢀ
tives of 4ꢀaminobenzoic acid, methyl 4ꢀaminobenꢀ
The synthesized products were extracted from their
zoate, 4ꢀaminoacetophenone, and 1ꢀhexylamine reaction solutions with ethyl acetate and these
(Scheme 2). Possibilities of any side reactions ignored extracted products were identified and characterized
1
since the rate of side reactions is low; also, this manuꢀ by HPLC, IR, and H NMR techniques. Since only
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PANKAJ KUMAR CHAURASIA et al.
2.0
1.5
1.0
0.5
0
(a)
(b)
3.0
2.5
2.0
1.5
1.0
0.5
0
(c)
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
(d)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
1
2
3
4
5
Minutes
6
7
8
9
10
Fig. 2. HPLC profiles of coupling products of 3ꢀ(3,4ꢀdihydroxyphenyl)ꢀpropionic acid with 4ꢀaminobenzoic acid (a), methyl
4ꢀaminobenzoate (b), 4ꢀaminoacetophenone (c), and 1ꢀhexylamine (d).
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SELECTIVE OXIDATION AND NꢀCOUPLING
459
small amounts of chemical auxiliaries are applied
which remain in the aqueous phase after extraction of product of 3ꢀ(3,4ꢀdihydroxyphenyl)ꢀpropionic acid
the aldehydes with an organic solvent (ethyl acetate), with 4ꢀaminobenzoic acid is described below: = 8.15
1H NMR spectral data obtained for the coupling
δ
very pure compounds are obtained requiring no furꢀ (d, 2H), 7.03 (d, 2H), 5.87 (s, 1H), 6.27 (s, 1H), 2.59
ther purification. During these oxidations, no side (t, 2H), 2.41 (t, 2H), and 3.73 ppm (s, 1H).
1H NMR spectral data obtained for the coupling
product of 3ꢀ(3,4ꢀdihydroxyphenyl)ꢀpropionic acid
with methyl 4ꢀaminobenzoate, and 4ꢀaminoaceꢀ
tophenone were almost similar to those obtained in
the case of 4ꢀaminobenzoic acid, except for the sinꢀ
reactions occur because of the high specificity of lacꢀ
case as biocatalyst. Thus, authors have used ethyl aceꢀ
tate as organic solvent for the extraction of products
and found almost pure benzaldehydes and substituted
benzaldehydes in high yields (average yield was 95%).
glets at
δ
= 4.13 and 2.25 due to the methyl groups,
one present as ester and another one, attached to
ketonic carbon, respectively.
Synthesis of 3ꢀ(3,4ꢀdihydroxyphenyl)ꢀpropionic Acid
Derivatives by Nꢀcoupling of Amines
NMR results obtained for the coupling product of
3ꢀ(3,4ꢀdihydroxyphenyl)ꢀpropionic acid with 1ꢀhexyꢀ
(i) Coupling of 3ꢀ(3,4ꢀdihydroxyphenyl)ꢀpropionic
acid with 4ꢀaminobenzoic acid and 4ꢀaminoacetopheꢀ
none [16]. The enzyme was diluted with 20 mM
sodium acetate buffer, pH 4.5. The substrates, 3ꢀ(3,4ꢀ
dihydroxyphenyl)ꢀpropionic acid (1 mM) and 4ꢀamiꢀ
nobenzoic acid (1 mM), were added to 2 mL of this
diluted solution and reaction mixture was incubated
for 3:45 h at room temperature and stirred vigorously.
lamine were
δ
= 5.95 (s, 1H), 6.18 (s, 1H), 2.67 (t,
2H), 2.31 (t, 2H), 3.21 (t, 2H), 1.61 (q, 2H), 1.52 (q,
2H), 1.33 (q, 2H), 1.32 (sextet, 2H), 1.25 (t, 3H), and
3.85 (s, 1H).
ACKNOWLEDGMENTS
Similar method was used for coupling of 3ꢀ(3,4ꢀ
dihydroxyphenyl)ꢀpropionic acid with methyl 4ꢀamiꢀ
nobenzoate, and 4ꢀaminoacetophenone.
(ii) Coupling of 3ꢀ(3,4ꢀdihydroxyphenyl)ꢀpropionic
acid and 1ꢀhexylamine [16]. Similar method was
applied for this synthesis also; the substrates, 3ꢀ(3,4ꢀ
dihydroxyphenyl)ꢀpropionic acid (1 mM), and 1ꢀhexꢀ
ylamine (6 mM), were added to 2 mL of diluted soluꢀ
tion and reaction mixture was incubated for 6 h at
room temperature and stirred vigorously.
The authors acknowledge the financial support of
CSIRꢀHRDG, New Delhi, for the award of SRF
(NET), award no. 09/057(0201)2010ꢀEMRꢀI, to Mr.
Pankaj Kumar Chaurasia. Dr. Shashi Lata Bharati is
thankful to UGC–New Delhi for the award of UGCꢀ
PDF for Women.
REFERENCES
1. Hoegger, P.J., Kilaru, S., Jomes, T.Y., Thacker, J.R.,
and Kuees, U., FEBS J., 2006, vol. 273, pp. 2308–
2326.
2. Messerschmidt, A., MultiꢀCopper Oxidases, Singapore:
World Scientific, 1997.
3. Riva, S., Trends Biotechnol., 2006, vol. 24, no. 5,
All the synthesized products were extracted from
their reaction solutions with ethyl acetate and prodꢀ
ucts were identified and characterized by HPLC, IR,
and 1H NMR techniques.
pp. 219–226.
Characterization
4. Baldrian, P., FEMS Microbiol. Rev., 2006, vol. 30,
pp. 215–242.
Infrared (IR) spectroscopy. IR results obtained for
the expected products 2ꢀfluorobenzaldehyde, 4ꢀfluoꢀ
robenzaldehyde, and 2ꢀchlorobenzaldehyde were
~3010, ~2890, ~1705, ~1355, and ~1250 cm–1.
5. Dwivedi, U.N., Singh, P., Pandey, V.P., and Kumar, A.,
J. Mol. Cat. B: Enzymatic, 2011, vol. 68, no. 2, pp. 117–
128.
6. Solomon, E.I., Baldwin, M.J., and Lowery, M.D.,
Important bands appeared in the IRꢀspectrum for
the coupling products of 3ꢀ(3,4ꢀdihydroxyphenyl)ꢀ
propionic acid with 4ꢀaminobenzoic acid, methyl
4ꢀaminobenzoate, 4ꢀaminoacetophenone, and 1ꢀhexyꢀ
lamine; they include ~2940, ~3048, ~1715, ~1695,
~3441, ~2570, ~3610, and ~2950 cm–1.
Chem. Rev., 1992, vol. 92, pp. 521–542.
7. Bento, I., Armenia, Corrondo, M., and Lindley, P.F., J.
Biol. Inorg. Chem., 2006, vol. 5, pp. 539–547.
8. Wandrey, C., Liese, A., and Kihumbu, D., Org. Proc.
Res. Develop., 2000, vol. 4, no. 4, pp. 285–290.
9. Couto, S.R. and Harrera, J.L.T., Biotechnol. Advan.
,
1H NMR. 1H NMR spectral data obtained for the
2006, vol. 24, pp. 500–513.
expected products, i.e. 2ꢀfluorobenzaldehyde and 2ꢀ
10. Xu, F., Ind. Biotechnol., 2005, vol. 1, pp. 38–50.
11. Acunzo, D.F. and Galli, C., J. Europ. Biochem., 2003,
chlorobenzaldehyde, were ~ 9.13 (s, 1H), ~7.92 (d,
δ
1H), ~7.53 (d, 1H), ~7.31 (t, 1H), and ~6.85 (t, 1H).
vol. 270, pp. 3634–3640.
1H NMR spectral data obtained for the expected
12. Morozova, O.V., Shumakovich, G.P., Shleev, S.V., and
Yaropolov, Y.I., Appl. Biochem. Microbiol., 2003,
vol. 43, pp. 523–535.
product, 4–fluorobenzaldehyde were
7.78 (d, 1H), and 7.42 (d, 1H).
δ
~ 9.26 (s, 1H),
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 40
No. 4
2014

460
PANKAJ KUMAR CHAURASIA et al.
13. Coniglio, A., Galli, C., and Gentili, P., J. Mol. Cat. B: 18. FritzꢀLanghals, and Kunath, B., Tetrahedron Lett.,
Enzymatic, 2008, vol. 50, no. 1, pp. 40–49.
1998, vol. 39, pp. 5955–5956.
14. Mikolasch, A., Niedermeyer, T.H.J., Lalk, M., Witt, S.,
Seefeld, S., Hammer, E., Schauer, F., Gesell, M., Hesꢀ
sel, S., Julich, W.D., and Lindoquist, U., Chem.
Pharma. Bull., 2006, vol. 54, no. 5, pp. 632–638.
15. Mikolasch, A., Niedermeyer, T.H.J., Lalk, M., Witt, S.,
Seefeld, S., Hammer, E., Schauer, F., Salazar, G., Hesꢀ
sel, S., Julich, W.D., and Lindequist, U., Chem.
Pharma. Bull., 2007, vol. 55, no. 3, pp. 412–416.
19. Chaurasia, P.K., Yadav, A., Yadav, R.S.S., and Yadava, S.,
J. Chem. Sci., 2013, vol. 125, no. 6, pp. 1395–1403.
doi: 10.1007/s12039ꢀ013ꢀ0525ꢀ4.
20. Chaurasia, P.K., Yadav, R.S.S., and Yadava, S., Int. J.
Res. Chem. Environ., 2013, vol. 3, no. 1, pp. 188–197.
21. Chaurasia, P.K., Yadav, A., Yadav, R.S.S., and Yadava, S.,
Appl. Biochem. Microbiol., 2013, no. 6, pp. 592–599.
22. Chaurasia, P.K., Yadav, R.S.S., and Yadava, S., Bioꢀ
chem.: An Indian Journal, 2012, vol. 6, no. 7, pp. 237–
242.
16. Mikolasch, A., Hammer, E., Jonas, U., Popowski, K.,
Stielow, A., and Schaner, F., Tetrahedron, 2002, vol. 58,
pp. 7589–7593.
17. Potthest, A., Rosenanu, T., Chen, C.ꢀL., and Gratzl, 23. Chaurasia, P.K., Yadav, R.S.S., and Yadava, S. Int. J.
J.S., J. Org. Chem., 1995, vol. 60, pp. 4320–4321. Res., Chem. Environ., 2013, vol. 3, no. 2, pp. 93–101.
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2014