Baker's yeast (Saccharomyces cerevisiae) mediated transformations of C-aryl-N-phenylnitrones

Article abstract of DOI:10.1016/j.tetlet.2006.05.035

C-Aryl-N-phenylnitrones are transformed to a mixture of azoxybenzene and aryl aldehydes when treated with a mixture of Baker's yeast and sucrose in pH = 6.0 phosphate buffer medium at 32 °C.

Full text of DOI:10.1016/j.tetlet.2006.05.035

Tetrahedron Letters 47 (2006) 4893–4895
Baker’s yeast (Saccharomyces cerevisiae) mediated
transformations of C-aryl-N-phenylnitrones
Ananda S. Amarasekara,* Wendy Hernandez and Paul Bonham
Department of Chemistry, Prairie View A&M University, Prairie View, TX 77446, USA
Received 21 November 2005; accepted 8 May 2006
Available online 30 May 2006
Abstract—C-Aryl-N-phenylnitrones are transformed to a mixture of azoxybenzene and aryl aldehydes when treated with a mixture
of Baker’s yeast and sucrose in pH = 6.0 phosphate buffer medium at 32 ꢀC.
ꢁ 2006 Elsevier Ltd. All rights reserved.
Baker’s yeast (Saccharomyces cerevisiae) mediated enzy-
matic transformations of organic compounds are well
known reactions in organic chemistry.1–6 The most
widely studied of these is the Saccharomyces cerevisiae
promoted enzymatic reduction of the carbonyl com-
pounds1 like keto esters and ketones. Advantages in
these reactions are the production of essentially enantio-
pure alcohols under mild and economical reaction
conditions.
be stable at high pH and temperature used in the type II
conditions. Aromatic nitroso compounds4 containing
halogens and other labile substituents are known to
reduce selectively to their corresponding amines under
neutral conditions at 80 ꢀC. On the other hand nitro
aromatics2e could be efficiently reduced to amines only
in the strongly basic conditions employing aqueous
sodium hydroxide medium and at temperatures in
the range of 70–80 ꢀC. Aromatic and heteroaromatic
N-oxides6 have been deoxygenated using the same type
II conditions.
Reactions of nitrogen containing functional groups2–6
are relatively less explored, and a survey in the current
literature showed that selective and efficient reduction
of nitro groups,2 nitroso groups4 and deoxygenation of
N-oxides6 have been achieved by these Saccharomyces
cerevisiae mediated enzymatic processes. Further it was
found that two types of reaction conditions have been
employed in the reduction of nitrogen containing func-
tionalities. The first type2a–d,3b,5,6a involved the reactions
carried out at room temperature or 25–32 ꢀC range and
in the pH 5.5–6.0 buffered medium, with or without an
added sugar such as glucose or sucrose. The second type
of reaction conditions2e,f,3a,6b involved the reactions car-
ried out at 70–80 ꢀC or sometimes under reflux condi-
tions and in the presence of a high concentration of
sodium hydroxide in the medium with pH >12. Presum-
ably different mechanisms are operating under these two
different reaction conditions and the yeast is unlikely to
Our interest7 in the synthesis and chemistry of the nitrone
functional group have revealed that there are no reports
of any Saccharomyces cerevisiae promoted enzymatic
transformations of the nitrone function. Nitrones are
known for their properties as free radical scavengers as
they can form stable free radicals in combining with
hydroxyl and other radicals, and there are attempts to
explore this radical trapping ability to develop nitrone
based pharmaceuticals8 as well. During these metabolic
studies,9 it has been reported that phenyltbutylnitrone
hydrolyzes to a mixture of benzaldehyde and tbutylhydr-
oxylamine when incubated with human epithelial
fibroblasts cells and tbutylhydroxyl amine further
oxidizes to tbutyl nitroxide as well.
We have under taken to study the possible enzymatic
transformations of C-aryl-N-phenylnitrones, when trea-
ted with Baker’s yeast–sucrose mixture in the pH = 6.0
phosphate buffer medium at room temperature. These
nearly neutral conditions were chosen for the study, as
nitrones are known10 to hydrolyze to hydroxylamines
and aldehydes in strongly acidic or basic conditions.
Keywords: Baker’s yeast (Saccharomyces cerevisiae); C,N-Diarylnitrones;
Azoxybenzene.
*
Corresponding author. Tel.: +1 936 857 2616; fax: +1 936 857
2095; e-mail: asamarasekara@pvamu.edu
0040-4039/$ - see front matter ꢁ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.05.035

4894
A. S. Amarasekara et al. / Tetrahedron Letters 47 (2006) 4893–4895
Bakers Yeast
+
+
2
Sucrose
pH = 6.00 buffer
32 ºC
N
N N
2 R-CHO
R
+
_
O
_
O
R = Aryl
1a-f
3a-f
2
Figure 1.
Table 1.
NMR used in this study. W.H. thanks American Che-
mical Societies SEED program for summer research
fellowship.
Nitrone (1)
Reaction time (h)
Product
yield
2
3
1a, R = C6H5–
40
40
24
72
40
40
92
85
78
65
88
78
76
80
71
38a
70
88
References and notes
1b, R = p-CH3–C6H4–
1c, R = p-OCH3–C6H4–
1d, R = p-NO2–C6H4–
1e, R = o-OH–C6H4–
1f, R = 2-Furanyl–
1. (a) Tsuboi, S.; Sakamoto, J.; Kawano, T.; Utaka, M.;
Takada, A. J. Org. Chem. 1991, 56, 7177; (b) Tsuboi, S.;
Furutani, H.; Ansari, M. H.; Sakai, T.; Utaka, M.;
Takeda, A. J. Org. Chem. 1993, 58, 486; (c) Nakamura,
K.; Kawai, Y.; Nakajima, N.; Ohno, A. J. Org. Chem.
1991, 56, 4778; (d) Nakamura, K.; Kawai, Y.; Ohno, A.
Tetrahedron Lett. 1991, 32, 2927; (e) Nakamura, K.;
Kawai, Y.; Miyai, T.; Ohno, A. Tetrahedron Lett. 1990,
31, 3631; (f) Nakamura, K.; Kawai, Y.; Miyai, T.; Ohno,
A. Tetrahedron Lett. 1990, 31, 1159; (g) Org. Synth. Coll.
2004, 8, 312; (h) Org. Synth. 1990, 68, 56; (i) Org. Synth.
1985, 63, 1; (j) Org. Synth. Coll. 2004, 10, 84.
2. (a) Davey, C. L.; Powell, L. W.; Turner, N. J.; Wells, A.
Tetrahedron Lett. 1994, 35, 7867; (b) Takeshita, M.;
Yoshida, S.; Kiya, R.; Higuchi, N.; Kobayashi, Y. Chem.
Pharm. Bull. 1989, 37, 615; (c) Takeshita, M.; Yoshida, S.
Heterocycles 1990, 31, 2201; (d) Kamal, A. J. Org. Chem.
1991, 56, 2237; (e) Baik, W.; Han, J. L.; Lee, K. C.; Kim,
B. H.; Hahn, J. T. Tetrahedron Lett. 1994, 35, 3965; (f)
Baik, W.; Park, T. H. J. Org. Chem. 1995, 60, 5683.
3. (a) Takeshita, M.; Yoshida, S.; Kohno, Y. Heterocycles
a 12% p-Amino benzaldehyde was also found as a product.
In this study we have found that C,N-diphenyl nitrone11
(1a) converts into a mixture of azoxybenzene and benz-
aldehyde12 in 92% and 76% yields, respectively, when
incubated with Baker’s yeast–sucrose mixture in a
pH = 6.00 phosphate buffer medium for 40 h at 32 ꢀC
(Fig. 1).
In a control experiment with sucrose and pH = 6.00
phosphate buffer, in the absence of yeast, no hydrolysis
or decomposition was observed and all the nitrone could
be recovered unchanged after 72 h. In another experi-
ment carried out without sucrose, only about 10% of
the nitrone was converted into azoxybenzene and benz-
aldehyde and the remaining nitrone was recovered
unchanged. In an attempt to identify the intermediates
of this transformation, samples withdrawn after 6 and
24 h, were analyzed by NMR, after extraction into
methylenechloride. These samples showed only partial
conversions to the same products and unreacted nitrone,
and the attempts to observe any intermediates were not
successful.
1994, 37, 553; (b) Navarro-Ocana, A.; Jime˘nez-Estrada,
˜
´
´
M.; Gonzalez-Paredes, M. B.; Barzana, E. Synlett 1996,
695.
4. Baik, W.; Rhee, J. U.; Lee, S. H.; Lee, N. H.; Kim, B. H.;
Kim, K. S. Tetrahedron Lett. 1995, 36, 2793.
5. (a) Bianchi, G.; Comi, G.; Venturini, I. Gazz. Chim. Ital.
1994, 114, 285; (b) Easton, C. J.; Hughes, C. M.; Kirby,
K. D.; Savage, G. P.; Simpson, G. W.; Tiekink, E. R. T.
J. Chem. Soc., Chem. Commun. 1994, 2035.
6. (a) Takeshita, M.; Yoshida, S. Heterocycles 1990, 30, 871;
(b) Baik, W.; Kim, D. I.; Koo, S.; Ree, J. U.; Shin, S. H.;
Kim, B. H. Tetrahedron Lett. 1997, 38, 845.
7. Amarasekara, A. S. Tetrahedron Lett. 2005, 46, 2635.
8. (a) Goldstein, S.; Lestage, P. Curr. Med. Chem. 2000, 7,
1255; (b) Bergami, A.; Fracasso, C.; Caccia, S. Environ.
Toxicol. Pharmacol. 1997, 3, 289; (c) Thomas, C. E.;
Ohlweiler, D. F.; Taylor, V. L.; Schmidt, C. J. J.
Neurochem. 1997, 68, 1173.
Five other C-aryl-N-phenylnitrones11 (1b–f) also reacted
similarly to yield azoxybenzene (2) and the correspond-
ing aldehydes (3b–f) as shown in Table 1. Results show
that verity of C-aryl-N-phenylnitrones can undergo the
Saccharomyces cerevisiae mediated hydrolytic process
and electron withdrawing groups on the aryl ring
appears to retard the reaction as shown in the case of
C-p-nitrophenyl-N-phenylnitrone (1d) (Table 1).
9. (a) Chamulitrat, W.; Parker, C. E.; Tomer, K. B.; Mason,
R. P. Free Radical Res. 1995, 23, 1; (b) Atamna, H.; Paler-
´
In summary these results represent the first Baker’s yeast
mediated enzymatic transformation of the nitrone func-
tion and it appears to be an enzymatic hydrolysis
followed by a reduction of the intermediate led to the
formation of azoxybenzene.
Martınez, A.; Ames, B. N. J. Biol. Chem. 2000, 275,
6741.
10. Kim, T. R.; Kwang, I. Bull. Korean Chem. Soc. 1991, 12,
273.
11. Nelson, D. W.; Owens, J.; Hiraldo, D. J. Org. Chem. 2001,
66, 2572.
12. Typical procedure: C-aryl-N-phenylnitrone (0.635 mmol)
was dissolved in 10 mL of 95% ethanol and sucrose
(1.00 g) was added to this solution. Then 50 mL of
pH = 6.00 phosphate buffer was added and swirled for
5 min to dissolve the sucrose in the medium. Baker’s yeast
(Saccharomyces cerevisiae) (250 mg) was then added and
Acknowledgments
We gratefully acknowledge NSF (MRI Grant CHE-
0421290) for the funds used to purchase the 400 MHz

A. S. Amarasekara et al. / Tetrahedron Letters 47 (2006) 4893–4895
4895
further swirled for 2 min to yield a turbid solution, which
was incubated in a warm water bath at 32 ꢀC. Reaction
was monitored by TLC (silica, solvent: ethylacetate:hex-
anes 1:9) and stopped after complete disappearance of the
nitrone. After the reaction period, the solution was
methylene chloride layer was dried over anhydrous
MgSO4 and concentrated under reduced pressure to give
the crude product, which was chromatographed on silica,
eluting with 10% ethylacetate in hexanes to isolate pure
products. The products were identified by comparison of
1
transferred to
a
separatory funnel and repeatedly
the H and 13C NMR of authentic samples of azoxybenz-
extracted with methylene chloride (5 · 20 mL). Combined
ene and aldehydes.