A facile 1,5-rearrangement of β-formylenamides and cleavage of esters catalysed by Pseudomonas fluorescens

Article abstract of DOI:10.1016/S0040-4039(02)00114-4

β-Formylenamides undergo a facile 1,5-rearrangement of their N-acetyl groups under the influence of the soil bacterium Pseudomonas fluorescens to afford β-acetoxyenones in good yields. Further, the soil microorganism efficiently cleaves steroidal and non-steroidal acetates to alcohols.

Full text of DOI:10.1016/S0040-4039(02)00114-4

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 2269–2271
A facile 1,5-rearrangement of b-formylenamides and cleavage of
esters catalysed by Pseudomonas fluorescens
U. Bora,a M. Longchar,a A. Chetia,a B. S. D. Kumar,b R. C. Boruaha,* and J. S. Sandhua
aOrganic Chemistry Division, Regional Research Laboratory, Jorhat 785006, India
bSoil Microbiology Division, Regional Research Laboratory, Jorhat 785006, India
Received 15 November 2001; revised 2 January 2002; accepted 14 January 2002
Abstract—b-Formylenamides undergo a facile 1,5-rearrangement of their N-acetyl groups under the influence of the soil bacterium
Pseudomonas fluorescens to afford b-acetoxyenones in good yields. Further, the soil microorganism efficiently cleaves steroidal and
non-steroidal acetates to alcohols. © 2002 Elsevier Science Ltd. All rights reserved.
The application of enzymes in microbial transforma-
tion reactions is an emerging area in the field of
organic chemistry.1 Although, fluorescent Pseudomon-
ads are the most extensively studied bacterial biocon-
trol agents for a diverse range of soil-borne diseases,2
their potential in biotransformation reactions has
received little attention, except for recent reports
where Pseudomonas spp. have been employed for the
hydroxylation of nicotinic acid3 and aromatic com-
pounds.4 On the other hand, an acyl group is a fre-
quently used protective group for alcohols and there
has been continued search for mild and efficient
methods for the cleavage of esters employing enzymes5
and Lewis acid catalysts.6 A b-formylenamide is an
interesting functionality bearing an acetyl group that
has been exploited for the syntheses of various
steroidal and non-steroidal heterocycles.7 Our attempts
to utilise soil micro-organisms in bio-organic transfor-
mations has led to a facile 1,5-rearrangement of the
N-acetyl group of b-formylenamides as well as ester
cleavage catalysed by the Pseudomonas fluorescens
strain RRLJ 134.8
stant shaking for 40 h. After TLC indicated the com-
pletion of the reaction, the product was isolated by
preparative thin layer chromatography and identified
as
16-(Z)-acetoxymethylene-epiandrost-5-ene-17-one
1
(2a) from its spectroscopic properties.10 The H NMR
spectrum showed a distinctive singlet at l 8.35 for a
conjugated olefinic proton and a signal at l 2.30 for
an acetoxy methyl group. Further evidence was pro-
vided by its mass spectrum, which showed a signifi-
cant ion peak at m/z 339 (M−18) corresponding to
facile loss of water typical of C-substituted steroids.11
Treatment
of
3-acetoxy-16-formyl-17-acetamido-
androst-5,16-diene (1b) with the P. fluorescens strain
under identical conditions led to product 2a. How-
ever, 1c under the influence of the microorganism
afforded the conjugated enone (2b) without cleavage of
the 3-benzyloxy group. Similarly, P. fluorescens
catalysed the 1,5-rearrangement of the alicyclic-b-
formylenamides (1d and 1e) affording the correspond-
ing conjugated enones (2c and 2d) in good yields
(Table 1).
In a typical reaction, a solution of 3-hydroxy-16-for-
myl-17-acetamido-androst-5,16-diene (1a, 0.1 mmol)
in methanol (10 ml) was evenly distributed into five
100 ml nutrient broth media9 containing P. fluores-
cens strain RRLJ 134. The culture was inoculated at
ambient temperature (28–30°C) at pH 7.4 with con-
Concerning the reaction mechanism for the formation
of 2a, it may be that under the influence of the
microorganism, the canonical form A of 1a facilitates
a 1,5-rearrangement of the N-acetyl group to give the
imine intermediate B, followed by hydrolysis to give
the product 2a. The catalytic role of P. fluorescens is
evidenced from the fact that no rearrangement of 1a
takes place in the absence of the microorganism. How-
ever, the use of strong alkaline conditions led to the
normal deacetylated product, 17-amino-16-formyl-3-
hydroxy-androst-5,16-diene.
Keywords: Pseudomonas fluorescens; b-formylenamides; soil microor-
ganism; bio-organic transformation.
* Corresponding author. Tel.: 091 376 3370327; fax: 091 376 3370011;
e-mail: rc boruah@yahoo.com
–
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00114-4

2270
U. Bora et al. / Tetrahedron Letters 43 (2002) 2269–2271
Table 1. Rearrangement reaction of b-formylenamides catalysed by P. fluorescensa
In order to investigate the role of P. fluorescens in ester
hydrolysis, an attempt was made to treat alicyclic and
aromatic acetates with the microorganism under identi-
cal conditions. It was observed that cleavage of the
acetates (3–9) with P. fluorescens proceeded within 20–
28 h to afford the alcohols (10–16) in high yields (Table
2). The aromatic acetate bearing an electron withdraw-
ing group at the p-position (entry 6) proceeded with a
faster reaction rate than alicyclic analogues (entries
1–3). However, an attempt to carry out the microbial
catalysed cleavage of alicyclic and aromatic benzoates
(3–9, R=Bz) failed in our hands.
rangement of b-formylenamides to the corresponding
b-acetoxyenones in high yields. In addition, the
microorganism has proven to be an efficient catalyst for
the mild6 cleavage of acetates. Further work on acetate
cleavage using microbial transformation reactions is in
progress.
Acknowledgements
We thank the Department of Science and Technology
(DST), Govt. of India, New Delhi for financial support
and the University Grant Commission, New Delhi for a
teacher fellowship to M.L.
In summary, we have demonstrated that the P. fluores-
cens strain RRLJ 134 efficiently catalyses the 1,5-rear-

U. Bora et al. / Tetrahedron Letters 43 (2002) 2269–2271
2271
Table 2. Hydrolysis of esters catalysed by P. fluorescensa
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