Tetrahedron Letters
The influence of wavelength of light on cyanobacterial asymmetric
reduction of ketone
b
c
c
a
Ken-ichi Itoh a, , Kaoru Nakamura , Tadashi Aoyama , Tsuyoshi Kakimoto , Masahiko Murakami ,
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Toshio Takido c
a Department of Liberal Arts and Science, College of Science and Technology, Nihon University, 7-24-1 Narashinodai, Funabashi-shi, Chiba 274-8501, Japan
b Graduate School of Human Development and Environment ‘Science Shop’, Kobe University, 3-11 Tsurukabuto, Nada-ku, Kobe-shi, Hyogo 657-8501, Japan
c Department of Material and Applied Chemistry, College of Science and Technology, Nihon University, 1-8-14 Kandasurugadai, Chiyoda-ku, Tokyo 101-0062, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Asymmetric reduction of ketone by a microalga, Synechocystis sp. PCC 6803, smoothly afforded to the cor-
responding (S)-alcohol in excellent enantiomeric excess by the aid of illumination of orange and red LED
lights which are more effective than other LEDs such as blue and green lights. The condition under min-
imum energy flux (1.0 W/m2) of orange-red LEDs is enough for the reduction of ketone, and it seems that
orange-red light rather effectively forwarded the regeneration of coenzyme.
Received 1 October 2013
Revised 9 November 2013
Accepted 13 November 2013
Available online 20 November 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Cyanobacterial asymmetric reduction
Effective utilization of light energy
Influence of wavelength of light
LED illumination
Regeneration of coenzyme
Microalgae are useful microorganisms; they produce approxi-
mately half of the atmospheric oxygen and use simultaneously car-
bon dioxide (CO2) to grow photoautotrophically. Furthermore,
microalgae can work as biocatalysts and have the potential for pro-
ducing valuable substances.1 Usually, microalgae are used as the
sources of fine chemicals and biofuels.2 Synechocystis sp. PCC
6803 is a unicellular cyanobacteria and is used as a model micro-
alga by scientists around the world because it was the first photo-
synthetic organism for which the entire genome sequence was
determined.3
We have developed the use of microalgae as biocatalysts for
converting artificial substrates to useful products. Chiral alcohols
were obtained by asymmetric reduction of ketones using microal-
gae such as cyanobacteria and chlorella under fluorescent light
illumination.4 In the reduction, ketones were converted into the
corresponding optically active alcohols by NADPH generated in
the chlorophyll of microalgae using light energy.4b Moreover, since
this reaction was conducted by the living cells of algae, a consumed
NADPH was regenerated by light energy and H2O in the microalgae
body.
LED illumination (Scheme 1). In this Letter, we studied the rela-
tionship between the yield of reductive product and both wave-
length and intensity of LED light.
Photomicroorganisms require light for growing and also as an
energy source to carry out reduction of artificial ketones.4 In mic-
roalgae, photons of light are one of the major energy sources for
the growth of cells. Therefore, both wavelength and intensity of ap-
plied light are known to contribute to the growth of microalgae,5
and are thought to also affect bioconversion of artificial substrates.
Hence, aiming to develop a more efficient bioconversion system
that works with less energy consumption, we have studied the ef-
fect of such factors on the bioconversion with microalgae by using
light-emitting diodes (LEDs) as a light source. Since LEDs are highly
monochromatic efficient light sources and are now available to
emit each of several colors from red through purple, LEDs are suit-
able for our present study. All irradiation intensities were deter-
mined by the radiometer (Delta OHM: HD2302.2 with LP471RAD
probe) and were adjusted to give certain energy fluxes (0, 1.0,
2.5, 5, 12, 22 and 60 W/m2) by both the number of LEDs used
and shading the light by using the appropriate number of copier
paper.
Herein, we would like to report the asymmetric reduction of
20,30,40,50,60-pentafluoroacetophenone
1
into the corresponding
The substrate, 20,30,40,50,60-pentafluoroacetophenone 1, was re-
acted in the suspension culture of Synechocystis sp. PCC 6803 under
red LED illumination (660 nm),6 and the effect of the light intensity
on the yield of the product alcohol was investigated. The results are
shown in Figure 1.
fluorinated chiral alcohol 2 using Synechocystis sp. PCC 6803 under
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Corresponding author. Tel./fax: +81 80 47 467 5307.
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.