Life science
Fine chemicals, Drug discovery

Photocontrol of an enantioselective reaction using a chiralsupramolecular catalyst
Department of Synthetic Organic Chemistry, The Institute of Scientific and Industrial Research (SANKEN)
Associate Professor Shinobu Takizawa

Researchmap https://researchmap.jp/read0068650

Guest Assistant Professor Masaru Kondo

Researchmap https://researchmap.jp/300Kondo

Life science

Abstract

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We have developed a supramolecular photoswitchable crownether which can work as a chiral phase transfer catalyst for the firsttime. The crown ether bearing a wide variety of ring sizes can beprepared in a short step from commercially available chemicals.
The developed catalyst was applied to the asymmetric synthesisof chiral amino acid precursors. Under the irradiation of UV, thephotoswitchable crown ether promoted the asymmetric reaction toafford the desired product in a good yield and high enantioselectivity. In contrast, the catalyst activity greatly dropped in the absenceof light irradiation.

▍ Background & Results
The development of green catalytic asymmetric processes
has been important for the efficient synthesis of optically active
compounds toward SDGs. In recent, photo-responsive chiral catalysts using a light as a clean energy have also attracted muchattention. These catalysts can switch the reactivity and selectivity
on the enantioselective reaction through the control of the period
and wavelength of light irradiation. Although acid-base and metal
catalysts have been investigated to date, the development of chiralphase transfer catalysts, which is useful for asymmetric synthesisof unnatural amino acid derivatives, has been unexplored. Moreover, conventional light-responsive asymmetric catalysts often
require a multi-step synthesis, being a barrier for a practical use.
This time, we developed a photoresponsive chiral phase transfer
catalysts that can be synthesized in a short step from commerciallyavailable chemicals such as BINOL and azobenzene. Polyethylene
glycol linkages between chiral BINOL backbone and azobenzene
as a photoresponsive unit led to formation of the designed crownether. The NMR and UV-Vis studies of the catalyst structure indicated that the reversibly change by irradiation of UV and visible lights.
When the catalyst with KOH was applied to the enantioselective reaction of glycine Schiff bases with benzyl bromides, under the UVirradiation the desired amino acid precursor was obtained in highyields and high stereoselectivities. In contrast, the reactivity wasdecreased in the absence of light or under visible light irradiation.
The photoisomerization made a change of the catalyst structure,
resulting in control of the reactivity.

Photoswitchable chiral phase transfer catalyst (Azobenezene binaphthyl crownether)

Photocontrol of reactivity for enantioselective alkylation of glycine Schiff base▍ Significance of the research and Future perspective
Toward the SDGs, environmentally friendly, energy- and resource-saving synthetic methodologies of fine chemicals havebeen highly demanded. The present photoswitchable organocatalyst could express multiple functions for on-demand synthesis of
optically active compounds as well as saving cost for developmentof catalyst. Although we focus on the reactivity switching with theexternal stimulus at this moment, the chemo- and stereoselectivities could be controlled by just irradiation of various light wave-P a t e n t
Kondo, Masaru; Takizawa, Shinobu; Sasai, Hiroaki et al. Photoswitchable Chiral Phase Transfer Catalyst. ACS Catalysis. 2021; 11 (3): 1863-1867. doi: 10.1021/
acscatal.1c00057
Kondo, Masaru; Takizawa, Shinobu; Sasai, Hiroaki et al. Azopyridine-based Chiral Oxazolines with Rare-earth Metals for Photoswitchable Catalysis. Chem.
Commun. 2021; 57 (60): 7414-7417. doi: 10.1039/D1CC02602J
UR
L https://www.thieme-connect.de/products/ejournals/abstract/10.1055/s-0040-1706168
K e y w o r d photoswitchable catalyst, asymmetric reaction, amino acid synthesis, crown ether

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