Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany.
Clemens-Schöpf-Institut für Organische Chemie und Biochemie , Technische Universität Darmstadt , Alarich-Weiss-Str. 16 , 64287 Darmstadt , Germany.
J Org Chem. 2020 Feb 21;85(4):1835-1846. doi: 10.1021/acs.joc.9b01913. Epub 2020 Jan 7.
We present a novel concept for the in situ control of site-selectivity of catalytic acetylations of partially protected sugars using light as external stimulus and oligopeptide catalysts equipped with an azobenzene moiety. The isomerizable azobenzene-peptide backbone defines the size and shape of the catalytic pocket, while the π-methyl-l-histidine (Pmh) moiety transfers the electrophile. Photoisomerization of the - to the -azobenzene catalyst (monitored via NMR) with an LED (λ = 365 nm) drastically changes the chemical environment around the catalytically active Pmh moiety, so that the light-induced change in the catalyst shape alters site-selectivity. As a proof of principle, we employed (4,6--benzylidene)methyl-α-d-pyranosides, which provide a change in regioselectivity from 2:1 () to 1:5 () for the monoacetylated products at room temperature. The validity of this new catalyst-design concept is further demonstrated with the regioselective acetylation of the natural product quercetin. In situ irradiation NMR spectroscopy was used to quantify photostationary states under continuous irradiation with UV light.
我们提出了一种新颖的概念，即在原位控制部分保护糖的催化乙酰化的选择性，使用光作为外部刺激和带有偶氮苯部分的寡肽催化剂。可异构化的偶氮苯-肽骨架定义了催化口袋的大小和形状，而π-甲基-l-组氨酸（Pmh）部分转移亲电试剂。通过使用 LED（λ=365nm）对 - 到 - 偶氮苯催化剂（通过 NMR 监测）进行光异构化，会极大地改变催化活性 Pmh 部分周围的化学环境，从而使催化剂形状的光诱导变化改变了选择性。作为原理的证明，我们使用了（4,6--亚苄基）甲基-α-d-吡喃糖苷，它们在室温下提供了单乙酰化产物的区域选择性从 2:1（）变化为 1:5（）。该新型催化剂设计概念的有效性还通过对天然产物槲皮素的区域选择性乙酰化得到了证明。原位辐照 NMR 光谱用于在连续紫外光辐照下定量光稳定态。
