Visible light-mediated cis/trans isomerization of ortho-hydroxy cinnamates: from coumarins to polymers David Diaz Diaz 1 , Alex Abramov 1 , B. Maiti 1 , Sebatian Bonardd 2,3 1 Institut für Organische Chemie, Universität Regensburg, Germany, 2 Departamento de Química Orgánica, Universidad de La Laguna, Spain, 3 Instituto Universitario de Bio-Orgánica Antonio González, Universidad de La Laguna, Spain In this contribution we describe a versatile methodology for the synthesis of a variety of coumarins in almost quantitative yields via a catalyst free, visible light mediated isomerization/cyclization sequence, taking advantage of a UV-to-vis bathochromic shift of ortho -hydroxy-cinnamates ( o HC) under basic conditions. This methodology was used for the pH-triggered degradation of polymers or for the release of drugs under visible light irradiation. Herein, the key o HC structural motif can be readily incorporated into the rational design of novel photocleavable polymers via click chemistry. This main-chain moiety undergoes a fast photocleavage when irradiated with 455nm light provided that a suitable base is added. In particular, a series of polyethylene glycol- alt - ortho -hydroxy cinnamate (polyethylene glycol (PEG) n - alt - o HC)-based polymers were synthesized and the time-dependent visible-light initiated cleavage of the photoactive monomer and polymer was investigated in solution by a variety of spectroscopic and chromatographic techniques. The photo-degradation behavior of the water-soluble poly(PEG 2000 - alt - o HC) was investigated within a broad pH range (pH = 2.1–11.8), demonstrating fast degradation at pH 11.8, while the stability of the polymer was greatly enhanced at pH 2.1. Moreover, the neat polymer showed long-term stability under daylight conditions, thus allowing its storage without special precautions. In addition, two water-soluble PEG-based drug-carrier molecules (mPEG 2000 - o HC-benzhydrol/phenol) were synthesized and used for drug delivery studies, monitoring the process by UV–vis spectroscopy in an ON/OFF intermittent manner. [1] Furthermore, this strategy was also applied for the visible-light-triggered degradation of pH-responsive micelles. Specifically, micelles made by connecting hydrophobic and hydrophilic chains via photo-responsive o HC units underwent complete degradation within 10 min under visible light irradiation at basic pH values. The controlled cyclization of the o HC moiety afforded the corresponding coumarin with the concomitant separation of the hydrophobic portion. Moreover, the neat polymeric micelles were also stable under daylight conditions at neutral pH. These systems were characterized by fluorescence analysis, transmission electron microscopy, dynamic light scattering and zeta potential measurements. [2] References 1. A. Abramov, B. Maiti, I. Keridou, J. Puigagalí, O. Reiser, D. Díaz Díaz, Macromol. Rapid Commun. 2021 , 42, 2100213. 2. A. Abramov, S. Bonardd, C. Saldías, D. Díaz Díaz, ChemPhotoChem 2022 , 6, e202100282.
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