Synthesis and Photochromic Properties of Azobenzene‐Derived Glycomacrolactones

• Published in: European journal of organic chemistry 2019-02, Vol.2019 (8), p.1770-1777
• Main Authors: Lin, Chaoqi, Maisonneuve, Stéphane, Theulier, Cyril, Xie, Juan
• Format: Article
• Language: English
• Subjects: Azo compounds; Biological properties; Bistability; Carbohydrates; Chemical Sciences; Chirality; Fatigue strength; Isomerization; Isomers; Macrolactones; NMR; Nuclear magnetic resonance; Photochromism; Synthesis; Thermal stability
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201801832

Reversible photocontrol of glycosides and glycoconjugates structures is a very attractive approach to modulate, in a spatiotemporal way, the various properties and biological activities of carbohydrates. We have synthesized three new azobenzene‐derived glycomacrolactones from thioglycopyranosides. The synthesized cyclic glycoazobenzenes can be reversibly photoisomerized between E and Z isomers with high fatigue resistance. A 1H NMR spectroscopic study shows that E → Z isomerization of glycomacrocycles induces large conformational change of the macrocyclic structures, without changing sugar 4C1 chair conformation. The Z‐glycoazobenzenes can be thermally converted back to the E‐isomers. Interestingly, these 16 to 17‐membered Z‐glycomacrolactones display higher thermal stability than the reported macrocyclic azobenzenes, the half‐life varying from 37 to 72 days. The excellent photoswitching property and bistability of the synthesized glycoazobenzenes open a new opportunity for the convergent synthesis of diastereomers of glycomacrocycles. Furthermore, chiroptical properties have been observed for both E and Z glycomacrolactones. The geometry of different isomers of macrocycles has been optimized with DFT calculations. Theoretical CD spectra obtained by TD‐DFT suggest that the E and Z glycomacrocycles adopt preferentially (P) helical structure for the azobenzene moiety. Photoswitchable and bistable glycomacrolactones: Azobenzene‐based glycomacrolactones have been synthesized from gluco and manno thioglycosides. These glycoazobenzenes display excellent photochromic properties and bistability. The E→Z photoisomerization induced a large change in the conformation and the chirality of the macrolactones. Both E‐ and Z‐glycomacrolactones show a (P) helical structure, as suggested by TD‐DFT calculations.