Reversible shape switching due to external stimuli is an attractive property for the control of molecular features. Hence, we aimed at macrocycles to investigate photoswitching of molecular shape. We prepared the first carbohydrate-based macrocycles comprising a photoresponsive azobenzene hinge. These macrocycles were readily obtained by cyclization of isothiocyanate-armed bis-azobenzene glycosides with piperazine. The unprotected macrocycles exhibit favorable photochromic properties in water and DMSO. Notably, the efficient trans→cis isomerization results in a remarkable shape transformation of the molecule. Additionally, the structure is characterized by restricted conformational freedom of the backbone, resulting in a single main conformer in each geometrical state (trans or cis). Measurement of optical rotation values and circular dichroism spectra revealed a tremendous change in chirality upon photoisomerization, with a strong helical induction in the cis state. These findings highlight the applicability of the new macrocycles as chiroptical molecular switches.

A combination of the Mitsunobu reaction and Glaser coupling was used to achieve a new glycoazobenzene macrocycle. This photosensitive macrocycle can be efficiently and reversibly switched between two stable conformational isomers, which are characterized with photoswitchable shape, chiroptical and solubility behaviour.

The Mitsunobu reaction basically consists in the conversion of an alcohol into an ester under inversion of configuration, employing a carboxylic acid and a pair of two auxiliary reagents, mostly triphenylphosphine and a dialkyl azodicarboxylate. This reaction has been frequently used in carbohydrate chemistry for the modification of sugar hydroxy groups. Modification at the anomeric position, leading mainly to anomeric esters or glycosides, is of particular importance in the glycosciences. Therefore, this review focuses on the use of the Mitsunobu reaction for modifications of sugar hemiacetals. Strikingly, unprotected sugars can often be converted regioselectively at the anomeric center, whereas in other cases, the other hydroxy groups in reducing sugars have to be protected to achieve good results in the Mitsunobu procedure. We have reviewed on the one hand the literature on anomeric esterification, including glycosyl phosphates, and on the other hand glycoside synthesis, including S- and N-glycosides. The mechanistic details of the Mitsunobu reaction are discussed as well as this is important to explain and predict the stereoselectivity of anomeric modifications under Mitsunobu conditions. Though the Mitsunobu reaction is often not the first choice for the anomeric modification of carbohydrates, this review shows the high value of the reaction in many different circumstances.

The Mitsunobu reaction has been revisited to join hydroxyazobenzene and mannose derivatives to supply photoswitchable glycoconjugates. These are suited to modulating and controlling carbohydrate‐lectin interactions, as well as to switching bacterial adhesion to surfaces. Employing hydroxyazobenzene in a Mitsunobu protocol, free mannose led to a mixture of azobenzene pyranosides and furanosides. Protected reducing mannose derivatives can give good yields of azobenzene β‐D‐mannopyranoside, and unprotected alkyl α‐D‐mannosides can be converted to 6‐O‐azobenzene‐modified glycosides in a single step. Thus, valuable “sweet switches” can be obtained under Mitsunobu conditions, requiring a minimum (or no) protecting group chemistry.

Chemiegeschichte(n), Medizin und Grundlagenforschung – diese drei Zugänge für ganz unterschiedliche Interessen‐ und Motivationslagen bei Schülerinnen und Schülern lassen sich über einen gemeinsamen Kontext zusammenführen, in dessen Mittelpunkt ein roter Farbstoff steht. Schwangerschaftsdiabetes und Lactoseunverträglichkeit erfordern geeignete Nachweise, deren Entdeckung, Nutzung und Aufklärung der zugrundeliegenden Mechanismen spannende Fragen für den Chemieunterricht im Themenfeld Kohlenhydrate bereithalten, verbunden mit einem Blick zurück in europäische Forschungsgeschichte(n) und mit einem Blick nach vorn auf heute noch offene Forschungsfragen.