![87. Contra-thermodynamic E → Z isomerization of cinnamamides via selective energy transfer catalysis](https://cdn.prod.website-files.com/6380be6ed1140b78394d35e6/6405de0b1f85c32fe64223e2_1-s2.0-S0040402020303331-fx1.jpg)
A bio-inspired, photocatalytic E → Zisomerization of cinnamides is reported using inexpensive (−)-riboflavin (vitamin B2) under irradiation at λ = 402 nm. This operationally simple transformation is compatible with a range of amide derivatives including –NR2, –NHSO2R and N(Boc)2 (up to 99:1 Z:E). Selective energy transfer from the excited state photocatalyst to the starting E-isomer ensures that directionality is achieved: The analogous process with the Z-isomer is inefficient due to developing allylic strain causing chromophore deconjugation. This is supported by X-ray analysis and Stern-Volmer photo-quenching studies. Preliminary validation of the method in manipulating the conformation of a simple model Leu-enkephalin penta-peptide is disclosed via the incorporation of a cinnamamide-based amino acid.