Syntheses of Bile Pigments. Part 18. Synthesis and conformational studies of oxa‐ and thia‐deaza‐biliverdin analogues

Following the conventional methodology used for the synthesis of bile pigments, some oxa- and thia-deazabiliverdin analogues were synthetized for the first time. Both UV/VIS spectroscopic and 1H{1H}-NOE difference studies reveal that the oxa-deaza-biliverdin analogue 8a occurs in apolar solvents in a partly ‘stretched’ conformation, whereas the corresponding thia derivative 8b behaves rather like a genuine bile pigment. Unexpectedly, the helical-shaped conformation is also preponderant in a trioxa-trideaza-biliverdin analogue, which could be only characterized in its protonated form 14.