Does the photochemical conversion of colchicine into lumicolchicines involve triplet transients? A solvent dependence study.

A L Nery, F H Quina, P F Moreira Jr, C E Medeiros, W J Baader, K Shimizu, L H Catalani, E J Bechara

Instituto de Química, Universidade de São Paulo, São Paulo, Brazil.

Photochemistry and photobiology 2001 Mar

filter terms:

beta- and gamma-lumicolchicines are photoproducts formed by the cycloisomerization of the tropolone ring of colchicine (COL) alkaloids. The mechanism of the photoconversion, suggested to involve the triplet state, is examined here by studying the effect of the solvent polarity on the lumicolchicine photoisomer ratio. Triplet COL, detected by laser flash photolysis, is quenched by oxygen, but not by transtilbene or 1-methylnaphtalene. Neither the quantum yield of conversion of COL nor the photoproduct ratio was altered by the presence of oxygen. Likewise, energy transfer to COL from triplet acetone produced by either isobutanal/horseradish peroxidase system or tetramethyldioxetane thermolysis failed to provoke photoreaction of COL. Our data argue against the intermediacy of a COL triplet state in the photoisomerization and stress on the role of specific solvent-solute interactions in determining the partitioning of excited singlet state into the beta- and gamma-isomer formation.

Citation

A L Nery, F H Quina, P F Moreira Jr, C E Medeiros, W J Baader, K Shimizu, L H Catalani, E J Bechara. Does the photochemical conversion of colchicine into lumicolchicines involve triplet transients? A solvent dependence study. Photochemistry and photobiology. 2001 Mar;73(3):213-8