BREAKDOWN OF CHLOROPHYLL - A TETRAPYRROLIC CHLOROPHYLL CATABOLITE FROM SENESCENT RAPE LEAVES

The experiments leading to the isolation and to the elucidation of the constitution of Bn-NCC-1, a colourless non-fluorescent chlorophyll catabolite from senescent cotyledons of rape (Brassica napus L.), are described. A series of fast-atom-bombardment (FAB) mass and H-1- and C-13-NMR spectral experiments are used to determine the constitution of the catabolite Bn -NCC-1. The structural information available indicates Bn-NCC-1 to be a 1-formyl-19-oxobilane, structurally related to 'RP 14', isolated earlier from artificially aged primary leaves of barley. The major differences between the constitution of the metal-free chlorophyll pheophorbide a and that of Bn-NCC-1 concern oxygenolytic opening of the porphinoid macrocycle at C(4)-C(5), saturation at the other meso positions, hydrolysis of the methyl-ester function, and functionalization by a malonic-acid unit of the side chain at C(8). This work provides for the first time the structural data of a chlorophyll-degradation product from senescent plant leaves formed under normal growth conditions.