Breakdown of Chlorophyll: A Tetrapyrrolic Chlorophyll Catabolite from Senescent Rape Leaves. Preliminary communication

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 1H‐ and 13C‐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.