A Design of Experiments Approach to the Radical-Induced Oxidation of Dimeric C4-C8 Linked B-Type Procyanidins

This study systematically investigated the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical induced oxidation of all dimeric C4-C8 linked B-type procyanidins (PCs) B1–B4 to maximise the formation of the oxidation products using a Design of Experiments (DoE) approach. The C4 β -C8 linked B1 and B2 formed the A1 ( 1 ) and A2 ( 2 ) ( m / z 575 [M-H] − ) with an ether bridge between C2u-O-C7t as expected. Interestingly, the oxidation of the C4 α -C8 linked dimers B3 and B4 yielded for each two main oxidation products with m / z 575 [M-H] − . One of them required only a short reaction time (10.0 min, 25.0 °C for B3 ( 3 ) and B4 ( 5 )), whereas the other was maximally formed at a longer time and higher temperature (314 min and 75.0 °C for B3 ( 5 ); 360 min, 53.7 °C for B4 ( 6 )). The formation rates were optimised to 47.4 ± 1.14% (A1; 1 ), 27.5 ± 0.76% (A2; 2 ), 48.6 ± 4.01% ( 3 ), 32.0 ± 1.14% ( 4 ), 45.0 ± 5.14% ( 5 ) and 60.2 ± 3.68% ( 6 ).