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<i>β</i>-C8 linked B1 and B2 formed the A1 (<b>1</b>) and A2 (<b>2</b>) (<i>m</i>/<i>z</i> 575 [M-H]^-) with an ether bridge between C2u-O-C7t as expected. Interestingly, the oxidation of the C4<i>α</i>-C8 linked dimers B3 and B4 yielded for each two main oxidation products with <i>m</i>/<i>z</i> 575 [M-H]^-. One of them required only a short reaction time (10.0 min, 25.0 °C for B3 (<b>3</b>) and B4 (<b>5</b>)), whereas the other was maximally formed at a longer time and higher temperature (314 min and 75.0 °C for B3 (<b>5</b>); 360 min, 53.7 °C for B4 (<b>6</b>)). The formation rates were optimised to 47.4 ± 1.14% (A1; <b>1</b>), 27.5 ± 0.76% (A2; <b>2</b>), 48.6 ± 4.01% (<b>3</b>), 32.0 ± 1.14% (<b>4</b>), 45.0 ± 5.14% (<b>5</b>) and 60.2 ± 3.68% (<b>6</b>).