Two benzophenone glucosides (<b>1</b> and <b>2</b>), five flavan-3-ol dimers (<b>5</b>-<b>9</b>), and 17 known compounds (<b>3</b>, <b>4</b>, and <b>10</b>-<b>24</b>) were identified from the bark extract of <i>Cassia abbreviata</i>. The chemical structures display two points of interest. First, as an unusual characteristic feature of the <sup>1</sup>H NMR spectra of <b>1</b> and <b>2</b>, the signals for the protons on glucosidic carbons C-2 are shielded as compared to those generally observed for glucosyl moieties. The geometrically optimized 3D structures derived from conformational analysis and density functional theory (DFT) calculations revealed that this shielding effect originates from intramolecular hydrogen bonds in <b>1</b> and <b>2</b>. Additionally, <b>3</b>-<b>15</b> were identified as dimeric B-type proanthocyanidins, which have 2<i>R</i>,3<i>S</i>-absolute-configured C-rings and C-4-C-8″ linkages, as evidenced by X-ray crystallography and by NMR and ECD spectroscopy. These results suggest the structure-determining procedures for some reported dimers need to be reconsidered. The trypanocidal activities of the isolated compounds against <i>Trypanosoma brucei brucei</i>, <i>T. b. gambiense</i>, <i>T. b. rhodesiense</i>, <i>T. congolense</i>, and <i>T. evansi</i> were evaluated, and the active compounds were identified.