Bioactive Compounds from the Aerial Parts of Brachystemma calycinum and Structural Revision of an Octacyclopeptide

Four new cyclic peptides, brachystemins F–I (1–4), and 11 known compounds were isolated from the aerial parts of Brachystemma calycinum. The absolute configurations of compounds 1–4 were assigned using Marfey’s method. The structure of compound 5 was revised from cyclo(Pro¹–Phe²–Leu³–Ala⁴–Thr⁵–Pro⁶–Ala⁷–Gly⁸) to cyclo(Pro¹–Pro²–Ala³–Gly⁴–Leu⁵–Ala⁶–Thr⁷–Phe⁸) with QTOF/MS and X-ray diffraction analysis. The N-containing compounds were assessed for their inhibitory effects on the secretion of monocyte chemokine ligand 2 (CCL-2), interleukin 6 (IL-6), and collagen IV against high-glucose-stimulated mesangial cells. Compound 5 was evaluated for its effects on collagen I, reactive oxygen species (ROS), superoxide anion (O₂^•–) production, and cell viability in mesangial cells, and on nitric oxide (NO) production in macrophage cells.