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.