Ruehssiosides A–R, 18 Previously Undescribed Pregnane Glycosides from Ruehssia caatingae : Structural Elucidation, Potential Anti-Inflammatory Activity, and Insights into Structure–Activity Relationships

Abstract Nature has always inspired the discovery of novel compounds to treat human inflammatory processes, which are related to many diseases in acute and chronic conditions. Found in some Apocynaceae species, pregnane glycosides (PGs) have been attracting attention due to their promising anti-inflammatory potential. Ruehssia is a neotropical genus endemic to arid regions and, in Brazil, the Caatinga serves as a major hotspot for its occurrence. However, no in-depth chemical or pharmacological investigations have yet been conducted on Ruehssia species. Based on this, the present work sought to isolate, characterize, and investigate the potential anti-inflammatory activity of PGs obtained from the roots of R. caatingae. To achieve this goal, classical and instrumental chromatographic techniques were applied, followed by 1D and 2D NMR experiments, as well as IR and HR-ESI-MS analyses to assist structural elucidation. To assess potential anti-inflammatory activity, murine macrophage-like J774.A1 cells, stimulated with lipopolysaccharide (LPS) and interferon-gamma (IFN-γ), were used. As a result, 18 previously undescribed PGs were obtained, named ruehssiosides A–R (1–18). Among them, ruehssioside J (compound 10) stood out as the most potent of the series, exhibiting a half-maximal inhibitory concentration (IC50) of 17.5 μM for nitric oxide inhibition and significantly reducing IL-6 and IL-1β production. Additionally, structure–activity relationship (SAR) analysis was carried out, highlighting the structural elements contributing to the observed anti-inflammatory effects. This work encourages the continued study of Apocynaceae species, especially from underinvestigated environments, as sources of substances with anti-inflammatory potential.