Selective Antibacterial and Moderate Anti-Inflammatory Activity with Distinct Cytotoxic Profiles of Pulcherrin H and Pulcherrimin A-First Isolated from Caesalpinia pulcherrima Yellow Flowers.

Cassane diterpenoids constitute a structurally diverse class of plant-derived natural products that have attracted considerable attention because of their broad spectrum of biological activities. In this study, pulcherrimin A and pulcherrin H were obtained from the yellow flowers of Caesalpinia pulcherrima, representing the first identification of both metabolites in this plant part. Their antibacterial activity, effects on macrophage viability, and ability to modulate nitric oxide production were subsequently investigated. Structural identities were elucidated using 1D and 2D NMR spectroscopy. Pulcherrimin A inhibited selected bacterial species, with greater activity against Gram-positive organisms and MIC values of 62.5-250 μg/mL. Limited activity was also observed against selected Gram-negative bacteria, including Acinetobacter baumannii. In contrast, pulcherrin H showed little or no antibacterial activity under the conditions tested. Cytotoxicity assessment in RAW 264.7 macrophages revealed that pulcherrimin A maintained relatively high cell viability (>85% at ≤ 100 μg/mL), whereas pulcherrin H showed pronounced cytotoxicity in a concentration-dependent manner. In the nitric oxide (NO) inhibition assay, pulcherrimin A produced a modest reduction in NO levels (up to ∼17% inhibition), while pulcherrin H showed no inhibitory effect. The combined results indicate that pulcherrimin A possesses moderate antibacterial and anti-inflammatory activity with a comparatively favorable cytotoxicity profile, whereas pulcherrin H is limited by cytotoxicity and lack of functional activity. These findings suggest that pulcherrimin A exhibits biological and antimicrobial activities with relatively low cytotoxicity supporting its suitability for further investigation.