Phytochemical profile and biological activities of Kerianthera preclara, Kutchubaea insignis, Pagamea duckei, Pagamea macrophylla, and Rudgea lanceifolia (Rubiaceae)
Abstract
Rubiaceae is a botanical family recognized as a rich source of bioactive natural products with diverse pharmacological properties. However, the biological potential of many species within this family remains poorly explored. This study aimed to characterize the phytochemical profiles of hexane and methanolic extracts from five Rubiaceae species — Kerianthera preclara J.H.Kirkbr., Kutchubaea insignis Fisch. ex DC., Pagamea duckei Standl. (PD 1, collected from a shaded area, and PD 2, from a sunny area), Pagamea macrophylla Spruce ex Benth., and Rudgea lanceifolia Salisb. — using comparative thin-layer chromatography (TLC) and proton nuclear magnetic resonance ( 1 H NMR), and to evaluate their biological activities through Artemia salina toxicity assays, contact toxicity against Sitophilus zeamais , antibacterial activity, and antioxidant assays. 1 H NMR analyses revealed characteristic signals of terpenes, aromatic compounds, and nitrogen-containing metabolites, corroborating the TLC results. Among the species evaluated, only the methanolic extracts of the branches and leaves of K. preclara showed traces of alkaloids, as indicated by orange spots after development with Dragendorff’s reagent. The methanolic extract of P. duckei PD 2 exhibited intense aromatic proton signals (δ H 6.00–8.00 ppm), as well as phenolic compounds detected using ferric chloride, and showed significant antioxidant activity in both the 1,1-diphenyl-2-picrylhydrazyl (DPPH) and Fe 3+ /phenanthroline assays. Among the extracts evaluated, the methanolic extract of K. preclara branches showed complete inhibition of Escherichia coli (100%), while the leaves extract inhibited Klebsiella pneumoniae by 95.27%. Methanolic extracts of P. duckei from both collection sites also exhibited antibacterial activity, particularly PD 1, which inhibited Citrobacter freundii (73.86%), E. coli (71.77%), and Serratia marcescens (75.85%). In contact toxicity assays against S. zeamais , the methanolic leaf extract of P. macrophylla showed the highest activity, with a median lethal concentration (LC 50 ) of 3.82 μg/mL. Overall, K. preclara, P. duckei , and P. macrophylla exhibited promising phytochemical profiles and biological activities, highlighting their potential as sources of bioactive compounds and supporting their prioritization for future phytochemical and pharmacological investigations.