The team, led by Luana da Conceição Moreira and Cecilia Veronica Nunez of the National Institute of Amazonian Research (INPA) in Manaus, collected branches, leaves, fruits, and inflorescences from sites around Manaus, Amazonas, including the Adolpho Ducke Forest Reserve and the Campina Biological Reserve. Plant material was dried at 35 degrees Celsius, ground, and extracted sequentially with hexane and methanol, solvents of increasing polarity that pull out different chemical classes. In total, 14 hexane extracts and 14 methanolic extracts were generated, each standardized to 10 milligrams per milliliter for analysis. Notably, Pagamea duckei was collected twice from individuals growing under contrasting light conditions — one in deep shade, one in full sun — a deliberate design choice that would later prove chemically consequential.

Chemical profiling relied on two complementary techniques. Thin-layer chromatography (TLC) on silica gel plates, developed with class-specific visualization reagents, provided a rapid fingerprint of each extract. Anisaldehyde-sulfuric acid and ceric sulfate revealed terpenes as lilac, pink, and brown bands; ferric chloride and NP/PEG reagent flagged phenolic compounds; potassium hydroxide detected quinones; and Dragendorff’s reagent identified nitrogen-containing metabolites, particularly alkaloids. Proton nuclear magnetic resonance spectroscopy at 300 megahertz then corroborated and extended these assignments. The hexane extracts were dominated by resonances between 0.60 and 1.80 parts per million, characteristic of terpenoid methyl groups, along with a prominent signal at 1.25 parts per million from fatty acid chains. Olefinic resonances at 5.35 and 5.12 parts per million pointed to the phytosterols beta-sitosterol and stigmasterol.

The methanolic extracts told a richer story. Signals between 3.00 and 4.50 parts per million — anomeric, oxymethine, and oxymethylene protons — indicated glycosylated metabolites such as iridoid glycosides and phenolic glycosides. Kutchubaea insignis showed a diagnostic doublet at 6.00 and broad singlet at 7.50 parts per million, the olefinic fingerprint of iridoids bearing a C-3/C-4 enol ether system, consistent with the chemotaxonomic importance of iridoids in the Ixoroideae subfamily. Only Kerianthera preclara produced orange bands with Dragendorff’s reagent, revealing traces of alkaloids in its branch and leaf extracts — a finding echoed by low-intensity deshielded resonances between 9.00 and 10.00 parts per million in its NMR spectra. Pagamea duckei, meanwhile, displayed intense aromatic proton signals between 6.00 and 8.00 parts per million, and ferric chloride confirmed phenolic constituents.

That last observation carried an ecological twist. The sunny-site collection of Pagamea duckei (PD 2) showed markedly more intense aromatic resonances than the shaded-site collection (PD 1), a pattern the researchers attribute to ultraviolet radiation stimulating the accumulation of phenolic compounds involved in photoprotection and antioxidant defense. This environmental influence translated directly into biological performance. In antioxidant assays, only Pagamea duckei extracts were active, and the branch extract from the sunny site outperformed everything else, achieving 1.6 ascorbic acid equivalents in the DPPH radical-scavenging assay and 2.8 equivalents in the Fe3+/phenanthroline reducing-power assay — values that place it among the very active samples on the standard equivalence scale. The shaded-site branch extract, by contrast, was inactive in DPPH.

The antibacterial results were equally dramatic. Tested by broth microdilution against eleven bacterial strains at 1,000 micrograms per milliliter, the methanolic branch extract of Kerianthera preclara achieved complete, 100 percent inhibition of Escherichia coli, while its leaf extract inhibited Klebsiella pneumoniae by 95.27 percent. Pagamea duckei extracts from both collection sites also showed broad activity: the shaded-site branch extract inhibited Citrobacter freundii by 73.86 percent and E. coli by 71.77 percent, the shaded-site leaf extract suppressed Serratia marcescens by 75.85 percent, and the sunny-site leaf extract hit Citrobacter freundii at 75.28 percent and Aeromonas hydrophila at 68.62 percent. Rudgea lanceifolia hexane extracts showed more modest inhibition, reaching 69.75 percent against Morganella morganii.

Yet the study’s authors urge caution on potency. When extracts showing more than 70 percent inhibition were subjected to minimum inhibitory concentration testing by two-fold serial dilution, none completely suppressed bacterial growth at the highest tested concentration of 500 micrograms per milliliter, yielding MIC values above that threshold. This suggests the active constituents occur at relatively low abundance within the crude extracts — a common scenario in natural products research that typically motivates bioassay-guided fractionation to isolate and concentrate the responsible molecules. The team also noted that all extracts showed limited activity against Pseudomonas aeruginosa and Acinetobacter baumannii, Gram-negative pathogens whose low outer membrane permeability, efficient efflux pumps, and detoxification capacity blunt the effect of both conventional antibiotics and plant-derived compounds.

Perhaps the most agriculturally significant finding came from contact toxicity assays against Sitophilus zeamais, the maize weevil, one of the most destructive pests of stored grains worldwide. Methanolic extracts were topically applied to the dorsal thorax of adult weevils in acetone solution, with mortality assessed after seven days. The leaf extract of Pagamea macrophylla proved the standout, killing half the insects at a median lethal concentration of just 3.82 micrograms per insect and 90 percent at 15.73 micrograms per insect. Kerianthera preclara leaves (LC50 of 8.94 micrograms per insect) and Pagamea duckei branches (11.46 micrograms per insect) also performed well, while Rudgea lanceifolia leaves required nearly 91 micrograms per insect to reach the same endpoint. The researchers suggest that terpenoids, fatty acid derivatives, and nitrogen-containing alkaloids — all detected in the chemical profiles — may disrupt insect respiration, penetrate the cuticle, or interfere with nervous system function.

General toxicity screening using the brine shrimp Artemia salina lethality assay added a further dimension. Only a handful of extracts were active, but the methanolic branch extract of Kerianthera preclara showed clear concentration-dependent mortality — 43.3 percent at 250 micrograms per milliliter rising to 70 percent at 1,000 micrograms per milliliter — hinting at constituents with possible cytotoxic potential. The authors stress that such preliminary signals require confirmation through isolation of individual compounds and testing on tumor and healthy cell lines before any pharmacological claims can be made. Comparable toxicity has been reported for Isertia hypoleuca, a relative in the same tribe, whose extracts killed brine shrimp at concentrations below 10 micrograms per milliliter.

Overall, the study delivers the first integrated phytochemical and biological assessment of these five Amazonian Rubiaceae species, three of which — Kerianthera preclara, Pagamea duckei, and Pagamea macrophylla — emerge with particularly promising profiles. Kerianthera preclara offers antibacterial activity and preliminary evidence of alkaloids; Pagamea duckei combines antioxidant and antibacterial potential tied to phenolic-like metabolites; and Pagamea macrophylla demonstrates exceptional insecticidal potency against a major grain pest. The researchers emphasize that all compound assignments remain putative, based on crude extract analysis, and that definitive identification will require liquid chromatography-tandem mass spectrometry, compound isolation, and multidimensional NMR spectroscopy. Still, the message is clear: in the chemical darkness of the Amazon, even the most overlooked members of the coffee family may be harboring the next generation of medicines and biopesticides.

Subject of Research: Phytochemical profile and biological activities of Kerianthera preclara, Kutchubaea insignis, Pagamea duckei, Pagamea macrophylla, and Rudgea lanceifolia (Rubiaceae)

Article Title: Phytochemical profile and biological activities of Kerianthera preclara, Kutchubaea insignis, Pagamea duckei, Pagamea macrophylla, and Rudgea lanceifolia (Rubiaceae)

Article References: Phytochemical profile and biological activities of Kerianthera preclara, Kutchubaea insignis, Pagamea duckei, Pagamea macrophylla, and Rudgea lanceifolia (Rubiaceae). (n.d.). https://doi.org/10.3389/fntpr.2026.1913240

Image Credits: AI Generated

DOI: 10.3389/fntpr.2026.1913240

Keywords: Phytochemical, profile, biological, activities, Kerianthera, preclara, Kutchubaea, insignis, Pagamea, duckei, macrophylla, Rudgea