Hydnophytum formicarum Jack. (Rubiaceae) is a medicinal plant whose tubers possesses cardiovascular, anti-inflammatory and
antiparasitic effects and have been used for the treatment of
hepatitis,
rheumatism and
diarrhea. Herein we report the isolation of its active constituents and the testing of their antimicrobial activity against 27 strains of microorganisms using an
agar dilution method and of their antioxidative activity using the DPPH and SOD assays. The results show that the crude
hexane,
dichloromethane, ethylacetate and
methanol extracts exert such activities. Particularly, the crude
ethyl acetate extract exhibits antigrowth activity against many Gram-positive and Gram-negative bacteria with MIC 256 microg/mL. Shewanella putrefaciens ATCC 8671 is completely inhibited at a lower MIC (128 microg/mL). Interestingly, Corynebacterium diphtheriae NCTC10356 is inhibited by all the tested extracts. Significantly, the
ethyl acetate extract is also the most potent
antioxidant, showing 83.31% radical scavenging activity with IC50 8.40 microg/mL in the DPPH assay. The other extracts display weak to moderate antioxidative activities, ranging from 28.60-56.80% radical scavenging. The SOD assay shows that
methanol extract exhibits the highest activity (74.19% inhibition of
superoxide radical). The
dichloromethane and
ethyl acetate extracts display comparable SOD activity. The promising bioactivities of the crude
ethyl acetate extract guided the first isolation of bioactive
flavonoid and phenolic compounds:
isoliquiritigenin (2),
protocatechualdehyde(3),
butin (4) and
butein (5) from this species. Their structures have been fully established by 1D and 2D NMR. In addition,
stigmasterol was isolated from the crude
hexane and
dichloromethane extracts. The antimicrobial and cytotoxic activities of compounds 3-5 were evaluated. The tested compounds were inactive against HuCCA-1 and KB cell lines,showing ED50> 10 microg/mL.
Protocatechualdehyde (3) completely inhibits the growth of Plesiomonas shigelloides with MIC <or=60 microg/mL. As a result, we propose that Hydnophytum formicarum Jack. can serve as a new source enriched with potent antioxidative and
antimicrobial agents.