Background: Several species of the genus Erythrina have been used as sedative, antidepressant,
and anticonvulsant. Erythrina crista-galli is native to the Pampa Biome and is widely
used for medicinal purposes. Erythrinan alkaloids exhibit a range of pharmacological properties.
Objective: The aim of this study was to evaluate the basic fractions and the alkaloids isolated from
E. crista-galli bark against a collection of bacteria and fungi for the first time.
Methods: Erythrina crista-galli stem bark was extracted with MeOH under reflux. The crude extract
was dissolved in water, acidified and extracted with diethyl ether. Basification of the aqueous
solution followed by diethyl ether and ethyl acetate extractions gave the basic ether and basic ethyl
acetate fractions. Chromatographic purification of these fractions afforded five known alkaloids:
erytharbine (1), erysotrine (2), erysotramidine (3), erysotrine N-oxide (4) and erythratidine (5)
along with a new alkaloid named here erythratidine N-oxide (6). Alkaloids 1-6 were investigated
against a collection of bacteria and fungi using the broth micro dilution method.
Results: In this work, a new alkaloid was isolated from E. crista-galli. The most significant bacterial
inhibitory effect of alkaloidal fractions was observed against the Gram-negative Pseudomas
aeroginosa (MIC values of 31.25 µg.mL-1). Basic ether fraction displayed good antimicrobial activity
against Shigella sonnei with MIC= 62.5 µg.mL-1. Isolated alkaloids 1-6 showed inhibitory
activity against all bacteria tested (MIC values of 50-100 µg.mL-1). In addition, the crude extract
and alkaloids 1, 2, and 5 also showed good antifungal potential against Candida krusei (MICs between
12.5 and 31.25 µg.mL-1). The previously undescribed alkaloid 6 presented MIC values between
50 and 100 µg.mL-1 against all tested microorganisms.
Conclusion: In general, as with a considerable number of phytochemicals with antimicrobial activity,
alkaloids 1-6 may be considered with potential as antibacterial/antifungal agents. The MIC
values of the extract, alkaloidal fractions and compounds 1-6 indicate that, at least in part, the isolates
were responsible for the antimicrobial activity observed.