A glycosylated β-Sitosterol, isolated from Tacinga inamoena (Cactaceae), enhances the antibacterial activity of conventional antibiotics.

• Five new compounds of T. inamoena were isolated. • Were isolated one phytosteroid and four amides derived from hydroxycinnamic acid. • Fractions derived from the plant extract showed antibacterial activity;. • The products from this species reduced the MIC of conventional antibiotics. Tacinga inamoena is a cactus na''tive to the Northeast region of Brazil, used in popular medicine to treat disorders of the urethra as well as asthma and inflammation. Of the roots from T. inamoena , five previously unreleased compounds in the genus, β-sitosterol-3- O - d -glucopyranoside, N -trans-feruloyl-4- O -methyldopamine, N -cis-feruloyl-4- O -methyldopamine, N-trans-feruloyl tyramine and N -cis-feruloyl tyramine were isolated and their structures were elucidated by spectroscopic analysis (IR, MS and NMR). The antimicrobial activities of the partitioned phases were evaluated against bacterial and fungal strains, with promising results, especially of the ethyl acetate phase against Staphylococcus aureus ATCC 25,923. Furthermore, in the modulation tests between the phases and β-sitosterol-3- O - d -glucopyranoside with aminoglycosides, cephalosporins and quinolones, against the strains of E. coli 5A and Pseudomonas aeruginosa , there was a substantial increase of the activity of these antibiotics, with a significant decrease of MICs. The products from T. inamoena showed low toxicity in human erythrocytes. The present study presented relevant compounds and important antibacterial activities and suggests that the glycosylated β-sitosterol can be used to modulate the activity of antibiotics. [ABSTRACT FROM AUTHOR]

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