Quest for antibacterial alkaloids from Rauhia multiflora through bioassay complementary-guided fractionation

The clinical efficacy of many existing antibiotics is currently threatened by the emergence of microbial resistance. This recognized worldwide situation prompts to greater efforts to discover antimicrobial agents of natural origin, including plant sources. The objective of this work was to evaluate the antimicrobial activities of extracts, fractions and pure compounds from Rauhia multiflora using a bioguided complementary fractionation, contributing also to explain some traditional uses of this genus. Some subfractions showed antimicrobial activity against the Gram-negative and Gram-positive bacteria. Galantamine was identified and isolated as the main alkaloid, together with two additional structures of the same skeleton. Characterization by GC-MS revealed the presence of twelve galantamine-type and four crinane-type compounds. The tentative structure of one of the galantamine-type skeletons is proposed here for the first time. Altogether, these results support the use of Rauhia genus to inhibit bacterial growth.