Antibacterial activity of indole alkaloids from Aspidosperma ramiflorum
Tanaka, J.C.A.; Silva, C.C. da; Oliveira, A.J.B. de; Nakamura, C.V.; Dias Filho, B.P.
We evaluated the antibacterial activities of the crude methanol extract, fractions (I-V) obtained after acid-base extraction and pure compounds from the stem bark of iAspidosperma ramiflorum/i. The minimum inhibitory concentration (MIC) was determined by the microdilution technique in Mueller-Hinton broth. Inoculates were prepared in this medium from 24-h broth cultures of bacteria (10sup7/sup CFU/mL). Microtiter plates were incubated at 37ºC and the MICs were recorded after 24 h of incubation. Two susceptibility endpoints were recorded for each isolate. The crude methanol extract presented moderate activity against the Gram-positive bacteria iB. subtilis/i (MIC = 250 µg/mL) and iS. aureus/i (MIC = 500 µg/mL), and was inactive against the Gram-negative bacteria iE. coli/i and iP. aeruginosa/i (MIC gt; 1000 µg/mL). Fractions I and II were inactive against standard strains at concentrations of span style=font-family: Symbol;£/span1000 µg/mL and fraction III displayed moderate antibacterial activity against iB. subtilis/i (MIC = 500 µg/mL) and iS. aureus /i(MIC = 250 µg/mL). Fraction IV showed high activity against iB. subtilis/i and iS. aureus /i(MIC = 15.6 µg/mL) and moderate activity against iE. coli/i and iP. aeruginosa/i (MIC = 250 µg/mL)i. /iFraction V presented high activity against iB. subtilis/i (MIC = 15.6 µg/mL) and iS. aureus /i(MIC = 31.3 µg/mL) and was inactive against Gram-negative bacteria (MIC gt; 1000 µg/mL). Fractions III, IV and V were then submitted to bioassay-guided fractionation by silica gel column chromatography, yielding individual purified ramiflorines A and B. Both ramiflorines showed significant activity against iS/i. iaureus/i (MIC = 25 µg/mL) and iE. faecalis/i (MIC = 50 µg/mL), with ECsub50 /subof 8 and 2.5 µg/mL for ramiflorines A and B, respectively, against iS. aureus/i. These results are promising, showing that these compounds are biologically active against Gram-positive bacteria.
Keywords: Aspidosperma ramiflorum; Antibacterial activity; Monoterpenoid indole alkaloids; Ramiflorines A and B.