New Polyhydroxylated Steroidal Saponins from Solanum paniculatum L. Leaf Alcohol Tincture with Antibacterial Activity against Oral Pathogens

Solanum paniculatum L. is widely used in Brazilian folk medicine for the treatment of liver and gastrointestinal disorders as well as for culinary purposes and beverage production. Fractionation of hydroalcoholic [ethanol (EtOH) 70%] tincture from S. paniculatum leaves led to the isolation of six new spirostanic saponins which included 6-O-α-l-rhamnopyranosyl-(1″→3′)-β-d-quinovopyranosyl-(22S,23R,25S)-3β,6α,23-trihydroxy-5α-spirostane (1), 6-O-β-d-xylopyranosyl-(1″→3′)-β-d-quinovopyranosyl-(22S,23R,25R)-3β,6α,23-trihydroxy-5α-spirostane (4), 3-O-α-l-rhamnopyranosyl-(1″→3′)-β-d-quinovopyranosyl-(22S,23S,25R)-3β,6α,23-trihydroxy-5α-spirostane (5), 3-O-β-d-xylopyranosyl-(1″→3′)-β-d-quinovopyranosyl-(22S,23S,25R)-3β,6α,23-trihydroxy-5α-spirostane (6), 6-O-α-l-rhamnopyranosyl-(1″→3′)-β-d-quinovopyranosyl-(22S,25S)-1β,3β,6α-trihydroxy-5α-spirostane (7), and 6-O-β-d-xylopyranosyl-(1″→3′)-β-d-quinovopyranosyl-(22S,25S)-3β,4β,6α-trihydroxy-5α-spirostane (8) together with two known spirostanic saponins (2, 3). The structures of these compounds were determined by one-dimensional (1D) and two-dimensional (2D) NMR experiments in addition to high-resolution electrospray ionization mass spectrometry (HRESIMS) analyses. The 70% alcohol tincture, used as phytomedicine, exhibited promising activities against oral pathogens, including, Steptococcus sanguinis, St. oralis, St. mutans, St. mitis, and Lactobacillus casei with minimal inhibitory concentration (MIC) values ranging from 6.25 to 50 μg/mL. The saponin fraction, nonetheless, showed lower activity against all the strains tested (from 100 to >400 μg/mL).