Alkaloids from the stem barks of Scutia buxifolia Reissek (Rhamnaceae): Structures and antimicrobial evaluation.

A reinvestigation of the chemical constituents of the stem barks of Scutia buxifolia, a member of the Rhamnaceae, resulted, along with the known alkaloids scutianine C and scutianene L, in the isolation of three undescribed diastereoisomeric alkaloids - scutianine N, 27-epi-scutianine N and 3, 4, 7-tri-epi-scutianine N -, one undescribed non macrocyclic alkaloid - scutianine Q - and a neutral compound -scutianene M. Their structures were determined using extensive NMR techniques and HRMS. The absolute configurations of the stereogenic centers of the three diastereoisomeric alkaloids have been assigned by gas chromatography employing modified cyclodextrins as chiral stationary phases. Scutianine Q had its structure and stereochemistry defined by single crystal X-ray crystallographic analysis. All tested compounds showed good to moderate antibacterial activity (MICs between 1.56 and 100 µg mL-1) when evaluated in vitro against a panel of Gram-positive and Gram-negative bacteria. Some stereochemistry-activity relationships have been identified for the antibacterial activity of diastereoisomeric alkaloids against the Gram-negative bacteria Enterobacter aerogenes. The alkaloid 27-epi-scutianine N was as active as the standard antibiotic chloramphenicol (MIC = 1.56 µg mL-1), while scutianine N and 3,4,27-tris-epi-Scutianine N were inactive (>100 µg mL-1).

Antibacterial activity of Discaria americana Gillies ex Hook (Rhamnaceae).

ETHNOPHARMACOLOGY RELEVANCE: Discaria americana Gillies ex Hook (sin. Discaria febrifuga and Discaria longispina) (Rhamnaceae) is a plant native from Rio Grande do Sul (Southern Brazil), Uruguay and Argentine, and has been used in Brazilian traditional medicine as antipyretic agent, and for stomach disorders. In Rio Grande do Sul, Uruguay and Argentine, the roots, in decoction, are used as tonic and febrifuge. Although it is a plant widely used by the population, there are no studies proving this popular use. MATERIAL AND METHODS: The crude neutral methanol extract, and pure isolated alkaloids, were investigated in vitro for antimicrobial activities against four Gram-positive bacteria: Staphylococcus aureus, Bacillus subtillis, Bacillus cereus, Enterococcus faecium; and five Gram-negative bacteria: Escherichia coli, Enterobacter cloacae, Enterobacter aerogenes, Salmonella enterica serovar Typhimurium and Pseudomonas aeruginosa. RESULTS: The crude neutral methanol (CME) extract of the root bark of Discaria americana showed antibacterial activity, ranging from 62.5 to 250 µg mL-1 (MIC), against the tested bacteria. From the fractions obtained from the crude extract, the basic ethereal fraction (BEF) showed to be more effective, with MICs between 31.5 and 125 µg mL-1 against the tested bacteria. The bioassay-guided fractionation of the ethyl ether basic fraction yielded eight cyclopeptide alkaloids: frangufoline (1), frangulanine (2), adouetine Y' (3), discarine A (4) discarine B (5), discarine C (6), discarene C (7) and discarine D (8). When evaluated against the Gram-positive bacteria Enterococcus faecium, discarine B (5) proved to be the most active alkaloid with a MIC/MLC = 0.77/1.55 µg mL-1, near the most active antibacterial agent levofloxacin (MIC/MLC = 0.77/0.77 µg mL-1). Moreover, discarine C (6) was the more active alkaloid against Salmonella enterica serovar Typhimurium, with a MIC/MLC = 3.1/6.2 µg mL-1, the same observed for the antibacterial agent azithromycin. Kinetic measurements of the bacteriolytic activities of discarine B (5) against Enterococcus faecium (Gram-positive), and of discarine C (6) against Salmonella enterica serovar Typhimurium (Gram-negative) were determined by optical density based on real time assay, suggesting that both mode of action are partially bacteriolytic. CONCLUSION: In conclusion, five 14-membered cyclopeptide alkaloids isolated from Discaria americana Gillies ex Hook (Rhamnaceae) showed promising antibacterial activity, making this metabolites a class of scientific interest. The good activity presented by the extract and the alkaloids against the Gram-positive bacteria Enterococcus faecium and against the Gram-negative bacteria Salmonella enterica serovar Typhimurium, Enterobacter. aerogenes and Escherichia coli, corroborate with the popular use of this plant for stomach disorders and as antifebrile.

Root bark of Discaria americana attenuates pain: A pharmacological evidence of interaction with opioidergic system and TRP/ASIC channels.

ETHNOPHARMACOLOGICAL RELEVANCE: Discaria americana (Rhamnaceae) root bark infusion have been used in traditional medicine as antipyretic, tonic, ameliorative of stomach and skin diseases and diabetes. This study was designed to investigate whether the methanolic extract of the root bark of Discaria americana (MEDa) exhibits antinociceptive effects in mice. Furthermore, it was investigated the involvement of the opioidergic system in MEDa mechanism of action as well the interactions with TRP/ASIC channels in its effect. MATERIALS AND METHODS: The antinociceptive effect of intra-gastric gavage (i.g.) of MEDa (0.3-300 mg/kg) was evaluated in mice subjected to acute chemical (acetic-acid, formalin, glutamate, capsaicin, cinnamaldehyde, and acidified saline) or thermal (hot plate) tests of pain. The involvement of opioid system was evaluated in the formalin test. A nonspecific effect of MEDa was observed by measuring locomotor activity and exploratory behavior in open field test. RESULTS: MEDa significantly reduced the number of writhing induced by acetic acid and inhibited the nociception in the two phases of formalin. These effects were inhibited by pretreatment with naloxone. The nociception induced by hot plate and intraplantar injection of glutamate, capsaicin, cinnamaldehyde and acidified saline were significantly inhibited by MEDa. Only the dose of 300 mg/kg altered the locomotor activity. CONCLUSIONS: Our results demonstrated, for the first time, that the methanolic extract of the root bark of Discaria americana presents antinociceptive effect in chemical and thermal stimuli and its analgesic properties can be due activation of the opioidergic system. These results support the use of Discaria americana in traditional medicine and demonstrate that this plant presents a therapeutic potential for the development of phytomedicines with antinociceptive profile.

Cyclopeptide alkaloids: stereochemistry and synthesis of the precursors of discarines C and D and myrianthine A.

The stereochemistry of discarines C (1) and D (2) and myrianthine A (3), three cyclopeptide alkaloids isolated from Discaria febrifuga, was determined by a combination of NMR studies of 1-3, enantioselective gas chromatography, and comparison of NMR data with those of synthetic tripeptides. For the synthesis of peptides, the nonproteinogenic amino acid 3-phenylserine was also obtained in its four diastereoisomeric forms (l and d threo, obtained by recrystallization of the diastereoisomeric tripeptide, and l and d erythro, obtained by a Mitsunobu reaction with the threo-tripeptides). The general synthetic strategy described in this paper allows the tripeptide to be obtained with the free N-terminal extremity protected or dimethylated. This strategy also allows the synthesis of the corresponding peptide with an imidazolidinone ring.