Antimicrobial compounds from root, stem bark and seeds of Melia volkensii.

Three compounds, toosendanin (1), kulactone (2) and scopoletin (3), were isolated from either the root bark and/or the stem bark of Melia volkensii. Their structures were determined on the basis of spectroscopic data generated and by comparison with data from the literature. 1 and 2, isolated for the first time from M. volkensii, exhibited significant (p < 0.05) activity against Escherichia coli with minimum inhibitory concentration of 12.5 µg/mL, close to that of neomycin (6.25 µg/mL). The compounds also exhibited high activity against Aspergillus niger (MIC 6.25 µg/mL compared to 2.5 µg/mL for clotrimazole). Dichloromethane and methanol seed, hexane stem bark and methanol root bark extracts exhibited activities towards Escherichia coli, Staphylococcus aureus, Aspergillus niger and Plasmodium falciparum, respectively. Antimicrobial activity of the plant towards A. niger, P. falciparum and S. aureus is reported for the first time in the current work.

Erythrinaline alkaloids from the flowers and pods of Erythrina lysistemon and their DPPH radical scavenging properties.

Fourteen different erythrinaline alkaloids have been isolated from the flowers and pods of Erythrina lysistemon with four being reported for the first time in nature and five for the first time in this species and the rest having been re-isolated. The new compounds are (+)-11beta-hydroxyerysotramidine (1), (+)-11beta-methoxyerysotramidine (2), (+)-11beta-hydroxyerysotrine N-oxide (4) and (+)-11beta-hydroxyerysotrine (8). (+)-11alpha-Hydroxyerysotrine N-oxide (3), earlier misidentified as erythrartine N-oxide (beta-hydroxyerysotrine N-oxide 4), was also re-isolated along with four other alkaloids. Correct identification of compounds 4 and 8 was aided by the fact that the two sets of C-11 epimers 3, 4 and 8, 9 were both isolated in this study thus making it easier to identify and assign the individual epimers. (+)-Erythristemine (14) was found distributed in most of the plant parts investigated. Preliminary work on the crude chloroform/methanol (1:1) showed moderate toxicity to brine shrimp (LC50 23 ppm) and moderate (IC50 86 microg/ml) radical scavenging properties against stable 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical. The DPPH radical scavenging properties of the isolated compounds were assessed using TLC autographic and spectrophotometric assays whereupon only compounds 11 (1 microg; 90 microg/ml) and 12 (0.1 microg; 160 microg/ml) showed any notable activity. It appears the two compounds are slow reacting and do not reach steady state conditions within the standard half an hour time frame but only seemed to have reached steady state conditions after 4 h.

Erythrinaline alkaloids and antimicrobial flavonoids from Erythrina latissima.

The seed pods of Erythrina latissima yielded erysotrine, erysodine, syringaresinol, vanillic acid, a new erythrina alkaloid, (+)-10,11-dioxoerysotrine, which was lethal to brine shrimp and 2-(5'-hydroxy-3'-methoxy phenyl)-6-hydroxy-5-methoxybenzofuran, which showed strong antimicrobial activity against the yeast spores, Gram-positive and Gram-negative bacteria. The root bark gave four known pterocarpans which showed moderate to strong antifungal activity against the yeast spores and three known flavonoids showed antimicrobial activity against all test microorganisms.