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A methanol extract of the peels of Citrus sudachi gave five new compounds (1-5) and 27 known compounds. The structures were elucidated on the basis of spectroscopic evidence. Several of these compounds were assayed for antimicrobial activity against methicillin-resistant Staphylococcus aureus and Helicobacter pylori, and sudachitin (6) and 3'-demethoxysudachitin (7) were the most active.

Six new sesquiterpenes, (Z)-2beta-hydroxy-14-hydro-beta-santalol (1), (Z)-2alpha-hydroxy-albumol (2), 2R-(Z)-campherene-2,13-diol (3), (Z)-campherene-2beta,13-diol (4), (Z)-7-hydroxynuciferol (5), and (Z)-1beta-hydroxy-2-hydrolanceol (6), together with five known compounds, (Z)-alpha-santalol (7), (Z)-beta-santalol (8), (Z)-lanceol (9), alpha-santaldiol (10), and beta-santaldiol (11), were isolated from Santalum album, by using bioassay-guided fractionation for Helicobacter pylori. The structures were determined by extensive NMR studies. The absolute configuration of compound 3 was determined by a modified Mosher method. The crude extracts as well as the isolated compounds showed antibacterial activity against H. pylori. Especially, compounds 7 and 8 have strong anti-H. pylori activities against a clarithromycin-resistant strain (TS281) as well as other strains.

We found that ethyl gallate purified from a dried pod of tara (Caesalpinia spinosa) intensified beta-lactam susceptibility in methicillin-resistant and methicillin-sensitive strains of Staphylococcus aureus (MRSA and MSSA strains, respectively). This compound and several known alkyl gallates were tested with MRSA and MSSA strains to gain new insights into their structural functions in relation to antimicrobial and beta-lactam susceptibility-intensifying activities. The maximum activity of alkyl gallates against MRSA and MSSA strains occurred at 1-nonyl and 1-decyl gallate, with an MIC at which 90% of the isolates tested were inhibited of 15.6 microg/ml. At concentrations lower than the MIC, alkyl gallates synergistically elevated the susceptibility of MRSA and MSSA strains to beta-lactam antibiotics. Such a synergistic activity of the alkyl gallates appears to be specific for beta-lactam antibiotics, because no significant changes were observed in the MICs of other classes of antibiotics examined in this study. The length of the alkyl chain was also associated with the modifying activity of the alkyl gallates, and the optimum length was C5 to C6. The present work clearly demonstrates that the length of the alkyl chain has a key role in the elevation of susceptibility to beta-lactam antibiotics.

Two new stilbene derivatives, (E)-resveratrol 3-(6' '-galloyl)-O-beta-D-glucopyranoside (1) and (E)-resveratrol 3-(4' '-acetyl)-O-beta-D-xylopyranoside (2), and five known stilbene derivatives (3-7) were isolated from the dried aerial parts of Calligonum leucocladum. Their structures were established on the basis of spectroscopic evidence. Compound 1 showed antioxidant activity and a restorative effect of the inhibition of oxacillin to oxacillin/methicillin-resistant Staphylococcus aureus.

Nine new polyprenylated benzoylphloroglucinol derivatives, hyperibones A-I (1-9), were isolated from the aerial parts of the Uzbekistan medicinal plant Hypericum scabrum. Their structures were determined mainly on the basis of spectroscopic evidence (2D NMR and HRMS). Compounds 1, 2, and 4 showed mild in vitro antibacterial activity against methicillin-resistance Staphylococus aureus (MRSA) and methicillin-sensitive Staphylococus aureus (MSSA).

A careful investigation of the subterranean part of Vitex rotundifolia has shown that this plant contains five novel lignans having a 1-phenylnaphthalene-type skeleton together with four known lignans. These structures were elucidated on the basis of spectroscopic data. Furthermore, some of the isolated compounds showed antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA).

This study was conducted to find constituents of an annual herb, Xanthium sibiricum Patr er Widd, with effective antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). By monitoring antibacterial activity against MRSA strains, it was shown that a sesquiterpene lactone, identified as [3aR-(3a alpha, 7 beta,8a beta)]-3,3a,4,7,8,8a-hexahydro-7- methyl-3-methylene-6-(3-oxo-1-butenyl)-2H-cyclohepta[b]furan-2-one, or xanthatin, isolated from leaves of the herb, had outstandingly potent activity against S. aureus species, including MRSA; its activity against MRSA and MSSA strains was similar. Other bacteria, e.g. Staphylococcus epidermidis, Klebsiella pneumoniae, Bacillus cereus, Pseudomonas aeruginosa and Salmonella typhi, were also susceptible at the concentrations tested but the compound had no inhibitory effect on some other bacteria, including Escherichia coli. The results show that xanthatin has outstandingly potent activity against strains of S. aureus but that the activity of the compound is highly species-specific.

Examination of the EtOH extract of the fruiting bodies of Terminalia chebula RETZ. led to the isolation of two potent antimicrobial substances against even methicillin-resistant strains of Staphylococcus aureus. On the basis of spectroscopic evidence, the two isolates have been identified as gallic acid and its ethyl ester.