Inhibition of Mycobacterium tuberculosis growth by saringosterol from Lessonia nigrescens.

Assay-guided fractionation of an antitubercular extract obtained from Lessonia nigrescens yielded the phytosterol saringosterol as its active component. No appreciable toxicity against Vero cells was observed for this compound. Saringosterol was also synthesized by oxidation of fucosterol. The MIC values for antitubercular activity of saringosterol and its 24S and 24R epimers were determined as 0.25, 1, and 0.125 microg/mL.

Biological and mechanistic activities of xanthorrizol and 4-(1',5'-dimethylhex-4'-enyl)-2-methylphenol isolated from Iostephane heterophylla.

Xanthorrizol (1) and 4-(1',5'-dimethylhex-4'-enyl)-2-methylphenol (2) were identified as the principal antimicrobial components of a CH(2)Cl(2)-MeOH (1:1) extract derived from Iostephane heterophylla. Compound 2 is a new natural product, but has been synthesized. Both compounds exhibited low level activity (MICs of 16-32 microg/mL) against methicillin-resistant staphylococci and vancomycin-resistant enterococci. They were either inactive or poorly active against Gram-negative bacteria and yeast. Mechanistic studies performed in Escherichia coli imp suggested nonspecific inhibition of DNA, RNA, and protein synthesis by both of these compounds. Compound 1 was tested in an in vivo model; it did not provide protection to mice infected with Staphylococcus aureus.

Biological activity of guanacastepene, a novel diterpenoid antibiotic produced by an unidentified fungus CR115.

Fermentation extracts of culture CR115, an unknown plant endophyte originally isolated from Costa Rica, were found to be active against antibiotic-resistant bacteria. The metabolite responsible for activity was identified as a novel diterpenoid antibiotic guanacastepene (mol. wt. 374.47 and mol. formula C22H30O5). Mechanistic studies done in an E. coli imp strain suggested membrane damage as the primary mode of bactericidal action. This compound also lysed human RBCs and caused leakage of intracellular potassium from E. coli imp.

Novel polyketide metabolites from a species of marine fungi.

Fermentation of a marine fungal species obtained from a tissue sample of a marine sponge collected in Indonesia in October 1996, yielded the novel hexaketide compounds iso-cladospolide B (1); seco-patulolide C (2); the 12-membered macrolides, pandangolide 1 (3) and pandangolide 2 (4); and the known terrestrial fungal metabolite, cladospolide B (5).

Antibacterial diterpenoid acids from Azorella compacta.

The two novel diterpenoid acids mulin-12,14-dien-11-on-20-oic acid (1) and mulin-12-ene-11,14-dion-20-oic acid (2) have been isolated from Azorella compacta. Their structures have been elucidated by 1D and 2D NMR methods. In contrast to the closely related known mulinolic acid (3) and its dehydration product (4) these new natural products have been shown to exhibit antimicrobial activity.

Phytochemical, morphological, and biological investigations of propolis from Central Chile.

Propolis from central Chile was investigated for its plant origin by microscopical analysis of pollen grains and leaf fragments found in the sample. The pollen grains that appear with significant higher frequency in the sample corresponded to four native and two introduced species, whereas leaf fragments corresponded to four native species. Seventeen phenolic compounds that belong to the phenylpropane, benzaldehyde, dihydrobenzofuran, or benzopyran classes, were isolated from an organic extract that was found to have a moderate growth inhibitory activity against Mycobacterium avium, M. tuberculosis, and two strains of Staphylococcus aureus. The components responsible for activity were determined.

Marine microorganisms as a source of new natural products.

Over the past decade, marine microorganisms have become recognized as an important and untapped resource for novel bioactive compounds. The oceans cover greater than 70% of the earth's surface and, taking this into account by volume, represent better than 95% of the biosphere. Given this fact, the oceans present themselves as an unexplored area of opportunity for the discovery of pharmacologically active compounds. In this review, data have been presented to illustrate the diversity of microorganisms living in the sea and the plethora of chemical compounds that have been discovered from them. However, it is important to pursue basic research on the marine environment in order to permit the continued isolation of unique microorganisms. There is still limited knowledge of the physiological requirements of most marine microorganisms, and a greater understanding of their conditions for growth will offer new insights into the complex world of marine microbiology. Clearly, a greater investment in the development of marine biotechnology will produce novel compounds that may contribute significantly toward drug development over the next decade.

Isolation, characterization and structure of a new allenic polyine antibiotic produced by fungus LL-07F275.

Antibiotic 07F275 (1), produced by submerged fermentations of fungal culture LL-07F275, was isolated and characterized despite its inherent instability. Its UV spectrum was identical with that of nemotin, a member of the allenic polyacetylene family, but a molecular weight of 218 daltons indicated a new compound. Structure 1 was determined on the basis of spectroscopic evidence, particularly NMR. Since 1 is a thirteen carbon-containing allenic diyne, it is closely related to mycomycin.

Bioxalomycins, new antibiotics produced by the marine Streptomyces sp. LL-31F508: taxonomy and fermentation.

An actinomycete strain designated LL-31F508 was isolated from an intertidal sediment sample collected in Key West, Florida. Culture LL-31F508 was assigned to the Streptomyces genus based on the presence of LL-diaminopimelic acid (DAP) in the cell wall and observations of spiny spores using scanning electron microscopy (SEM). Excellent antimicrobial activity against Staphylococcus and Enterococcus spp. were detected in both the supernatant and cell extract samples from fermentations of culture LL-31F508. Production of antibiotic activity peaked at 48-50 hours and closely paralleled cell growth, during which time glucose was more rapidly assimilated than dextrin. A series of new antibiotics called the bioxalomycins was identified as the antibacterial products from fermentations of this culture. Fermentation conditions for production of bioxalomycin alpha differed substantially from those required for production of a related compound, naphthyridinomycin, by the reference culture Streptomyces lusitanus NRRL 8034.

Martinomycin, a new polyether antibiotic produced by Streptomyces salvialis. I. Taxonomy, fermentation and biological activity.

Actinomycete culture LL-D37187 has been found to produce the new polyether antibiotic martinomycin. Taxonomic studies, including morphological, physiological, and cell wall chemistry analyses, revealed that culture LL-D37187 is a novel streptomycete species, and the proposed name is Streptomyces salvialis. Martinomycin exhibits activity against the Southern Army Worm (Spodoptera eridania) and Gram-positive bacteria.

Pyrroindomycins, novel antibiotics produced by Streptomyces rugosporus LL-42D005. II. Biological activities.

The pyrroindomycins, a complex of novel antibiotics identified in fermentation broths of "Streptomyces rugosporus" LL-42D005, demonstrated excellent in vitro activity against Gram-positive bacteria. The semisynthetic diacetyl derivative of pyrroindomycin B (pyrroindomycin B-Ac2) was bactericidal for exponential-phase cells, but not for stationary-phase cells. This compound also exhibited marginal protection against a lethal Staphylococcus aureus challenge in mice. The poor in vivo activity of this antibiotic complex may be related to binding to blood components, as suggested by elevated MICs observed in blood-containing media. Incorporation of radiolabeled precursors into DNA, RNA, and protein was inhibited in an exponential-phase culture of Bacillus subtilis within ten minutes of exposure to pyrroindomycin B-Ac2. Microscopic examinations of drug-treated cells revealed lysis within the same ten minute period. These data are consistent with an effect of pyrroindomycin B-Ac2 on the integrity of the bacterial membrane.

Pyrroindomycins, novel antibiotics produced by Streptomyces rugosporus sp. LL-42D005. I. Isolation and structure determination.

Pyrroindomycins A and B were isolated from fermentations of culture LL-42D005, a strain of Streptomyces rugosporus. Pyrroindomycins possess potent antimicrobial activities against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci. Their structures have been determined by using 1- and 2-D NMR, mass spectroscopy and chemical degradations. Pyrroindomycins are the first natural products that contain the highly unsaturated pyrroloindole moiety.

Glycothiohexides, novel antibiotics produced by "Sebekia" sp. LL-14E605. I. Taxonomy, fermentation and biological evaluation.

The new glycothiohexide antibiotics, which are related to nosiheptide, were identified in fermentations of an actinomycete belonging to the genus "Sebekia". Strain LL-14E605 was classified as a "Sebekia" based on the presence of both mesodiaminopimelic acid and madurose in the cell wall and the presence of pseudosporangia encasing the spores. Culture LL-14E605 was successfully fermented in 10 to 3,000 liters of a complex medium. Antibiotic activity closely followed cell mass accumulation and usually peaked after 4 to 5 days of incubation. Glycothiohexide alpha demonstrated excellent in vitro activity against Gram-positive bacteria with MICs of 0.03 to 0.06 microgram/ml against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis. However, glycothiohexide alpha failed to protect mice against a lethal challenge with Staphylococcus aureus Smith unless it was administered prior to challenge.

Glycothiohexide alpha, a novel antibiotic produced by "Sebekia" sp., LL-14E605. II. Isolation and physical-chemical characterization.

Glycothiohexide alpha was recovered from the fermentation broth of a "Sebekia" sp. by mixed solvent extraction, selective precipitation and adsorption chromatography on Diaion HP-20. The amount of glycothiohexide alpha present in the crude preparation was enriched by photolysis. Purification of glycothiohexide alpha was accomplished by repetitive countercurrent chromatography.

Mechanistic studies and biological activity of bioxalomycin alpha 2, a novel antibiotic produced by Streptomyces viridodiastaticus subsp. "litoralis" LL-31F508.

The bioxalomycins, a novel complex of broad-spectrum antibiotics, were isolated from fermentations of Streptomyces viridodiastaticus subsp. "litoralis" LL-31F508. Bioxalomycin alpha 2, the major component of this complex, exhibited antibacterial activity. The MICs ranged from < or = 0.002 to 0.008 micrograms/ml for gram-positive organisms and from 0.50 to 4 micrograms/ml for gram-negative organisms. Bioxalomycin alpha 2 was found to be bactericidal and to inhibit bacterial DNA synthesis preferentially. Bioxalomycin alpha 2 protected mice from a lethal challenge with Staphylococcus aureus Smith. The 50% effective dose of bioxalomycin alpha 2 administered orally was 10 times greater than that when the drug was given subcutaneously or intravenously. These data suggest a stability or bioavailability problem when the compound is administered orally.

Mode of action of the cyclic depsipeptide antibiotic LL-AO341 beta 1 and partial characterization of a Staphylococcus aureus mutant resistant to the antibiotic.

The antibacterial activity of the cyclic antibiotic LL-AO341 beta 1 was examined. The antibiotic was a narrow spectrum agent, effective principally against Gram-positive organisms. The intrinsic insusceptibility of Escherichia coli was due to exclusion of the drug by the outer membrane. The antibiotic was bactericidal against Staphylococcus aureus, and cell death was associated with lysis of the bacteria. The antibiotic did not specifically inhibit the synthesis of DNA, RNA, protein, lipid or peptidoglycan since these synthetic activities continued for several minutes after exposure to lethal concentrations of the antibiotic and then all abruptly ceased between about 8 and 15 minutes post antibiotic exposure. These results are consistent with the cytoplasmic membrane being the primary target for LL-AO341 beta 1. Mutants of S. aureus 8325-4 selected on 10- or 20-times the MIC of LL-AO341 beta 1 occurred spontaneously with a frequency of about 3 x 10(-6). A mutant expressing a 160-fold increase in the MIC of LL-AO341 beta 1 was obtained by exposing cultures to progressively increasing concentrations of the antibiotic. This mutant displayed no cross-resistance to other agents apart from telomycin (a structural analogue of LL-AO341 beta 1), apparently did not modify or degrade LL-AO341 beta 1 and had only a slightly longer doubling time than the parent strain.

An assay for the detection of bacterial DNA gyrase inhibitors.

In summary, we have developed a sensitive detection system for inhibitors of bacterial DNA gyrase. The use of B. subtilis as the host organism confers the advantage that it is sensitive to both gyrase subunit A and B inhibitors, whereas E. coli is relatively insensitive to B subunit inhibitors in vivo. Using this assay, we identified a new DNA gyrase inhibitor with a novel structure.