Biosynthesis of marcfortine A

This report describes the results of a biosynthesis study of marcfortine A (MA). We report here that MA is derived from methionine, tryptophan, lysine and two isoprene units, the latter two being derived from acetic acid. From the 13C enrichment pattern of the pipecolic acid moeity we further conclude that this unit is derived from lysine via alpha-ketoglutarate. Therefore, we have accounted for the biogenesis of every carbon atom of MA and established the biosynthetic pathway for the pipecolic acid moiety of MA.

Development of a mechanism of action-based screen for anthelmintic microbial metabolites with avermectinlike activity and isolation of milbemycin-producing Streptomyces strains

A high-volume screen for anthelmintic microbial metabolites with an avermectinlike mode of action was developed. The primary screen used the free-living nematode Caenorhabditis elegans in a whole-organism assay. The specificity for avermectinlike compounds resides in the secondary screen, which takes advantage of the chloride channel-opening properties of the avermectins. By using standard microelectrode techniques, membrane conductance changes following exposure to extracts of microbial cultures were measured in the walking leg stretcher muscle fibers of the lined shore crab Pachygrapsus crassipes. The avermectins and related milbemycins give a characteristic response of rapid loss of membrane resistance coupled with a slight hyperpolarization of the membrane. This is partially (near 50%) reversible with the chloride channel blocker picrotoxinin. Four morphologically similar cultures that produced avermectinlike activities were identified by this screen. Isolation of the active components from one of these cultures (strain UC 8984) followed by nuclear magnetic resonance spectroscopy resulted in the identification of milbemycins alpha 1 and alpha 3. These metabolites are members of a large family of milbemycins produced by Streptomyces hygroscopicus subsp. aureolacrimosus NRRL 5739. Systematic studies revealed that strain UC 8984 is also a S. hygroscopicus strain, but which is taxonomically distinct from NRRL 5739.

Effects of dihydroavermectin B1a and analogs on stretcher muscle of the lined shore crab, Pachygrapsus crassipes

1. Dihydroavermectin B1a (DHAVM, Ivermectin) at 1 microM reduces excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs, respectively) in stretcher muscle fibres of the lined shore crab, Pachygrapsus crassipes. IPSPs decline faster and more extensively than EPSPs and, unlike EPSPs, do not recover upon replacement of DHAVM with picrotoxinin-containing medium. 2. Intracellular recordings show DHAVM reduces membrane resistance (Rin) and hyperpolarizes muscle fibres in a concentration-dependent manner, beginning at 10 nM. The rate and magnitude of DHAVM effects on Rin mirror its effects on EPSPs. 3. The decline in Rin due to DHAVM is sustained over time (i.e. there is no tendency for desensitization); it is also irreversible and not affected by coadministration of 1 mM gamma-aminobutyric acid (GABA), 0.1 mM bicuculline methiodide or addition of 20 mM Co2+ to the recording medium. 4. Replacement of DHAVM-containing medium with medium containing Cl- channel blockers (picrotoxinin or lindane) results in partial recovery of Rin, while channel blockers specific for other ions (TTX, TEA, 4-AP or verapamil) are without effect. The decline of Rin following application of DHAVM is attenuated in Cl(-)-free medium. 5. Results of tests using compounds structurally related to DHAVM reveal that relatively minor changes in the molecule often reduce biological activity significantly. Removal of one sugar, for instance, results in a ten-fold reduction in potency. 6. In general, avermectins that stimulate conductance in shore crab muscle also possess anthelmintic activity at similar concentrations, based on studies using the free-living nematode, Caenorhabditis elegans.(ABSTRACT TRUNCATED AT 250 WORDS)

The isolation and characterization of rubradirin B

Rubradirin B, C40H33N3O15, was separated from other components of the rubradirin complex by chromatographic and crystallization procedures. The spectrum of antibacterial activity is similar to that of rubradirin, but the antibiotic is less active.

Antibiotics produced by Streptomyces ficellus. I. Ficellomycin

Ficellomycin is a new basic antibiotic produced by Streptomyces ficellus. Ficellomycin, C13H24N6O3, inhibits the growth of gram-positive bacteria in vitro and is effective in the treatment of experimental Staphylococcus aureus infections in mice.