Donald B. Borders

Structure determination of LL-F28249α, β, γ, and λ, potent antiparasitic macrolides from Streptomyces cyaneogriseus ssp. noncyanogenus

The structures of four antiparasitic macrocyclic lactones, LL-F28249α, λ, β, and γ(1)–(4) derived from the actinomycete Streptomyces cyaneogriseus ssp. noncyanogenus, were determined by spectroscopic methods and by X-ray crystallography of the γ-component (4).

Biosynthesis of ravidomycin. Use of 13C-13C double quantum NMR to follow precursor incorporation

A biosynthetic scheme is proposed for the ravidomycin aglycone. Incorporation of 13C-labeled precursors was followed by conventional and 2-dimensional NMR techniques.

Reactions of the trisulfide moiety in calicheamicin

Abstract Calicheamicin γ1I ( 1 ) reacts with Ph3P to form a dimeric trisulfide ( 3 ), MeSSMe, Ph3PS, and Ph3PO, as well as an aromatic degradation product ( 2 ). The oxygen of the Ph3PO is derived from O2. Calicheamicin also reacts with thiols to produce disulfides (eg. 4 ) with high selectivity. Dimeric trisulfide 3 is generated during this reaction.

Structures of LL-AC541 and LL-AB664 : New streptothricin-type antibiotics

Abstract Structures for LL-AC541, LL-AB664, and two other related antibiotics are proposed. These compounds appear to be the first reported streptothricin-type antibiotics which do not contain β-lysine.

Structure determination of simaomicins α and β, extremely potent, novel anticoccidal agents produced by Actinomadura

The structure of simaomicins α(1) and β(2), novel polycyclic xanthone-type antibiotics produced by Actinomadura madura subspecies simaoensis, were determined by X-ray crystallography and spectroscopic methods.

Direct biochemical nitration in the biosynthesis of dioxapyrrolomycin. A unique mechanism for the introduction of nitro groups in microbial products

The nitro group of dioxapyrrolomycin (1) was shown to be introduced via direct biochemical nitration in cultures of the producing organism Streptomyces fumanus containing K15N18O3 as the sole source of nitrogen; the nitro group of dioxapyrrolomycin produced under these conditions contained the same ratio of 18O to 15N as was present in the labelled nitrate precursor, the extent of 18O enrichment of the nitro group being determined by negative electron impact mass spectrometry and 15N n.m.r. spectroscopy.

Strevertenes, antifungal pentaene macrolides produced by Streptoverticillcum LL-30F848

Abstract This report describes new polyenes isolated from fermentations with Streptoverticillium sp. LL-30F848. Structure elucidation using a variety of spectroscopic techniques, including extensive NMR studies, revealed that these pentaene macrolides lacked the otherwise common hemiketal-tetrahydropyran and aminoglycoside moieties, but still carried a carboxylic acid group. The unambiguous assignment of NMR signals attributed to the olefinic region of the pentaenes was possible for the first time, and the relative stereochemistry of the macrolide was established according to ROESY correlations. Strevertene A is the principal pentaene of the antibiotic polyene complex produced.

Biosynthetic origins of the polycyclic xanthone antibiotic, citreamicin

The biosynthesis of citreamicin 1 has been studied by feeding 13C- and 18O-labelled precursors to Micromonospora citrea cultures. 13C-NMR spectroscopic analysis of the enriched products demonstrated a labelling pattern indicating that the antibiotic is derived from a polyketide which undergoes rearrangement by a mechanism unique for xanthone biosynthesis.

Process-scale reversed-phase high-performance liquid chromatography purification of LL-E19020α, a growth promoting antibiotic produced by Streptomyces lydicus ssp. Tanzanius

LL-E19020 alpha is a novel antibiotic produced by fermentation of the soil microorganism Streptomyces lydicus ssp. tanzanius. The compound is highly effective in inducing increases in weight gain and feed conversion efficiency in livestock. In order to obtain kilogram quantities of the material for field trials, pilot plant scale fermentations (up to 7500 l) were carried out. The antibiotic was recovered from the fermentation broth by solvent extraction. The resultant crude extract was subjected to reversed-phase (C18) chromatography on a process-scale high-performance liquid chromatography (HPLC) unit. The heart of the instrumentation is the Millipore Kiloprep chromatograph with the standard 12-l cartridge column. The laboratory housing the chromatograph has been specifically designed for this work. Tanks for mobile phase preparation are mounted on load cells for precise measurement of components. In this explosion-proof laboratory, all solvent handling areas are well ventilated and a separate breathing air system is provided for the operators. For the purification of the LL-E19020 antibiotics, the mobile phase consisted of a gradient of acetonitrile in 0.1 M ammonium acetate at pH 4.5. The effluent was monitored by UV absorbance at 325 nm. Fractions were collected across the peaks of interest and these were analyzed by analytical HPLC. The maximum yield of LL-E19020 alpha obtained in a single run was approximately 100 g. The antibiotic was recovered from the mobile phase by extraction with methylene chloride. The methylene chloride phase was concentrated under reduced pressure to yield a gummy residue which was finally freeze-dried from tertiary butanol to yield an off-white solid suitable for blending with various feed components.