The metabolism of [14C]ceftiofur following intramuscular (im) administration to cattle and oral dosing in rats produced a single metabolite, desfuroylceftiofur, which was observed in the plasma of both species. Desfuroylceftiofur existed free in the plasma of cattle but was covalently bound to plasma proteins in rats. Urinary metabolites from both species appear qualitatively similar but quantitatively different depending on the dose, route of administration, and the time interval posttreatment. Most of the urinary metabolites in rats and cattle are derivatives of desfuroylceftiofur and are probably artifacts due to the ease of its oxidation in base, lactonization in acids, and hydrolysis of lactones. An interesting metabolite ceftiofur sulfoxide cysteine is the major metabolite in the urine of rats dosed orally at or above 100 mg/kg. However, it was not present at oral doses of 7-15 mg/kg nor after im treatment of cattle and rats.Ceftiofur (I-B, Table I) is very effective in control of Gram-positive and Gram-negative bacterial pathogens of veterinary importance both in vivo and in vitro (Yancey et al, 1986). Its sodium salt, NAXCEL, has recently been

Quantities of material required for structural analysis were reduced substantially following the introduction of 3 mm microinverse and microdual NMR probes in 1992. We now report the first very low-level results obtainable with a new 1.7 mm submicro-inverse-detection gradient or SMIDG NMR probe. Using this technology at 600 MHz, it was possible to fully characterize an 8% impurity contained in a 0. 55 &mgr;mol sample of cryptolepine (1) that had been standing in excess of 2 years since its initial isolation. The impurity was unequivocally identified as cryptolepinone (2) through the concerted interpretation of GHSQC, GHMBC, homonuclear TOCSY, and ROESY spectra in conjunction with APCI LC/MS and CID data acquired from a portion of the serial dilution solution used to prepare the NMR sample. Submicro-inverse-detection gradient probes offer the prospect of reducing still further the quantities of sample required for full characterization under favorable circumstances, making rare and potentially novel natural products amenable to structural determination. SMIDG NMR technology is equally applicable to a range of small samples requiring characterization such as isolated impurities from drug substances, isolates from drug degradation studies, and secondary metabolites.

No abstract

No abstract