Mass spectroscopy Antibiotics

A polyurethane was synthesised from 1,6-hexane diisocyanate, polycaprolactone diol and a fluoroquinolone antibiotic, ciprofloxacin and characterised by size exclusion chromatography and elemental analysis. The PU was incubated in a solution of an inflanunatoiy cell-derived enzyme, cholesterol esterase or phosphate buffer for 30 days at 37C and its biodegradability determined by HPLC, mass spectroscopy and Carbon 14 radiolabel release. Analysis of the solution revealed that ciprofloxacin was released and able to inhibit the growth of Pseudomonas aeruginosa. 53 refs. 

Additionally, a variety of analytical equipment and techniques that allow the examination of small- (and micro-) scale microbial cultures and their products have become available. Examples include near infrared and Fourier transform infrared spectroscopy, which offer the ability for in situ detection of specific compounds in fermentation broth [22]. However, sensitivity and the required sample volumes pose serious obstacles that still have to be overcome. Another alternative is offered by sensitive pyrolysis mass spectroscopy, which was demonstrated to be suitable for quantitative analysis of antibiotics in 5-pl aUquots of fermentation broth when combined with multivariate calibration and artificial neural networks [91]. The authors concluded that a throughput of about 12,000 isolates per month could be expected. Furthermore, standard chromatographic methods such as gas chromatography or high-performance liquid chromatography, possibly in combination with mass spectroscopy (MS) for detection, can provide simultaneous quantitative detection of many metabolic products. 

The discovery of Gentamydn and its successful utilisation for the treatment of serious gram-negative infections has contributed in the last years to increasing clinical use and to a rapid development of the chemistry and biochemistry of aminoglycoside antibiotics. Also of importance in the further exploration of this class of compounds are the new chemical and physico-chemical methods, e.g. H- and C-NMR-spectroscopy, mass spectroscopy. X-ray analysis and the different chromatographic methods. Synthetic efforts and studies of the inactivation mechanism have provided a preliminary insight into the relationship between structure and activity. 

Because of the complexity of the polyether antibiotics tittle progress has been made in stmcture determination by the chemical degradation route. X-ray methods were the techniques most successfully applied for the early stmcture elucidations. Monensin, X206, lasalocid, lysocellin, and salinomycin were included in nineteen distinct polyether x-ray analyses reported in 1983 (190). Use of mass spectrometry (191), and H (192) and nmr (141) are also reviewed. More recently, innovative developments in these latter techniques have resulted in increased applications for stmcture determinations. Eor example, heteronuclear multiple bond connectivity (hmbc) and homonuclear Hartmann-Hahn spectroscopy were used to solve the stmcture of portimicin (14) (193). East atom bombardment mass spectrometry was used in solving the stmctures of maduramicin alpha and co-factors (58). 

The antibacterial and cytotoxic bicyclic alkaloid phloeodictine B (473) was isolated from a New Caledonian species of Phloeodictyon and is unusual as it contains a cyclic aminoketal functionality. The structure was proposed on the basis of spectral data [398], A Phloeodictyon sp. from New Caledonia contained the cytotoxic and antibiotic alkaloids, phloeodictines Ci (474) and C2 (475). Their structures were elucidated by mass spectrometry and NMR spectroscopy [399]. 

R. Katahira, Y. Uosaki, H. Ogawa, Y. Yamashita, H. Nakano, and M. Yoshida, UCH9, a new antitumor antibiotic produced by Streptomyces. II. Structure elucidation of UCH9 by mass and NMR spectroscopy, J. Antibiot., 51 (1998) 267-274. 

A resurgence of interest and accomplishment in the field of biosynthe sis of natural products - including antibiotics - has occurred. The powerful methods for determination of a new structure with small amounts of material (mass and nmr spectroscopy, etc.) together with the development of 13C nmr spectroscopy for following the pattern of incorporation of precursors into these structures is one major reason. The subject of biogenesis of antibiotics has not been dealt with specifically in this series and this brief review will include some literature from earlier years than 1976. 

A comprehensive review on the biosynthesis of aminocyclitol antibiotics was published by K. L. Rinehart and R. M. Stroshane Most of the biosynthetic studies have been directed to the largest and most important group, the deoxystreptamine-containing antibiotics. The biosynthesis was followed by C-or C-isotope labelling of subunits and determination of the level of activity in isolated intermediates and in final products by degradation, NMR-spectroscopy and mass spectrometry. 

The structure of the branched-chain amino-disaccharide (106), a component of a novel glycopeptide antibiotic of the vancomycin group, has been elucidated by FAB mass spectrometry and 2D n.m.r. spectroscopy. ... 

Unlike other members of this group, the DNA strand scission by C-1027 occurs without activation by a thiol or nucleophile [207, 208]. The formation of radical intermediates causing DNA cleavage by the antibiotic C-1027 was confirmed by spin trapping. The signals of the spin adducts with 2-methyl-2-nitrosopropane were recorded by ESR spectroscopy. The spin adducts were also detected by mass spectrometry (Scheme 3.1) [208]. It was shown that the antibiotic C-1027 is an equilibrium mixture of forms 3.407 and 3.410, the latter in very low concentrations. The process of hydrogen atom elimination from the DNA and the formation of aromatic structure 3. 411 were found to proceed in two steps first, slowly from atom C and then from atom C in a fast step [208, 209]. These data help us to understand the mechanisms of DNA strand scission by the antibiotic and thus contribute to the development of new anticancer drugs with specific delivery systems [208, 209]. Maduropeptin 3.408 is also able to form diradicals without activation [210]. 

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