Analytical and chromatographic studies on aminoglycoside antibiotics.

  • Jonathan Ernest Lacy

Student thesis: Doctoral ThesisPhD


Minor components of the gentamicin series were isolated from commercial samples of gentamicin sulphate. Mass spectrometry and nuclear magnetic resonance (NMR) were applied to elucidate structures. Total identification was not achieved for all components though evidence for novel central sub-units was presented. An unusual site for N-methylation was discovered at the 3-position on gentamicin C2. Reversed phase high performance chromatography (HPLC) with pre-column derivatisation was used to quantitate gentamicin component levels in commercial samples from various sources. A method for the measurement of gentamicin in blood plasma by HPLC was developed. Methods for extraction of gentamicin from plasma constituents were evaluated and a chosen method used to determine levels in over fifty patient samples. These values were compared with those found by microbiological assay and a close relationship was observed. Pharmacokinetic parameters were estimated for the individual gentamicin components Cla and C2). Gentamicin Cla was found to possess a longer plasma half life than the other two components. The fluorometric reaction of ortho-phthalaldehyde (OPA) with the gentamicin components was studied using 1H and 13C NMR. The reactive intermediate was shown to be as dihydro- isobenzofuran and a reaction pathway proposed. The OPA reagent was found to react with all the primary amino functions on the gentamicin components. Ninhydrin was used to confirm this result. The retention characteristics of the gentamicin-OPA derivatives in the HPLC system used were investigated and an explanation of the factors governing the observed behaviour, proposed. Differences in the order of elution of the components, reported in the literature, were also explained.
Date of Award1984
Original languageEnglish
Awarding Institution
  • University of Bath

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