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Epimerization kinetics of moxalactam in frozen solution
N Hashimoto1, T Ichihashi, E Yamamoto
1Shionogi Research Laboratories, Shionogi & Co., Ltd., Osaka, Japan.
Pharmaceutical Research
|May 1, 1988
Summary
The epimerization rate of moxalactam (LMOX) slows in frozen solutions as temperature drops. Equilibrium ratios shift with temperature due to differing activation energies between R- and S-epimers.
Area of Science:
- Pharmaceutical Chemistry
- Physical Chemistry
- Chemical Kinetics
Background:
- Moxalactam (LMOX) is a beta-lactam antibiotic.
- Understanding epimerization kinetics is crucial for drug stability and formulation.
- Frozen aqueous solutions present unique environments for chemical reactions.
Purpose of the Study:
- To investigate the epimerization rate constants of R- and S-epimers of moxalactam in frozen aqueous solutions.
- To determine the effect of temperature on these epimerization rates and equilibrium.
- To elucidate the factors influencing the equilibrium ratio of epimers at different temperatures.
Main Methods:
- Preparation of frozen aqueous solutions of moxalactam.
- Monitoring epimerization rates at various sub-zero temperatures.
- Analysis of the unfrozen solvent region within the frozen matrix.
- Determination of collapse temperature for moxalactam aqueous solutions.
Main Results:
- Epimerization rate constants for both R- and S-moxalactam decreased with decreasing temperature.
- The reaction occurred in the unfrozen liquid phase and was unaffected by ice formation.
- The reaction ceased completely below the collapse temperature of the moxalactam solution.
- The equilibrium ratio of R- to S-epimers increased as temperature decreased.
Conclusions:
- Temperature significantly influences moxalactam epimerization kinetics in frozen solutions.
- The observed shift in equilibrium ratio is attributed to differences in activation energy between the two epimers.
- These findings have implications for the storage and formulation of moxalactam.
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