Hydrolysis and epimerization kinetics of hetacillin in aqueous solution

Area of Science:

• Pharmaceutical Chemistry
• Organic Chemistry
• Chemical Kinetics

Background:

• Hetacillin is a prodrug that degrades into ampicillin.
• Understanding degradation pathways is crucial for drug stability and efficacy.
• Alkaline conditions can significantly impact the stability of beta-lactam antibiotics.

Purpose of the Study:

• To develop methods for quantifying epimerization and hydrolysis of hetacillin.
• To determine the degradation rates of hetacillin in deuterium oxide and water.
• To elucidate the kinetics and mechanism of hetacillin's alkaline degradation.

Main Methods:

• Quantitation of epimerization to epihetacillin and hydrolysis to ampicillin.
• Kinetic studies in deuterium oxide (D2O) at 35°C and water (H2O) at various temperatures.
• Analysis of degradation rate dependence on pH/pD and determination of activation energy.

Main Results:

• Developed methods for quantifying hetacillin epimerization and hydrolysis.
• Established first-order dependence of epimerization on hydroxide/deuteroxide ion concentration.
• Determined activation energy for epimerization as 21.2 kcal/mole, indicating epimerization is the major degradation pathway at high pH.

Conclusions:

• Epimerization to epihetacillin is the predominant alkaline degradation pathway for hetacillin.
• The beta-lactam ring of hetacillin exhibits significant resistance to hydroxide ion attack.
• Degradation kinetics are influenced by solvent (H2O vs. D2O) and temperature.