Studies of the Rate Constant of l-DOPA Oxidation and Decarboxylation by HPLC

Abstract

The objective of current investigation was to study the degradation behavior of L-DOPA under different conditions by high performance liquid chromatography (HPLC), and to develop and validate a stability-indicating HPLC method. The developed RP-HPLC method was validated with respect to linearity, accuracy, precision and specificity. Oxidation was found to occur in alkaline and to some extent in thermal conditions, while the drug was stable when incubated at acidic conditions and under photolytic stress. The oxidation of L-DOPA was observed to follow first-order kinetics. The degradation rate constants and half-life were calculated. The cytotoxicity and enzymatic degradation of L-DOPA was examined using the human intestinal epithelial Caco-2 cells. The drug was rapidly decarboxylated by aromatic amino acid decarboxylase to dopamine. The conversion of L-DOPA to dopamine was dose-and time-dependent.

Ternary mutual diffusion coefficients of aqueous {l-dopa (1)+β-CD (2)} solutions at T=298.15K

“…That is, pH 6.3 and 6.8 for solute fraction of L-dopa X 1 = 0 and X 1 = 1, respectively. Under these conditions and from the pK values [19] pK a1 = 2.3, pK a2 = 8.11, pK a3 = 9.92, we can consider that this drug is present mostly in the zwitterionic form. In recent years, the Taylor dispersion method has emerged as a simple and rapid technique for the reliable determination of mutual diffusion coefficients in liquids.…”

Molecularly imprinted cyclodextrin nanosponges for the controlled delivery of L-DOPA: perspectives for the treatment of Parkinson’s disease

“…However, it is an unstable compound; when exposed to light or added to aqueous solution (especially basic solution), it may degrade, compromising its therapeutic properties. Approximately 99 % of orally administered L-DOPA is degraded through peripheral decarboxylation and oxidation [5,6]. The remaining 1 % can reaches the brain unchanged.…”

“…The remaining 1 % can reaches the brain unchanged. To reduce the peripheral conversion of this drug into dopamine, carbidopa and benserazide are usually added to the drug formulation as inhibitors of the decarboxylase activity [1][2][3][4][5][6]. Additionally, it is not possible to reach and maintain a constant L-DOPA plasma concentration via oral administration of conventional immediate-release systems because the concentration fluctuates widely with time [7].…”

An Electrochemical Sensor Based on Electroreduction of Graphene Oxide on a Glassy Carbon Electrode Using Multiple Pulse Amperometry for Simultaneous Determination of L-Dopa and Benserazide

“…It is noteworthy that the methodology of modification of the surface of the GCE is rapid and that the data obtained when compared with those present in the literature [23,[26][27][28][29][30][31][32][33] has performance as good as the sensors described; however, the preparation methodology of some is more laborious than the proposal in this work.…”