Detection by HPLC and structural characterization by NMR and MS of a natural deuterium isotopologue of ulipristal acetate

Optimization and Validation of HPTLC Method for Estimation of Ulipristal Acetate in Presence of Its Forced Degradation Products

Ulipristal acetate (UPA) is used as emergency contraceptive and for uterine fibroids. No validated method has been reported to estimate UPA in presence of its degradation products. Therefore it is mandatory to develop method which can accurately measure it in presence of impurity. A simple and sensitive high-performance thin-layer chromatography (HPTLC) method was developed for the estimation of UPA. Pre-coated silica gel 60F254 TLC plates were as stationary phase and ethyl acetate:toluene:glacial acetic acid (4:7:0.3, v/v/v) was used as mobile phase. Drug was subjected to acid and alkali hydrolysis, oxidation, photo degradation and thermal degradation to study its degradation behavior. UPA eluted with Rf value 0.38 ± 0.02. The method was found to be linear in the concentration range of 400-3,600 ng/band. Limit of detection and limit of quantitation were found to be 72.7786 ng/band and 220.5412 ng/band, respectively. The % recovery of the proposed method was found to be 100.05-100.65%. The proposed method was specific to measure UPA in presence of degradants. The method was found to be accurate, precise, robust and can be useful for routine analysis of formulations containing UPA in presence of its degradation products.

Selective deuteration of [(pyridylmethyl)sulfinyl]benzimidazole antisecretory drugs. A NMR study where DMSO-d6 acts as deuteration agent

The use of deuterated drug bioisosteres to obtain superior pharmacokinetic properties or to investigate biotransformations at the molecular level is a growing field of pharmaceutical research. This work presents a NMR study on the deuteration of three structurally related antisecretory proton-pump inhibitors, the sodium salts of esomeprazole, 1, pantoprazole, 2, and rabeprazole, 3. It has been found that the methylene adjacent to the sulfinyl group displays stereoselective deuteration when the sodium salts of these products are dissolved at room temperature in D₂O or CD₃OD, a process that also occurs very efficiently in DMSO-d₆ (a solvent considered non-deuterating) if a catalytic amount of NaOH is added. The stereoselectivity of the deuteration is consequence of the asymmetry around the sulfur atom of the sulfinyl group, and the rate of the H-D exchange seems to be mainly related to the polarity of the solvents. In addition, unusually long-range (up to seven bonds) NMR deuterium isotopic effects on proton have been detected. Density Functional Theory (DFT) calculations (DFT/6-31G**) have been performed on the rotamers about the CH₂SO bond of 1, as well as about the equivalent bond in its entiol, N-anion, and entiolate. Less conformers than possible were obtained in all cases indicating strong preference for some spatial dispositions. Computed NMR shielding agrees with the experimentally obtained chemical shifts and help in identifying the most accessible diastereotopic hydrogen.