Development and validation of an LC-MS/MS method by one-step precipitation for cinacalcet in human plasma.

A sensitive, convenient, rapid and economic liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to determine cinacalcet concentration in human plasma. A stable isotope cinacalcet (cinacalcet-D3) was selected as internal standard and the analytes were extracted from plasma samples by a one-step precipitation procedure. Chromatography separation was conducted on an Eclipse Plus C18 column by gradient elution with mobile phase of methanol-water-ammonium formate system at a constant flow rate of 0.6 mL/min. Mass spectrometric detection was conducted by multiple reaction monitoring using positive electrospray ionization. Cinacalcet concentrations in human plasma were determined over the concentration range of 0.1-50 ng/mL. The accuracies of lower limit of quantification (LLOQ) and quality control samples were all within the range of 85-115%, and the inter- and intra-batch precisions (CV%) were all within 15%. The average extraction recovery rates were 95.67-102.88%, and the quantification was not interfered by the matrix components. The validated method was successfully applied to determined cinacalcet concentrations in human plasma from secondary hyperparathyroidism patients.

Pierisformotoxins A-D, polyesterified grayanane diterpenoids from Pieris formosa and their cAMP-decreasing activities.

Four highly acylated diterpenoids, designated as pierisformotoxins A-D (1-4, resp.), along with 26 known compounds, were isolated from the flowers of Pieris formosa. Among them, pierisformotoxins A and B (1 and 2, resp.) were new highly acylated grayanane diterpenoids, of which the five-membered ring A has undergone an oxidative cleavage between C(3) and C(4), followed by lactonization, to give rise to a five-membered lactone ring between C(3) and C(5), differing from the previously reported grayanane diterpenoids with a 5/7/6/5 ring system. Results of the cAMP-regulation-activity assay showed that pierisformotoxin C (3) at 10 µM (inhibitory ratio (IR): 10.1%) or 2 µM (9.8%), and pierisformotoxin B (2) at 50 µM (13.9%) significantly decreased the cAMP level in N1E-115 neuroblastoma cells (p<0.05).

Three new highly acylated 3,4-seco-grayanane diterpenoids from the fruits of Pieris formosa.

Phytochemical investigation on the fruits of Pieris formosa resulted in the isolation of three new highly acylated 3,4-seco-grayanane diterpenoids, pierisformotoxins E-G (1-3). Their structures were elucidated on the basis of extensive spectroscopic analysis, including 1D-, 2D-NMR, electrospray ionization-mass spectra (ESI-MS) and high resolution (HR)-MS.