Isolation, structural characterization and quantification of impurities in bupivacaine.

Bupivacaine was found to be unstable during the accelerated storage condition(40 â„ƒ and 75% relative humidity), and two degradation impurities with the same protonated molecular ion were observed by high performance liquid chromatography-mass spectrometry (LC-MS). A semipreparative method was used to separate and purify the two impurities, and their structures were elucidated via comprehensive HR-MSMS and NMR spectroscopy analyses. Their stereo structures were characterized through single crystal X-ray diffraction. Meanwhile, an LC-MS method was developed and validated to quantify the two degradation impurities of bupivacaine. Chromatographic separation was performed on a C18 reversed-phase column (4.6 × 150 mm, 5 µm) using an equivalent elution with water and methanol. The limits of quantitation for the two degradation impurities (named RS1 and RS2) were 0.89 and 0.65 ng, respectively, and the average recoveries were in the range of 90∼108% and relative standard deviations were less than 5.0%. The proposed LC-MS method can be used to control the quality of bupivacaine and its formulations. DATA AVAILABILITY: Data will be made available on request.

Structural identification of lysophosphatidylcholines as activating ligands for orphan receptor GPR119.

Lysophosphatidylcholine (LPC) is an essential mediator in human lipid metabolism and is associated with a variety of diseases, but the exact identity of LPC receptors remains controversial. Through extensive biochemical and structural analyses, we have identified the orphan receptor GPR119 as the receptor for LPC. The structure of the GPR119-G-protein complex without any added ligands reveals a density map that fits well with LPC, which is further confirmed by mass spectrometry and functional studies. As LPCs are abundant on the cell membrane, their preoccupancy in the receptor may lead to 'constitutive activity' of GPR119. The structure of GPR119 bound to APD668, a clinical drug candidate for type 2 diabetes, reveals an exceedingly similar binding mode to LPC. Together, these data highlight structural evidence for LPC function in regulating glucose-dependent insulin secretion through direct binding and activation of GPR119, and provide structural templates for drug design targeting GPR119.

Synthesis of A B C-ring subunit of C-nor-D-homo-steroidal alkaloids: towards the total synthesis of cyclopamine.

A practical approach to the synthesis of the A, B and C-ring subunit of cyclopamine has been developed. This synthetic tactic highlights the utility of mandelate acetal-mediated resolution of the fused ring ketone (±)-4 and IBX-mediated oxidation cascades from 12 to 9. The availability of advanced intermediates from enantiomerically pure (+)-4 and 2 could provide efficient access to biologically active and structurally diverse C-nor-D-homo-steroidal alkaloids such as cyclopamine.