Separation and characterization of phenylamides from Piper kadsura using preparative supercritical fluid chromatography and ultra-high-performance supercritical fluid chromatography-tandem mass spectrometry.

Abstract

A preparative supercritical fluid chromatography method for the separation of Piper kadsura obtained five phenylamide compounds, which had the same structural skeleton, but changed in the number and position of methoxyl substituents. To improve the separation selectivity of these structural analogues, silica, phenyl, and chiral stationary phases were screened. Only through the combination of Chiral C and phenyl columns could the separation of the five phenylamides be solved. The two-step strategy using preparative supercritical fluid chromatography presented good orthogonality that ensured the purity of the phenylamides. Then, an ultra-high-performance supercritical fluid chromatography hyphened tandem mass spectrometry method was developed, and the fragmentation pattern of phenylamides was summarized. It mainly cleaved in the amide bond to produce the fragment ion, which could help to judge the substituent positions. Twenty-eight possible molecular weights of hydroxyl and methoxyl substituted phenylamides were calculated and screened. Nine compounds were extracted in three [M + H]+ ions at m/z 284.13, 314.13, and 344.13, including five purified compounds and the other four positional or trans-cis phenylamide isomers in low content. The methods developed in this research were useful in the separation and characterization of phenylamide analogues.