Paternò-Büchi reaction-mediated high-selectivity screening of isoprene-containing naturals by LC-HRMS

The selective analysis of isoprene-containing natural products, such as triterpenoid saponins and prenylated flavonoids, remains a major challenge in analytical chemistry due to their substantial structural diversity and poor ionization efficiency, which hampers their detection in complex matrices like herbal extracts. To address this pressing need, we developed an analytical platform that integrates the Paternò-Büchi (PB) reaction with LC-HRMS, employing 4,4'-dichlorobenzophenone as the derivatization agent. High selectivity was achieved through a novel dual-filtering strategy combining a characteristic neutral loss (Δm/z = 276.03) with a distinctive chlorine isotope signature (M+2:M+3 ≈ 9:6). This approach significantly enhanced detection sensitivity for model compounds (up to 3.8-fold) and reduced false-positive signals in complex herbal extracts by up to 79 %. The method was successfully validated using Panax notoginseng and Epimedium extracts, enabling the tentative identification of 42 isoprene-containing natural products, including 29 triterpenoid saponins and 13 flavonoids. In addition, the stereoselectivity of the PB reaction provided structural insight into local steric hindrance, critical for analyzing isomeric saponins, and the platform demonstrated excellent reproducibility, with relative standard deviations (RSDs) below 5.0 %. This study presents a robust and highly selective platform for functional group-specific analysis, offering a powerful new tool for natural product research. By significantly enhancing the accuracy and efficiency of isoprenoid screening, it facilitates the discovery of bioactive compounds and holds promise for broad applications in metabolomics, herbal medicine quality control, and the discovery of novel drug leads from natural sources.