QSAR-guided strategy for accurate annotation of FAHFA regioisomers

Branched fatty acid esters of hydroxy fatty acids (FAHFAs) represent a novel class of bioactive lipids with significant physiological roles. However, their identification, particularly of low-abundance FAHFA regioisomers, remains challenging due to their high structural similarity, low natural abundance, and the limited availability of reliable FAHFA standards. In this study, we present a QSAR-based FAHFA annotation strategy that integrates a QSAR model with an ester bond position (EP) rule to determine the EPs of FAHFA regioisomers. The QSAR model quantitatively relates the retention index (RI) of FAHFAs to the EP descriptor and the GATS2m descriptor, while the EP rule establishes a quantitative relationship between the RI of FAHFA regioisomers and their EP within a given FAHFA family. By applying this QSAR-based strategy, we successfully identified a comprehensive set of 507 FAHFA regioisomers from 1207 FAHFA candidates detected across 16 food samples, achieving nearly a threefold increase in annotation coverage compared to our previous method. Overall, this strategy significantly enhances the identification capability in determining EP for FAHFA regioisomers, providing a promising analytical tool for the further exploration into these lipids.