Targeted Isolation of New Lignans from Justicia aequilabris Based on Molecular Networks

Justicia aequilabris (Nees) Lindau is a native semiarid species commonly found in Caatinga, its chemical and pharmacological properties have not been evaluated in the light of scientific research. Thus, this study aims to identify and isolate J. aequilabris metabolites based on molecular networks. A voucher was deposited at Manuel de Arruda Câmara Herbarium (HACAM-1252), and then registered in SisGen under the number: A35A42B. The crude ethanolic extract of the aerial parts was produced and subsequently partitioning. The ethyl acetate phase (FAcOEt) was analyzed by LC-MS/MS and the data were submitted to online platform Global Natural Product Social Molecular Networking (GNPS; https://gnps.ucsd.edu). Annotation for the FAcOEt MS/MS spectral network indicated the presence of phenolic acids, lignans and flavonoids. From molecular network analysis, a cluster of potentially new Secoisolariciresinol-derived substances were observed. After that, these molecules were prioritized for isolation by LC/MS monitoring the fractions obtained from FAcOEt purification. After structural characterization by spectroscopic and spectrometric analyzes, aequilabrin A, B and C (1-3) were identified (figure 1), new lignans of J. aequilabris. This work demonstrated the effectiveness of molecular networks to isolate new compounds and also the importance of this approach for the dereplication of J. aequilabris constituents.