Antimalarial constituents from a high-throughput UPLC-MS-ELSD-PDA generated natural product library

In this investigation, we report the identification of antimalarial constituents from Berberis thunbergii and Eugenia rigida by analyzing QC data of active fractions generated by an automated high- throughput system (HTS), using UPLC-MS-ELSD-PDA. Using the active fractions as a reference standard, bioassay-guided isolation was conducted and structures of the isolated actives were elucidated in order to prove the validity of HTS fractionation methodology. The protoberberine alkaloid berberine (1) has shown to be the active constituent against P. falciparum 3D7 and K1 strains (EC₅₀ 0.46 and 0.44µM) in B. thunbergii. In addition, seven known alkaloids (2-8) were also identified rapidly from HTS fractions. Furthermore, two triterpenoids, namely α-betulinic acid (11) and β-betulinic acid (13), were identified as antimalarial active constituents from HTS hits of E. rigida. In order to prove the concept of HTS methodology, compounds 1, and 11 and 13 were confirmed by scale-up extraction and isolation from B. thunbergii and E. rigida, respectively. These results have demonstrated that the natural product library of active HTS fractions consisting fewer numbers of small molecules analyzed by QC data is a valuable tool for drug discovery, which facilitates the identification of lead compounds.

[This work was supported by the USDA-ARS SCA No. 58 – 6408 – 1-603.]