LC-MS- and 1H NMR Spectroscopy-Guided Identification of Antifungal Diterpenoids from Sagittaria latifolia

Antifungal screening of small-molecule natural product libraries showed that a column fraction (CF) derived from the plant extract of Sagittaria latifolia was active against the fungal pathogen Cryptococcus neoformans. Dereplication analysis by liquid chromatography mass spectrometry (LC-MS) and proton nuclear magnetic resonance spectroscopy (H-1 NMR) indicated the presence of new compounds in this CF. Subsequent fractionation of the plant extract resulted in the identification of two new isopimaradiene-type diterpenoids, 1 and 2. The structures of 1 and 2 were determined by chemical methods and spectroscopic analysis as isopimara-7,15-dien-19-ol 19-O-alpha-L-arabinofuranoside and isopimara-7,15-dien-19-ol 19-O-alpha-L-(5'-acetoxy)-arabinofuranoside, respectively. Compound 1 exhibited IC50 values of 3.7 and 1.8 mu g/mL, respectively, against C. neoformans and C. gattii. Its aglycone, isopimara-7,15-dien-19-ol (3), resulting from acid hydrolysis of 1, was also active against the two fungal pathogens, with IC50 values of 9.2 and 6.8 mu g/mL, respectively. This study demonstrates that utilization of the combined LC-MS and H-1 NMR analytical tools is an improved chemical screening approach for hit prioritization in natural product drug discovery.