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

Abstract

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