Isolation and Quantification of Alternariols from Endophytic Fungus, Alternaria alternata: LC‐ESI‐MS/MS Analysis

An endophytic fungus, Alternaria alternata was isolated from Grewia asiatica. Upscaling of the fermentation broth led to the isolation of a new structural isomer of alternariol (3), along with alternariol (1) and alternariol 9‐methyl ether (2). Additionally, an LC‐ESI‐MS/MS method was developed for the simultaneous detection and quantification of 1–3 through multiple reaction monitoring (MRM). The limit of quantification (LOQ) and detection (LOD) were fewer than 5.0, 2.0, 0.3 and 1.5, 0.7, 0.1 μg/ml, respectively for 1–3. Furthermore, 1 and 3 showed significant activity against gram‐positive bacteria, Staphylococcus aureus and 1 displayed MIC comparable to that of ciprofloxacin against VRE and MRSA. A novel alternaiol analogue (3) along with alternariol (1) and alternariol 9‐methyl ether (2) were isolated from Alternaria alternata, an endophytic fungus from Grewia asiatica. Moreover, a robust LC‐ESI‐MS/MS method was developed for simultaneous detection and quantification of 1–3 through multiple reaction monitoring (MRM). The limit of quantification (LOQ) and detection (LOD) were fewer than 5.0, 2.0, 0.3 and 1.5, 0.7, 0.1 μg/ml, respectively for 1–3. Furthermore, 1 showed activity comparable to that of ciprofloxacin against MRSA i. e., 8 μg/ml.