Liquid chromatography–electrospray time-of-flight mass spectrometry for on-line accurate mass determination and identification of cyclodepsipeptides in a crude extract of the fungus Metarrhizium anisopliae

Electrospray ionisation time-of-flight mass spectrometry (ESI-TOF-MS) has been used for the detection and identification of destruxins (cyclodepsipeptides) in a crude extract of the fungus Metarrhizium anisopliae. HPLC–MS analyses were performed with a post-column addition of erythromycin as a reference compound (lock mass procedure). Seven destruxin derivatives could be identified on-line from their accurate masses (deviation from calculated values <5.5 ppm) through elemental composition calculations. As a highly sensitive and accurate method, ESI-TOF-MS proved to be very powerful for the analysis and dereplication of natural products in complex mixtures.