Electron impact mass spectra of synthetically modified milbemycins

Abstract

The potent endectocide 23-(O-methyloximino)-F28249a and related compounds were identified and characterized by mass spectrometry. The fragmentation pathway of 23-(O-methyloximino)-F28249a was identified by its highresolution mass spectrum and the electron impact unit mass spectra of its homologs. This fragmentation pathway is presented and discussed.

Mass spectrometry of Avermectins: structural determination of two new derivatives of Ivermectin B 1a

“…The EI data agreed with the published fragmentation pathways 2,. 9 The DCI data was also in agreement with the literature 10. Under EI conditions low intensity signals were often observed for both the molecular ion and for the fragment ion corresponding to loss of water.…”

“…The behaviour of the McLafferty rearrangement that involves C(1) and C(19) is quite interesting. While Jones et al 9 proposed for the EI fragmentation process that the H‐atom is transferred from C(20), we observed for the ESI‐MS/MS process that the transfer occurs also from C(18), as shown in Scheme . This means that, after McLafferty rearrangement, the double bond can be formed in two different positions, in C(19)‐C(20) or in C(18)‐C(19).…”

Moxidectin: Characterization of Cattle, Sheep, and Rat in vitro and in vivo Metabolites by Liquid Chromatography/Tandem Mass Spectrometry

“…As shown in Figure 5, the daughter ion spectrum of moxidectin is rich in structural information ¿lowing the sites of hydroxylation to be localized to different regions of the parent. The fragmentations observed in the daughter ion spectrum of moxidectin also correlate well with those present in its electron impact mass spectrum (Jones et al, 1993). The principal high mass fragment ion at m/z 528 (Figure 6) arises from the same side-chain loss observed in LC/MS of the parent (Figure 4).…”

Isolation and characterization of degradation products of moxidectin using LC, LTQ FT-MS, H/D exchange and NMR

“…In addition, the use of such comprehensive analysis was found very useful for unambiguous characterization of DPs during our recent work undertaken for another ML, eprinomectin [22]. Therefore, the aim of the present work was to evaluate the EP 6.8 HPLC method to distinguish related substances and DPs and evaluate its ability to be a stability indicating 17 …”

“…Nevertheless, several MS methods for the confirmation of MOX and related compounds in API, biological and environmental samples have been published [11,[14][15][16]. MOX and several related compounds/homologs were identified and characterized by MS, and their fragmentation pathways were established by high resolution as well as electron impact mass spectra [17]. There has been a focus on the determination of MOX and its residues with a particular emphasis on developments of new screening technologies [18,19].…”