The significance of monoisotopic and carbon-13 isobars for the identification of a 19-component dodecapeptide library by positive ion electrospray Fourier transform ion cyclotron resonance mass spectrometry

Abstract

Harnessing the ultra high resolution capabilities of Fourier transform ion cyclotron resonance mass spectrometry (FTICR‐MS) and positive ion electrospray, we have demonstrated the significance and utility of cumulative mass defect high resolution mass separation stable isotope distribution, exact mass measurement and elemental formula as a means of simultaneously identifying 19 components of the dodecapeptide library Ac‐ANKISYQS[X]STE‐NH2. With an instrument resolution of 275 000 (average), isobaric multiplets attributed to monoisotopic and carbon‐13 components of peptides: Ac ∼ SLS ∼ NH2; Ac ∼ SNS ∼ NH2; Ac ∼ SOS ∼ NH2; Ac ∼ SDS ∼ NH2; within the mass window of 1380–1385 Da, and Ac ∼ SQS ∼ NH2; Ac ∼ SKS ∼ NH2; Ac ∼ SES ∼ NH2; Ac ∼ SMS ∼ NH2, within the mass window 1395–1400 Da, were mass resolved, accurately mass measured and identified from the computed molecular formulas. This experimental procedure enabled the separation of monoisotopic and carbon‐13 isobars yielding enhanced selectivity and specificity and serves to illustrate the significance of monoisotopic and carbon‐13 isobars in final product analysis. Chromatographic separation (HPLC) was of limited utility except for monitoring the overall extent of reaction and apparent product distribution. Positive ion electrospray‐FTICR‐MS and fast atom bombardment (FAB) MS were used to assess final product quality and apparent component distribution. Copyright © 2000 John Wiley & Sons, Ltd.

Ultra-high resolution for mass spectrometric analysis of complex and low-abundance mixtures – the emergence of FTICR-MS as an essential analytical tool

“…The number of components identified, however, decreased with increasing library size. The authors point out the difficulties they observed with increasing complexity -coalescence of peaks of similar m/z value, because of space-charge effects Ramjit and coworkers [29] of Merck Research Laboratories in West Point demonstrated the significance and utility of cumulative mass defect, stable-isotope distribution, exact mass measurement, and elemental formula as a (Fig. 5).…”

FTICR-mass spectrometry for high-resolution analysis in combinatorial chemistry

“…Ramjit et al 65 identified the components of a library containing 19 dodecapeptides simultaneously within the mass windows of 1380-1385 and 1395-1400 Da using direct infusion ultrahigh mass resolution ESI-FTICR-MS without a prior separation. Within these detection windows an average resolution of 275,000 (FWHM) was achieved, allowing the resolution of monoisotopic signals from the 13 C signals of other constituents.…”

Utility of the Hybrid LTQ-FTMS for Drug Metabolism Applications

“…The unique advantage of externally calibrated robust accurate mass measurements provided by the FTMS instruments has also received a lot of attention and it has been discussed in detail in recent comprehensive reviews [3,9]. The first small molecule FTMS applications in the pharmaceutical industry were for accurate mass measurements of pure/isolated drug candidates [10][11][12] and related degradants [13], and in the analysis of combinatorial chemistry libraries [14][15][16][17] without (or with minimal) LC separation. There are very few reports on pharmaceutical FTMS applications specifically for drug metabolism analyses and the majority of them use the advantage provided by the accurate mass measurements to *Address correspondence to this author at the Bristol-Myers Squibb PRI, Mail Stop L14-09, PO Box 4000, Princeton, NJ 08543-4000, USA; Tel: (609) 252 5722; E-mail: mark.sanders@bms.com confirm/elucidate structures for parent drug molecules and corresponding metabolites [12,18].…”

“…There are numerous examples in the literature for on-line low-flow (< 0.1 mL/min) LC-FTMS for both proteomic [23][24][25][26][27] and small molecule studies [15,28]; however, for traditional small molecule analyses where flow rates typically vary between 0.2 -1 mL/min, there are few reports [29]. The big step forward for drug metabolism analyses and small molecules analyses in general came with the introduction of the hybrid FTMS instruments, including the quadrupole FTMS from Bruker Daltonics (Billerica, MA) and IonSpec (Lake Forest, CA) and the linear ion trap FTMS (LTQ-FT) from Thermo Electron (San Jose, CA).…”