Abstract
Compound 1 N-[1(R) — [(1,2-dihydro-1-methylsulfonylspiro[3H-indole-3,4′-piperidin]-1′-yl)carbonyl]-2-(phenylmethyloxy)ethyl]-2-amino-2-methylpropanamide(MW 528) is an orally-active growth hormone secretagogue (GHS). As part of a continual effort to analyze the ESI/MS and MSn data of novel drugs, the ESI/MS and MS/MS data of protonated 1 (m/z 529) are analyzed and reported here. The analyses reveal that under low-energy collision-induced dissociation (CID) in an ion trap or a quadrupole collision cell, protonated 1 undergoes a gas-phase rearrangement to form protonated 3 (m/z 357) which competes with the y- and b-type product ions during the amide bond cleavages of protonated 1. It is proposed that when the b-type ion is formed by cleavage of the piperidine amide bond, piperidine (a neutral species) and the b-ion (a cation) form an ion-neutral complex. In this complex, piperidine functions as a nucleophile to attack the benzylic carbon of the b-ion, and the protonated ether group in the b-ion acts as a leaving group, which results in the migration of the benzylic group to the piperidine amine to form protonated 3. Protonated 2 (an analog of 1) was studied under the same experimental conditions. The results show that protonated 2 undergoes a similar rearrangement to form protonated 3. While this rearrangement is a relatively minor fragmentation process for protonated 1, it is a predominant process for protonated 2. This phenomenon is explained in terms of the proposed ion-neutral-complex mechanism.
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Qin, XZ. Tandem mass spectrum of a growth hormone secretagogue: Amide bond cleavage and resultant gas-phase rearrangement. J Am Soc Mass Spectrom 13, 371–377 (2002). https://doi.org/10.1016/S1044-0305(02)00350-1
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DOI: https://doi.org/10.1016/S1044-0305(02)00350-1