An Investigation on the Relationships between Mass Spectrometric Collisional Data and Biological Activity/Stability of Some N-Acylethanolamine Acid Amidase (NAAA) β-Lactone Inhibitors

The rationale of the present study is that relationships between in vitro biological activity and mass spectrometric (MS) collisional data of molecular species have been already reported in the literature. Herein, the same approach has been employed to investigate possible correlations between MS stability and biological activity/stability data of a series of β-lactone amides and carbamates N-acylethanolamine acid amidase (NAAA) inhibitors. Electrospray ionization MS experiments were performed using an LCQ Deca ion trap and samples were introduced by direct infusion. Mass spectra of positive and negative ions have been obtained, and collisional experiments were performed on selected ionic species. Collisional-induced fragmentation pathways of molecular species related to β-lactone amide inhibitors are different in comparison to those of carbamates, being the former species more stable than the latter, due to β-lactone reactivity. Correlations were found between the characteristic collision energy (CE50) obtained by the breakdown curves and in vitro NAAA inhibitory potency of the β-lactone amides and carbamates analyzed. In the case of carbamates, a relationship between CE50 values and bovine serum albumin (BSA) stability data was also found, while any correlation was not found for amides due to their instability to BSA. β-Lactone NAAA inhibitors’ activity can be qualitatively associated with their lability, as measured by CE50 values. The results obtained could suggest that MS may be used as a preliminary experimental tool to identify carbamate NAAA inhibitors endowed with good biological stability.