Figure 9. Poloxin alkylates nucleophilic amino acid side chains.

Benzoylated lysine (B) and histidine (C) derivatives were detected by LC-MS. For the 3 amino-protected amino acids, the scheme of the reaction, Total Ion Chromatogram (TIC), and mass spectrum (m + 1) are presented. Poloxin did not react with protected cysteine (A); only the hydrolysed Poloxime form was detected. Poloxin reacted to completion with amino-protected lysine (B) and histidine (C) after only approximately 10 minutes at room temperature, where a cleaved Poloxime form was also observed in all cases. TIC peaks corresponding to reaction products analyzed by MS are indicated by red boxes. Note that benzoylated histidine derivative was not stable and was no longer detected after a few hours, when only the Poloxime form was detected (data not shown).