Borinium adduct ion formation with barbiturates in a quadrupole ion-trap mass spectrometer

Barbiturates are a class of drugs that are utilized as anesthetics and sleeping agents and are used for the treatment of anxiety, epilepsy and other psychiatric disorders. Because of their pyrimidine structures, barbiturates are highly basic compounds. The evaluation of the formation of adducts involving the borinium ion, B(OCH3)2+, and the barbiturates in a quadrupole ion trap is described. The adducts [M + 73]+ dissociate by elimination of methanol followed by the attachment of a trimethylborate or water molecule. This multi-step pathway is characteristic of a basic, nitrogen-containing structure that has at least one acidic hydrogen. Model compounds were used to probe the nature of this unusual reaction pathway, which involves nucleophilic attack by a methoxyl oxygen of neutral trimethyl borate at the boron atom of the adduct.