Alkylation of complementary ribonucleotides by 1,2-dodecyl-epoxide in a micellar environment: a liquid chromatography-electrospray ionization-sequential mass spectrometry investigation

Alkylation of a pair of complementary ribonucleotides, adenosine monophosphate (AMP) and uridine monophosphate (UMP), was accomplished by 1,2-dodecyl-epoxide (DE) in a oil-in-water microemulsion based on the cationic surfactant Cetyl-trimethyl-ammonium-bromide, providing a suitable catalytic interface for the reagents. Several, often isomeric, alkylation products, bearing one or two hydroxy-dodecyl moieties on their structures, were identified in the reaction mixtures by high-performance liquid chromatography coupled to electrospray ionization ion trap mass spectrometry. In particular, mass spectrometry (MS)/MS spectra, implemented by extracted ion chromatograms obtained for peculiar MS/MS product ions, indicated alkylation to occur on uracil and on uracil/phosphate OH groups in singly and doubly alkylated UMP, respectively. Adenine NH2 group and phosphate or ribose OH groups were found to be involved as such (single alkylation) or in combination, in the case of alkylated derivatives of AMP. The reaction of both endocyclic N and C=O groups (tautomerized to C-OH groups) of uracil and the predominance of nucleophilic attack to the more accessible carbon of the DE epoxydic bridge (the only exception being the reaction by the NH2 group of adenine) were inferred from MS3 spectra with the help of extracted ion chromatograms for specific fragment ions, after their structural characterization. Interestingly, alkylation on one of the uracil C=O groups and, partially, on the adenine NH2 group, both potentially involved in AMP/UMP base pairing in the micellar environment, were found to be hindered when both ribonucleotides were present in the reaction mixtures.