Negative ion fast atom bombardment mass spectrometry.In situreactions of boronic acids with triols and related compounds, sugars and nucleosides

Abstract

On the probe tip of a fast atom bombardment mass spectrometer, boronic acids react with a wide range of trifunctional compounds of appropriate configuration yielding negatively-charged boronate cage compounds. Formation of 5-to 8-membered rings occurs readily in the mass spectrometer. The reaction constitutes a simple and effective means of pre-ionizing boronic acids, triols, aminodiols, monomercaptodiols and related compounds including sugars and nucleosides. The resulting boronate complexes exhibit excellent negative ion fast atom bombardment mass spectra, indicating wide application for (1) analysing polyhydroxy compounds and boronic acids, (2) providing information on configuration of polyhydroxy compounds, and (3) measuring affinity constants of polyfunctional compounds for boronic acids. The use of polyethylene glycol as solvent and mass calibrant is also discussed.

Positive-Ion Analysis of Boropeptides by Chemical Ionization and Liquid Secondary Ionization Mass Spectrometry

“…Molecular ions for the appropriate boronate ester, (M‘ + H) + , are observed in all spectra. These results call into question the assumption of preferential boronate anion complex formation, or pre-ionization, in the LSIMS matrix postulated by Rose et alan assumption which is not supported in that study by any corroborating data. It seems more likely that the molecular ions of the boronate ester are formed in a two-step process: (1) benchtop derivatization of the free boronic acid to a neutral ester and (2) ionization of the ester by LSIMS (positive or negative).…”

“…The derivatization technique was extended to negative-ion liquid secondary ion mass spectrometry (LSIMS) where it was presumed that mixtures of boronic acids and certain trifunctional nucleophilic compounds (e.g., glycerol) reacted in situ to produce negatively charged boronate complexes which were subsequently sputtered from the liquid surface and mass analyzed . This approach has been used to study a number of polyfunctional nucleophilic compounds as their corresponding boronate esters. − In situ derivatization was also used to characterize 20-hydroxyecdysteroids as their phenylboronate esters by positive-ion LSIMS, − which seems to belie the mechanism of direct boronate complex ion formation (“pre-ionization”) postulated by Rose et al Subsequently, there have been broader negative-ion LSIMS studies of boron-containing compounds. − The presumption that pre-ionization of a boronic acid to a boronate complex anion occurs in situ may account for the preferential use of negative LSIMS mode in conjunction with the derivatization technique. However, this assumption has apparently precluded the investigation of the positive-ion LSIMS of boronic acids and esters; no positive-ion LSIMS studies of boronic acids have been reported.…”

Poly(ethyleneglycol) as a calibrant and solvent for fast atom bombardment mass spectrometry: Application to carbohydrates

“…6 Their results suggest that propargyl iodide, in contrast, produces exclusively the linear propargyl ion. At energies above threshold, however, a mixture of [C3H3]+ ion structures may be produced, due to higher internal energy imparted to the ions in the electron impact process.…”

“…In situ reactions of trifunctional compounds and boronic acids have been put to analytical use. 6 In this case glycerol is again reactive and hence unsuitable as a solvent. Aiternative solvents are obviously required and it is shown here and el~ewhere'.~.~ that poly-(ethyleneglycol) fulfils this role.…”

Acetone chemical ionization mass spectrometry of monosaccharides

“…Later on, the El mass spectrometry of the cyclic alkaneboronate derivatives of sugars was studied for a similar purpose (2). By using negative ion fast atom bombardment mass spectrometry, Rose (3) made an interesting study of in situ reaction of sugar with boronic acid and obtained analytical information on stereochemistry. Each of these approaches is based on a certain appropriate bimolecular reaction which converts the stereoisomers to compounds with different actual bonding leading to significantly different El mass spectra.…”