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2. Enantiodiscrimination of chiral alpha-aminophosphonic acids by mass spectrometry

Author

Paladini, Alessandra, Calcagni, C., DI PALMA, T., Speranza, Maurizio, Lagana', Aldo, Fago, Giovanna, Filippi, Antonello, Satta, Mauro, and Giardini, Anna

Subjects
metal clusters, aminophosphonic acids, gas-phase enantioselectivity, chirality, gas-phase enantioselectivity, aminophosphonic acids, metal clusters, chirality, mass spectrometry, mass spectrometry
Abstract

Diastereomeric clusters between first-group metal ions (M(+)) and chiral alpha-aminophosphonic acids (A and B) have been readily generated in the gas phase by electrospray ionization (ESI) and their fragmentation investigated by mass spectrometry. The complexes studied had the general formula [MA(S)B(2)](+) and [MA(R)B(2)](+), where M = H, Li, Na, or K, A(S) and A(R) are the two enantiomers of a given acid A, and B is a reference alpha-aminophosphonic acid of defined configuration. Collision-induced decomposition (CID) of [MA(S)B(2)](+) and [MA(R)B(2)](+) leads to fragmentation patterns characterized by [MAB](+)/[MB(2)] abundance ratios which depend on the configuration of ligand A. These different spectral features were correlated to the different stability of the diastereomeric [MA(S)B(2)](+) and [MA(R)B(2)](+) complexes in the gas phase. The results have been discussed in the light of MM2 Molecular Mechanics Force Field calculations.

Published
2001

3. Boyer's Reaction and.

Author

Fraschetti, Caterina, Speranza, Maurizio, Guarcini, Laura, Roselli, Graziella, and Filippi, Antonello

Subjects
*STEREOCHEMISTRY, *CYCLOHEXANE, *CHIRALITY, *BISMUTH, *ALCOHOLS (Chemical class), *ETHERS
Abstract

The progress and stereochemistry of Boyer's reaction were analyzed using several simple, chiral, alcoholic substrates, a variable amount of BiBr3 and different solvents. Basic solvents inhibit the reaction, while cyclohexane works very well; thus, it was our choice for the present study. In contrast to previous works, BiBr3 behaves as a true catalyst, being not consumed during the reaction. Although poisoning of the catalyst occurs to some extent, it does not prejudice the reaction yields (>90%). Gas chromatography/mass spectrometry (GC-MS) monitoring of the reaction revealed that, for example, in the presence of alcohol rac-1, isomeric ethers 4 transetherificate to 3. We propose a unifying mechanistic model for both Boyer's and reactions, in which the electronic properties of n-adducts intermediates, formed by combination of bismuth(III) of BiBr3 and oxygen atoms of alcohols and ethers, play the key role for both the reactivity and the stereochemical outcome of the reaction. Chirality 28:269-275, 2016. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Published
2016
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