Differentiation of diastereoisomers of protected 1,2-diaminoalkylphosphonic acids by EI mass spectrometry and density functional theory.

Electron ionization mass spectrometry and density functional theory (DFT) calculations have been used to study the fragmentation of diastereoisomers of protected 1,2-diaminoalkylphosphonic acids. The loss of a diethoxyphosphoryl group and the elimination of diethyl phosphonate were found to be competitive fragmentation processes, which can be used to differentiate both stereoisomers. Selective deuterated analogs and product- and precursor-ion mass spectra allowed the elucidation of the fragmentation mechanisms.

Molecular modeling of the lipase-catalyzed hydrolysis of acetoxymethyl(i-propoxy)phenylphosphine oxide and its P-borane analogue.

The molecular modeling of the CAL-B-promoted hydrolysis reactions of acetoxymethyl(i-propoxy)phenylphosphine oxide and its P-borane analogue, acetoxymethyl(i-propoxy)-phenylphosphine P-borane, confirms that the reactions proceed with the same stereochemistry and in both cases the (S)-enantiomers are preferentially transformed by the enzyme. Molecular mechanics calculations show that the main reason for the particular stereoselectivity of the substrates is the steric effect of the phenyl group which causes a remarkable hindrance when placed inside the active site. The replacement of the oxygen by a borane group at the phosphorus stereogenic center does not nullify the stereorecognition by the enzyme, although for the P-borane a lower stereoselectivity is observed.

Solid state NMR spectroscopy as a precise tool for assigning the tautomeric form and proton position in the intramolecular bridges of o-hydroxy Schiff bases.

Two analogous Schiff bases, (S,E)-2-((1-hydroxy-3-methyl-1,1-diphenylbutan-2-ylimino)methyl)phenol (1) and (S,Z)-2-hydroxy-6-((1-hydroxy-3-methyl-1,1-diphenylbutan-2-ylamino)methylene)cyclohexa-2,4-dienone (2), exist in the solid state as phenol-imine and keto-amine tautomers, respectively. Their crystal structures were solved using the X-ray diffraction method. Sample 1 forms orthorhombic crystals of space group P2(1)2(1)2(1), while 2 forms monoclinic crystals of space group P2(1).