Diastereoisomerism of thiol complexes of arsenic acids and pseudoasymmetry of arsenic: a 1 H and 13 C NMR study

Diastereoisomeric complexes of methylphenylarsinic acid and ( L )‐glutathione could be partially separated by HPLC, but the separated compounds rapidly racemized, presumably by pyramidal inversion at the arsenic atom. Hydrolysis of the diastereoisomeric complexes yielded methylphenylarsinous acid as a pair of enantiomers revealed by a 1 H NMR study with an asymmetric lanthanide shift reagent. Methylphenylarsinous acid was also synthesized as an enantiomeric pair, shown by an asymmetric shift reagent experiment, by the hydrolysis of iodomethylphenylarsine. 1 H and 13 C NMR spectroscopy were used to demonstrate that complexing of phenylarsonic acid with ( R , S )‐3‐mercapto‐1,2‐propanediol and with ( R , S )‐1‐mercapto‐2‐propanol yielded, in each case, a pair of enantiomers, PhAs[( R )‐ligand)] 2 , PhAs[( S )‐ligand)] 2 , in which the homomorphic ligands were diastereotopic, and a pair of diastereoisomers, PhAs[( R )‐ligand][( S )‐ligand], which differed from each other in the configuration about the pseudoasymmetric arsenic atom. Copyright © 2005 John Wiley & Sons, Ltd.