The preference profile in ruthenium tetroxide oxidations

The preference profile of Ru-VIII-generated in a catalytic cycle, maintaine d by periodate in carbon tetrachloride : acetonitrile : water has been exam ined from a practical vantage using tyrosine, phenylalanine and lysine as p rimary substrates. Other factors such as pH, acetonitrile versatility, tran sport of oxidized ruthenium species across the layers and hydrophobic align ment, influence the course of the reaction. Aryl oxidation, which takes pla ce at the organic interface, is strongly influenced by ring perturbation (p OH-C6H4CH2CH,++; PhCH2CH,+, PhCH2O,+; PhCH2OCONH(Z),-; PhCH2OCO,-; pOH-C6H4 CH2CO,+; PhCH2CO,-; PhCO,-). In the case of tyrosine, the preference profil e switches from ring oxidation at pH 3 to alpha-amino group oxidation at pH 6 and 9, whilst with phenylalanine, the amino group is exclusively oxidize d even at pH 3. With lysine, the reasonable differences in pK(2) between th e alpha-amino group (8.95) and the omega-amino unit (10.53), elicit sharp p references. At pH 3 as well as at 6, the a-amino group is selectively oxidi zed leading to glutaric acid mono-amide, a finding supported by studies wit h N-alpha and N-omega protected lysines. Lysine and arginine side-chains ar e found largely unaffected by the reagent at pH 3 and 6. The findings have been rationalized on the basis of an integrated mechanism. The work has endeavoured to reconcile seemingly conflicting reports in the literature and to project the reagent for selective modifications in synthe sis.