Intrinsic Reactivities of Amino Acids towards Photoalkylation with Benzophenone − A Study Preliminary to Photolabelling of the Transmembrane Protein Glycophorin A

A systematic study of the photoalkylation of amino acids by benzophenone, a standard photosensitive probe of biomolecules, was performed addressing for the first time chemo-, regio-, and stereoselectivities. The high reactivity of the capto-dative substituted α-carbon, particularly in glycine, could be demonstrated as well as the chemical lability of the α-coupling products. Methionine was shown to be favoured both in the sense of reactivity as well as product stability. Preliminary to a project directed towards the elucidation of the topography of glycophorin A in membranes, the present model experiments focussed on the ten amino acids that constitute the transmembrane part of this protein.