Site-specific functionalisation of proteins by a Staudinger-type reaction using unsymmetrical phosphites

Unsymmetrical phosphites react efficiently in a Staudinger reaction with p-azido-phenylalanine, which can be applied for the biotinylation of proteins, thereby expanding the scope of the chemoselective Staudinger-phosphite reaction of aryl azides with symmetrical phosphites to the corresponding phosphoramidates.