The present invention relates to triorthogonal reagents useful for site-specifically modifying a protein with two orthogonal groups that can be subsequently functionalized in a single one-pot procedure. This approach relies on the selective tagging of proteins containing an appended farnesyltransferase or geranylgeranyltransferase I substrate sequence. The incorporation of a bifunctional ethynyl-hydroxybenzaldehyde into the farnesyl or geranylgeranyl group facilitates the facile labeling of proteins with two different moieties.