serine modification) and oxathiophospholanes (chemoselective serine modification in peptides and a small protein) although there has not been a general chemoselective modification method applicable to protein and cellular samples. Historically, organic chemists, on the other hand, began utilizing aprotic organic solvents to address the challenges of the alkylalcohol reactions. Of course, the majority of aprotic organic solvents are incompatible with proteins because of their denaturation/aggregation, but it is intriguing that serine-targeting protein bioconjugation in nonaqueous media that is compatible with biomolecules has not been pursued to date even though such an approach would address the challenges of serine labeling.