The present invention relates to targeted conversion of alpha-hydroxyalkylated residues in biomolecules in the presence of a directing methyltransferase, namely to targeted removal of the alpha-hydroxyalkyl moieties to give unmodified residues, or targeted derivatization of the alpha-hydroxyalkyl groups by covalent coupling of non-cofactor compounds represented by formula HQ-LX, wherein X represents a functional group or a reporter group attached via a linker moiety L, and QH is selected from HS—, HSe—, HO—H2N—, HN3 or HCN in the presence of a directing methyltransferase. Further development of the method of targeted conversion comprises methods for targeted labeling a biomolecule and method for detecting hydroxymethylated target sites in a biomolecule according to the present invention.