This invention relates to a solid phase method of synthesising biomolecule-drug conjugates. In particular, this invention relates to a solid phase method of synthesising antibody-drug conjugates (ADCs). The method comprises contacting a biomolecule (such as an antibody) with a capture resin to immobilise the biomolecule, wherein the resin comprises a biomolecule capture moiety selected from the group consisting of a peptide or non-peptide based (including an amino acid-based) protein A, protein G, or protein L mimetic a nucleotide binding site capture moiety and a glycoprotein capture moiety optionally chemically modifying the immobilised biomolecule, contacting the immobilised biomolecule with a drug component to form the immobilised biomolecule-drug-conjugate, and releasing the biomolecule-drug-conjugate from the capture resin. This invention also relates to intermediate methods of producing immobilised, chemically modified biomolecules, e.g. antibodies. The invention also relates to various uses of capture resins and to biomolecule-drug-conjugates, intermediate products and compositions.
