Abstract: Conformationally constrained peptides that mimic BH3-only proteins and their conjugation to antibodies and other cell targeting compounds, compositions containing the conjugates and their use in the regulation of cell death are disclosed. The conformationally constrained peptides are capable of binding to and neutralising pro-survival Bcl-2 proteins. Processes for preparing the conformationally constrained peptides conjugated to antibodies and other cell targeting compounds and use of the conjugates in the treatment and/or prophylaxis of diseases or conditions associated with deregulation of cell death are also disclosed.