Description SBAP is a sulfhydryl-reactive and amine-reactive heterobifunctional crosslinker. The reagent′s NHS ester reacts with primary amines at pH 7-9 to form stable amide bonds, and the bromacetyl reacts with sulfhydryl groups at pH >7.5 to form stable thioether bonds This reagent is useful for preparing cyclic peptides and peptide conjugates because the spacer maintains peptide-like character in the crosslinked species.