Abstract: The present invention provides compounds that are surrogates of post-translationally modified proteins and uses thereof. Numerous diseases are associated with post-translationally modified proteins that are difficult to obtain in homogenous form and in quantities needed for immunization and use as convenient standards, calibrators, and/or reference compounds that facilitate the detection and analysis of endogenous post-translationally modified proteins. The surrogate compounds of the invention typically comprise antigenic epitopes (one of which carries a post-translational modification) that are tethered by a flexible and hydrophilic linker. The resulting compound behaves like a surrogate of the post-translationally modified protein because it preserves the character of the included antigens and allows recognition by specific antibodies targeting the individual antigens.