Posttranslational modifications regulate the location, interactions, and destruction of a protein, controlling fundamental cellular processes. However, unravelling precise effects of these modifications on proteins is challenging because of difficulties obtaining proteins bearing site-specific modifications for structural and functional studies. Furthermore, effects of posttranslational modifications on protein structure are seldom investigated, leaving a gap in our knowledge of how posttranslational modifications modulate protein function. In this presentation, I will discuss our work towards an understanding of the structural effects of posttranslational modifications in intrinsically disordered proteins. I will demonstrate how solid phase peptide synthesis provides access to modified peptides for structural studies and how protein semi-synthesis tools can be used to generate site-specifically modified and segmentally isotope labelled proteins, such as the Tau protein, for NMR spectroscopy. I aim to show how integrating chemical protein synthesis with structural biology allows us to gain new insights into the effects of protein posttranslational modifications on protein structure, dynamics and regulation.