Finally, we wanted to probe the capacity of our allylfunctional ITL derivative 3b to react with a more complex substrate, such as a protein. As proteins possess higher molecular weights their reactivity is often reduced. Additionally, potential reactive groups might be buried inside the tertiary protein structure and therefore are less accessible to react with the chosen reagent. As model protein we chose hen-egg white lysozyme also known as lysozyme C. Lysozymes are immunologically important, as they provide defense against bacteria by damaging their cell walls. Further to this, lysozyme C has been well characterized: Out of its 129 amino acid residues, six are lysines located at the periphery amounting to a molar mass of 14305 Da. Moreover, lysozyme C is thermally sta- ble up to 72 • C and maintains a large activity range (pH = 7-9) with an isoelectric point of pI = 11.35. It is therefore the ideal candidate for our modification and the following conditions were applied for its modification with 3b: The protein concentration was set to 50 µM and NaPi buffer was used as reaction medium. The reaction was started by addition of 1 eq 3b for the single modification and 1 eq of both 3b and NMM for the double modification. After 24 h, samples were frozen to halt the reaction prior to their analysis by mass spectrometry. The MaxEnt algorithm was used for the statistical deconvolution of the combined ion series.