Peptide arrays were synthesized by Schafer-N, Copenhagen, Denmark using a maskless photolithographic technique [41] in which 365 nm light is projected onto NPPOC-photoprotected [42, 43] amino groups on a glass surface in patterns corresponding to the synthesis fields. Details of the technique will be published elsewhere, but briefly, the patterns were generated using digital micromirrors and projected onto the synthesis surface using UVimaging optics. In each layer of amino acids, the relevant amino acids were coupled successively to predefined fields after UVinduced removal of the photoprotection groups in those fields. The couplings were made using standard Fmoc-amino acids activated with HBTU/DIEA in NMP. After coupling of the last Fmocamino acid in each layer, all Fmoc-groups were removed in 20% piperidine in NMP and replaced by NPPOC groups coupled as the chloroformate in DCM with 0.1 M DIEA. The procedure was then repeated until all amino acids had been added to the growing peptide chains. Final cleavage of side protection groups was performed in TFA:1,2-ethanedithiol:water 94:2:4 v/v/v for 2 h at room temperature.