... peptide synthesis (SPPS) of the NLS and CPP peptide modules For solid phase syntheses of both, the NLS ad-dress peptide as well as of the CPP transport peptide, we employed the Fmoc-strategy ... purified peptides were lyophilized. Ligation of the tetrazine diene compound N-(2-Amino-propyl)-4-(6-(pyrimidine-2-yl)-1,2,4,5-tetrazine-3-yl)benzamide (4) with the NLS-Cys peptide and coupling ... N-(2-Aminopropyl)-4- (6-(pyrimidine-2-yl)-1,2,4,5-tetrazine-3-yl)benzamide (4) 4-(6-(pyrimidine-2-yl)-1,4-dihydro-1,2,4,5-tetrazine-3-yl)benzoic acid 3 was prepared from 2-pyrimidinecarbonitrile 1 and p- cyano...