Improved chemical synthesis of o-nirtrobenzyl-tyrosine for concise site-specific 15N-tyrosine NMR analysis demonstrated by plant ABA receptor PYL10

Abstract The yield of unnatural amino acid o -nitrobenzyl-tyrosine (oNBTyr), which was able to recover to natural tyrosine after UV-photocleavage was greatly improved from 20% to 81% by using 2-nitrobenzyl bromide as the nucleophilic reagent. Through genetically introducing 15 N-oNBY and consequent photo-cleavage, the site-specific 15 N-Tyr NMR analysis of plant ABA (abscisic acid) receptor PYL10 was implemented without any residue variation. This isotope labelling of tyrosine onto protein backbone provides a convenient strategy for NMR analysis.