A rapid method for the preparation of amino acid resin esters for merrifield solid‐phase peptide synthesis

An improved method for the preparation of Merrifield resin esters is presented. This method is rapid, is free of racemization, and is not complicated by a quaternization side reaction. Chloromethylated resin beads, t‐butoxycarbonyl amino acid, and potassium t‐butoxide are heated at 80 °C in dimethylsulfoxide for one‐half hour to yield resin esters of suitable substitution for solid‐phase petide synthesis. All twenty of the BOC protected common amino acids were esterified to the resin by this method. Resin substitution values lie in the range of 0.13 meq/g (BOC‐Glu (NH₂)) to 0.66 meq/g (BOC/Pro), with most of the amino acids yielding 0.3–0.4 meq/g (on a resin containing 0.8 meq Cl/g).