4,4′-Dimethyloxytrityl chloride: a reagent for the spectrophotometric determination of polymer-supported amino groups

Abstract

A rapid and sensitive spectrophotometric method for the determination of free amino groups on a solid support is described. The method is based on the reaction of polymer-supported amino groups with an excess of 4,4′-dimethoxytrityl chloride (DMTrCl) in the presence of tetrabutylammonium nitrate as a catalyst. The solid support was washed thoroughly to remove the excess of reagent and subsequently treated with perchloric acid solution to release the DMTr cation. The DMTr cation was then determined spectrophoto-metrically at 498 nm (ε₄₉₈= 70 000 l mol^–1 cm^–1). The method was found to be useful for the determination of solid-supported amino groups and for monitoring the functionalisation of polymer supports used for the synthesis of peptides and oligonucleotides. In addition the polymer supports can be reused after the determination of the solid-supported amino groups.