A convenient method for the preparation of hapten phosphoramidites

Automated incorporation of haptens at the 3' or 5' end of oligonucleotides required the preparation of the corresponding hapten phosphoramidites. The requisite 1,3-diol framework was prepared in two steps from a carboxylic acid precursor first by a two-carbon homologation using Meldrum's acid to form the corresponding 3-oxo ester and then subsequent reduction to the diol. The primary alcohol was protected with a dimethoxytrityl group, while the secondary alcohol was converted to the reactive phosphoramidite.