New phosphoramidite reagents for the synthesis of oligonucleotides containing a cysteine residue useful in peptide conjugation

The preparation is described of four 2-cyanoethyl-N,N-diisopropyl phosphora midites of N-alpha -Fmoc-S-protected cysteine hydroxyalkyl amides. The phos phoramidites were used in solid-phase synthesis of 5'-cysteinyl oligonucleo tides, useful intermediates in the preparation of peptide-oligonucleotide c onjugates through reaction with a maleimide peptide or with a peptide thioe ster via "native ligation".