Thiol-derivatized oligonucleosides

A compound comprising a plurality of linked nucleosides, wherein:

• each nucleoside comprises a ribofuranosyl sugar portion and a base portion;
• and
• at least one of said nucleosides bears at a 2'-O-position, a 3'-O-position, or a 5'-O-position a substituent having formula:
• --R.sub.s --S--R.sub.1
• where:
• R.sub.s has formula R.sub.A, R.sub.A --C(O)--Q--R.sub.A, R.sub.A --Q--R.sub.A --Q--R.sub.A ;
• each R.sub.A is independently selected from alkyl having from 1 to about 10 carbon atoms;
• each Q is, independently, NH, O or S;
• R.sub.1 is H or a thiol protecting group or has formula
• S--R.sub.2, CH.sub.2 C(O)--NH--R.sub.2, CH.sub.2 --CH=CH--C(O)--R.sub.2, --CH.sub.2 --CH.sub.2 --NH--S(O).sub.2 --R.sub.2,
• or (maleimido)--R.sub.2 ;
• and
• R.sub.2 comprises a steroid molecule, a reporter molecule, a lipophilic molecule, a reporter enzyme, a peptide, a protein, a reporter group, an alkylator, an intercalator, a cell receptor binding molecule, a crown ether, a crown amine, a porphyrin, a crosslinking agent, a peptide nucleic acid, or a thiol attached to a poly(ethylene glycol).