Reagents for the preparation of 5'-biotinylated oligonucleotides

A chemical compound of the formula

• Bt-(SG)-A-Q
• wherein
• Bt is ##STR23## SG is an organic diradical spacer group that separates Bt from A at a distance sufficient to allow efficient complexation of Bt to avidin or streptavidin;
• A is selected from the group consisting of --O--, --S--, ##STR24## wherein R and R.sup.1 are independently selected from the group consisting of H, C.sub.3-10 branched alkyl, C.sub.1-10 unbranched alkyl, C.sub.6-10 aryl, C.sub.7-12 alkaryl, and C.sub.7-12 aralkyl;
• Q is selected from the group consisting of ##STR25## and salts thereof;
• wherein R.sup.2 and R.sup.3 are independently selected from the group consisting of C.sub.3-10 branched alkyl and C.sub.1-12 unbranched alkyl;
• R.sup.4 is selected from the group consisting of --(CRR.sup.1).sub.m (A).sub.n (CRR.sup.1 )m--, ##STR26## R, R.sup.1 and A are as defined above;
• m=1-6;
• n=0-1;
• p=1-10;
• q=0-10, provided that 2m+n.ltoreq. 12, and further provided that 2.ltoreq.n+p+q.ltoreq.13;
• and Y is any phosphate-protecting group.