Nucleotide analogs

A compound having the structure of formula (1) ##STR36## wherein B is 5-fluorocytosin-1-yl, 5-methylcytosin-1-yl, or a heterocyclic base having the structure (a) ##STR37## R is --S(O).sub.2 N(R.sup.3).sub.2 ;

• each R.sup.1 is independently hydrogen, cyano, nitro, alkyl, O-alkyl, --C(O)R.sup.3, --S(O).sub.2 OH, --N(R.sup.3).sub.2 or --CHO;
• each R.sup.3 is independently hydrogen, alkyl, phenyl, phenyl substituted with C.sub.1-20 alkyl, --CH.sub.2 C.sub.6 H.sub.5 or --CH.sub.2 CH.sub.2 C.sub.6 H.sub.5, but when R.sup.1 is --N(R.sup.3).sub.2, one R.sup.3 is hydrogen and the other R.sup.3 is C.sub.2-6 alkyl or when R.sup.1 is --N(R.sup.3).sub.2, both R.sup.3 are the same and are C.sub.2-6 alkyl;
• R.sup.6 is --NH.sub.2, --NHR.sup.7, --NHR.sup.8, --N.dbd.CHN(R.sup.7).sub.2 or --N.dbd.C(CH.sub.3)N(R.sup.7).sub.2 ;
• R.sup.7 is C.sub.1 -C.sub.6 alkyl;
• R.sup.8 is a protecting group;
• and
• each R.sup.9 independently is N or CH.