Pyrimidine derivatives for labeled binding partners

A method comprising mixing a compound having the structure (1):

• ##STR37## and tautomers, solvates and salts thereof, wherein R.sup.1 is an oligonucleotide, a protecting group, a linker, or H;
• R.sup.2 is A(Z).sub.X1, wherein A is a spacer and Z independently is a label bonding group optionally bonded to a detectable label, but R.sup.2 is not amine, protected amine, nitro or cyano;
• R.sup.27 is independently --CH.dbd., --N.dbd., --C(C.sub.1 -C.sub.8 alkyl).dbd. or --C(halogen).dbd., but no adjacent R.sup.27 are both --N.dbd., or two adjacent R.sup.27 are taken together to form a ring having the structure, ##STR38## where Ra is independently --CH.dbd., --N.dbd., --C(C.sub.1 -C.sub.8 alkyl).dbd. or --C(halogen).dbd., but no adjacent Ra are both --N.dbd.,
• R.sup.34 is --O--, --S--, or --N(CH.sub.3)--;
• and
• X1 is 1, 2 or 3;
• with a sample suspected of containing a target nucleic acid having a base sequence that is substantially complementary or complementary to the compound's base sequence to form a mixture and optionally incubating the mixture to form a complex.