Affymetrix of Santa Clara, Calif., has received US Patent No. 6,965,020, "Nucleic acid labeling compounds." The patent claims nucleic acid labeling compounds that are capable of being enzymatically incorporated into a nucleic acid. The nucleic acids to which the compounds are attached maintain their ability to bind to a complementary nucleic acid sequence nucleic acid labeling. The patent describes these compounds and provides heterocyclic derivatives containing a detectable moiety.