Compounds having structure (1) ##STR00001## wherein R.sup.1 is --H a
protecting group, a linker or a binding partner; and R.sup.2 and R.sup.34
are as defined in the specification. The invention also provides
intermediates and methods make the structure (1) compounds, as well as
methods to use the compounds as labels in diagnostic assays and to
enhance binding to complementary bases.