“…labelled phosphoramidites. Whatever positions of the oligonucleotide chain are substituted, hydroxyl termini (15)(16)(17)(18)(19) or nucleobases (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), the labelling groups must fulfil the following conditions: (i) they should produce a signal detectable at a level as low as possible, (ii) they should not interfere with hybridisation and (iii) they should not interfere with enzymatic chain elongation. Presumably, with respect to condition (iii), the labelling of the 3′-terminal base of synthetic primers, so far, has been avoided.…”