Abstract
The synthesis of protected nucleoside phosphoramidites bearing various markers such as biotinyl, dinitrophenyl, dansyl and pyrenyl groups are reported. These labelled deoxynucleosides phosphoramidites were used for solid phase oligonucleotide synthesis in the same way than the usual protected phosphoramidities without any change in the synthetic cycle and the deprotection step. The new labelled building blocks described herein have been used in conjunction with the labile base protected phosphoramidites ('PAC phosphoramidites') which allowed mild ammonia deprotection, especially recommended for the dinitrophenyl-labelled oligonucleotides. Multiple labelling (i.e. 10 to 20 biotins) can be efficiently and easily performed, on the same oligonucleotide which results in an increase of sensitivity. The polylabelled oligonucleotides are chemically well defined and gave increased signal and low background coloration for in situ hybridisation. The modified oligonucleotides can still be kinased in the normal way as the reporter groups are on the heterocycles.