Syntheses of Fluorescent Pteridinyl Base-Containing Phosphoramidite Analogs for Use in

Pteridines are fused ring compounds that are similar in overall size and shape to purines, but can also be strongly fluorescent. This enables their possible use as nucleoside analogs that can be inserted intimately and site-specifically into the backbones of oligonucleotides, enabling unique studies of oligonucleotide interactions to be performed.1 In related work as described,2 and partially reproduced by IPDC, pteridine nucleoside analogs of deoxyribonucleic acid were made for incorporation into synthetic DNA strands, via solid phase phosphoramidite chemistry.3 In this work, the synthetic methodology is extended to the preparation of a ribosyl-pteridine analog intended for use in pteridinyl-RNA oligonucleotide syntheses. Chemistry Based on the methods reported in the literature for syntheses of pteridine typed nucleosides,2; 3 the amino function of the pteridine (1), previously synthesized by us for the DNA analog work, was converted into a dimethylaminomethyl Schiff base, in order to improve its solubility in organic solvents. Pteridine (2) was synthesized by reacting (1) with dimethylformamide diethylacetal, in 92 % yield. Conjugation of the modified pteridine (2) with the protected ribosyl bromide (3) was performed in 1 equivalent of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) t