Synthesis of oligoribonucleotides with sequences identical to the nucleation region of Tobacco Mosaic Virus RNA: Preparation of AAG, AAGAAG and AAGAAGUUG <i>via</i> phosphotriester methods

Abstract

Abstract The synthesis of the oligoribonucleotides AAG ( 23 ), AAGAAG ( 24 ) and AAGAAGUUG ( 25 ), corresponding to fragments of the nucleation region of Tobacco Mosaic Virus RNA, is described. The assemblage of the oligomers 23–25 was effected using a phosphotriester method which was based on the use of the monofunctional phosphorylating agents 2,2,2‐trichloroethyl 2‐chlorophenyl phosphorochloridate (7) and the analogous 2,2,2‐tribromoethyl 2‐chloro‐4‐tert‐butylphenyl phosphorochloridate ( 8 ). The levulinyl function, which was introduced into the monomeric building blocks 1 (see Scheme 1) by an improved procedure, was used for the protection of the 5′‐hydroxyl group of phosphotriester intermediates. Deblocking of the fully protected oligomers 15f, 17g and 19h with fluoride ions, followed by ammonia and acid treatment, afforded the desired derivatives AAG, AAGAAG and AAGAAGUUG, respectively, in good yields.