[81006-79-3] · C9H6N4O6S · p-Nitrobenzenesulfonyl-4-nitroimidazole · (MW 298.26)
(condensing agent for the triester coupling of nucleotide fragments1)
Alternate Name: p-NBSNI.
Physical Data: mp (sealed tube) 179-185 °C (dec); UV (dioxane) 253 nm.
Solubility: sol pyridine, DMSO; slightly sol dioxane, ethyl acetate.
Form Supplied in: white needles; not available commercially; may be contaminated with p-nitrobenzenesulfonic acid.
Analysis of Reagent Purity: 1H NMR (60 MHz, DMSO-d6) d 8.45 (s, 4H); 8.55 (d, J = 2 Hz, 1H); 9.10 (d, J = 2 Hz, 1H); sulfonic acid impurities are easily detected as higher field signals.
Preparative Method: by treatment of 4-nitroimidazole (1.025 equiv) and p-nitrobenzenesulfonyl chloride (1.0 equiv) with Triethylamine (1.1 equiv) in dry dioxane at 0 °C.1
Purification: recrystallization from ethyl acetate.
Handling, Storage, and Precautions: stable to air and moisture in screw cap bottles at rt for over six months.
p-Nitrobenzenesulfonyl-4-nitroimidazole has been used as a condensing agent in the triester synthesis of oligonucleotides. The reagent activates the phosphodiester towards attack by the incoming 5´-hydroxyl through formation of a mixed phosphoric-sulfonic anhydride. Typically, the suitably protected nucleotide fragments, in pyridine solution, are treated with p-NBSNI (2.5 equiv) and stirred at rt for approximately 15 h. After workup, purification is achieved through two chromatographic separations over silica gel, affording the desired polynucleotide in 60-83% yield (eq 1).1
p-Nitrobenzenesulfonyl-4-nitroimidazole holds the advantage over older reagents, such as triisopropylbenzenesulfonyl chloride, of giving fewer side products resulting from sulfonation of the free 5´-hydroxyl. The long reaction times necessary are a disadvantage and the condensing agents 2,4,6-triisopropylbenzenesulfonyl-1,2,3,4-tetrazole (TPSTe) and 1-(mesitylenesulfonyl)-3-nitro-1,2,4-triazole (MSNT) are preferable.2
Matthew P. Braun & Carl R. Johnson
Wayne State University, Detroit, MI, USA