Beaucage reagent

The Reformatsky type of reaction with Zn(0) was performed in situ and led to somewhat unstable phosphonodiamidite (step a) which was coupled with 5 -DMTr-thymidine to give the intermediate mononucleoside phospho-noamidite (step b). The latter was further coupled with 3 -acetyl-thymidine (step c). Couplings described in steps b and c were activated by tetrazole. The intermediate dinucleoside phosphonite was oxidized with (lS)-(+)-(10-camphorsulphonyl)oxaziridine (step d) or sulfurized with Beaucage reagent. The phosphonoamidites mentioned above were used in the solid-phase chemical synthesis of phosphonoacetate and thiophosphonoacetate oligonucleotides. 

The chemistry of dithiazole derivatives has received a new impetus due to their sulfur-transfer applications in the solid-phase synthesis of oligodeoxyribonucleotide phosphorothioates via the phosphoroamidite method they are advantageous alternatives to the previously used Beaucage reagent. The general mechanism of the sulfur-transfer reaction is presented in Scheme 32 . 

Radioactive [35S]-phosphorothioates have been used for in vivo evaluation of chronic or cumulative toxicity of oligonucleotides. To achieve site-specific 35S-labeling in phosphoramidite chemistry, either a mixture of [35S]/carbon disulfide/pyridine/triethylamine [329] or 35S-la-beled Beaucage reagent [330] have been used in the sulfurization step. 3H- and 14C-labeled compounds have been tools in investigations of the metabolic fate of the nucleobases of an oligomer [331]. 3H may be inserted at the 5 -end by formation of the 5 -carboxyaldehyde by Mofatt-Pfitzner reagent, followed by reduction with [3H]-sodium borohydride in 2-propanol... 

The ODNs used here were prepared on an automated DNA synthesizer and with the standard j6-cyanoethyl phosphoramidite coupling reaction. The ferrocenyl ODN (T12Fc) was synthesized by the coupling of amino-terminated ODN with the activated ester of ferrocenecarboxylic acid. A 16 mer ODN (el6S), which has five successive phosphorothioate units on its 5 -terminus, was synthesized using Beaucage s reagent... 

Beaucage and co-workers have prepared thymidine derivatives which contain an ethyl linkage inserted into the glycosidic bond and these have been transformed into reagents suitable for DNA synthesis (167a-d), ... 

Apart from TETD, Beaucage s reagent (3/7-1,2-benzodithiol-3-one-l,1-dioxide) [74] is used most frequently for sulfurization after coupling of the phosphoramidite. The latter is applied in 0.05 molar solution in anhydrous acetonitrile. Sulfurization proceeds within 0.5 min. 

Figure 12. Preparation of phosphorothioate oligomers using Beaucage s reagent. Mechanism as proposed in [74].

Andrus A, Beaucage SL. 2-Mercaptobenzothiazole An improved reagent for the removal of methylphosphate protecting groups from oligodeoxynucleotide phosphotriesters. Tetrahedron Lett 29 5479-5482, 1988. 

In continuation of work in Just s laboratory on the diastereoselective synthesis of dinucleoside phosphorothioates, the chlorophosphoramidite 219 (for the synthesis of the aminoalcohol see Chapter 14) was converted as indicated in Scheme 8 into the Sp-isomer 220, in a 6 1 ratio with the diastereomer, and this ratio could be improved by the use of a more hindered base in step ii. The auxiliary 221, derived from L-tryptophan, has also been used. When 221 was treated sequentially with 5 -0-Tbdms-thymidine, 3 -0-Tbdms-thymidine and Beaucage s reagent, a phosphorothioate triester was produced. The auxiliary could be removed as the aminomethyl compound by treatment with ammonia, to give the i p-isomer of 220, in 40 1 excess. ... 

Reagents i, S -O-Tbdms-thymidine, EtaN ii, 3 -0-Tbdms-thymidine, 2-bromo-4,5-dicyanoimidazole ill, Beaucage s reagent iv, NH3 aq., then TBAF... 

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