Beaucage

For a review in which the use of various trityl groups in nucleotide synthesis is discussed in the context of the phosphoramididite approach, see S. L. Beaucage and R. P. Iyer, Tetrahedron, 48, 2223 (1992). 

The disadvantage of this method is that the dichloridites and monochloridites are sensitive to water and thus could not be used readily in automated oligonucleotide synthesis. This problem was overcome by Beaucage and Caruthers, who developed the phosphoramidite approach. In this method, derivatives of the form R 0P(NR2)2 react with one equivalent of an alcohol (catalyzed by species such as l//-tetrazole) to form diesters, R OP(OR")NR2, which usually are stable, easily handled solids. These phosphoroamidites are easily converted to phosphite triesters by reaction with a second alcohol (catalyzed by l//-tetrazole). Here, again, oxidation of the phosphite triester with aqueous iodine affords the phosphate triester. Over the years, numerous protective groups and amines have been examined for use in this approach. Much of the work has been reviewed. ... 

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... 

Phalen RF, Oldham HJ, Beaucage CB, et al. 1985. Postnatal enlargement of human tracheobronchial airways and implications for particle deposition. Anat. Rec. 212 368-380. 

The chain structure (length, entanglement, branching, tacticity,...) of polymers is discussed further in the next chapter (Chapter 4) by Beaucage and Kulkarni. 

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