Trichloro-tert.-butyl-cyclic-enediol-phosphate (TCB-CEP), proposed reagent for the syntheses of oligonucleotides using the triester approach

Protected nucleosides, phosphorylated using 4.5- dimethyl-2-oxo-2-trichloro-tert.-butyl-1, 3, 2^λ5-dioxaphospholene, can be cleaved to yield either 5'- or 3'-building blocks for triester syntheses. Reaction of the title compound 1 (1 is prepared and reacts in analogy to its methyl analog¹⁾) with 5'leosides yields 3'-trich1oro-tert.-buty1-acetoiny1-phosphates. They can be selectively either detritylated in acidic medium or the acetoinyl group cleaved in basic medium. So 3'- and 5'-building blocks for oligonucleotide syntheses following a triester strategy²⁾are at hand. Coupling proceeds with benzene sulfonyl tetrazole. Because of their lipophilic nature all intermediates can easily be purified on silica gel. The phosphate protecting trichloro-tert.-buty1 group can be cleaved by reductive fragmentation³⁾.