Novel capping reagents

X. Wu and R. R. Schmidt, Solid-phase synthesis of complex oligosaccharides using a novel capping reagent,./. Org. Chem., 69 (2004) 1853—1857. 

Andrus, A., Bfcavitch, J. W., McBride, L. J., and Giusti, B. (1988) Novel activating and capping reagents for improved hydrogen-phosphonate DNA synthesis Tetrahedron Lett 29, 861-8W. 

The approach taken to achieve these goals was to first select a set of novel reagents, then react these compounds with simple reagents to cap the reactive functionalities. Virtual products for the selected compounds were created and are then passed through an in silico filtering process. Finally, the filtered libraries were synthesized via combinatorial libraries. 

Indoleamines and indole alcohols, typically acid-sensitive compound, may be smoothly acylated with HFB-imidazole. The indolic compounds (1—2 mg) are dissolved in HFB-imidazole (100—200 fil) and heated in a reaction vial with a PTFE-lined screw-cap at 80 °C for 2-3 hours. After cooling, the products are extracted into hexane (3x5 ml). The hexane extracts are combined and chilled to —14 "C to precipitate residual reagent. The hexane layer is decanted, the precipitate is washed with hexane and the combined hexane solutions are concentrated to 500 1 for analysis by GC (113, 114]. Alternatively, excess reagent may be decomposed with water (1 ml) in the presence of toluene (2 ml), the aqueous layer being extracted with three further 2 ml portions of toluene. These extracts are washed once more with water, separated and filtered through filter paper before concentration for analysis [115,116). A novel way of separating the layers is to freeze the two layers in a solid COj/acetone bath and to withdraw the upper layer from the ice with a Pasteur pipette [117[. Phenolic acids, after esterification, may be acylated in a similar procedure, but here with 10% PFP-imidazole in ethyl acetate for 10 minutes at 70 °C [118]. 

So much for the excursion through my past and the preoccupation with what enzymes do and how they do it. Many Ufetimes could be devoted to further study of the enzymes I came to know intimately perhaps there will be time to renew acquaintances at some future time. For now there is another opportunity to exploit the unique catalytic cap-abiUly and exquisite specificity of enzymes as reagents to solve novel genetic problems. 

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