Enzymatic protecting group techniques.

The proper introduction and removal of protecting groups is one of the most important and widely carried out synthetic transformations in preparative organic chemistry. In particular, in the highly selective construction of complex, polyfunctional molecules, e.g., oligonucleotides, oligosaccharides, peptides, and conjugates thereof, and in the synthesis of alkaloids, macrolides, polyether antibiotics, prostaglandins, and further natural products, regularly the problem arises that a given functional group has to be protected or deprotected selectively under the mildest conditions and in the presence of functionalities of similar reactivity as well as in the presence of structures being sensitive to acids, bases, oxidation, and reduction. For the manipulation of protecting groups, numerous classical chemical methods have been developed.1-3 Nevertheless, severe problems still remain caused by the need to selectively introduce or remove specific blocking functions which cannot or can only with great difficulties be solved by using classical chemical tools only. However, the arsenal of available protecting group techniques has been substantially enriched by the application of biocatalysts. In addition to their stereodiscriminating properties, enzymes offer the opportunity to carry out highly chemoand regioselective transformations. They often operate at neutral, weakly acidic, or weakly basic pH values and in many cases combine a high selectivity for the reactions they catalyze and the structures they recognize with a broad substrate tolerance. Therefore, the application of these biocatalysts to effect the introduction and/or removal of suitable protecting groups offers viable alternatives to classical chemical methods.4-11