Selective deacylation preparation

Representative Experimental Procedures 128 Representative Procedure for Preparation of Cl-Hemiacetal Donors Through a Peracylation-Selective Anomeric Deacylation Sequence 128... 

Enzymes are widely recognized as valuable tools for the synthesis of optically active compounds [22]. Thus, lipase-catalyzed acylation or deacylation is one of the most efficient methods for the preparation of optically active alcohols, acids, and esters. Because lipases retain activity and selectivity in non-conventional media such as organic liquids, their use as biocatalysts in enantioselective synthetic reactions has considerably increased. 

The reductive ring closure and selective O-deacylation procedure was also used for preparing optically active benzotriazole derivatives illustrated in Eq. 2 ... 

By similar strategies, Schmidt and coworkers have also prepared a partial structure of the GPI anchor of T. gondii (O Scheme 12) [89]. First, the trichloroacetimidate 138 of a tetrasaccharide as the glycosyl donor was prepared and utilized to glycosidate pseudodisaccharide 114. The resultant hexasaccharide 139 was then selectively deprotected and phosphorylated at Man III and inositol respectively to yield 141. Quantitative deacylation followed by debenzylation over Pearlman s catalyst gave the deprotected GPI anchor 142 in a 92% yield. 

Ammonium salts with two different alkyl chains were prepared directly via subsequent alkylations of dimethylamine with primary bromides and crystallization. Commercial hexadecyl-methylamine can be conveniently applied in the same way in order to convey functionality to cationic synkinons. A recent example describes subsequent alkylations with a small functional and a long-chain primary bromide (Scheme 2.4). A-acylated / -phenylenediamine was also alkylated at the second nitrogen atom which had two different alkyl chains, with or without extra functionality . After deacylation, this head group can be diazotized or coupled oxidatively with various heterocycles in water (Scheme 2.4). Photoactive and coloured membrane surfaces are thus obtained. Phenylene-diamine, pyridine and in particular A-methyl-4,4-bipyridinium chloride are relatively weak nucleophiles. Substitution of bromides is slow and the more reactive iodides can rarely be obtained commercially, but the selection of nitromethanes as solvent for bromide substitution is of great help as well as the addition of sodium iodide to enforce a Finkelstein reaction or a combination of both. 

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