2- ethyl ester protect phosphates

Protection of phosphates as 2-(trimethylsilyl)ethyl esters was first developed by the Masamune group as part of their efforts to synthesise Calyculin A with its highly hindered phosphate monoester.77 A diallyi phosphate was evaluated in a model compound, but it was rejected because of incomplete deprotection under Pd(0)-catalysis, The corresponding bis-[2-(trimethylsilyl)ethyl] ester 37 1, on the... 

In the first step, we showed by analytical studies that compound 28 was a donor substrate for transketolase in the presence of D-ribose-5-phosphate as acceptor substrate and that in the second step, the hydroxylated aldehyde released 29 led to the P-elimination of protected L-tyrosine. We showed that the free L-tyrosine can thus be obtained by enzymatic deprotection of N-acetyl-L-tyrosine ethyl ester using acylase and subtilisine. In this conditions, it should be possible to carry out this assay in vivo in the presence of host cells overexpressing transketolase and auxotrophic for L-tyrosin. This strategy should offer the first stereospecific selection test of transketolase mutants. The principle of this assay may be extended to other enzymes that can release aldehydes P-substituted by L-tyrosine. 

Protection of Phosphates and Phosphonates. 2-Hydroxy ethyl phenyl sulfone (1) has been used to differentially protect phosphate esters for nucleotide synthesis. Thus, reaction of the diphosphate (8) with 1 and l-(mesitylene-2-sulfonyl)-3-nitro 1,2,4-trIazole (MSNT) in pyridine afforded the differentially protected phosphate 9 in very good yield (eq 5). The 2-phenylsulfonylethyl phosphate can be cleaved under mild conditions by treatment with triethylamine. 

Introduction of a phosphate monoester and removal of its protecting groups was a serious impediment in a synthesis of the serine-threonine phosphatase inhibitor Calyculin A by Evans and co-workers [Scheme 7,22].38 The four phosphate protecting groups evaluated were 2-cyanoethyl and 2-(trimethylsi]y])ethyl (see below), benzyl and p-methoxybenzyl. Of these, the p-methoxybenzyl phosphate ester offered the best compromise between base stability (it survived a Wittig reaction in the presence of a metal amide base) and acid lability required for the final deprotection step in which three secondary terf-butyldimethylsiiyl... 

Protection of 5 -phosphate group in synthesis of dinucleotides. The 5 -phosphate group of mononucleotides is converted into 5 -esters by reaction with (I) in the presence of triisopropylbenzenesulfonyl chloride (TPS 1, 1228-1229 3, 308) or DCC. The esters are then condensed with a 3 -0-acetylated mononucleotide in pyridine with TPS to form TPTE-dinucleotides in 50 0% yield. The value of (1) is that it confers lipophilic properties on the protected dinucleotides so that they can be extracted into ethyl acetate-butanol or methylene chloride-butanol. The protecting group is removed by oxidation to the corresponding sulfone (NCS) and -elimination. 2-(p-Tritylphenyl)sulfonylethanol (TPSE) can be used in place of (1) in this event, the oxidation step is not necessary. A number of tri-and tetranucleotides were also prepared by this new method. ... 

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