Deprotection phosphate groups

Allyl phosphates 332 are deprotectd using HCO2H amine [146] or HSnBu3 [147], The method is applied to the protection and deprotection of the amino and phosphate groups in nucleotides synthesized in the solid phase [148],... 

Carboxylic acid, 1,2-diol and aldehyde functional groups have been incorporated into DNA using 2 -modified phosphoramidite building blocks, in order to introduce reactive functional groups for further modification after oligonucleotide synthesis. The 2 -0-phosphate-3 -0-phosphoramidite monomers of U and A have been prepared which allows the synthesis of RNA with selectively placed 2 -0-phosphate groups. The 2 -0-phosphate is protected as the t-butyl triester, and deprotected with 0.01 M HCl. 

Phosphatidyl-D-glucose (13) and its thiophosphate analogue have been prepared by reaction of the amidite (14) with 1,2,3,4-tetra-O-acetyl-D-gluco-pyranose followed by oxidation of P to P by nitric oxide (or sulphur), deprotection of the glyceryl and phosphate groups, acylation with stearoyl... 

The value of — 22.6 0.6 kj mor obtained is similar to that of other hemi-acetal phosphoric esters. Treatment of 4-( -acetyl-2,3-< -carbonyl-a-L-rhamno-pyranosyl bromide with dibenzyl phosphate-triethylamine, followed by deprotection, yielded j3-L-rhamnopyranosyl phosphate. The same paper contains a synthesis of thymidine 5 H/ L fhamnopyranosyl)pyrophosphatc. Long-chain (C10-C16) alkyl 0-D-glucopyranosyl phosphates have been prepared via the orthoester method and described as novel anionic detergents. The MacDonald procedure (anhydrous phosphoric acid in vacuo at 56-60 for 2 h) has been used to convert di- and tri-saccharides into their a-glycosyl phosphates. The syntheses and n.m.r. of 2-acetamido-2-deoxy-D-glucose 1-, 3-, 4-, and 6-phosphates have been published. The chemical shifts were studied with respect to the position of the phosphate group D-Ribofuranosyl ribitol... 

Allyl-based protection for the phosphate group in phosphoserine-containing peptides has also been employed. In this case, the Af-alloc-bis(allyl)phosphate of serine was incorporated into a resin-bonnd peptide using standard solid phase peptide synthesis methodology and deprotected nsing trimethylsilyl azide and tetrabutylammonium flnoride as the nucleophile (Scheme 10). 

The sequence (1) DMT hydrolysis, (2) coupling, and (3) oxidation can be repeated multiple times in the synthesizer machine until the desired ohgonucleotide is assembled in its protected and immobilized form. The final task is to remove the product from the silica and deprotect the DMT-bearing terminal sugar, all the bases, and the phosphate group, without cleaving any of the other bonds. Remarkably, this task can be done in just two steps, first treatment with acid and then with aqueous ammonia, as shown here for the dinucleotide made in the preceding scheme. 

The phthalimido group has always been an attractive alternative to amine protection in chemical synthesis. Native phthalyl amidase was isolated from Xanthiobacter agilis and subsequently cloned and overexpressed in Streptomyces lividans. Phthalyl amidase selectively deprotects phthalimido groups under very mild conditions (30°C in 200 mM potassium phosphate buffer, pH 8.0) in a one-pot reaction to produce phthalic acid and the free amine. The enzyme has been shown to deprotect several primary amines of distinctly different structures [19]. 

The steps involved in automated oligonucleotide synthesis illustrate the current use of protective groups in phosphate chemistry (Scheme 1). Oligonucleotide synthesis involves the protection and deprotection of the 5 -OH, the amino groups on adenine, guanine, and cytosine, and -OH groups on phosphorus. 

All the approaches for deblocking protective groups described earlier in this book have found application in the removal of protective groups from phosphorus derivatives. Because phosphate protection and deprotection are commonly associated with compounds that contain acid-sensitive sites (e.g., glycosidic linkages and DMTr-O- groups of nucleotides), the most widely used protective groups on phosphorus are those that are deblocked by base. 

---