Phosphorothioate Anti-sense Oligonucleotides: The Kinetics and Mechanism of the Sulfurisation of Phosphites by Phenylacetyl Disulfide (PADS)

James Scotson, Ben Andrews, Andrew Laws, Michael Page

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

In the pharmaceutical industry the sulfurisation of nucleotide-phosphites to produce more biologically stable thiophosphates is often achieved using ‘aged’ solutions of phenylacetyl disulfide (PADS) which consist of a mixture of polysulfides that are more efficient sulfur transfer reagents. However, both ‘fresh’ and ‘aged’ solutions of PADS are capable of the sulfurisation of phosphites. The rates of both processes in acetonitrile are first order in sulfurising agent, phosphite and a pyridine base, although with ‘aged’ PADS the rate becomes independent of base at high concentrations. The Brönsted β values for sulfurisation using ‘fresh’ and ‘aged’ PADS with substituted pyridines are 0.43 and 0.26, respectively. With ‘fresh’ PADS the Brönsted βnuc = 0.51 for substituted trialkyl phosphites is consistent with a mechanism involving nucleophilic attack of the phosphite on the PADS disulfide bond to reversibly generate a phosphonium intermediate, the rate-limiting breakdown of which occurs by a base catalysed elimination process, confirmed by replacing the ionisable hydrogens in PADS with methyl groups. The comparable polysulfide phosphonium ion intermediate seen with ‘aged’ PADS presents a more facile pathway for product formation involving S–S bond fission as opposed to C–S bond fission.
LanguageEnglish
Pages10840-10847
Number of pages8
JournalOrganic and Biomolecular Chemistry
Volume14
Issue number46
DOIs
Publication statusPublished - 26 Oct 2016

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Phosphorothioate Oligonucleotides
Phosphites
oligonucleotides
Antisense Oligonucleotides
disulfides
Kinetics
kinetics
polysulfides
fission
pyridines
Pyridines
phenylacetyl disulfide
Drug Industry
Sulfur
nucleotides
Disulfides
Hydrogen
attack
acetonitrile
reagents

Cite this

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title = "Phosphorothioate Anti-sense Oligonucleotides: The Kinetics and Mechanism of the Sulfurisation of Phosphites by Phenylacetyl Disulfide (PADS)",
abstract = "In the pharmaceutical industry the sulfurisation of nucleotide-phosphites to produce more biologically stable thiophosphates is often achieved using ‘aged’ solutions of phenylacetyl disulfide (PADS) which consist of a mixture of polysulfides that are more efficient sulfur transfer reagents. However, both ‘fresh’ and ‘aged’ solutions of PADS are capable of the sulfurisation of phosphites. The rates of both processes in acetonitrile are first order in sulfurising agent, phosphite and a pyridine base, although with ‘aged’ PADS the rate becomes independent of base at high concentrations. The Br{\"o}nsted β values for sulfurisation using ‘fresh’ and ‘aged’ PADS with substituted pyridines are 0.43 and 0.26, respectively. With ‘fresh’ PADS the Br{\"o}nsted βnuc = 0.51 for substituted trialkyl phosphites is consistent with a mechanism involving nucleophilic attack of the phosphite on the PADS disulfide bond to reversibly generate a phosphonium intermediate, the rate-limiting breakdown of which occurs by a base catalysed elimination process, confirmed by replacing the ionisable hydrogens in PADS with methyl groups. The comparable polysulfide phosphonium ion intermediate seen with ‘aged’ PADS presents a more facile pathway for product formation involving S–S bond fission as opposed to C–S bond fission.",
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Phosphorothioate Anti-sense Oligonucleotides: The Kinetics and Mechanism of the Sulfurisation of Phosphites by Phenylacetyl Disulfide (PADS). / Scotson, James; Andrews, Ben; Laws, Andrew; Page, Michael.

In: Organic and Biomolecular Chemistry, Vol. 14, No. 46, 26.10.2016, p. 10840-10847.

Research output: Contribution to journalArticle

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