Chiral sulfurization for synthesis of antisense oligonucleotides
Item
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Title
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Chiral sulfurization for synthesis of antisense oligonucleotides
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Identifier
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d_2009_2013:5d415338f8de:10640
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identifier
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10765
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Creator
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Mukhlall, Joshua Andrew,
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Contributor
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William H. Hersh
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Date
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2010
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Language
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English
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Publisher
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City University of New York.
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Subject
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Organic chemistry
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Abstract
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Chapter 1: Antisense and RNA interference (RNAi) reagents are two of the most widely studied oligonucleotide-based therapeutics. Phosphorothioate oligonucleotide, an antisense reagent, has a stereogenic center at the phosphorothioate linkage and in the absence of enantioselective synthesis, a mixture of diastereomers results. Stereodefined phosphorothioates have shown greater antisense activity; however, only a few research groups have successfully designed methods for enantioselective synthesis of phosphorothioates with >98% de, albeit in low yields. This dissertation presents a conceptually different method for enantioselective synthesis of phosphorothioate oligonucleotides via a Curtin-Hammett system that requires epimerization of the phosphite triester on the reaction time scale and selective sulfurization of one of the equilibrating epimers with a chiral sulfurizing reagent.;Chapter 2: 2-Cyanoethyl[5'-O-acetyl-2'-deoxythymylyl]-(3',5')-3'- O-(acetyl)-2'-deoxythymidine phosphite triester was found to invert at 150ºC with DeltaG† = 33.0 +/- 0.2 kcal/mol. Separation of the two diastereomers of the phosphite triester was successfully achieved via its 2-cyanoethyl[5'-O-(p,p'-dimethoxytrityl)-2'-deoxythymylyl]-(3',5')-3'- O-(tert-butyldimethylsilyl)-2'-deoxythymidine boranophosphate analogue. For the inversion study the p,p'-dimethoxytrityl and tert-butyldimethylsilyl groups were substituted with acetyl groups to reduce decomposition during heating. Attempts to induce inversion at lower temperature with acidic and radical species failed.;Chapter 3: Chiral analogues of phenylacetyl disulfide (PADS) and 5-methyl-3 H-1,2,4-dithiazol-3-one (MEDITH) were synthesized from the same alpha-alkylated carboxylic acids to give products with enantiomeric purities of 99.0 to >99.9% and 86.1-99.4%, respectively. X-ray diffraction results for one pair of enantiomers unequivocally establish the absolute configurations of two disulfides, and density functional theory (DFT) calculations suggest that the observed high specific rotations could be due to preferred retention of helicity about the S--S bond in solution.;Chapter 4: Phosphite triesters with varying degrees of steric hindrance around the phosphorus atom (beta-cyanoethyl, TMS, TBDMS, and TPS derivatives) were screened against chiral analogues of PADS and MEDITH. The RPS:SPS diastereomeric ratios of the resulting phosphite sulfides or phosphorothioates were determined by reverse-phase HPLC, and a numerical procedure was developed to express the diastereoselectivity of the reactions. The best selectivities to give RPS enriched and SPS enriched phosphorothioates were achieved with MEDITH analogues (S)- 6d (naproxen derivative) (14.7% de) and (S)- 6c (isopropyl group at the alpha position) (-7.9% de), respectively, when reacted with the phosphite triester bearing the TMS group.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Chemistry
