An Oxazaphospholidine Approach for the Stereocontrolled Synthesis of Oligonucleoside Phosphorothioates

• Published in: Journal of the American Chemical Society Vol. 125; no. 27; pp. 8307 - 8317
• Main Authors: Oka, Natsuhisa, Wada, Takeshi, Saigo, Kazuhiko
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 09.07.2003; Amer Chemical Soc
• Subjects: Carbohydrates. Nucleosides and nucleotides; Chemistry; Chemistry, Multidisciplinary; Exact sciences and technology; Models, Molecular; Nucleosides - chemical synthesis; Nucleosides, nucleotides and oligonucleotides; Oligodeoxyribonucleotides - chemical synthesis; Organic chemistry; Oxazoles - chemical synthesis; Oxazoles - chemistry; Physical Sciences; Preparations and properties; Science & Technology; Stereoisomerism; Thionucleotides - chemical synthesis; Thymidine - analogs & derivatives; Thymidine - chemistry; SUPPORT; MONOMERS; RNA; DNA; STEREOCHEMICAL COURSE; STEREOSELECTIVE-SYNTHESIS; DITHYMIDINE PHOSPHOROTHIOATES; OLIGO(NUCLEOSIDE PHOSPHOROTHIOATE)S; Organic synthesis; Five membered ring; Oxygen nitrogen phosphorus heterocycle; Solid state reaction; Organic thiophosphate; Oligodeoxyribonucleotide; Diastereoselectivity
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja034502z

The stereocontrolled synthesis of oligodeoxyribonucleoside phosphorothioates (PS-ODNs) using nucleoside 3‘-O-oxazaphospholidine derivatives as monomer units is described. 2-Chloro-1,3,2-oxazaphospholidine derivatives were prepared from six kinds of enantiopure 1,2-amino alcohols and used for the phosphitylation reactions of 5‘-O-protected nucleosides. A detailed study of these reactions revealed that the diastereoselectivity of the reaction depended on the structure of the enantiopure 1,2-amino alcohol, the reaction temperature, and the amine used as a scavenger of HCl. In addition, ab initio molecular orbital calculations for the 2-chlorooxazaphospholidine derivatives were carried out to elucidate the mechanism of these diastereoselective phosphitylation reactions. The LUMO of the 2-chloro-5-phenyloxazaphospholidine derivatives on the phosphorus atom was found to be almost orthogonal to the P−Cl bond. This LUMO may be involved in the phosphitylation reactions with predominant retention of the P-configuration. A series of dialkyl(cyanomethyl)ammonium salts were developed and used as activators for the condensation reactions of the diastereopure nucleoside 3‘-O-oxazaphospholidines with 3‘-O-protected nucleosides. In the presence of the new activators, the reactions proceeded rapidly to give the corresponding dinucleoside phosphite triesters. The diastereoselectivity of the condensation reaction did not depend on the counteranion but on the structure of the dialkyl(cyanomethyl)amine. In the presence of the activator, which consists of a relatively small dialkyl(cyanomethyl)amine, the condensation proceeded with excellent diastereoselectivity. After sulfurization and deprotection, diastereopure (R p)- and (S p)-dinucleoside phosphorothioates were obtained in excellent yields. The present methodology was also applied to the solid-phase synthesis of stereoregulated PS-ODNs. all-(R p)-[TPS]3T, all-(S p)-[TPS]3T, all-(R p)-d[GPSAPSCPS]T, and all-(R p)-[TPS]9T were synthesized on a highly cross-linked polystyrene resin.