Oka Natsuhisa, Wada Takeshi, Saigo Kazuhiko
Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Bioscience Building 702, Kashiwa, Chiba 277-8562, Japan.
J Am Chem Soc. 2003 Jul 9;125(27):8307-17. 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))-T(PS)T, all-(S(p))-T(PS)T, all-(R(p))-d[G(PS)A(PS)C(PS)]T, and all-(R(p))-T(PS)T were synthesized on a highly cross-linked polystyrene resin.
描述了使用核苷3'-O-氧氮磷杂环戊烷衍生物作为单体单元立体控制合成寡脱氧核糖核苷硫代磷酸酯（PS-ODN）。由六种对映体纯的1,2-氨基醇制备2-氯-1,3,2-氧氮磷杂环戊烷衍生物，并将其用于5'-O-保护核苷的亚磷酸化反应。对这些反应的详细研究表明，反应的非对映选择性取决于对映体纯的1,2-氨基醇的结构、反应温度以及用作HCl清除剂的胺。此外，对2-氯氧氮磷杂环戊烷衍生物进行了从头算分子轨道计算，以阐明这些非对映选择性亚磷酸化反应的机理。发现2-氯-5-苯基氧氮磷杂环戊烷衍生物在磷原子上的最低未占分子轨道（LUMO）与P-Cl键几乎正交。该LUMO可能参与了主要保留P-构型的亚磷酸化反应。开发了一系列二烷基（氰基甲基）铵盐，并用作非对映体纯核苷3'-O-氧氮磷杂环戊烷与3'-O-保护核苷缩合反应的活化剂。在新的活化剂存在下，反应迅速进行，得到相应的二核苷亚磷酸三酯。缩合反应的非对映选择性不取决于抗衡阴离子，而是取决于二烷基（氰基甲基）胺的结构。在由相对较小的二烷基（氰基甲基）胺组成的活化剂存在下，缩合反应以优异的非对映选择性进行。硫化和脱保护后，以优异的产率得到非对映体纯的（R(p)）-和（S(p)）-二核苷硫代磷酸酯。本方法也应用于立体规整的PS-ODN的固相合成。全-（R(p)）-[T(PS)]3T、全-（S(p)）-[T(PS)]3T、全-（R(p)）-d[G(PS)A(PS)C(PS)]T和全-（R(p)）-[T(PS)]9T在高度交联的聚苯乙烯树脂上合成。
