Synthesis of Oligonucleotides Containing 2'-N-alkylaminocarbonyl-2'-amino-LNA (2'-urea-LNA) Moieties Using Post-Synthetic Modification Strategy.

The post-synthetic modification of an oligonucleotide is a powerful strategy for the synthesis of various analogs of the oligonucleotide, aiming to achieve the desired functions. In this study, we synthesized the thymidine phosphoramidite of 2'-N-pentafluorophenoxycarbonyl-2'-amino-LNA, which was introduced into oligonucleotides. Oligonucleotides containing a 2'-N-pentafluorophenoxycarbonyl-2'-amino-LNA unit could be isolated under ultra-mild deprotection conditions (50 mM K2CO3 in MeOH at room temperature for 4 h). Moreover, by treatment with various amines as a post-synthetic modification, the oligonucleotides were successfully converted into the corresponding 2'-N-alkylaminocarbonyl-2'-amino-LNA (2'-urea-LNA) derivatives. The duplex- and triplex-forming abilities of the synthesized oligonucleotides were evaluated by UV-melting experiments, which showed that 2'-urea-LNAs could stabilize the nucleic acid complexes, similar to the proto-type, 2'-amino-LNA. Thus, 2'-urea-LNAs could be promising units for the modification of oligonucleotides; the design of a substituent on urea may aid the formation of useful oligonucleotides. In addition, pentafluorophenoxycarbonyl, an amino moiety, acted as a precursor of the substituted urea, which may be applicable to the synthesis of oligonucleotide conjugates.

A Convenient Method for Preparation of α-Imino Carboxylic Acid Derivatives and Application to the Asymmetric Synthesis of Unnatural α-Amino Acid Derivative.

We describe herein a manganese(IV) oxide-mediated oxidation of N-p-methoxyphenyl (PMP)-protected glycine derivatives for the synthesis of α-imino carboxylic acid derivatives. Using this methodology, utilization of unstable glyoxic acid derivatives was avoided. Furthermore, using this methodology we synthesized novel α-imino carboxylic acid derivatives such as α-imino phenyl ester, perfluoroalkyl etsers, imides, and thioester. The asymmetric Mannich reaction of those novel imine derivatives with 1,3-dicarbonyl compound is also described, and the novel α-imino imide gave improved chemical yield and stereoselectivity compared with those obtained by the use of the conventional α-imino ester-type substrate.