A convenient method for the formation of internucleotide linkage

Stereocontrolled synthesis of oligonucleotide analogs containing chiral internucleotidic phosphorus atoms

Oligonucleotides, in which one of the two nonbridging oxygen atoms of internucleotidic phosphates is replaced by a different type of atom or a substituent, are useful as therapeutic agents and probes to elucidate mechanisms of enzymatic reactions. The internucleotidic phosphorus atoms of these oligonucleotides are chiral, and the properties of these oligonucleotides are affected by the absolute configuration of the chiral phosphorus atoms. In order to address the issue of chirality, various methods have been developed to synthesize these P-chiral oligonucleotide analogs in a stereocontrolled manner. This critical review focuses on the recent progress in this field (123 references).

DNA synthesis without base protection

DNA synthesis can be achieved by using O-selective methods for internucleotide bond formation. This greatly simplifies the synthesis of oligodeoxyribonucleotides by eliminating the need for nucleobase protection and deprotection steps. This unit describes strategies that can be used for DNA synthesis without base protection. The discussion includes synthesis of phosphoramidite and H-phosphonate monomers, solid-phase assembly by the phosphoramidite and H-phosphonate methods, and future prospects for DNA synthesis using N-unprotected approaches.

Nucleotide synthesis via methods without nucleoside-base protection

Oligonucleotide synthesis via methods without nucleobase protection (N-unprotected methods) is briefly reviewed. The N-unprotected methods are advantageous in the following respects over conventional approaches that use protectors, generally, acyl protectors for the nucleobase (N-protected method). Two steps, introduction and removal of the protecting groups, are eliminated, and consequently use of undesirable reagents involved in these steps are avoided. In the synthesis of DNA oligomers, the risk of depurination of deoxyadenosine and deoxyguanosine derivatives, which is a serious problem in the N-protected methods, is considerably reduced. The range of synthesizable artificial analogues bearing base-labile functions is extended because harsh base treatment for the deprotection is eliminated.