Stereocontrolled Synthesis of Oligo(nucleoside phosphorothioate)s

Abstract

Encouraging results obtained for modulation of gene expression by antisense oligonucleotides and their analogues have kindled hopes for a new generation of therapeutics against viral infections, cancer, and many other diseases. Among such analogues, oligo(nuc1eoside phosphorothioate)s (Oligo-S) have generally shown the highest efficacy in inhibiting the biosynthesis of "unwanted" proteins. The first clinical trials of antisense agents are now in progress using Oligo-S against genital warts and acute myeloid leukemia, and tests of Oligo-S against AIDS should follow soon. Nevertheless. their mechanism of action, internalization, cellular trafficking, subcellular localization, and interaction with cellular proteins is still poorly understood. It is assumed a priori that application involves rapid and efficient molecular recognition of target RNA by Oligo-S; however, the effects of the chirality of Oligo-S have so far been unappreciated, because Oligo-S has not yet been synthesized with stereocontrol. Indeed. the diastereomeric composition of Oligo-S has never been determined, primarily because of the lack of appropriate analytical methods. Since each of the diastereomers is a stereochemically unique chemical entity, questions arise as to which diastereomer is responsible for an observed biological response, including positive (curative) or possibly negative (toxic) side effects.In this review we intend provide a perhaps somewhat speculative assessment of the problems associated with the stereocontrolled synthesis of Oligo-S and to discuss the state-of-the-art in this field including strategies that may lead to Oligo-S of predetermined chirality. This article is not intended to discourage researchers from further studies of diasteromeric mixtures of Oligo-S as potential pharmaceuticals. Throughout the history of medicinal chemistry numerous useful medicines were discovered, developed, and employed without the detailed knowledge of their structure. Indeed, the composition of the vaccines discovered by Pasteur is a subject of vigorous study still today.

Stereodifferentiation—the effect of P chirality of oligo (nucleoside phosphorothioates) on the activity of bacterial RNase H

“…Consequently, each PS-oligo prepared by generally used techniques (15) consists of a mixture of 2n diastereomers, where n is the number of intemucleotide phosphorothioate linkages. Moreover, the contribution of each diastereomer cannot be described by the 2-n relationship, because each step of chain elongation is slightly stereoselective (16). Our recently elaborated oxathiaphospholane method for the synthesis of PS-oligos is, thus far, the only one allowing P stereocontrolled chemical synthesis of oligo(nucleoside phosphorothioates) (17,18) longer than tetramers in either the Sp orRp configuration (19,20).…”

Diastereomerically pure nucleoside‐5′‐O‐(2‐thio‐4,4‐pentamethylene‐1,3,2‐oxathiaphospholane)s—Substrates for synthesis of P‐chiral derivatives of nucleoside‐5′‐O‐phosphorothioates

“…Based on the literature data, under typical conditions of RP-HPLC (a C18 column, elution with a gradient of 0.1 M triethylammonium bicarbonate (TEAB) and acetonitrile), all 16 di(deoxyribonucleoside) phosphorothioates of R P -configuration have shorter retention times (fast-eluting species) than their S P -counterparts. 26,27 Since fast-and slow-eluting diastereomers of 4d furnished slow-and fast-7, respectively, one can conclude that fast-4d and slow-4d yield the dinucleotides 7 of S P and R P absolute configuration, respectively. The stereoselectivity of condensation was not lower than 98%.…”

Selenium-Derivatized Oligonucleotides

“…This means, that for oligonucleotides as long as decamers, the product obtained on non-stereocontrolled way (e.g., standard phosphoramidite 8 or H-phosphonate methods) exists as the mixture of 2 9 = 512 diastereomers and the content of given single diastereomer drops below 0.2% (1/512). 15 Short PS-Oligos prepared with a non-stereocontrolled or partially stereoselective mode, can be separated into diastereomeric species by means of chromatographic techniques, 16 but this method cannot be considered general as the efficiency of separation depends upon the sequence of nucleobases and the composition of the buffered eluent. At the time being, several phosphorothioate analogues of DNA (as random mixtures of all possible P-diastereomers) are evaluated in clinical studies 17 (Table 1), while one compound-Vitravene R (fomivirsen sodium)-targeting cytomegalovirus IE-2 gene has been accepted by FDA for the treatment of CMV -induced retinitis.…”