title: Probing the influence of stereoelectronic effects on the biophysical properties of oligonucleotides: comprehensive analysis of the RNA affinity, nuclease resistance, and crystal structure of ten 2'-O-ribonucleic acid modifications.
abstract: The syntheses of 10 new RNA 2'-O-modifications, their incorporation into oligonucleotides, and an evaluation of their properties such as RNA affinity and nuclease resistance relevant to antisense activity are presented. All modifications combined with the natural phosphate backbone lead to significant gains in terms of the stability of hybridization to RNA relative to the first-generation DNA phosphorothioates (PS-DNA). The nuclease resistance afforded in particular by the 2'-O-modifications carrying a positive charge surpasses that of PS-DNA. However, small electronegative 2'-O-substituents, while enhancing the RNA affinity, do not sufficiently protect against degradation by nucleases. Similarly, oligonucleotides containing 3'-terminal residues modified with the relatively large 2'-O-[2-(benzyloxy)ethyl] substituent are rapidly degraded by exonucleases, proving wrong the assumption that steric bulk will generally improve protection against nuclease digestion. To analyze the factors that contribute to the enhanced RNA affinity and nuclease resistance we determined crystal structures of self-complementary A-form DNA decamer duplexes containing single 2'-O-modified thymidines per strand. Conformational preorganization of substituents, favorable electrostatic interactions between substituent and sugar-phosphate backbone, and a stable water structure in the vicinity of the 2'-O-modification all appear to contribute to the improved RNA affinity. Close association of positively charged substituents and phosphate groups was observed in the structures with modifications that protect most effectively against nucleases. The promising properties exhibited by some of the analyzed 2'-O-modifications may warrant a more detailed evaluation of their potential for in vivo antisense applications. Chemical modification of RNA can also be expected to significantly improve the efficacy of small interfering RNAs (siRNA). Therefore, the 2'-O-modifications introduced here may benefit the development of RNAi therapeutics.
authors.affiliation: Department of Biochemistry, Vanderbilt University, Nashville, Tennessee 37232, USA. martin.egli@vanderbilt.edu
authors.forename: Martin
authors.initials: M
authors.lastname: Egli
authors.forename: George
authors.initials: G
authors.lastname: Minasov
authors.forename: Valentina
authors.initials: V
authors.lastname: Tereshko
authors.forename: Pradeep S
authors.initials: PS
authors.lastname: Pallan
authors.forename: Marianna
authors.initials: M
authors.lastname: Teplova
authors.forename: Gopal B
authors.initials: GB
authors.lastname: Inamati
authors.forename: Elena A
authors.initials: EA
authors.lastname: Lesnik
authors.forename: Steve R
authors.initials: SR
authors.lastname: Owens
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Ross
authors.forename: Thazha P
authors.initials: TP
authors.lastname: Prakash
authors.forename: Muthiah
authors.initials: M
authors.lastname: Manoharan
mesh_terms: D001483:Base Sequence; D055592:Biophysical Phenomena; D001703:Biophysics; D003460:Crystallization; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004795:Enzyme Stability; D005092:Exonucleases / Q000378:metabolism; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009841:Oligonucleotides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012313:RNA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012260:Ribonucleases / Q000378:metabolism*; D055672:Static Electricity; D013696:Temperature
chemical_list: D009841:Oligonucleotides; D012313:RNA; D004247:DNA; D005092:Exonucleases; D012260:Ribonucleases