| Abstract
| - The cyanoborane (−BH2CN) nucleosides and nucleotidesare a new class of compounds that mimicnatural and synthetic congeners in many ways and exhibit interestingbiochemical and biophysicalproperties. The B−N bond is isoelectronic with theC−N+ bond of N7-alkylated 2‘-nucleosides,aswell as the C−C bond of naturally occurring7-alkyl-7-deazanucleosides. These compounds differfromnormal guanosine in that they are incapable of hydrogen bonding at the7-position. The syntheses ofN7-cyanoborane 2‘-deoxyguanosine,N2-(dimethylaminomethylene)-N7-cyanoborane5‘-(dimethoxytrityl)-2‘-deoxyguanosine (3), andN2-isobutyryl-N7-cyanoborane5‘-(dimethoxytrityl)-2‘-deoxyguanosine (9)are described. Removal of the dimethoxytrityl (DMT) group from3 or 9 is accompanied by significantloss of the cyanoborane moiety. Additionally, dimethoxytritylationof a cyanoboronated nucleosideleads to partial deboronation, thus limiting use of the commerciallyavailable 5‘-DMT nucleosides asviable precursors in base-boronated oligonucleotide synthesis. Theincompatibility of the cyanoboranemoiety under DMT removal/addition conditions necessitated the searchfor an alternative method ofprotecting the 5‘-hydroxyl of the nucleoside. This paper addressesthe possible cause of deboronationand describes the synthesis of N7-cyanoboronatednucleosides by a method that avoids transientprotection of the sugar hydroxyls.
|
