Preparation of Azacrown-Functionalized 2-O-Methyl Oligoribonucleotides, Potential Artificial RNases

An improved synthesis for 3-(3-aminopropyl)- and 3-(3-mercaptopropyl)-1,5,9-triazacyclododecane has been developed and alternative methods for their conjugation to oligonucleotides have been described. Accordingly, the 3-aminopropyl azacrown and its N-(3-aminopropanoyl)-3-aminopropyl analogue have been tethered to the 3ʹ-terminus of a 2ʹ-O-methyloligoribonucleotide by aminolytic cleavage of the thioester linker utilized for the chain assembly. Studies on a monomeric model compound verify that the reaction proceeds solely by the attack of the primary amino group. 5ʹConjugation has been achieved by introducing a 2-benzylthio-2-oxoethyl group to the 5ʹ-terminus as a phosphoramidite reagent and cleaving the thioester bond with the 3-aminopropyl azacrown. For intrachain conjugation, a phosphoramidite reagent derived from 1-deoxy-1-(2-benzylthio-2oxoethyl)-(beta)-D-erythro-pentofuranose has been inserted in a desired position within the chain and subjected to on-support aminolysis with the 3-aminopropyl azacrown or its N-(3-aminopropanoyl)-3aminopropyl and N-(6-aminohexanoyl)-3-aminopropyl analogues. The 3-mercaptopropyl-derivatized azacrown has been tetherd by a disulfide bond to a 3ʹ-(3-mercaptoalkyl)phosphate-tailed oligonucleotide. The 3ʹ- and intrachain-tethered conjugates have been shown to cleave as their Zn(II) chelate complementary oligoribonucleotide sequences.