Recent developments of artificial functional oligo nucleic acids

Natural, modified and conjugated carbohydrates in nucleic acids

Storage of genetic information in DNA occurs through a unique ordering of canonical base pairs. However, this would not be possible in the absence of the sugar-phosphate backbone which is essential for duplex formation. While over a hundred nucleobase modifications have been identified (mainly in RNA), Nature is rather conservative when it comes to alterations at the level of the (deoxy)ribose sugar moiety. This trend is not reflected in synthetic analogues of nucleic acids where modifications of the sugar entity is commonplace to improve the properties of DNA and RNA. In this review article, we describe the main incentives behind sugar modifications in nucleic acids and we highlight recent progress in this field with a particular emphasis on therapeutic applications, the development of xeno-nucleic acids (XNAs), and on interrogating nucleic acid etiology. We also describe recent strategies to conjugate carbohydrates and oligosaccharides to oligonucleotides since this represents a particularly powerful strategy to improve the therapeutic index of oligonucleotide drugs. The advent of glycoRNAs combined with progress in nucleic acid and carbohydrate chemistry, protein engineering, and delivery methods will undoubtedly yield more potent sugar-modified nucleic acids for therapeutic, biotechnological, and synthetic biology applications.

Concise Synthesis of 4'-Modified Thymidines via 1,5-Hydrogen Atom Transfer/Intermolecular 1,4-Addition Process

A concise approach is presented for preparing 4'-modified thymidines from oxime imidates using readily generated 4'-carbon radicals. This method produces 4'-modified thymidines from natural thymidine using the Mitsunobu reaction, the protection of 3'-hydroxy group (when necessary), and 1,5-hydrogen atom transfer (1,5-HAT)/intermolecular 1,4-addition with electron-deficient olefins. Moreover, using a one-pot synthesis involving 1,5-HAT/intermolecular 1,4-addition, followed by the hydrolysis of the imidate intermediate under basic conditions, 4'-modified thymidine was diastereoselectively isolated. This is because the 4'-isomer transferred to the water layer in the work-up process.