A simple method for N-acylation of adenosine and cytidine nucleosides using carboxylic acids activated In-Situ with carbonyldiimidazole

Nucleobase Protection of Deoxyribo- and Ribonucleosides

Oligonucleotides carrying a variety of chemical modifications including conjugates are finding increasing applications in therapeutics, diagnostics, functional genomics, proteomics, and as research tools in chemical and molecular biology. The successful synthesis of oligonucleotides primarily depends on the use of appropriately protected nucleoside building blocks including the exocyclic amino groups of the nucleobases, the hydroxyl groups at the 2'-, 3'-, and 5'-positions of the sugar moieties, and the internucleotide phospho-linkage. This unit is a thoroughly revised update of the previously published version and describes the recent development of various protecting groups that facilitate reliable oligonucleotide synthesis. In addition, various protecting groups for the imide/lactam function of thymine/uracil and guanine, respectively, are described to prevent irreversible nucleobase modifications that may occur in the presence of reagents used in oligonucleotide synthesis. © 2017 by John Wiley & Sons, Inc.

Synthesis and cytostatic evaluation of 4-N-alkanoyl and 4-N-alkyl gemcitabine analogues

The coupling of gemcitabine with functionalized carboxylic acids (C9-C13) or reactions of 4-N-tosylgemcitabine with the corresponding alkyl amines afforded 4-N-alkanoyl and 4-N-alkyl gemcitabine derivatives. The analogues with a terminal hydroxyl group on the alkyl chain were efficiently fluorinated under conditions that are compatible with protocols for (18)F labeling. The 4-N-alkanoylgemcitabines showed potent cytostatic activities in the low nanomolar range against a panel of tumor cell lines, whereas cytotoxicity of the 4-N-alkylgemcitabines were in the low micromolar range. The cytotoxicity for the 4-N-alkanoylgemcitabine analogues was reduced approximately by 2 orders of magnitude in the 2'-deoxycytidine kinase (dCK)-deficient CEM/dCK(-) cell line, whereas cytotoxicity of the 4-N-alkylgemcitabines was only 2-5 times lower. None of the compounds acted as efficient substrates for cytosolic dCK; therefore, the 4-N-alkanoyl analogues need to be converted first to gemcitabine to display a significant cytostatic potential, whereas 4-N-alkyl derivatives attain modest activity without measurable conversion to gemcitabine.

Highly efficient chemoselective N-acylation with water microreaction system in the absence of catalyst

A high-speed, highly efficient chemoselective N-acylation by anhydride was achieved in the absence of catalyst for exothermic (DeltaH>0) and endothermic (DeltaH<0) acylation of various amines and anilines with the microreaction system of ambient water (micro-onH2O) and subcritical water (micro-subH2O), where the desired N-acylated products are chemoselectively obtained with high yield(s) and excellent selectivity (>95%).

Regioselective 2'-silylation of purine ribonucleosides for phosphoramidite RNA synthesis

This unit describes high-yield procedures for protection of purine ribonucleosides based on a reaction that allows concomitant highly regioselective 2'-silylation and 3'-phosphitylation to give, in one step, monomers that are ready for H-phosphonate synthesis. For preparation of phosphoramidites, the H-phosphonate monoester is cleaved without silyl migration to give intermediates ready for phosphitylation by standard methods.