Solid-Phase Synthesis of Heterocyclic Nucleoside Analogues: Substituted Uracils Tethered to Isoxazoles, Isoxazolines, and Triazoles from a Selenopolystyrene Resin

Traceless Solid-Phase Organic Synthesis

Traceless solid-phase synthesis represents an ultimate sophisticated synthetic strategy on insoluble supports. Compounds synthesized on solid supports can be released without a trace of the linker that was used to tether the intermediates during the synthesis. Thus, the target products are composed only of the components (atoms, functional groups) inherent to the target core structure. A wide variety of synthetic strategies have been developed to prepare products in a traceless manner, and this review is dedicated to all aspects of traceless solid-phase organic synthesis. Importantly, the synthesis does not need to be carried out on a linker designed for traceless synthesis; most of the synthetic approaches described herein were developed using standard, commercially available linkers (originally devised for solid-phase peptide synthesis). The type of structure prepared in a traceless fashion is not restricted. The individual synthetic approaches are divided into eight sections, each devoted to a different methodology for traceless synthesis. Each section consists of a brief outline of the synthetic strategy followed by a description of individual reported syntheses.

Efficient Syntheses of 1,2,3-Triazoloamide Derivatives Using Solid- and Solution-Phase Synthetic Approaches

Efficient synthetic routes for the preparation of secondary and tertiary 1,2,3-triazoloamide derivatives were developed. A secondary α-1,2,3-triazoloamide library was constructed and expanded by a previously developed solid-phase synthetic route and a tertiary 1,2,3-triazoloamide library was constructed by a parallel solution-phase synthetic route. The synthetic routes rely on amide formation with secondary amines and chloro-acid chlorides; S_N2 reaction with sodium azide; and the selective [3 + 2] Hüisgen cycloaddition with appropriate terminal alkynes. The target secondary and tertiary 1,2,3-triazoloamide derivatives were obtained with three-diversity points in excellent overall yields and purities using the reported solid- and solution-phase synthetic routes, respectively.

Synthesis of heterocycle-tethered acylbenzofurans and benzodifurans from odorless and recyclable organoseleno polystyrene resin

Recyclable organoseleno resin-supported solid-phase synthesis (SPS) provided a quick access to heterocycle-tethered acylbenzofurans and benzodifurans in satisfactory overall yields and purities after multiple step reactions.

Solid-Phase Organic Synthesis of 1-(E)-Phenylethenyl-4-Substituted-1,2,3-Triazoles from Polystyrene-Supported (2-Azido-1-Phenyl)Ethyl Selenide

A facile method for solid-phase organic synthesis of 1-( E)-phenylethenyl-4-substituted-1,2,3-triazoles from polystyrene-supported (2-azido-1-phenyl)ethyl selenide and substituted ethynes has been developed. The advantages of this method include straightforward operation, high yield and purity of the products, as well as lack of odour and good stability of the polymeric reagent.

Solid-phase synthesis of smac peptidomimetics incorporating triazoloprolines and biarylalanines

Apoptotic induction mechanisms are of crucial importance for the general homeostasis of multicellular organisms. In cancer the apoptotic pathways are downregulated, which, at least partly, is due to an abundance of inhibitors of apoptosis proteins (IAPs) that block the apoptotic cascade by deactivating proteolytic caspases. The Smac protein has an antagonistic effect on IAPs, thus providing structural clues for the synthesis of new pro-apoptotic compounds. Herein, we report a solid-phase approach for the synthesis of Smac-derived tetrapeptide libraries. On the basis of a common (N-Me)AVPF sequence, peptides incorporating triazoloprolines and biarylalanines were synthesized by means of Cu(I)-catalyzed azide-alkyne cycloaddition and Pd-catalyzed Suzuki cross-coupling reactions. Solid-phase procedures were optimized to high efficiency, thus accessing all products in excellent crude purities and yields (both typically above 90%). The peptides were subjected to biological evaluation in a live/dead cellular assay which revealed that structural decorations on the AVPF sequence indeed are highly important for cytotoxicity toward HeLa cells.

Nucleoside and nucleotide analogues by catalyst free Huisgen nitrile oxide-alkyne 1,3-dipolar cycloaddition

An efficient, catalyst free, 1,3-dipolar cycloaddition strategy to conjugate nucleosides and nucleotides with isoxazoles under atmospheric conditions and in an aqueous environment is reported. The protocol involves chloramine-T as a practical reagent to induce in situ nitrile oxide formation and the alkyne partner is attached to the sugar residue or the nucleobase. The reactions are regiospecific, fast and high yielding.