Palladium-catalysed reactions in solid phase organic synthesis

Peptide/protein-polymer conjugates: synthetic strategies and design concepts

This feature article provides a compilation of tools available for preparing well-defined peptide/protein-polymer conjugates, which are defined as hybrid constructs combining (i) a defined number of peptide/protein segments with uniform chain lengths and defined monomer sequences (primary structure) with (ii) a defined number of synthetic polymer chains. The first section describes methods for post-translational, or direct, introduction of chemoselective handles onto natural or synthetic peptides/proteins. Addressed topics include the residue- and/or site-specific modification of peptides/proteins at Arg, Asp, Cys, Gln, Glu, Gly, His, Lys, Met, Phe, Ser, Thr, Trp, Tyr and Val residues and methods for producing peptides/proteins containing non-canonical amino acids by peptide synthesis and protein engineering. In the second section, methods for introducing chemoselective groups onto the side-chain or chain-end of synthetic polymers produced by radical, anionic, cationic, metathesis and ring-opening polymerization are described. The final section discusses convergent and divergent strategies for covalently assembling polymers and peptides/proteins. An overview of the use of chemoselective reactions such as Heck, Sonogashira and Suzuki coupling, Diels-Alder cycloaddition, Click chemistry, Staudinger ligation, Michael's addition, reductive alkylation and oxime/hydrazone chemistry for the convergent synthesis of peptide/protein-polymer conjugates is given. Divergent approaches for preparing peptide/protein-polymer conjugates which are discussed include peptide synthesis from synthetic polymer supports, polymerization from peptide/protein macroinitiators or chain transfer agents and the polymerization of peptide side-chain monomers.

Pd Catalysis on Dendronized Solid Support: Generation Effects and the Influence of the Backbone Structure

Recent studies revealed that catalysts, prepared on dendronized support, frequently exhibit enhanced activity and selectivity as compared to their non-dendronized analogues. Regretfully, in early studies of the supported dendritic catalysis, no particular attention was paid to the coordinative nature of the dendritic backbone. In this study, we functionalized Wang polystyrene support with three types of dendritic templates: poly(aril benzyl ether), poly(aryl benzyl thioether), and poly(aryl benzyl amine). These dendronized resins were further decorated with phosphine ligands on the periphery and complexed with a Pd(0) catalytic precursor. The catalysis of the Heck and Suzuki reactions of bromobenzene with the first to third generation supported dendritic catalysts was examined and compared to that of the non-dendritic analogues. All of the examined reactions revealed a positive dendritic effect, reflected in up to 5-fold increase in yield, in the most prominent case. The reasons for the observed effect are the proximity of the ligating sites translated into reduced cross-linking and, probably, the increased distance of the catalyst from the polymer matrix. We proved, however, that the latter could not be achieved with a linear spacer. Although the Suzuki reaction was rather insensitive to the backbone structure, the Heck reaction catalysis at 80 degrees C exhibited substantial sensitivity to the nature of the dendritic backbone, with the polyether structure demonstrating the best outcome. This is the first demonstration of the influence of the coordinative ability of the backbone on the activity of a supported dendritic catalyst.

Solid-Phase Synthesis of Linked Heterocycles from a Selenopolystyrene Resin

A linked heterocycle library of isoxazoles, 1,2,3-triazoles, bicyclo[2.2.1]hepta-2,5-diene or 4-methylcyclohexa-1,3-diene and 1,2,4-oxadiazoles was prepared by solid-phase organic synthesis. Key steps on resin-bound selenium were electrophilic additions; 1,3-dipolar cycloaddition; Porco's two-step, one-pot condensation of amidoxime and carboxylate; and Diels-Alder reaction.

Solid-phase synthesis of quinol fatty alcohols, design of N/O-substituted quinol fatty alcohols and comparative activities on axonal growth

Following the promising activity of Q2FA15 on axonal growth, two new series of N/O-substituted QFAs were synthesized, based on a SN2-type reaction. O-alkylated QFA bearing 14 carbon atoms on the side chain (n=14) shows a very potent activity on axonal growth though lowered when compared to Q2FA15. While O-alkylation allows good retention of the biological activity, N-alkylation abolishes it nonetheless. A solid-phase-supported synthesis of Q2FA15 allowing the conception of new hybrid compounds is also described.

Palladium-Catalyzed Buchwald-Hartwig Type Amination of Fluorous Arylsulfonates

Palladium-catalyzed cross-coupling reactions of aryl perfluorooctanesulfonates with amines are introduced. Application of the fluorous tag in multistep synthesis of triaryl-substituted pyrimidine is also described.

Solid-Phase Synthesis of 2-Aminoquinazolinone Derivatives with Two- and Three-Point Diversity

A versatile solid-phase method for the synthesis of various substituted 2-amino-4(3H)-quinazolinones with two- and three-point diversity is described. The synthesis commenced with the generation of polymer-bound S-methylisothiourea followed by N-acylation with different substituted o-nitrobenzoic acid. Finally, reduction of the nitro group triggered intramolecular cyclization via formation of guanidine to afford 2-amino-4(3H)-quinazolinone and its derivatives in high yields and purities.

Carbon−Carbon and Carbon−Heteroatom Bond Formation on Solid Phase Using Cationic Iron Carbonyl Complexes

Iron-mediated methodology for the formation of carbon-carbon and carbon-heteroatom sp(3) bonds on solid phase has been developed. Treatment of a polymer-bound cationic iron cyclohexadienyl complex with carbon, oxygen, nitrogen, and phosphorus nucleophiles, followed by cleavage with amines and subsequent decomplexation, yielded 18 different cyclohexadienoic acid amides of high purity. [reaction: see text]

Formation of Nanoarchitectures Including Subnanometer Palladium Clusters and Their Use as Highly Active Catalysts

Subnanometer Pd clusters stabilized within micelles of random copolymers were formed by direct immobilization of Pd(0) via ligand exchange. The clusters were estimated to contain approximately seven Pd atoms on average (cluster diameter approximately 0.7 nm). Several Pd-containing micelle morphologies could be obtained by polymer cross-linking. These micelles containing Pd clusters were demonstrated to be efficient catalysts for hydrogenations and Heck reactions.

Efficient solid phase synthesis of benzo[1,2,3]thiadiazoles and related structures

The first solid-phase synthesis of benzo[1,2,3]thiadiazoles was achieved by starting from resin bound ortho bromo or iodo triazenes and using a functionalization on cleavage.

Solvent-free photooxygenation of 5-methoxyoxazoles in polystyrene nanocontainers doped with tetrastyrylporphyrine and protoporphyrine-IX

A solvent-free route for the photooxygenation of the 5-methoxyoxazoles (1) is described. The substrates were embedded in nanosized polystyrene particles generated by the emulsifier-free emulsion polymerization of styrene with divinylbenzene and porphyrine dyes as cross-polymerizable reagents. From the photooxygenation of , the 1,2,4-dioxazoles (2) were formed and isolated from the reaction cavities by ethanol extraction. From comparison of the substrate conversions, the efficiency of singlet oxygen generation from the porphyrine dyestuff and the stability of the sensitizing material were estimated.

The virtue of the multifunctional triazene linkers in the efficient solid-phase synthesis of heterocycle libraries

With the implementation of combinatorial chemistry into the modern drug discovery process, the approach to novel diverse heterocycle libraries is an indispensable requirement. Triazenes, which are concealed diazonium salts, can be used to link functionalized arenes and amines to generate various heterocyclic structures, namely, benzoannelated nitrogen heterocycles, upon cleavage from the resin. Since triazene anchors are stable toward various reagents and perform well under a range of reaction conditions, these multifunctional linkers are well suited for automated solid-phase syntheses and the syntheses of complex organic molecules, such as natural products, on solid supports.

Solid-Phase Synthesis of N-Bi- and N-Terarylpiperazines via Three Different and Consecutive Palladium-Catalyzed Cross-Coupling Reactions

Novel nonsymmetrical N-bi- and N-terarylpiperazines were synthesized on solid phase via three consecutive palladium-catalyzed cross-coupling reactions in which C-N, C-B, and C-C bonds are formed consecutively.