New supports for solid-phase organic synthesis: development of polystyrene resins containing tetrahydrofuran derived cross-linkers

Circular Aqueous Fmoc/t-Bu Solid-Phase Peptide Synthesis

Circular economy and aqueous synthesis are attractive concepts for sustainable chemistry. Here it is reported that the two can be combined in the universal method for peptide chemistry, fluorenylmethoxycarbonyl(Fmoc)/t-Bu solid-phase peptide synthesis (SPPS). It was demonstrated that Fmoc/t-Bu SPPS could be performed under aqueous conditions using standard Fmoc amino acids (AAs) employing TentaGel S as resin and 4 : 1 mixture of water with inexpensive green solvent PolarClean. This resin/solvent combination played a crucial dual role by virtue of improving resin swelling and solubility of starting materials. In a model coupling, TCFH and 2,4,6-collidine afforded a full conversion at only 1.3 equiv. AA, and these conditions were used in SPPS of Leu enkephaline amide affording the model peptide in 85 % yield and 86 % purity. A method to recycle the waste by filtration through a mixed ion exchange resin was developed, allowing reusing the waste without affecting quality of the peptide. The method herein obviates the use of unconventional or processed AAs in aqueous SPPS while using lower amounts of starting materials. By recycling/reusing SPPS waste the hazardous dipolar aprotic solvents used in SPPS were not only replaced with an aqueous medium, solvent use was also significantly reduced. This opens up a new direction in aqueous peptide chemistry in which efficient use of inexpensive starting materials and waste minimization is coupled with the universal Fmoc/t-Bu SPPS.

The development of a dedicated polymer support for the solid-phase oligosaccharide synthesis

Reported herein is the development of a novel polystyrene-based resin that we named PanzaGel. The resin was equipped with diethylene glycol-derived cross-linker with the dedicated application to polymer supported glycan synthesis in mind. After investigating its swelling properties and obtaining encouraging data for its chemical and thermal stability we accessed the amenability of PanzaGel to the HPLC-based platform for the automated synthesis. Comparable glycosylation results to those with traditional supports have been obtained in the synthesis of glycans up to pentasaccharide that was obtained in 30% overall yield. The automated synthesis set-up implemented a common analytical autosampler for delivering all reagents for all steps of the glycan synthesis and cleavage.

Automated Chemical Oligosaccharide Synthesis: Novel Approach to Traditional Challenges

Advances in carbohydrate chemistry have certainly made common oligosaccharides much more accessible. However, many current methods still rely heavily upon specialized knowledge of carbohydrate chemistry. The application of automated technologies to chemical and life science applications such as genomics and proteomics represents a vibrant field. These automated technologies also present opportunities for their application to organic synthesis, including that of the synthesis of oligosaccharides. However, application of automated methods to the synthesis of carbohydrates is an underdeveloped area as compared to other classes of biomolecules. The overarching goal of this review article is to present the advances that have been made at the interface of carbohydrate chemistry and automated technology.

Chiral catalysts immobilized on achiral polymers: effect of the polymer support on the performance of the catalyst

Achiral polymeric supports can have important positive effects on the activity, stability and selectivity of supported chiral catalysts.

Design, Synthesis, and Application of Polymer-Supported Silicon-Transfer Agents for Cross-Coupling Reactions with Organolithium Reagents

The initial design, synthesis, and validation of polymer-supported siloxane transfer agents have been achieved that permit the direct use of organolithium reagents in the palladium-catalyzed cross-coupling reactions. Through rational design, two generations of polymer support were developed that significantly simplify product purification and the transfer agent recycling.

PS-BEMP as a basic catalyst for the phospha-Michael addition to electron-poor alkenes

PS-BEMP was used as a heterogeneous catalyst for the phospha-Michael addition of phosphorus nucleophiles to a variety of electron-poor alkenes. The addition reactions were generally performed with equimolar amounts of reagents under solvent free conditions. The protocol proved to be very efficient for the addition to aromatic, non-aromatic and cyclic ketones, giving good yields (78-85%) in all cases. The protocol was also extended with good results to α,β-unsaturated esters and nitriles. This demonstrates that PS-BEMP is a good catalyst for the phospha-Michael addition to electron-poor alkenes.

Synthesis, characterization and catalytic activity of novel large network polystyrene-immobilized organic bases

In view of searching for efficient solid catalysts to be used in environmentally friendly reaction conditions, novel gel-type cross-linked polystyrenes functionalized with diethylamine and 1,5,7-triazabicyclo[4.4.0]dec-5-ene, have been prepared.

Recyclable polystyrene-supported siloxane-transfer agent for palladium-catalyzed cross-coupling reactions

The rational design, synthesis, and validation of a significantly improved insoluble polymer-supported siloxane-transfer agent has been achieved that permits efficient palladium-catalyzed cross-coupling reactions. The cross-linked polystyrene support facilitates product purification with excellent siloxane recycling. Drawbacks of a previous polymer-supported siloxane-transfer agent, relating to reaction efficiency and polymer stability after repeated cycles, have been addressed.

Glycosylation efficiencies on different solid supports using a hydrogenolysis-labile linker

Automated oligosaccharide assembly requires suitable linkers to connect the first monosaccharide to a solid support. A new hydrogenolysis-labile linker that is stable under both acidic and basic conditions was designed, synthesized and coupled to different resins. Glycosylation and cleavage efficiencies on these functionalized solid supports were investigated, and restrictions for the choice of solid support for oligosaccharide synthesis were found.

Asymmetric Heterogeneous Catalysis

Limited natural resources and an increasing demand for enantiomerically pure compounds render catalysis and especially heterogeneous asymmetric catalysis a key technology. The field has rapidly advanced from the initial use of chiral biopolymers, such as silk, as a support for metal catalysts to the modern research areas. Mesoporous supports, noncovalent immobilization, metal-organic catalysts, chiral modifiers: many areas are rapidly evolving. This Review shows that these catalysts have more to them than facile separation or recycling. Better activities and selectivities can be obtained than with the homogeneous catalyst and novel, efficient reaction mechanisms can be employed. Especially fascinating is the outlook for highly ordered metal-organic catalysts that might allow a rational design, synthesis, and the unequivocal structural characterization to give tailor-made catalysts.

ULTRAMINE: a high-capacity polyethylene-imine-based polymer and its application as a scavenger resin

The synthesis of a novel high-loading polyethylene-imine resin (ULTRAMINE) is described, and its application as a scavenger resin in various acylation reactions is demonstrated. The inverse suspension polymerization technique was used for the synthesis of well-defined spherical polymer beads. Polymer beads with different cross-linking densities were synthesized according to the degree of acryloylation of the polyethylene-imine polymer. The resin was characterized by various spectroscopic techniques. The size, shape, and morphological features of the resin were demonstrated by microscopy. The resin showed excellent swelling properties in both polar and nonpolar solvents. The chemical stability of the resin in various reagents and solvents was investigated and monitored by IR spectroscopy. The mechanical stability of the beads was determined by a single-bead compressive experiment. The ULTRAMINE beads can be used as an excellent scavenger for excess acylating reagent, as demonstrated for a variety of reactions. ULTRAMINE-red resin was derived from ULTRAMINE through exhaustive reduction of the amide carbonyl groups to yield an all-amine resin.

A novel supported Katsuki-type (salen)Mn complex for asymmetric epoxidation

We have successfully prepared an unsymmetrical analogue of a Katsuki-type salen ligand having a hydroxyalkyl group at the 6-position of just one of the binaphthyl units in the ligand, and also several Mn(III) complexes; these complexes have been attached to a polymer by an ester link and such polymer catalysts have been shown to be highly enantioselective and recoverable catalysts for the epoxidation of 1,2-dihydronaphthalene.

A multipolymer system for organocatalytic alcohol oxidation

A system involving two polymer-supported reagents for the selective and organocatalytic oxidation of alcohols to aldehydes or ketones has been developed in which both polymeric reagents can be recovered and reused.

Affinity chromatography techniques based on the immobilisation of peptides exhibiting specific binding activity

Affinity chromatography is one of the powerful techniques in selective purification and isolation of a great number of compounds. New challenges in scientific research, such as high-throughput systems, isolation procedures that allow to obtain a single substance from a complex matrix in high degree of purity, low costs and wide availability, have led to the discovery of new tailor-made synthetic recognition systems. In this review the design, synthesis, purification and characterisation of peptides with recognition properties are discussed. Applications of peptide ligands are described and analytical tools mentioned.

Simple Strategy for the Immobilization of Dirhodium Tetraprolinate Catalysts Using a Pyridine-Linked Solid Support

Dirhodium tetracarboxylates are readily immobilized on agitation in the presence of highly cross-linked polystyrene resins with a pyridine attachment. A systematic study demonstrates that the polymer backbone, the linker, the terminal pyridine group, and the catalyst structure all contribute to the efficiency of dirhodium catalyst immobilization. The immobilization is considered to be due to the combination of ligand coordination and encapsulation. The dirhodium tetraprolinate catalysts, Rh2(S-DOSP)4 (1a), Rh2(S-TBSP)4 (1b), and Rh2(S-biTISP)2 (2), are all efficiently immobilized. The resulting heterogeneous complexes are very effective catalysts for asymmetric cyclopropanation between methyl phenyldiazoacetate and styrene, and under optimized conditions they can be recycled five times with virtually no loss in enantioselectivity. The three-phase test studies indicated that a very slow reaction occurs when both the catalyst and the diazo compound were immobilized, but the slow rate precluded the likelihood that the cyclopropanation was predominately occurring by a release-and-capture mechanism.