Tentagel resin beads

Quarrel R, Claridge TDW, Weaver GW, Lowe G, Structure and properties of tentagel resin beads Implications for combinatorial library chemistry, Mol. Diversity 1 223-232, 1995. 

Figure 9J1. (a) The conventional H spectrum of the analyte 9.1 bound to TentaGel resin beads solvated in DMSO and (b) the MAS (2 kHz) spectrum of the same sample. One tenth of the mass of the sample in (a) was used in (b) and both were collected in 16 transients. The large truncated signals arise from the resin itself (reproduced with permission from reference [81]). 

Transmission spectroscopy (2) is the simplest sampling technique in IR spectroscopy and is used for routine spectral measurements on diverse samples. Resin samples such as polystyrene or TentaGel (3) beads are usually prepared as a potassium bromide disc (pellet). A small amount, usually 1-3 mg, of finely ground solid sample is mixed with approximately 400 mg powdered potassium bromide and then pressed in an evacuated die under high pressure. The resulting discs are transparent and yield good spectra. 

Photoacoustic spectra of resin samples have also been reported (16,17). The photoacoustic spectrum of TentaGel S beads coupled via a trityl linker with Fmoc-protected tryptophan is shown in Fig. 4. Compared with the photoacoustic spectrum of native aminoethyl TentaGel S beads, the appearance of diverse carbonyl bands is clearly seen the ester band of the linker at 1750 cm-1, the carbamate band of Fmoc protecting group at 1723 cm-1, and the amide I band at 1660 cm-1. 

For combinatorial chemistry applications, high-quality FT-Raman spectra can be obtained directly from resin beads, i.e., no cleavage of the molecules from the polymeric support is necessary. This is shown in Fig. 5, where the spectra of TentaGel S beads coupled via a trityl linker with Fmoc-protected tryptophan and the native aminoethyl TentaGel S beads are overlaid. As expected, significant differences in the spectra occur in the spectral region between 1620 and 1500 cm-1 where aromatic rings show pronounced Raman activity. 

Polystyrene resin, frequently used resin material for solid-phase peptide synthesis (SPPS). The polymeric support for SPPS must be chemically inert, mechanically stable, completely insoluble in the solvents used, and easily separated by filtration. For many applications a copolymer of polystyrene with 1% of divinyl benzene as crosslinker is used. The dry resin beads are able to swell up to the five-or sixfold volume in the different organic solvents mainly used for peptide synthesis (e.g., dichloromethane or dimethylfor-mamide). For SPPS the resin material must be chemically functionalized in order to allow for attachment of a handle/liker (e.g. Wang resin), or the first amino acid (—> Merrifield resin). Hydrophilic tentacle polymers gels (TentaGel) are obtained by grafting polyethylene glycol (PEG) chains with an arbitrary degree of polymerization onto porous polystyrene beads. 

Kahne, Still and coworkers reported recently the solid-phase parallel synthesis and screening of a carbohydrate library using the sulfoxide glycosylation reaction. The library was constructed on TentaGel resin and contained approximately 1300 di- and trisaccharides. A chemical tag was incorporated after every reaction step in order to monitor the history of the beads and to facilitate structure elucidation. The synthesis of the library is outlined in Scheme 2.6.3. 

While polystyrene is an inexpensive resin that has been used widely, especially in Boc-SPPS and in Fmoc-SPPS of shorter sequences, other resins provide certain advantages. An important class of resins is constructed from a polystyrene core onto which PEG chains have been attached. TentaGel (Rapp Polymere, Germany) carries amino groups at the end of the PEG chains. It is important to realize that these polystyrene microparticles have been functionalized with PEG inside out, thus not only on the surface of the resin bead. These supports often provide higher purity of synthesized peptide, especially with longer sequences and with peptides that are prone to aggregate. 

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