Solid supports swelling

Solid support lasoiuble. functionalized polymeric material to which library members or reagents may be attached, often via u linker, allowing them to be readily separated fmtn solvent, cxcc.ss reagent, etc. Typically, the solid support swells in. solvent. allowing reactions to occur in the interior of the bead nr oilier form. This greatly increases the available surface area for reaction. 

Cross-hnked polyacrylamides are a group of hydrophihc solid supports introduced primarily for preparation of biopolymers (Fig. 4). Unhke PS resins, polyacrylamides have excellent swelling capacity in both protic (water, alcohols) and aprotic (dichloromethane, dimethylformamide) solvents [88]. These beads are stable towards bases, acids, and weak reducing and oxidizing agents [89]. Predictably, conditions under which amide bonds are cleaved (i.e., sodium in liquid ammonia) [90] lead to rapid decomposition of the polymer. 

Bis(indolyl)nitroethanes are obtained readily in 7-10 min in high yields (70-86%) on fine TLC-grade silica gel (5-40 pm) by Michael reaction of 3-(2 -nitrovinyl) indole with indoles. The same reaction reported requires 8-14 h for completion at room temperature [77]. Several functionalized resins have been prepared from Merrifield resin via a MW-assisted procedure that utilized mixed solvent system to facilitate the swelling of resins and coupling with microwaves [78], These resins can function as solid supports or polymeric scavengers in solid phase synthesis. 

Low cross-linked polystyrene resins (1% divinylbenzene) is probably the most popular solid support. These resins swell to 2-6 times their original volume depending on the solvent used. Swollen resin, after removal of solvent and without excessive drying, remains in a rubbery state and can be easily flattened for FTIR study in the transmission mode. The support-bound compound should be washed free of reagent and solvent. 

While considerable efforts have been spent in the past few years in the field of solid supports for combinatorial chemistry [73], most of them were devoted to modified polystyrenic beads with different sizes, loadings or swelling properties [74], or carrying different functionalities or linkers for library synthesis [75], or to solid supports different from resin beads (pins [76], cellulose [77], soluble supports [78], and so on). Few reports dealt with labelled solid supports prepared by chemical reactions (see the previous paragraphs) and significant efforts in the field of material sciences to obtain intrinsically labeled, nonchemically encoded, easily readable, combinatorial solid supports have not been reported. 

Weigh out 10 pmol solid support, put this into a reactor well and swell the support with 1 mL DMF for 15 min. 

Incompatibility between the swelling behavior of the solid support and the solvents needed in the reaction. 

The use of such methods for the detection and monitoring of other resin-bound functional groups will become common as more and more staining protocols will be transferred from solution synthesis to SPS. Adaptation of these reagents to the presence of the solid support, for example, by choosing a solvent where the beads swell properly, may sometimes be necessary. 

Gel-phase NMR spectroscopy is a very convenient technique for the spectroscopic characterization of functionalized solid supports.Optimal conditions for acquiring standard gel-phase NMR spectra from a variety of resins are well-established optimal conditions, i.e. maximum swelling, result in reasonably narrow lines for the pendant groups. This method has the additional advantage of not requiring any special instrumentation besides a conventional FTNMR spectrometer and a conventional probe. In addition to NMR spectroscopy, NMR l and NMRt l spectroscopy can also be used in those cases where fluorine or phosphorous is present in the handle or in the first amino acid. 

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