Solution phase synthesis instruments

It is generally accepted that the translation of solution-phase reactions to solid-phase procedures for the production of compound libraries is usually time-consuming and not always successful. The most robust solid-phase synthesis instrumentation has operational temperature and solvent compatibility limitations that impinge on the direct translation of solution-phase chemistries to the solid phase. These instrument restrictions necessitate a considerable investment in experimentation to rcdclinc the solution-phase reaction protocol for the solid phase. In spite of this apparent obstacle, a substantial number of reactions for solid-phase library production has been pubhshed. Many of these reachons cannot be exploited because the overall product yields are too low (which could lead to ambiguity in the interpretahon of the eventual assay results). Also, some reachons have a restricted range of potential monomers that lead to a hmited diversity of the compounds in the resulting library. 

Microwave and fluorous technologies have been combined in the solution phase parallel synthesis of 3-aminoimidazo[l,2-a]pyridines and -pyrazines [63]. The three-component condensation of a perfluorooctane-sulfonyl (Rfs = CgFiy) substituted benzaldehyde by microwave irradiation in a single-mode instrument at 150 °C for 10 min in CH2CI2 - MeOH in the presence of Sc(OTf)3 gave the imidazo-annulated heterocycles that could be purified by fluorous solid phase extraction (Scheme 9). Subsequent Pd-catalyzed cross-coupling reactions of the fluorous sulfonates with arylboronic acids or thiols gave biaryls or aryl sulfides, respectively, albeit it in relatively low yields. 

Finally, the introduction of focused microwave instruments further enabled to speed up the synthesis of libraries, by reducing the actual time needed for reaction [28-34]. The combination of using dedicated microwave instruments and sohd or solution phase tagging subsequently became a very powerful tool for PASP and SPOS apphcations [25,26,33-51]. 

One of the earliest instruments for automated organic synthesis was developed at Takeda in the late 1980s [90], This system was later utilized to generate more than 200 derivatives of substituted /V-(carboxyalkvl)amino acids [72] by solution-phase chemistry. 

Profile The company develops software for combinatorial chemistry, including instrument control, and product data generation, storage, and access. It also offers solution phase and solid phase combinatorial synthesis instruments that are low cost and offer a high throughput. Software runs on PCs under Windows 95 and NT 4.0 and on SGI workstations. Free short-term evaluation licenses are offered for those interested in evaluating the software. 

With the trend in dmg discovery towards smaller focussed compound libraries and the increasing importance of solution-phase techniques in parallel synthesis, fully automated systems may have lost some of their appeal. Nevertheless, a few instruments are on the market... 

In solution-phase syntheses, purification and characterization are required after each step, and the solubility of the peptide worsens and becomes more unpredictable with increased chain length. With the advent of SPPS, particularly with aid of automated instruments, the time required for the synthesis of peptides has been reduced from weeks or months to hours or days. 

Since 1986, when the very first reports on the use of microwave heating to chemical transformations appeared [147,148], microwave-assisted synthesis has been shown to accelerate most solution-phase chemical reactions [24-27,32,35]. The first application of microwave irradiation for the acceleration of reaction rate of a substrate attached to a solid support (SPPS) was performed in 1992 [36]. Despite the promising results, microwave-assisted soHd-phase synthesis was not pursued following its initial appearance, most probably as a result of the lack of suitable instrumentation. Reproducing reaction conditions was nearly impossible because of the differences between domestic microwave ovens and the difficulties associated with temperature measurement. The technique became a Sleeping Beauty interest awoke almost a decade later with the publication of several microwave-assisted SPOS protocols [37,38,73,139,144]. There has been an extensive... 

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