Polymer-supported quenching reagents

Scheme 2.34 Polymer-supported quenching reagents for paraiiei purification.

Booth RJ, Hodges JC, Polymer-supported quenching reagent for parallel purification, J. Am. Chem. Soc., 119 4882-4886, 1997. 

RJ Booth, JC Hodges. Polymer supported quenching reagents for parallel purification. Am Chem Soc 119 4882,1997. 

Ault-Justus, S. E., Hodges, J. C. Wilson, M. W. Generation of a Library of 4-Thiazolidinones Utilizing Polymer Supported Quench (PSQ) Reagent Methodology, Biotechnol. Bioeng. 1998, 61, 17. 

During the last two years the interest in separation techniques based on reactive polymers had a renaissance and many applications of supported quenching reagents in solution phase parallel syntheses were described. Ion exchange resins - as well as polymers with covalently attached... 

Finally, a five-step solution phase synthesis of benzoxazinones used a combination of reactant-sequestering resins, a bifunctional linking reagent, a polymer-supported reagent, and solid-phase quench for synthesis and purification (Scheme 14)22 This features... 

The field of organic chemistry has seen the most extensive use of polymeric materials as aids in effecting chemical transformation and product isolation. Insoluble polymer supports have been used as handles to facilitate these functions. As chemical reagents can be bound to an insoluble polymer carrier and used in organic synthesis [117,118], polymer-bound reagents can also be used to assist in the purification step of solution-phase reactions [119,120]. The latter are known as scavenger resins. These are added to the reaction mixture upon completion of the reaction in order to quench and selectively bind to the unreacted reagents or by-products. The polymer-bound impurities are then removed firom the product by simple filtration to obtain pure compounds. For example, aminomethylated poly(styrene-co-divinyl benzene) can be used to remove acid chlorides, sulfonyl chlorides, isocyanates, thiocyanates, and proton. Similarly, 2-Chlorotrityl resins have been developed for the attachment of carboxylic acids, alcohols. 

A further example used the supported amino alcohols 45,46 and 47 (Scheme 4.76), where the reagents were pumped up from the bottom of the polymer using a pair of long needles connected to peristaltic pumps. The product was collected from the top using another pump and quenched in a solution of dilute hydrochloric acid. For the first run with catalyst 46, the yields and ee were excellent (94% yield in 97% ee), but when 46 was recovered and reused, the yield dropped to 75% and the ee to 50%. This was ascribed to degradation of both the chiral and backbone sites of the polymer by diethyl zinc, again demonstrating that not only do the solid supports need to be mechanically sound but both the backbone support and active site must be also chemically resistant to the reaction conditions [171]. 

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