Sequestering reagents

S. Chaberek and A. E. Martell, Organic Sequestering Reagents , Wiley, New York, 1959. 

The four, earliest, sequestering reagents used therapeutically for treating metal ion excesses have been used to illustrate the principle of... 

Table 4.1 Earliest sequestering reagents for treating metal ion excesses. The chemical formulae are given below. As one descends the Table, increasing softness of donor atoms is paralleled by increasing softness of the acid removed (From Fiabane and Williams, 1977, with permission.)... 

A further possible advantage of the use of dendrimers as sequestering reagents in comparison with more conventional complexing agents results from the inherently different design of dendrimers, whose internal and external functionaHties allow, as mentioned already, the creation of an inner binding microenvironment with defined coordination sites and a solvent-compatible, hydrophilic or hydro-... 

Polymer-supported reagents and other solid sequestering agents may be used to generate an array of 1,2,3,4-tetrasubstituted pyrrole derivatives using the Barton-Zard reaction as a key pyrrole formation reaction. Pure pyrroles are obtained without any chromatographic purification... 

The devices usually contain antibody immobilized on a membrane surface above a filter and absorbent pad (Figure 7.16). The sample is placed in the device and passes through the membrane into the absorbent pad. Where analyte is present in the sample it is sequestered by the antibody on the membrane and is then visualized by addition of a labelled second antibody. Labelled second antibody not bound to analyte also passes into the absorbent pad, sometimes with the aid of a wash solution. The labelled molecule may be an enzyme, which would then require addition of a suitable substrate, or a label such as colloidal gold, which has the virtue of being visible without the aid of a second reagent. 

A single, functionalized resin can be designed to capture more than one reactant. For instance, resin 3 has been used to sequester excess alde-hydes/ketones and thioacetic acids.28 Specifically, the polyamine resin 3 did this by forming the resin-bound thiazolidinones 11 and salts from the excess reagents, leaving the desired thiazolidinones in solution. 

Mercaptopropionic acid has been used as a scavenger in detritylation of protected imidazoles. In the purification, A-21 tertiary amine-functionalized resin 23 sequestered excess of this acidic reagent, the tritylated byproduct formed from it, and TFA (reaction 6).32... 

A polymer-bound guanidine base 31 has been used for the formation of aryl ethers from suitable phenols and alkyl halides. In addition to serving as a base to affect deprotonation, reagent 31 also acts as a sequestering agent for excess starting phenol (reaction 11).26... 

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... 

Polymer-assisted solution-phase synthesis offers strategies for chemical library construction that complement solid-phase methods. Tools now available include chemoselective sequestering resins, bifunctional solution-phase linking reagents, bifunctional chemically tagged reagents, and an... 

---