Synthesis based on affinity separation

Koichi Fukase et al. reported an example of oligosaccharide synthesis by combining microreactors and an isolation strategy called synthesis based on affinity separation (SAS) [72, 73], The glycosylation was carried out under continuous flow, and the mixture was directly sent to the stainless steel affinity column, and the flow channel was switched to wash the column with CH2C12. The labeled disaccharide was trapped in the column later to be eluted with a mixture of CH2C12 and methanol to obtain the isolated oligosaccharide product. 

Scheme 16.31. Synthesis based on affinity separation for oligosaccharide synthesis.

Synthesis Based on Affinity Separation A New Methodology for High-Throughput Synthesis Using Affinity Tags... 

Fig. 1. Synthesis based on affinity separation. S substrate, R reagent, SR product, B byproduct, a) reaction in solution, b) adsorption of tagged product, c) elution of excess reagent and untagged byproduct, d) desorption of tagged...

A new tag strategy, termed syndiesis based on affinity separation (SAS) , was developed for high throiq)ut synthesis of organic conq)oimds. In this method, the desired tagged conq)ound was separated from the reaction mixture by solid-phase extraction using specific molecular recognition. The interaction between a crown ether (32-crown-lO) and ammonium ion and the interaction between a barbituric acid derivative and its artificial receptor were used for SAS. 

Because carbon has a natural affinity for adsorption of heavy hydrocarbon species and polar molecules, CMS membranes need to be used at a sufficiently high temperature to eliminate contribution/interference of the adsorption. In contrast, strong adsorption of heavier molecules may be used to separate those species by adsorption as discussed earlier by the SSF mechanism (Rao and Sircar, 1993b). The SSF carbon membranes typically have pore dimensions much greater than those needed for CMS membranes since the separation is based on the adsorbed species effectively blocking permeation of other components (Fuertes, 2000). Carbon membranes are resistant to contaminants such as H2S and are thermally stable and can be used at higher temperatures compared to the polymeric membranes. For the synthesis gas environment, the hydrothermal stability of carbon in the presence of steam will be a concern limiting its operation temperature. 

Glycoconjugate polymers were prepared by the copolymerization of different monomers, and immobilized on cellulose membrane for affinity separation. The synthesis of the mannose-based monomer involved the photochemical addition of 2-aminoethanethiol hydrochloride onto an alkenyl a-D-mannoside derivative 36. Of note, 37 was formed in a quantitative yield upon irradiation in MeOH at room temperature, with no competitive addition of the amino group onto the alkene (Scheme 3.24) [59]. 

Fluorous separation is based on the fact that fluorophilic molecules have an affinity for fluorous media under certain condition, while non-fluorous ones do not have such affinity. Fluorous media can differentiate such affinity, therefore, can rapidly separate fluorous compounds from the rest The choice of the method depends on the nature of the components in the mixture to be separated and the purpose of the synthesis. 

---