Boronic Acids Mediate Glycoside Transport through a Liquid Organic Membrane via Reversible Formation of Trigonal Boronate Esters

A supported liquid membrane (SLM) with resorcinarene for facilitated transport of methyl glycopyranosides: Parameters and mechanism relating to the transport

“…According to the results of Table 3, we find that the values of apparent diffusion coefficients obtained (about 10 −4 cm 2 s −1 ) for each studied methyl aldopyranoside are higher compared to literature values (about 10 −6 cm 2 s −1 ) [15,19,[35][36][37][38]. The same remark was made for alditols and sugars [12,23,39,40].…”

“…To explain this phenomenon, we suggested in the transport of alditols [23], that the diffusion process is perhaps accompanied by a convection movement, which would be responsible for accelerating the diffusion of complexes in the membrane. While the hypothesis of "fixed-site jumping" proposed by Smith et al in the transport of sugar through a plasticized membrane of triacetate cellulose [18][19][20][21][35][36][37][38][41][42][43] is another suggestion, more likely to clarify this point. This theory assumes that the substrate moves by jumping from site to site, inside the membrane.…”

Sugar Separation Using Liquid Membranes and Boronic Acid Carriers

“…The transport mechanism invoked to explain these observations is described in Figure 1. Subsequent studies by Czarnik (14,15) and our group (16)(17)(18)(19)(20) showed that other hydrophilic diol-containing compounds, namely nucleosides and aryl glycosides, could be transported by this ionpair process. Under low extraction conditions the order of transport enhancements reflected the known order of boronic acid affinities for cyclic diols which is cis-α,β-diol > cis-a,y-diol > trans-a,y-diol » trans-a,P-diol.…”

Chemoselective reactions and their applications in metabolite isolation and analysis.

“…To avoid poisoning enzymatic transformations of sugars by degradation byproducts, the sugars can be chemically "transported" to a clean aqueous solution via reversible boronic ester formation [228]. Boronic acids can selectively chelate diols on sugar molecules and transfer the bound sugars to into an organic phase via ion matching and then release them in a "clean" aqueous phase prior to subsequent fermentation or other enzymatic processes [229]. This approach employs molecular recognition of cisdiols whereby the sugar diols are deprotonated by alkaline hydrolyzate and chelate with boronic acids across immiscible layers forming anionic tetrahedral boron centers.…”

“…Lipophilic cationic salts, such as ammonium salts, in organic phase pair with the boronate anions and pull them into the organic solution via a reactive solvent extraction process [229,230]. The resulting salts are readily hydrolyzed in a clean, aqueous acidic solution to regenerate the sugars, which then are employed for either of the techniques mentioned above (Figure 4.1.).…”