4-vinylphenylboronic acids

Scheme 15.2 Covalent imprinting of a-phenyl-D-mannopyranoside in a divinyl benzene/4-vinylphenylboronic acid matrix, via the formation of covalent boionic ester linkages between the 4-vinylphenylboronic acid and the carbohydrate. Adapted from Wulff, Vesper, et al. (1977). Copyright 1977 Wiley InterScience.

Covalent interactions (Fig. 7) this approach involves the formation of an easily cleavable functionalised monomer-template complex [61, 18]. The first example of an imprinted polymer network was prepared by Wulff s group and used the reversible formation of an ester bond between a diol and 4-vinylphenylboronic acid [15]. The reaction rates to reach equilibrium between the ester and boronic acid are comparable to those obtained with... 

Fig. 2-2 Covalent imprinting of mannopyranoside using its 4-vinylphenylboronic acid ester as a functional monomer...

By removing water under a reduced pressure at 40 °C, the ester of 4-vinylphenylboronic acid (0.30 g, 2.0 mmol) and sialic acid (0.62 g, 2.0 mmol) were prepared in dry pyridine (200 mL). The product was directly used for the polymerization (the covalent conjugate did not have to be isolated, since its formation was almost quantitative). This ester, ethylene glycol dimethacrylate (5.6 g, 28.2 mmol) and ADVN were dissolved in DMF (3.2 mL), and the polymerization was initiated by irradiating with UV light at 4 °C. After 12 h, the polymer was ground, and treated with 1 1 mixture of 0.01 M hydrochloric acid and methanol. By this post-treatment, the boronic acid esters were hydrolyzed and the sialic acids were removed from the polymer [2],... 

Preparation of a structure such as that represented in Figure 2-1 was possible by the attachment of two 4-vinylphenylboronic acids to a 3,4-disubstituted D-mannitol derivative yielding the templated monomer 1. This monomer was then copolymerized with a co-monomer such as methyl methacrylate (MMA) [17,18], As shown in Scheme 2-1, the copolymerization involves a cyclopolymerization of monomer 1, since no crosslinking... 

To clarify the second topic, boronic acids with strongly enhanced reactivity were prepared [6]. It was found that by the introduction of e.g. an o-dimethyl-aminomethylene group, an enhancement resulted in the kinetics of the transesterification as well as of the esterification and hydrolysis by 6-8 orders of magnitude. Therefore in monomer (1) the 4-vinylphenylboronic acid moiety was replaced by that of (2) [7] and crosslinked polymers were prepared from this monomer as described above. After splitting off the template, these polymers were also investigated by liquid chromatography. However, there was only some enhancement in mass transfer [8]. Similarly, chromatographic results were somewhat improved by the addition of piperidine or ammonia to the mobile phase. 

---