Abstract
Aldehyde groups enable facile conjugation to proteins, enzymes, oligonucleotides or fluorescent dyes, yet there are no literature examples of water‐soluble aldehyde‐functional vinyl monomers. We report the synthesis of a new hydrophilic cis‐diol‐based methacrylic monomer (GEO5MA) by transesterification of isopropylideneglycerol penta(ethylene glycol) using methyl methacrylate followed by acetone deprotection via acid hydrolysis. The corresponding water‐soluble aldehyde monomer, AGEO5MA, is prepared by aqueous periodate oxidation of GEO5MA at 22 °C. RAFT polymerization of GEO5MA yields the water‐soluble homopolymer, PGEO5MA. Aqueous periodate oxidation of the terminal cis‐diol units on PGEO5MA at 22 °C affords a water‐soluble aldehyde‐functional homopolymer (PAGEO5MA). Moreover, a library of hydrophilic statistical copolymers bearing cis‐diol and aldehyde groups was prepared using sub‐stoichiometric periodate/cis‐diol molar ratios. The aldehyde groups on PAGEO5MA homopolymer were reacted in turn with three amino acids to demonstrate synthetic utility.
Highlights
Aldehydes are extremely useful functional groups in synthetic organic chemistry: they can be oxidized to give carboxylic acids, reduced to afford alcohols, undergo Schiff base chemistry and formacetals.[1]
More than 99 % conversion was achieved and the resulting PAGEO5MA30 was well-defined, as indicated by its relatively narrow, unimodal GPC trace (Mn = 11 100 g molÀ1; = 1.18; Figure 2 b). 1H NMR signals for the terminal aldehyde and geminal diol groups were detected for this homopolymer
To investigate the scope of such new water-soluble aldehyde-functional polymers for conjugation with biologically-relevant compounds, PAGEO5MA37 homopolymer was reacted in turn with three amino acids to form the corresponding Schiff base, followed by in situ reductive amination using excess NaCNBH3 (Scheme 3)
Summary
Aldehydes are extremely useful functional groups in synthetic organic chemistry: they can be oxidized to give carboxylic acids, reduced to afford alcohols, undergo Schiff base chemistry and form (hemi)acetals.[1]. Utilizing NaIO4/cis-diol molar ratios of 0.10, 0.50 or 0.75 produced a series of water-soluble P(GEO5MAnstat-AGEO5MAm) statistical copolymers with approximate degrees of aldehyde functionality of 0.11, 0.49 and 0.78 respectively, as estimated from 1H NMR spectroscopy studies (Table 1, Figure 3). To investigate the scope of such new water-soluble aldehyde-functional polymers for conjugation with biologically-relevant compounds, PAGEO5MA37 homopolymer was reacted in turn with three amino acids (glycine, lysine or cysteine; amino acid/aldehyde molar ratio = 1.0) to form the corresponding Schiff base, followed by in situ reductive amination using excess NaCNBH3 (Scheme 3) These aqueous reaction mixtures were stirred at 35 8C for 48 h, with 1H NMR spectroscopy studies indicating very high extents of reaction (> 99 %) in each case (Figure S7). We anticipate that this new hydrophilic aldehydic vinyl monomer and its corresponding copolymers will offer a range of potential applications in the fields of cell biology and biomaterials
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