Hemiacetal Formation using Glutaraldehyde

Several authors have used glutaraldehyde (GTA) for HA crosslinking. GTA crosslinking needs to be performed under acidic conditions to obtain the acetal crosslinked product. Since this reaction is reversible under acidic pH, the acetal crosslinked hydrogel is obtained by neutralising the gel [41]. Another disadvantage of this strategy is the toxicity associated with GTA that limits its application in the biomedical field. 

Methacrylated HA was synthesised by esterification with methacrylic anhydride in water at basic pH. The HA-methacrylate derivative was photopolymerised into networks with a wide range of physical 

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When using aliphatic aldehydes tethered to arene motifs as substrates, an enan-tioselective sequential aza-hetero-Diels-Alder and Friedel-Crafts reaction was successfully achieved by the same group [63]. Similarly, optically active lactone[3,3-b] piperidine skeletons 140 can be obtained by tandem aza-hetero-Diels-Alder reaction-hemiacetal formation-oxidation from a,P-unsaturated imines 136 and glutaraldehyde (139) (Scheme 38.41) [64]. Enamine catalysis of the inverse-electron-demand aza-hetero-Diels-Alder reaction was further extended to o-benzoquinone diimide 141 by Chen s group [65]. Various hydroquinoxalinones 142 can be obtained in high yields with excellent enantioselectivities (Scheme 38.42). 

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