Urea, condensation with dialdehyde

GC of dialdehydes of the malonaldehyde type was performed after condensation with urea [116] (Scheme 4.22). The 2-hydroxypyrimidine produced is chemically stable, but... 

Several copolymers and condensates of oxidized starches with polymers have been developed. For example, products of starch dialdehyde condensation with acrylamide were prepared for further copolymerization with various monomers to form resins for coatings, molding powders,585 and materials for immobilization of enzymes, for instance, alpha amylase.586 Hypochlorite-oxidized starches were also reacted with acrylonitrile.507,521 Hypochlorite-oxidized starches were allowed to react with allylated starch dialdehyde,587 polycondensates of ammonia-dimethylamine-epichlorohydrin,588 polycondensates of starch dialdehyde with melamine,589 urea433,541,590 capable of precipitation of tannin591, carboxyamides,411 urea and formaldehyde,592 proteins,524,593,594 polyfyinyl alcohol),595 alkylammonium salts,519,596 alkoxyalkylamines,597... 

Factors influencing the choice of synthetic routes to pyrimidines depend very much upon the substitution pattern of the desired product. For pyrimidines unsubstituted at the 4- and 6-positions, a two-component ring synthesis reaction involving a 1,3-dialdehyde and a urea or amidine derivative is the most straightforward route, but only if the dialdehyde is readily available. For example, synthesis of 2-chloro-5-(2-pyridyl)pyrimidine 989, an intermediate in the synthesis of a selective PDE-V inhibitor, was achieved in two steps in 40% overall yield by condensation of 2-(2-pyridyl)malondialdehyde 987 with methylurea, followed by demethylation/chlorination of the pyrimidinone 988 with a mixture of POCI3 and PCls <20070PD237>. 

Reaction of starch dialdehyde with urea gave a condensation product.442,2633 Carboxyamides,2624 including acrylamide,524,585 were also allowed to react with starch dialdehyde. Condensation can occur between starch dialdehyde and macromolecules containing amido groups, for instance, epichlorohydrin-crosslinked polyamide resin,598 ammonia-diethylamine-epichlorohydrin copolymer,588 dicyanamide-formaldehyde resins,565,566 quaternary alkylam-monium compounds,596,610,611 amino acids,2634,2635 protein,626,2636-2639 and aminoalkylated starch.2515 The reactions are favored by low pH. The guanidino moieties of proteins entered the condensation the most readily. 

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