We have demonstrated for the first time that the syn-anti orientation of 5′-amino-5′-deoxyuridine (1b) can readily be switched by adding borate as an extermal controlling factor. In borate added phosphate buffer, the syn/anti ratio of 1b dramatically increased with increasing borate concentration. This unique syn preference is most probably driven by the cooperative action of cyclic esterification of the 1b’s 2′,3′-cis-diol with borate and of hydrogen-bonding formation between 2-carbonyl oxygen and 5′-amino proton.
Die Reaktion von Maleinsäure mit Harnstoff sowie Thioharnstoff wurde in wäßtriger Phosphorsäure bzw. Pyrophosphorsäure unternommen. In jenem Fall wurde Fumarsäuremonoureid, und in diesem Fall wurde 5-Carboxymethyl-thiazolidin-2,4-dion gewonnen. Die Umsetzungen der ungesättigten Monocarbonsäuren mit Harnstoff und Thioharnstoff respektiv zu Dihydrouracil- und Thiazandionderivaten wurden auch versucht.
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