Synthesis of O-glycolyl-linked neuraminic acids through a spirocyclic intermediate

[reaction: see text] The neuraminic acid derivative 5 is readily converted in several steps to the neuraminic acid dimer 12, linked through the hydroxyl of a 5-N-glycolyl group in an alpha-2,5 glycosidic linkage. The sequence is shown to proceed through a spirocyclic intermediate 9 by in situ NMR experiments. Similar derivatives of N-glycolylneuraminic acid (Neu5Gc), including polymers, have been identified from marine sources, including starfish and sea urchins, often as sulfated derivatives and are thought to mediate sperm-egg recognition.