Synthesis of the ABCD Ring System of Azaspiracid We thank Drs. D. H. Huang and G. Siuzdak for NMR spectroscopic and mass spectrometric assistance, respectively. This work was financially supported by the National Institutes of Health (USA), The Skaggs Institute for Chemical Biology, a predoctoral fellowship from Bristol-Myers Squibb (to F.B.), postdoctoral fellowships from The Skaggs Institute for Research (to W.Q.), the Academy of Finland, the Ella and Georg Ehrnrooth Foundation and the Tauno Tönning Foun

Abstract

Previously attempted spirocyclizations to form the ABCD ring system of azaspiracid (1) have proven unsuccessful owing to the anomeric effects that favor the formation of the undesired 13S diastereomer. By the use of a hydrogen bond donor as an auxiliary group, such anomeric effects were successfully overcome. Thus, the first synthesis of the ABCD ring system of azaspiracid with the proper 13R configuration of the C13 stereocenter was achieved.