Callipeltoside A: Assignment of Absolute and Relative Configuration by Total Synthesis We thank the National Science Foundation and the National Institutes of Health for their generous support of our programs. OD was supported in part by a fellowship from the Association pour la Recherche contre le Cancer (ARC). J.L.G. was supported in part by a NIH postdoctoral fellowship from the National Cancer Institute. Mass spectra were provided by the Mass Spectroscopy Facility at the University of California, San Francisco supported by the NIH Division of Research Resources, and the Mass Spectrometry Facility at University of California, Irvine. We thank Dr. John Greaves of the latter facility for his assistance.

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