STRUCTURES OF NOSTOCYCLOPHANES-A-D

Nostocyclophanes A-D are the cytotoxins associated with the blue-green alga Nostoc linckia (Roth) Bornet ex Bornet & Flahault (UTEX B1932). The gross structures of these [7.7]paracyclophanes have been elucidated by mass and NMR spectral analyses and the relative and absolute stereochemistry of nostocyclophane D determined by X-ray crystallography. Since the CD spectra of the four compounds are essentially identical, nostocyclophanes A-D are proposed to have the same stereochemistry. The sugar unit in nostocyclophanes A and B has been shown to be D-glucose by semisynthesis of nostocyclophane B 9-O-(2,3,4,6-tetra-O-acetyl)-beta-D-glucopyranoside from nostocyclophanes B and D.