One. Structure of tubercidin-5'-a-glucopyranose -- Two. Structures of nostocyclophanes A-D -- Three. Determination of the total structures of puwainaphycins A-E -- Four. Biosynthetic studies of microcystin-LR

Abstract

Tubercidin-5'-α-D-glucopyranose is the major cytotoxic and fungicidal nucleoside in Tofypothrix distorta (BL-11-2). Its structure was elucidated by spectral analysis and enzymatic degradation to tubercidin, which was first isolated from Streptomyces tubercidicus, and D-glucose. 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 0 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 nostocyclophane A and B has been shown to be D-glucose by semisynthesis of nostocyclophane B heptaacetate from nostocyclophanes B and D.