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Assignment of the stereochemistry of spiroxamine by two‐dimensional NMR spectroscopy and stereoselective chemical synthesis

Spiroxamine is a new powdery mildew fungicide in cereals consisting of four biologically active isomers (two diastereomers, four enantiomers). The four isomers were separated by preparative high‐performance liquid chromatography (HPLC) on a chiral stationary phase. At this stage it was not possible to assign their stereochemistry. Using stereoselective synthesis starting with the corresponding chirally pure glycerol derivates, the configuration at the asymmetric center, could be fixed. The resulting diastereomers were separated by preparative HPLC. Using COSY, HSQC and NOESY NMR spectroscopy it was possible to assign the configuration of the amino residue relative to the cyclohexyl ring. The 600 MHz 1H NMR spectra permitted a complete assignment of all proton signals. The stereochemical assignment is based on NOEs observed in the NOESY spectrum. © 1998 John Wiley & Sons, Ltd.