DEVELOPMENT OF NEW NMR TECHNIQUES AND THEIR APPLICATION TO STRUCTURAL ANALYSIS OF NATURAL PRODUCTS

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In this project, we have investigated the applications of a new NMR technique called decoupled-HMBC (D-HMBC) developed by our group to structural analysis of complicated natural products. In addition, we have carried out analysis of stereo-structures by computer calculations using a newly developed software program (MolSkop) by the JEOL group.As a result, D-HMBC has turned out to be an excellent method to observe small long-range ^<13>C-^1H couplings, which can not be detected by hitherto available techniques. In addition, we have improved the data processing procedures ; ood NMR spectra with improved signal to noise ratio were obtained when data processing was made by the phase sensitive mode of the t2 axis data and by power mode of the t1 axis data.Comparison of this new technique (D-HMBC) with the pulse field gradiet (PGF) technique has revealed that PFG is superior to D-HMBC in most cases, but when the signal intensities were considerably affected by J-modulation caused by ^1H-^1H spin couplings, D-HMBC gave better results and so a method of choice in such situation. In this project, we have established experimental conditions for obtaining good D-HMBC spectra. This technique has been implemented to commercially available NMR instruments is now being used by some groups.We have improved the MolSkop software program and proved that it is a useful method to structural analysis of complicated polycyclic systems.In addition, we have recently developed a new technique called TANGO-D-HMBC,which is quite useful for detecting ^<13>C-^<13>C couplings separed by two bonds. Such kinds of long-range ^<13>C-^<13>C couplings were hardly observed by other methods. This pulse sequence is quite useful for datailed analysis of the ^<13>C- labeling pattern with microbial products formed by arrangement of the carbon skeleton.