Confirmed by NOE measurements

In the reaction of fused aziridines with alkene dipolarophiles, the opportunity for stereoselectivity as well as facial selectivity arises since exo- or entfo-isomers can be formed (Scheme 10). In practice, maleic anhydride 6, A-methyl maleimide and JV-phenyl maleimide each reacted exo-stereoselectively with TV-benzyl aziridine 69 to form adducts of type 71 (Scheme 10b), the stereochemistries of which were confirmed by NOE measurement between Hb and He. Similar reaction of the Y-phenyl aziridine 67 with N-Ph maleimide gave a 1 1 mixture of endo-adduct 72 and exo-adduct 73 (Scheme 10c). Adducts 68, 71-73 all exhibited a low-field methano-bridge proton (Ha) in the range 5 3.06-3.60 confirming the syn-facial stereochemistry of the two bridges. 

To obtain further insight into the [3 + 2] cycloaddition of alkylideneallyl cation 5, the reaction with 2,3-benzofuran was carried out as shown in Scheme 15. The reaction of 4a gave a simple [3 + 2] cycloadduct 30 as a single regioisomer in 76 % isolated yield. The regioisomeric structure of 30 confirmed by NOE measurements is well compatible with the cyclic structure of 29. These... 

Stereoselective opening of such lactone ring has been described by Yin and Linker " as depicted in Fig. 1. The structures obtained for several compounds, including disaccharides, were confirmed by NOE measurements. Standard and advanced NMR methods were used to identify synthetic derivatives of mono- and disaccharides containing following moieties morpholine, triazole and 1,4-oxazine by Reddy et pyrazole by... 

After criticism [142] of the interglycosidic NOEs observed in the previously described study a very precise approach towards the conformational analysis of thea-(l-3) bond was performed by NOE measurements of specifically deuterated compounds [143], The conformation was determined earlier by several interglycosidic NOEs to protons that have their resonances in an area of high spectral overlap. The synthesis of C-deuterated di- and trisaccharides made an unequivocal assignment of the enhanced signals possible. Thus, the enhancements of H2, H3, and H4 of the P-D-mannose upon irradiation of Hl. as well as the enhancement of HS. upon irradiation of HS. man are indicative of the rigid conformation at the glycosidic bond and confirmed the previous study. 

The conformational behaviour in solution of a dermatan-derived tetra-saccharide has been explored by means of NMR spectroscopy, especially by NOE-based conformational analysis. RDCs were also measured for the tetrasaccharide in a phage solution and interpreted in combination with restrained MD simulations. The RDC-derived data substantially confirmed the validity of the conformer distribution resulting from the NOE-derived simulations, but allowed an improved definition of the conformational behaviour of the oligosaccharides in solution, which show a moderate flexibility at the central glycosidic linkage. Differences in the shapes of the different species with the IdoA in skew and in chair conformations and in the distribution of the sulphate groups were also highlighted.28... 

A solution of Cp2TiCl [52] (0.43 g, 2 mmol) in THF was added dropwise to a solution of the epoxide (1.0 mmol) in 20 mL of THF at room temperature. A solution of 1A HC1 in ether (4 mL) was added, and the mixture was stirred for 10 min. The precipitated solid was removed and the filtrate was added to excess (5 mL) of aqueous saturated sodium di-hydrogenphosphate. The organic layer was separated and the aqueous layer was extracted with ether. The product was isolated as a mixture of exo- and endo-Me isomers in 70% yield. The structures were confirmed by l3C-NMR, H-NMR, chemical shift correlation mapping, nOe measurements, and attached proton test (APT) experiments. No [a]D was recorded because the product was isolated as a mixture. 

In another application, 19F NMR studies have provided critical information on the bioactive conformation of taxoids. Fluorine-containing taxoids have been used as probes for NMR analysis of the conformational dynamics of paclitaxel in conjunction with molecular modeling [166], The dependence of the 19F chemical shifts and the Jm--ny values of these fluorinated analogues is examined through 19F and H variable-temperature (VT) NMR measurements. The experiments clearly indicate highly dynamic behavior of these molecules and the existence of equilibrium between conformers. The analysis of the VT NMR data in combination with molecular modeling, including restrained molecular dynamics (RMD), has identified three key conformers, which were further confirmed by the 19F- H heteronuclear NOE measurements. 

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