New Triterpenes from Maytenus robusta: Structural Elucidation Based on NMR Experimental Data and Theoretical Calculations

The structural elucidation, including the stereochemistry of compounds 4 and 7 , was based on the chemical shifts assignments obtained from 1D ( 1 H, 13 C and DEPT-135) and

Based on different spectroscopic data including HRESIMS, 1D ( 1 H NMR and 13 C NMR) and 2D NMR (COSY, HSQC, and HMBC), the structures of the compounds were established as

These signals were attributed to hydrogen atoms of conjugated double bond with carbonyl group.. The signal at δ C 29.5 corresponded to

Table 1 shows the 1 H-NMR chemical shifts of the methine protons (joined to C- α ), the 13 C-NMR chemical shifts of C-1, C- α , C-1’ and C-4’, the values of the Hammett..

The linkage between the two sugar units was established from the HMBC correlation between the signals of the anomeric proton of the rhamnose at G 5.36 and the carbon signal of

The relative stereochemistry for the major products was again determined based on the analysis of the 13 C NMR chemical shifts of the corresponding 5-membered

Selected bond length and bond angles from X-ray diffraction and B3LYP method, experimental and theoretical 1 H and 13 C NMR chemical shifts, experimental and theoretical

The NMR data of this new compound 136 (Figure 33 ) was assigned by 1D and 2D experiments and an R configuration at C-11 was confirmed by 1 H NMR analysis of the Mosher’s