Carnegie Mellon University and Mspin
Three tetranortriterpenoids were isolated as hemiacetals (the C-23 epimeric xylorumphiins M− O (4−6 )), which could not be purified due to the equilibration of the hemiacetal epimers in solution, hence giving complex spectra. In order to enable purification, compounds were acetylated and the R and S epimers could be separated. However, for these C-23 epimers, use of standard NOESY and ROESY techniques did not permit their differentiation, due to long distances between H-23 and protons from the main skeleton.
