Studies on aloe. Part 6. Conformation and absolute configuration of aloins A and B and related 10-C-glucosyl-9-anthrones

Abstract

The conformation and absolute configuration of the two diastereoisomeric aloins A (2a) and B (2b) were proven on the basis of shielding and deshielding effects and specific NOE (nuclear Overhauser effect) associations in ¹H NMR spectroscopy. Previous ¹H NMR assignments were corrected and ¹³C NMR spectra recorded for the first time. Taking into account analogies in CD spectra as well as in NOE effects, the absolute configuration of C-10 was suggested for the epimeric pairs of naturally occurring 1,8-dihydroxy-10-C-β-D-glucopyranosyl-9-anthrones.