Loddigesiinols G-J: α-glucosidase inhibitors from Dendrobium loddigesii.

Four new polyphenols, loddigesiinols G-J (compounds 1-4) and a known compound, crepidatuol B (5), were isolated from the stems of Dendrobium loddigesii that have long been used in Traditional Chinese Medicine and have recently been used to treat type 2 diabetes. Compounds 1-5 structures were elucidated based on spectroscopic analysis. The absolute configurations of compounds 1-4 were determined using theoretical calculations of electronic circular dichroism (ECD), and the absolute configuration of compound 5 was determined by a comparison of the experimental ECD spectra and the literature data. Compounds 1-5 are strong inhibitors of α-glucosidase, with IC50 values of 16.7, 10.9, 2.7, 3.2, and 18.9 µM, respectively. Their activities were significantly stronger than trans-resveratrol as a positive control (IC50 values of 27.9 µM).

Determination of the absolute stereochemistry of two new aristophyllene sesquiterpenes: a combined theoretical and experimental investigation.

Aristoyunnolins G (1) and H (2), two new diastereoisomeric sesquiterpenes featuring a rare aristophyllene skeleton, were isolated from the traditional Chinese medicine Aristolochia yunnanensis. Their absolute stereochemistry involving three chiral centers was determined by combined chemical, spectral, and Density Functional Theory (DFT) calculation methods.