Isolation, semi-synthesis, free-radicals scavenging, and advanced glycation end products formation inhibitory constituents from Parmotrema tinctorum

Abstract

Bioassay-guided separation of acetone extract from lichen Parmotrema tinctorum (Delise ex Nyl.) Hale led to the isolation of six major phenolic constituents (1–6). Compounds structures were established using NMR and mass spectral techniques. Further, to develop libraries on these scaffolds, a series of semi-synthetic derivatives were prepared (1a–1f, 2a–2b, 3a, 5a) and investigated for their free-radicals (2,2-diphenyl-1-picrylhydrazyl and 2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS)) scavenging and advanced glycation end products (AGEs) formation inhibitory activities. Amongst tested derivatives, 1a, 1d, 1e, 2a, and 5a showed strong ABTS scavenging potentials comparable to Trolox. In addition, these derivatives also manifested moderate AGEs formation inhibitory activities.