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

Abstract

Bioassay-guided separation of acetone extract from lichen <i>Parmotrema tinctorum</i> (Delise ex Nyl.) Hale led to the isolation of six major phenolic constituents (<b>1-6</b>). 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 (<b>1a-1f, 2a-2b, 3a, 5a</b>) 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, <b>1a, 1d, 1e, 2a</b>, and <b>5a</b> showed strong ABTS scavenging potentials comparable to Trolox. In addition, these derivatives also manifested moderate AGEs formation inhibitory activities. [Formula: see text].