Synthesis of 3-acyloxyxanthone derivatives as α-glucosidase inhibitors: A further insight into the 3-substituents' effect.

Considerable interest has been attracted in xanthone and its derivatives because of their important biological activities. In this paper, a series of novel 3-arylacyloxyxanthone derivatives 2a-p were synthesized and evaluated for their biological activities toward α-glucosidase. In comparison to the parent 1,3-dihydroxylxanthone 1a, 3-arylacyloxy derivatives 2a-p with additional aromatic ester groups at 3-position show up to 13.7-fold higher inhibitory activities. In particular, the IC50 values of compounds 2i, 2m, 2p reach 13.3, 10.6, 11.6 µM, respectively. These results suggest that addition of aromatic moieties by esterification at the 3-OH of the parent 1,3-dihydroxylxanthone is an efficient way to increase the inhibition against α-glucosidase. Different from previous multi-hydroxylxanthones, these 3-arylacyloxyxanthone derivatives show efficient inhibitory activities may due to the π-stacking or hydrophobic effects of the additional aromatic moieties rather than the H-bonding donor interaction of 3-OH. Structure-activity relationship analysis shows that the substituents on the additional aromatic ring also influence the inhibition. All the oxygen or nitrogen-containing groups, like hydroxyl, methoxy, methaminyl, and alkylsilyloxy, can enhance the inhibitory activities. In addition, the kinetics of enzyme inhibition measured by using Lineweaver-Burk plots shows that selected compounds 2i, 2m and 2p are non-competitive inhibitors. Docking simulations further support our structure-activity relationship analysis that additional aromatic moieties enhance inhibitory activities via hydrophobic effects. The new developed 3-arylacyloxyxanthone derivatives probably bind with α-glucosidase in an allosteric site different from traditional multi-hydroxylxanthones.

Toward potent α-glucosidase inhibitors based on xanthones: a closer look into the structure-activity correlations.

A series of novel xanthone derivatives 6-16 having non-coplanar and flexible structures were synthesized as potent α-glucosidase inhibitors. Biological evaluation indicated that compounds 6-12 bearing one or two naphthol moieties exhibited up to 30-fold enhanced activities compared with their corresponding parent compounds 2-5, whereas compounds 13-16 bearing one dihydroxylnaphthalenyl group showed decreased activities compared with their corresponding analogs 6-9 having one naphthol group. Among them, compounds 7-8, 10-12 and 15 were more active than 1-deoxynojirimycin, a well-known inhibitor for α-glucosidase. The structure-activity correlations suggested that inhibiting of α-glucosidase was a result of multiple interactions with the enzyme, including π-stacking, hydrophobic effect and conformational flexibility due to the structural non-coplanarity. In addition, compounds 4, 8 and 15 showed non-competitive inhibition.