Galloyl, caffeoyl and hexahydroxydiphenoyl esters of dihydrochalcone glucosides from Balanophora tobiracola

Seven galloyl, caffeoyl and (S)-hexahydroxydiphenoyl (HHDP) esters of dihydrochalcone glucosides were isolated from Balanophora tobiracola; based on spectroscopic and chemical evidence, their structures were determined to be 6'-O-galloyl-, 3',4'-di-O-galloyl-, 4',6'-di-O-galloyl-, 4',6'-O-(S)-HHDP-, 3'-O-galloyl-4',6'-O-(S)-HHDP-, 3'-O-caffeoyl-4',6'-O-(S)-HHDP-3-hydroxyphloretin 4'-O-beta-D-glucosides and 3'-O-galloyl-4',6'-O-(S)-HHDP-phloretin 4'-O-beta-D-glucoside, respectively. By contrast, these compounds were not found in the taxonomically related B. japonica. The 3'-galloyl-4',6'-HHDP esters of the dihydrochalcone glucosides showed strong inhibitory activities against alpha-glucosidase. Four known compounds were also isolated namely, (+/-)-eriodictyol 7-O-beta-D-glucoside, 1-O-caffeoyl-3-O-galloyl-beta-D-glucose, phloretin 4'-O-beta-D-glucoside, and 3-hydroxyphloretin 4'-O-beta-D-glucoside.     

Individual phenolic response and peroxidase activity in peel of differently sun-exposed apples in the period favorable for sunburn occurrence

Extreme weather events like high solar radiation can cause stress in apple fruits (Malus domestica Borkh.). The aim of the study was to make a screening of individual phenols and peroxidase activity in apple peel as a response to sunburn and different sun-exposures in the period when weather conditions are suitable for sunburn occurrence. Apple fruits of ‘Golden Delicious’ and ‘Braeburn’ were sampled. Fruit temperature and color were measured prior HPLC–MS² and peroxidase activity analyses. Sunburned peel was darker and more yellow-red in comparison to healthy peel, which appeared yellow-green. Fruit temperature, total as well as individual flavonols and dihydrochalcones, total hydroxycinnamics and perixodase activity were highest in sunburned peel in comparison with healthy sun-exposed peel, furthermore both were different than shaded sides of both fruits and peel of apples inside the tree crown; moreover in sunburned peel dihydrochalcones were determined for the first time. Chlorogenic acid was up to 2.5 times higher, 3-hydroxy-phloretin-2′-O-xyloglucoside was up to 10 times higher and quercetin-3-galactoside was up to 33 times higher in sunburned peel, comparing to shaded sided peels. Flavanols did not show a distinct pattern. A deeper insight in phenolic response against environmental stress caused by high solar radiation and high air temperatures has been made.     

Inhibition of tyrosinase activity by polyphenol compounds from Flemingia philippinensis roots

Flemingia philippinensis is used as a foodstuff or medicinal plant in the tropical regions of China. The methanol (95%) extract of the roots of this plant showed potent tyrosinase inhibition (80% inhibition at 30 μg/ml). Activity-guided isolation yielded six polyphenols that inhibited both the monophenolase (IC₅₀ = 1.01–18.4 μM) and diphenolase (IC₅₀ = 5.22–84.1 μM) actions of tyrosinase. Compounds 1–6 emerged to be three new polyphenols and three known flavanones, flemichin D, lupinifolin and khonklonginol H. The new compounds (1–3) were identified as dihydrochalcones which we named fleminchalcones (A–C), respectively. The most potent inhibitor, dihydrochalcone (3) showed significant inhibitions against both the monophenolase (IC₅₀ = 1.28 μM) and diphenolase (IC₅₀ = 5.22 μM) activities of tyrosinase. Flavanone (4) possessing a resorcinol group also inhibited monophenolase (IC₅₀ = 1.79 μM) and diphenolase (IC₅₀ = 7.48 μM) significantly. In kinetic studies, all isolated compounds behaved as competitive inhibitors. Fleminchalcone A was found to have simple reversible slow-binding inhibition against monophenolase.