Study On The Antioxidant Activity And Chemical Constituents Of Mondia Whiteii

Mondia whiteii?Hook.f.?Skeels?Apocynaceae?is a woody vine,widely distributed in the humid tropical and subtropical regions of Africa.Traditionally,M.whiteii is a medicinal and edible plant in Africa.Its roots have a strong vanilla fragrance.It is often used to relieve flatulence and calm the stomach,and as a tonic and aphrodisiac.Modern pharmacological studies have shown that M.whiteii has many biological activities,such as therapeutic dysfunction,bacteriostasis,antioxidant,antidepressant,antiepileptic,antidiarrheal,anti-inflammatory and analgesic activities.In order to evaluate the antioxidant activity of M.whiteii and to locate its correlated effective active fractions and identify its main responsible chemical components,the roots of M.whiteii were used as the research materials in present study,with three in vitro determination methods for antioxidant activities:DPPH free radical scavenging,ABTS free radical scavenging and FRAP methods,with which the ethanol total extract,petroleum ether fraction,dichloromethane fraction,dichloromethane fraction,n-butanol fraction and water fraction of M.whiteii were measured respectively.Among them,the antioxidant capacity of different extraction fractions of M.whiteii determined by DPPH method is as follows:dichloromethane fraction>n-butanol fraction>total extract>water fraction>petroleum ether fraction,the dichloromethane fraction was the strongest(IC₅₀=101.81±2.13?g/mL),and the petroleum ether fraction was the weakest(IC₅₀=1441.22±172.03?g/mL);the antioxidant capacity of different extraction fractions of M.whiteii determined by ABTS method is as follows:dichloromethane fraction>n-butanol fraction>total extract>petroleum ether fraction>water fraction.Among them,the dichloromethane fraction of M.whiteii exerted the strongest ability to scavenge ABTS radicals(IC₅₀=36.73±1.13?g/mL),the aqueous fraction was the weakest(IC₅₀=440.30±11.25?g/mL).The antioxidant capacity of different extraction fractions of M.whiteii determined by FRAP method is as follows:dichloromethane fraction>n-butanol fraction?total extract>petroleum ether fraction>aqueous fraction.Dichloromethane fraction exhibited the strongest antioxidant capacity(0.98±0.13mM Fe²⁺/g)and the weakest was water fraction(0.12±0.01 mM Fe²⁺/g).Based on the results measured by the above three methods,the antioxidative activity of the dichloromethane fraction from M.whiteii is the most strongest.At the same time,the content of total phenol and total flavonoids in different extraction parts of M.whiteii were determined.From high to low,the total flavonoid content in different extraction parts of M.whiteii was:n-butanol fraction>dichloromethane fraction>total extract>petroleum ether fraction>water fraction,the highest is the n-butanol fraction?80.08±0.19 mg RE/g?,the lowest is the water fraction?14.13±0.40 mg RE/g?;the total phenol content from high to low is:dichloromethane fraction>n-butanol fraction>total extract>petroleum ether fraction>water fraction,of which the highest is the dichloromethane fraction?136.50±6.22 mg GAE/g?,the lowest is the water fraction?12.93±0.74 mg GAE/g?.Based on the results of the antioxidant activity,the chemical composition of the dichloromethane fraction of M.whiteii was firstly analyzed by HPLC-ESI-MS technology,and finally 20 compounds were identified,but there are still many unknown compounds unidentified.In order to further clarify the chemical basis of the most effective fraction of M.whiteii,the dichloromethane fraction was systematically separated and purified,and 30 compounds were obtained.Combining the technologies of nuclear magnetic resonance spectroscopy?NMR?and liquid chromatography-mass spectrometry?LC-MS?,21 compounds were identified as phenols?1,7,8,9,14,15,16,18,19?,phenylpropanoids?2,3,4,5,6,11?,steroids?12,13,20,21?,fatty Acids?10?,among them,compounds 3-21 were isolated and identified from this plant for the first time.In this study,it was the first time to evaluate the antioxidant activity of different fractions of M.whiteii,and the dichloromethane fraction was displayed as the most effective part.Therefore,the chemical composition of this fraction was analyzed using modern chromatography-mass spectrometry technology,then this fraction was further systematically separated,and at least 19 compounds isolated from the plant for the first time,which revealed its chemical basis as a traditional medicinal and edible plant in Africa,and also provided scientific data valuable for its subsequent research and development in the near future.