Studies On The Antioxidant Activities And Volatile Constituents Of Medicinal Plants

This dissertation is composed of three chapters. The first chapter elaborated the antioxidant activity of thirty medicinal plants in vitro. The second chapter introduced the antioxidant activity of the isolated compounds from the plants with higher antioxidant activity, such as Mitragyna rotundifolia Kuntze and Securidaca inappendiculata Hassk. The third chapter reported the studies on the volatile constituents of three plants collected from Henan Province.Chapter 1. The antioxidant activity of thirty medicinal plantsThirty medicinal plants, belonging to twenty-nine species of twenty-two different families, were screened the antioxidant activity using the DPPH, ABTS, and FRAP assays. The results showed that the higher antioxidant active plants were mainly distributed in the three families, Rubiaceae, Juglandaceae and Oleaceae, and the DPPH assay was highly correlated with the ABTS assay (r=0.6856) by analyzing the correlation among the results from the twenty-four same samples screened by three antioxidant assay.Chapter 2. The antioxidant activity of the isolated compoundsi. Mitragyna rotundifolia Kuntze belongs to the family Rubiaceae. Several plants of this genus have been used in local folklore medicine for a wide variety of diseases, such as fever, colic, muscular pains and for the expulsion of worms. In our continuing studies on the M. rotundifolia, six compounds were isolated by the method of bioassay guiding using the DPPH assay from the ethyl acetate fraction by different chromatographic techniques. The structures were elucidated as follow: 1. 3,4-dihydroxybenzoic acid(1) 2. caffeic acid(2) 3. 3',4,5,5',7-pentahydroxyflavan(3) 4. 3',4,4',5,7-pentahydroxyflavan(4) 5. 3,3',5,5',7-pentahydroxyflavan(5) 6. 3,3',4',5,7-pentahydroxyflavan(6)Compounds 3-6 were isolated for the first time from the genus of Mitragyna. compound 5 showed the highest antioxidant activity, the IC50 values for DPPH and ABTS assays were 1.40μg/mL and 0.56μg/mL respectively. The correlations between DPPH and ABTS assays were relatively higher(r=0.9681).ii. Securidaca inappendiculata Hassk belongs to the family Polygalaceae. As a traditional Chinese herbal medicine, S. inappendiculata is used as anti-inflammatory, anti-bacterial and anti-rheumatism agents. Pharmacological investigations have shown that the xanthones, as main components accumulated in S. inappendiculata, have many bioactivities including MAO inhibition, cytotoxicity, anti-inflammatory properties, anti-tumor, anti-bacterial, anti-fungal, antioxidant activities and tuberculostatic. Nine compounds were isolated from CHCl3 extract of the roots of S. inappendiculata, including eight xanthones. Their structures were established by means of detailed spectral analysis. The compounds were determined as follow: 1. 1,2,5-trihydroxy-6,8-dimethoxy-9H-xanthen-9-one(7) 2. 1,5-dihydroxy-2,6,8-trimethoxy-9H-xanthen-9-one(8) 3. 3,8-dihydroxy-1,4-dimethoxy-9H-xanthen-9-one(9) 4. 4,6-dihydroxy-1,5,7-trimethoxy-9H-xanthen-9-one(10) 5. 7-hydroxy-1,2,3,8-tetramethoxy-9H-xanthen-9-one(11) 6. 1,7-dihydroxy-9H-xanthen-9-one(12) 7. 4-hydroxy-3,7-dimethoxy-9H-xanthen-9-one(13) 8. 1,7-dimethoxy-9H-xanthen-9-one(14) 9. aucuparin(15)Compounds 7 and 8 were new xanthones, compound 9 was isolated for the first time from a natural source, compounds 10 and 12 were isolated for the first time from the genus of Secutidaca. The antioxidant results show that, Compound 15 showed significant activity by the ABTS and FRAP assays; Compound 7 showed IC50 value of 0.31μg/mL by the DPPH assay. Scavenging capacity of compounds 7-15 determined by ABTS and FRAP assays was well correlated (r=0.9193).iii. The antioxidant activities of the other compounds were also screened, and five compounds showed higher antioxidant activity in DPPH, ABTS and FRAP assays. The structures of three compounds were established by means of detailed spectral analysis. 1. 5,7-dihydroxy-2-methyl-pyranone(17) 2. pinoresinol(18) 3. phillygenin(20)Compounds 16-20 showed very high antioxidant activity. In DPPH and ABTS assays, the compounds 16 and 17 showed higher antioxidant activity than that of BHA and BHT, lower than that of PG; in FRAP assay, the compound 17 had higher antioxidant activity than that of PG, BHA and BHT, the compound 16 only had higher activity than that of BHT. Scavenging capacity of compounds 16-20 determined by DPPH and ABTS assays was well correlated (r=0.8425).Chapter 3. Analysis of the volatile constituents of three plants collected from Henan Province by SPME-GC-MSi. Ligustrum quihoui Carr. belongs to the family Oleaceae. Its leaves can reduce fever, also can be used as an antidote. The volatile oils of the flowers and alabastrums of L. quihoui Carr. were analyzed by HS-SPME, and the main fragrance components of the flowers of L. quihoui Carr. are benzeneethanol and benzenemethanol. The fragrance of L. quihoui Carr. belongs to rose fragrance type, so the oils of the flowers of L. quihoui Carr. can be applied to flavor composition, smoking composition, and can be studied and developed as high-grade spice. The content of benzenemethanol in oil from flowers of L. quihoui Carr. is higher than that from the seed of L. lucidum Ait., and benzenemethanol as the main pharmic compound usually is used as anti-inflammatory, anti-bacterial agents and also can relieve pain.ii. Pittosporum tobira Ait. (Pittosporaceae) is a broadleaf evergreen shrub. Its roots, leaves, and seeds all have medicinal values. In order to compare the differences between steam distillation (SD) and solid-phase microextraction (SPME), the volatile oils extracted from the flowers and alabastrums of P. tobira Ait. were studied. The results showed that there were some identical volatile compounds extracted from the same part of P. tobira Ait. by SD and SPME, and some components that only could be extracted by SPME. The extract time could be obviously decreased using the method of HS-SPME. When comparing the volatile oils extracted from the flowers and alabastrums of P. tobira Ait. by the same method, the content of nerolidol in alabastrums is higher than that in flowers (for 20.13%) by SD. The nerolidol has fragrant odor, and can be used in spices production. The contents of the main components, including undecane, nonane andα- pinene, are almost the same in flowers as that in alabastrums by SPME, andα-pinene can obviously relieve cough and eliminate phlegm, and has anti-fungal activity.iii. Trifolium repens L. (Leguminosae) has medicinal values. It can eliminate phlegm, quench thirst, relieve pain, and also has antispastic activity. The volatile oils extracted from the flowers of T. repens L. was analyzed by the method of HS-SPME. The result is large difference with the reported results. It may be related to the the extraction method, or resulted from the different habitat of T. repens L. Comparing with the traditional extraction method, SPME is a rapid, simple, inexpensive and solvent free technique, and is a fine method for the extraction of volatile compounds from T. repens L.