Comparison of Antioxidative Activity of Phenolic Compounds in Boreava orientalis and Their Related Compound

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1 J. Jpn. Oil Chem. Soc. Vol. 46, No. 11 (1997) 1399 NOTE Comparison of Antioxidative Activity of Phenolic Compounds in Boreava orientalis and Their Related Compound Takashi MAOKA*1, Yoshihiro ITO*1 Akiyo SAKUSHIMA*2, Kosei OHNO*2 Maksut COSKUN*3, and Sansei NISHIBE*2 *1) Research Institute for Production Development (15 Shimogamomorimoto-cho, Sakyou-ku, Kyoto-shi, 606) *2) Faculty of Pharmaceutical Sciences, Health Sciences University of Hokkaido (Ishikari-Tobetsu, Hokkaido, ) *3) Department of Pharmacognosy and Pharmaceutical Botany University of Ankara (Ankara, Turkey), Faculty of Pharmacy, Abstract : Examination was made by the effects of antioxidative activity of phenolic compounds isolated from Boreava orientalis fruit (Cruciferae) and related compounds on free radical-oxidation of methyl linolate in solution. Based on methyl linolate hydroperoxide production using 2,2' -azobis(2,4- dimethyl valeronitrile) (AMVN) as the radical initiator. Dihydroxybenzoic acids and phenylpropanoids, particularly cinnamic acid derivatives, were shown to be strong antioxidatnts. Key words : Boreava orientalis, Cruciferae, fruits, antioxidative activity, phenolic compounds, phenolic acids derivatives, phenylpropanoids, cinnamic acid derivatives 1 Introduction Previously, we reported the isolation and identification of same phenolic compounds1) `5) from the fruits of Boreava orientalis (Cruciferae) which is used in traditional medicine for coughs and skin disease6),7) in Turkey. On the other hand, a number of studies have showed that the antioxidative activitie's of phenolic compounds possess antioxidative activity8)-12) In the present study, we investigated the antioxidative activity of phenolic compounds isolated from Boreava orientalis fruit and related compounds on free radical-oxidation of methyl linolate in solution. The relationship between structure and antioxidative activity will be discussed. 2 Experimental 2 E1 Material The structures of 24 phenolic compounds used in this study were shown in Fig. 1. Vanillic acid (1), pyrocatechuic acid (2), gentisic acid (3), 3,4-dihydroxybenzoic acid (4) syringic acid (6), vanillin (8), syringaldehyde (9), caffeic acid (15), ferulic acid(18), sinapic acid(19), sinapine (20), scopoletin (21), threo-guaiacylglycerol- -vanillic acid ether (22), chlorogenic acid (23), and 6-O- ƒà -D-(2' -O-sinapoyl) glucopyranose- -D-(1,2-O-disinapoyl) glucopyranose (24) were isolated from the fruit of B. orientalis1) `5). 2,6-Dihydroxybenzoic acid (5), 3,5-dihydroxybenzoic acid (7), 3,4-dihydroxyphenylacetic acid (10), cinnamic alcohol (11), cinnamic aldehyde (12), cinnamic acid (13), p-coumaric acid (14), coniferyl alcohol (16), 3.4-dimethvl caffeic acid (17) and ƒ -toconherol were purchased from Wako Chemical Co. Corresponding auther : Takashi MAOKA 65

2 1400 J. Jpn. Oil Chem. Soc. Vol. 46, No. 11 (1997) Fig. 1 Structures of Phenolic Compounds Used in This Study. Plants of B. orientalis specimens were collected near Ankara in 1990 and voucher specimen is retained in the Ankara Universitesi Eczacilik Fakiiltesi herbaryumu (AEF). Details of the isolation and the structural elucidation of these phenolic compounds were reported in previous papern-5). 2, 2' -Azobis(2,4-dimethylvaleronitrile) (AMVN) was purchased from Wako Chemical Co. Methyl linolate, supplied by Shigma Chemical Co., was further purified by silica gel column chromatography to remove any peroxides. 2.2 Measurment of antioxidative activity12),13) Phenolic compounds were dissolved in MeOH and used at a final concentration of in reaction mixture. 0.1 ml of the sample solution was added to 1 ml of 0.1 M methyl linolate solution [n-hexane/2-propanol (1/1, vol/vol)], and the solution was incubated at 37 C for 5 min. The oxidation reaction was then initiated by adding 0.1 ml of 100 mm n-hexane solution of AMVN, and the mixture was incubated with air at 37 C for 30 min. The oxidative reaction products, linolate hydroperoxides, were quantified by high performance liquid chromatography (HPLC). 2.3 HPLC HPLC was performed with a Hitachi L-6200 intelligent pump and L-4250 UV-VIS detector. The following HPLC conditions employed for the quantitative analysis of methyl linolate hydroperoxides : column : LiChrosorb Si 100 (5 Lim particle size) (4.6 x 250 mm) (Merck) ; solvent system : 2-propanol/n-hexane (1/99, vol/vol) ; flow rate : 1.0 ml/min, detection : 235 nm. 3 Results and Discussion The antioxidative activity of 24 phenolic compounds was monitored by measuring the accu- 66

3 J. Jpn. Oil Chem. Soc. Vol. 46, No. 11 (1997) 1401 mulation of methyl linolate hydroperoxides during the incubation of methyl linolate with AMVN as a radical initiator. These results are shown in Table 1. Most of the phenolic compounds studied showed antioxidative activity but their activity was less than that of ƒ -tocopherol. Hydroxy benzoic acids (1 `7) and benzaldehydes (8, 9) showed antioxidative effect. Among them dihydroxy benzoic acids such as 2, 3, and 4 exhibited strong activity, but compound 5 was less efficient than other dihydroxy benzoic acids. Furthermore, syringic acid (6) and syringic aldehyde (9), which have one or two methoxy groups at the ortho position relative to the phenolic hydroxyl group, showed strong activity. The strong activity of 6 and 9 might be due to the effect of electron donors from the methoxy group at the ortho position of phenolic hydroxy group, becouse the presence of such electron donors increase the stability of the aryloxy radica10) `12). Furthermore, 3,4-dihydroxyphenylacetic acid(10) showed remarkable activity. Phenyl propanoids (11 `20) also showed antioxidative activity. Of these compounds, cinnamic acid derivatives such as 15, 18, 19 and 20 exhibited significant activity. Caffeic acid (15), ferulic acid (18) and sinapic acid (19) were more active than their corresponding benzoic acids, namely, pyrocatechuic acid (2), vanillic acid (1) and syringic acid (6), respectively. This finding suggested that the presence of a conjugated olefinic group in the molecules Table 1 Inhibitory Effect of Phenolic Compounds on the Oxidation of Methyl Linolate. 67

4 1402 J. Jpn. Oil Chem. Soc. Vol. 46, No. 11 (1997) of these compounds might enhance the redical scavenging activity due to resonance stabilization of aryloxy redical10) `12) Furthermore, coniferyl alcohol (16) showed almost the same activity as the hydroxy cinnamic acid derivatives described above. On the other hand, compounds 11, 12 and 13, which lack the phenolic hydroxy group, showed a few activity. Scopoletin (21) exhibited the moderate activity, but 22 showed a few activity. This phenomenon also suggests that the presence of a conjugated olefinic group participated the enhancement of antioxidative activity. Furthermore, chlorogenic acid (23) and sinapic acid glycoside (24) exhibited significant activity, which might be due to the presence of caffeic acid and sinapic acid moiety in these molecule. Consequently, dihydroxybenzoic acids and phenylpropanoids, particularly cinnamic acid derivatives isolated from the fruits of B. orientalis were shown to be strong antioxidation. (Received Apr. 11, 1997 Accepted Jul. 31, 1997) References 1) A. Sakushima, M. Coskun, M. Tanker, N. Tanker., Phytochemistry, 35, 1981 (1994). 2) A. Sakushima, M. Coskun, T. Maoka., Phytochemistry, 40, 257 (1995). 3) A. Sakushima, M. Coskun, T. Maoka., Phytochemistry, 40, 483 (1995). 4) A. Sakushima, M. Coskun, T. Maoka, S. Nishibe., Phytochemistry, 43, 1349 (1996). 5) A. Sakushima, M. Coskun, M. Tanker, N. Tanker, S. Nishibe., Natu. Med., 50, 65 (1996). 6) N. Tanker, M. Yenen., Ankara Ecz. Fak. Mec., 8, 1 (1978). 7) M. Tanker, M. Ertan, M. Coskun, N. Sariseker, T. Yurdein., Doga Bilim. Dergisi: Tip. Cilt., 7, 99 (1981). 8) D.E. Pratt, B.J.F. Hudson, in "Food Antioxidants," ed. by B.J.F., Hudson, Elsevier Applied Science, Essex, England, 1990, p ) W. Porter, L. Levasseur, A, Henick, J. Food Sci., 42, 1533 (1977). 10) M.-E. Cuvelier, H. Richard, C. Berst, Biosci. Biotech. Biochem., 56, 342 (1992). 11) S-K. Chung, T. Osawa, S. Kawakishi, Biosci. Biotech. Biochem., 61, 118 (1997). 12) J. Terao, H. Karasawa, H. Arai, A. Nagao, T. Suzuki, K. Takama, Biosci. Biotech. Biochem., 57, 1204 (1993). 13) J. Terao, Lipid, 24, 659 (1989). 68

5 Boreava orientalis