Melanogenesis Inhibitory Effect of Fatty Acid Alkyl Esters Isolated from Oxalis triangularis

Abstract

Oxalis triangularis (purple shamrock or purple clover) in the family Oxalidaceae is an edible perennial plant that is easily cultivated. The leaves of Oxalis triangularis are especially appreciated due to their sour and exotic taste. Oxalis triangularis has intensely purple leaves with a monomeric anthocyanin content of 195 mg/100 g on a malvidin 3,5-diglucoside basis, which makes them a potential source of natural colorants.1) Additionally, it is known that treatment with the flavones, C-glycosides, as copigments effects the color and stability of anthocyanins. [2][3][4][5] To date, no studies have been conducted to investigate the inhibitory effect of Oxalis triangularis on melanogenesis. In this study, the fatty acid alkyl esters methyl linoleate, methyl linolenate, ethyl linoleate and ethyl linolenate from Oxalis triangularis were shown to play an active role in inhibition of the cellular production on melanin. MATERIALS AND METHODS General Methods1 H-and 13 C-NMR spectral data were determined using a Varian Unity Inova 500NB NMR instrument (500 MHz) using CDCl 3 as the solvent and tetramethylsilane (TMS) as an internal standard. The chemical shifts were reported in d (ppm) units relative to the TMS signal and coupling constants (J) in Hz. Gas chromatography-mass spectrometry (GC-MS) and GC-selected ion monitoring (SIM) were conducted using a 5972 Plus mass spectrometer (electron impact ionization, 70 electron volt, HewlettPackard, Palo Alto, CA, U.S.A.) connected to a 5890 gas chromatograph fitted with a fused silica capillary column (HP-5, 0.25ϫ30 m, 0.25 mm film thickness, HewlettPackard). The GC-conditions were as follows: on-column injection mode, He 1 ml/min; oven temperature 60°C for 2 min; and thermal gradient, 10°C/min to 260°C. Medium pressure liquid chromatography (MPLC) was conducted using a Combiflash Companion instrument with an UV/Vis detector (Teledyne ISCO, Inc., U.S.A.). Preparative HPLC (High Pressure Liquid Chromatography) was conducted Extraction and Isolation Whole bodies of Oxalis triangularis (1.6 kg dry weight) were homogenized and extracted with 80% ethanol (30 lϫ3). The extracts were then concentrated in vacuo, after which they were re-extracted with chloroform (2 lϫ3). After reducing to dryness in vacuo, the chloroform fraction (138 g) was solvent-partitioned between nhexane and 80% methanol (2 lϫ3). The concentrated nhexane soluble fraction (57.58 g) was then purified by silica gel column chromatography (100 g, Merck) and eluted stepwise with chloroform containing 0, 1, 2, 10 and 100% methanol (1 l each). The fractions eluted in 0% and 1% methanol in chloroform were combined and concentrated in vacuo (17.32 g), after which they were subjected to MPLC (RediSep, silica 40 g, 30ϫ140 mm; detection, UV at 254 nm; flow rate, 40 ml/min). The elution was performed stepwise in chloroform-methanol (0%, 2%, 10%, 100% methanol) for 10 min each to give 40 subfractions. Fraction 4 was subjected to reversed phase preparative HPLC (Phenomenex Luna C18(2), 21.2ϫ250 mm, 5 mm) and eluted with 40% a...

Constituents with tyrosinase inhibitory activities from branches of Ficus erecta var. sieboldii King

“…Repeated column chromatography of the EtOAc fraction through silica gel resulted in the isolation of eight constituents ( Figure 2): p-hydroxybenzoic acid (1) 14 , methyl p-hydroxybenzoate (2) 15 , vanillic acid (3) 16 , methyl vanillate (4) 17 , syringic acid (5) 18 , β-sitosterol (6) 19 , α-amyrin acetate (7) 20 , and ethyl linoleate (8) 21 . Compounds 1-5 were all p-hydroxybenzoic acid derivatives, which were fully identified by spectroscopic methods, including 1 H and 13 C NMR data.…”

Natural Melanogenesis Inhibitors Acting Through the Down-Regulation of Tyrosinase Activity

“…In addition, Huh et al . found that the methyl/ethyl linoenate (Figure 7c) from Oxalis triangularis exhibited melanogenesis inhibition, which was also mediated by a reduction in the cAMP level in cells [74]. …”

In Vitro and In Vivo Screening of Wild Bitter Melon Leaf for Anti-Inflammatory Activity against Cutibacterium acnes

“…Methyl palmitate has been shown to reduce chemical-induced hepatotoxicity in rats [ 27 ], and inhibit phagocytosis and the release of pro-inflammatory mediators in primary rat Kupffer cells [ 28 ]. Methyl linolenate significantly blocks melanogenesis and inhibits tyrosinase activity in mouse B16 melanoma cells [ 29 ]. However, to date, there are no published reports of the anti-inflammatory properties of fatty acid acyl esters.…”