Abstract
Vanda roxburghii has been used in traditional medicine to treat nervous system disorders including Alzheimer's disease (AD). We reported earlier a high acetylcholinesterase inhibitory and antioxidant activity in the chloroform fraction of this plant. Therefore, this study was designed to explore the compounds with acetylcholinesterase inhibitory and antioxidant activities from the chloroform fraction of Vanda roxburghii. Phytochemical investigation led to the isolation for the first time of a fatty acid ester: methyl linoleate (1), and three phenolics: syringaldehyde (2), vanillin (3), and dihydroconiferyl dihydro-p-coumarate (4) along with the previously reported compound gigantol (5). Among the isolates, vanillin (3) and dihydroconiferyl dihydro-p-coumarate (4) were found to significantly inhibit the activity of acetylcholinesterase, scavenge the free radicals, exhibit the reducing power and total antioxidant activity, and effectively reduce the peroxidation of lipid. Gigantol (5) and syringaldehyde (2), despite lacking the activity against acetylcholinesterase, exhibited antioxidant activity. Among the compounds, gigantol (5) appeared to be the most potent antioxidant. These findings revealed that V. roxburghii contained compounds with potential acetylcholinesterase inhibitory and antioxidant activity, which support its traditional use in the treatment of AD.
Highlights
Alzheimer’s disease (AD) is an age-related neurodegenerative disorder of the elderly people with symptoms of memory loss and cognition
It has been clearly demonstrated that Abeta protein, the major constituent of senile plaque, can increase the free radical production and reactive oxygen species (ROS), leading to oxidative stress [8]
Chromatography of the chloroform fraction, prepared from crude methanol extract of V. roxburghii by partitioning, resulted in the isolation of five compounds. e compounds were identified by the comparison of their 1H- and 13C-NMR spectral data with the published values in the literature [13, 17,18,19]. e compounds described in Figure 1 included a fatty acid ester: methyl linoleate (1), and four phenolics: syringaldehyde (2), vanillin (3), dihydroconiferyl dihydro-pcoumarate (4), and gigantol (5)
Summary
AD is an age-related neurodegenerative disorder of the elderly people with symptoms of memory loss and cognition. Cholinergic deficit, deposition of amyloid plaque and formation of neurofibrillary tangles, oxidative stress, and inflammation are the prominent features of AD [1, 2]. Only four drugs have been approved by the FDA for treating AD, among which three are AChE inhibitors—donepezil, galantamine, and rivastigmine. These drugs are effective in ameliorating the memory and cognition, they cannot stop the disease progression [5]. It has been clearly demonstrated that Abeta protein, the major constituent of senile plaque, can increase the free radical production and reactive oxygen species (ROS), leading to oxidative stress [8]. Interest in medicinal plants for natural drug has increased significantly due to toxicity of the synthetic drugs
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