Glucosyloxybenzyl derivatives of (R)-2-Benzylmalic acid from the aerial parts of Arundina graminifolia (D.Don) Hochr. (Orchidaceae)

Benzyl ester glycosides of natural organic acids such as citric [1], malic [2] or tartaric acid [3]are known to be specific secondary metabolites occurring in the orchid family. A rapid RP-HPLC-DAD-HRMS screening of the ethyl acetate extract from Arundina graminifolia aerial parts, suggested the presence of these compounds due to their high molecular weight, as well as their MS fragmentation patterns [4].Thus, a multiple step fractionation from the ethyl acetate extract led to the isolation of seven new glucopyranosyloxybenzyl derivatives of the (R)-2-benzylmalic acid, named Arundinosides A-G. Their structures were elucidated by means of extensive spectroscopic experiments. The structure novelty has the acetic and cinnamic esters distributed over two sugars in Arundinoside A and B, whereas those functionalities were previously reported on the C-2 glucose only [5]. On the other hand, the (R)-2-benzylmalic acid, here regarded as the centrepiece of the backbone structure, could also be found on the C-2 glucose in Arundinoside C. This particular class of glycosides was detected in this well-studied Asian orchid for the first time. Numerous studies have reported organic acid derivatives as promising drug agents for neurodegenerative diseases [6,7]. We therefore investigated the neuroprotective potential of these 2-benzylmalic acid glycosides on beta-amyloid-induced toxicity, using a PC12 cell model [8]. Only Arundinoside A significantly protected PC12 cells from the cytotoxic effect of β-amyloid peptide with a maximum viability gain of 44 ± 4% at 50µmol/L. A comparison of structural similarities of the tested compounds suggests that cinnamic(s) ester(s) could play a major role for the activity of Arundinoside A.

	R1	R2	R3	R4	R5	R6	R7
Arundinoside A	Ac	H	H	H	Cin	Cin	Ac
Arundinoside B	Ac	Ac	Ac	Ac	H	H	Ac	with	Ac =	Acetyl
Arundinoside C	Ac	Ac	Ac	2-BM	H	H	H
Arundinoside D	Ac	Ac	Ac	Ac	H	H	H		Cin =	trans-Cinnamoyl
Arundinoside E	Ac	Ac	H	Ac	H	H	H
Arundinoside F	Ac	H	H	H	H	H	H		2-BM =	2-Benzylmaloyl
Arundinoside G	Ac	H	H	Ac	H	H	H

Keywords: Arundina graminifolia, Orchidaceae, Benzyl-Ester Derivatives of (R)-2-Benzylmalic acid, Arundinosides.

References:

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