Isolation of ethyl caffeate from the petals of Prunus yedoensis
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Ethyl caffeate was isolated from the petals of Prunus yedoensis (Rosaceae). This is the first example of its isolation from Prunus plants.
KeywordsEthyl caffeate Prunus yedoensis Rosaceae Petals
Ethyl caffeate (ethyl 3,4-dihydroxy cinnamate, 1) was isolated from the petals of Prunus yedoensis (Rosaceae).
Dried petals of P. yedoensis (1.6 kg), cultivated in Aomori, Japan, were extracted with n-hexane, chloroform, and methanol successively, to furnish the corresponding extracts of 82, 89, and 400 g, respectively. Chromatography of a portion of the chloroform extract (10 g) over silica gel using chloroform–methanol (20:1, v/v) as solvent, followed by prep-TLC developed with chloroform–diethylether (3:1, v/v) afforded 1 (73 mg, 0.041% yield).
Some caffeic acid derivatives were isolated from the related Prunus sp. For example, 6-O-caffeoyl-d-glucopyranose was isolated from P. grayana barks , P. buergeriana barks , P. serrulata flowers , and P. ssiori barks . On the other hand, 1,6-di-O-dicaffeoyl-β-d-glucopyranoside was isolated from P. buergeriana barks  and P. serrulata flowers , and 3-O-caffeoyl-β-d-fructofuranosyl 2,3,4,6-tetra-O-acetyl-α-d-glucopyranoside was isolated from P. ssiori barks . Further, 1-O-caffeoyl-β-d-glucopyranoside was isolated from the twigs of P. spinosa .
The existence of 1 in the extracts of petals of P. serrulata was reported by Kurkin et al. . However, it has been considered as an artifact formed under extraction process using ethanol as a solvent . In the meantime, ethanol was not used in this study, and, in addition, 1 was also detected in the hexane extract of this plant material. Therefore, it was concluded that compound 1 must be obtained as a genuine compound and was not an artifact formed from caffeic acid and ethanol during isolation procedure.
This is the first example of the isolation of 1 from Prunus plants. From this plant material, other than compound 1, ursolic acid (0.005% yield) and β-sitosterol (0.01% yield) were isolated from the chloroform extract, and 1-O-caffeoyl-β-d-glucopyranoside (1.1% yield) was isolated from the methanol extract, respectively. These compounds had been formerly isolated from leaves of P. serrulata , seed coats of P. amygdalus , and twigs of P. spinosa , respectively whereas these compounds have been isolated from P. yedoensis for the first time.
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