New Oligomeric Proanthocyanidins from Bark of Platanus orientalis

Abstract

The genus Platanus (Platanaceae) is represented by four species in Central Asia [1]. The most widely distributed species is P. orientalis, eastern plane tree, the chemistry of which is little studied.The chemical composition of the leaves has been studied to a comparatively greater extent than that of the trunk bark. Phenolcarboxylic acids and flavonoids (hyperin, tiliroside) were isolated from the leaves. The hydrolysates contained quercetin, myricetin, cyanidin, and delphinidin [2,3]. Fallen leaves of plane tree are rich in α-tocopherol, its oxidized dimeric forms, and esters with higher fatty acids [4,5], and carbohydrates [6].The trunk bark contains neutral phytosterols (sito-and stigma-), α-tocopherol, and polyprenols [7] in addition to triterpenoids such as betulinic acid, betulinic aldehyde, platanoic and 3-dehydroplatanoic acids, and sitosterol [3,8].Trunk bark is used in folk medicine to treat dysentery, toothache, diarrhea, etc. [9, 10] and as an anticancer agent [11]. The goal of the present work was to investigate the chemical composition including proanthocyanidins of plane-tree trunk bark.Proanthocyanidins were isolated by fractionating the aqueous-alcohol extract of P. orientalis bark according to polarity using organic solvents. This produced low-molecular-weight, oligomeric, and polymeric fractions of proanthocyanidins.Column chromatography over finely crystalline cellulose and gel-filtration over Sephadex LH-20 isolated from the butanol fraction of the aqueous-alcohol extract two pure oligomeric glycosylated proanthocyanidins Pl-1 and Pl-7, which gave a red color with vanillin-H 2 SO 4 .Compound Pl-1 had empirical formula C 86 H 78 O 44 and molecular weight MW = 1814. Alkaline decomposition of Pl-1 under a N 2 atmosphere formed three compounds: fluoroglucinol (1) and protocatechoic (2) and gallic acids (3). Hydrolysis cleaved not only interflavane bonds but also flavan-3-ol units at the pyran heterocycle. Fluoroglucinol formed from ring A; phenolic acid, from ring B. Atoms C 3 -C 4 of ring C gave acetic acid [12,13].Acid hydrolysis of Pl-1 cleaved interflavane C-C bonds. This produced (-)-epicatechin-3-O-gallate (4), cyanidin (5), and glucose (6). Thiolytic cleavage of Pl-1 in the presence of thiophenol and acetic acid formed three compounds. The "lower" part of the molecule gave (-)-epicatechin-3-O-gallate (4); the "upper" blocks, a mixture of thioethers 7 and 8, which then decomposed catalytically in the presence of Raney Ni. The resulting compounds were identified by physicochemical and spectral properties as (-)-epicatechin (9) and (-)-epicatechin-3-O-gallate (4).

Identification of Triterpenes and β-sitosterol in the Bark of Plane Tree Extracts

“…A few constituents of the bark of Platanus occidentalis L. were identified [12,16,17], which were triterpenes, fatty acids and sterols. Dimeric and oligomeric proanthocyanidins were also isolated from the bark of Platanus orientalis L. [18][19][20].…”

New oligomeric proanthocyanidins from Alhagi pseudalhagi

“…The solvent was distilled off. The solid was chromatographed over a column of polyamide to afford three compounds with M + 126, mp 218-219°C, R f 0.64 (PC, system 3) (phloroglucinol); M + 154, mp 200°C (dec.), R f 0.72 (PC, system 3) (protocatechoic acid); and M + 170, mp 220-221°C, R f 0.56 (PC, system 3) (gallic acid) [7,18].…”

New oligomeric proanthocyanidin glycosides platanoside-A and platanoside-B from Platanus orientalis trunk bark

“…Based on the spectral data and chemical transformations, the structure and relative configuration of II were proposed as 7-O-E-D-Glcpo 6 Extraction and Isolation of Proanthocyanidins. Ground air-dried P. orientalis trunk bark (5.0 kg) was extracted with 80% EtOH (25 L and 5 u 20 L).…”

“…The remaining aqueous layer was evaporated in a porcelain dish on a water bath with constant stirring, dried, and ground to afford 234.7 g (4.7%) of total highmolecular-weight proanthocyanidins (light-brown solid) [6].…”

“…The solvent was distilled off. The solid was chromatographed over a column of polyamide to afford two compounds with M + 126, mp 218-219°C, R f 0.64 (PC, system 4) (phloroglucinol) and M + 154, mp 200°C (dec.), R f 0.72 (PC, system 4) (protocatechoic acid) [6].…”