Chemical Constituents with Immunological Activities from the Barks of Platanus acerifolia

Abstract

Platanus acerifolia (Aiton) Willd. (Platanaceae) is a hybrid of P. orientalis and P. occidentalis. P. acerifolia is highly resistant to powdery mildew and atmospheric contamination, so it is often used for landscaping and street planting. P. acerifolia was also used to treat toothache, dysentery and diarrhea in folk medicine and has rich resources. Studies have indicated that P. acerifolia consists mainly of the chemical constituents of flavonoids, triterpenes, tannins, and long-chain fatty compounds and possesses antibacterial, anti-HIV, antitumor, and uncoupling activity [1–4]. The 95% alcohol extract of the deciduous barks of P. acerifolia was separated by column chromatography on silica gel to yield compounds 1–6, which were individually identified as 3-acetylbetulinic aldehyde (1), betulonic acid (2), betulinic acid (3), daucosterol (4), 3,4,5-trimethoxyphenyl-O-D-glucopyranoside (5), and 3,4,5-trimethoxyphenyl-O-Dglucopyranoside-6 -sulfate sodium (6) by comparison of their spectral data to those reported in the literature [5, 6]. Compound 6 was obtained as a colorless granular crystalline powder. Its molecular formula was established as C15H21O12SNa by HR-ESI-MS at m/z 425.0759 [M – Na]– and 471.0543 [M + Na]+. Its 1H and 13C NMR spectra were typical of a glycoside of 3,4,5-trimethoxyphenol. The 13C NMR spectral data of the sugar moiety of 6 were consistent with those of glucose, except that the chemical shift of C-6 of 6 was shifted downfield by 5.0 ppm, which suggested compound 6 was the 6 -O-substituted glucopyranoside. The IR spectrum of 6 showed intense absorption at 1259 cm–1 and 814 cm–1, attributed to the stretching of the S=O bond and C–O–S bonds on the sulfate ester, and acid hydrolytic reaction gave sulfates (white precipitate with BaCl2), which indicated 6 is a glucosidal sulfate ester. 2D NMR including HMQC and HMBC experiments allowed us to assign all the proton and carbon signals of 6. 1H NMR (500 MHz, DMSO-d6, , ppm, J/Hz): 6.38 (s, H-2, 6), 3.75 (6H, s, CH3O-3, 5), 3.59 (3H, s, CH3O-4), 4.72 (d, J = 7.5, H-1 ), 3.21 (m, H-2 ), 3.23 (m, H-3 ), 3.06 (m, H-4 ), 3.53 (m, H-5 ), 4.15 (m, H-6 a), 3.68 (m, H-6 b), 5.23 (d, J = 5.0, 2 -OH), 5.07 (d, J = 4.5, 3 -OH), 5.10 (d, J = 5.5, 4 -OH). 13C NMR (125 MHz, DMSO-d6, , ppm): 154.2 (C-1), 94.5 (C-2, 6), 153.3 (C-3, 5), 132.6 (C-4), 101.3 (C-1 ), 73.4 (C-2 ), 76.7 (C-3 ), 70.5 (C-4 ), 75.1 (C-5 ), 66.1 (C-6 ). Thus, the structure of compound 6 was determined as 3,4,5-methoxyphenol-1-O-Dglucopyranoside-6 -sulfate sodium. Phenol glycoside and sulfate occur freely in Adiantum species of the family Adiantaceae [7], but this is the first report of their occurrence in the family Platanaceae.