Low-Molecular-Weight Compounds from Flowers of Apocynum lancifolium

Abstract

Fifteen steroidal and phenolic compounds were previously isolated and identified from the EtOAc fraction of flowers of Apocynum lancifolium (Apocynaceae) collected in Xinjiang-Uyghur Autonomous Region, PRC [1]. In continuation of research on the chemical composition of flowers of A. lancifolium, we chromatographed the n-BuOH fraction over a column of AB-8 macroporous resin. Compounds were eluted sequentially by H2O and EtOH (30 and 80%). The two fractions obtained using EtOH (30 and 80%) were rechromatographed over a column of ODS-A 120c (octadecylsilyl silica gel) using MeOH–H2O mixtures (20, 40, 60, and 80% and MeOH) to produce five fractions. The eluates of all fractions were separated by chromatography over a column of Sephadex LH-20 using MeOH–H2O (1:1) and MeOH to isolate six known pure compounds, the chemical structures of which were elucidated using PMR, 13C NMR, and 2D spectra in addition a comparison with the literature. Umbelliferone (1). Colorless crystals, C9H6O3, mp 230°C. Compound 1 was identified as umbelliferone using spectral data [2]. Protocatechoic acid (3,4-dihydroxybenzoic acid) (2), C7H6O4, mp 200–202°C. Spectral data agreed with those published [3]. 1-(3,4-Dihydroxycinnamoyl)-cyclopentane-2 ,3 -diol (3). Light-yellow crystals, C14H16O6, [ ]D 20 –54.0° (c 0.1, DMSO), mp 128–130°C. 1H NMR spectrum (600 MHz, DMSO-d6, , ppm, J/Hz): 7.45 (1I, d, J = 15.8, H-7), 7.08 (1H, d, J = 1.7, H-2), 6.97 (1I, dd, J = 8.2, 1.7, H-6), 6.77 (1I, d, J = 8.2, H-5), 6.23 (1H, d, J = 15.8, H-8), 5.19 (1H, m, H-1 ), 3.94 (1H, br.s, H-3 ), 3.50 (1H, dd, J = 9.7, 2.3, H-2 ), 1.99 (1H, d, J = 12.2, H-4 ), 1.85 (2H, m, H-5 ), 1.70 (1H, m, H-4 ). 13C NMR spectrum (150 MHz, DMSO-d6, , ppm): 166.34 (N-9), 148.60 (N-4), 145.79 (N-3), 144.71 (N-7), 125.46 (N-1), 121.21 (N-6), 115.87 (N-5), 114.77 (N-2), 114.52 (N-8), 73.13 (N-2 ), 71.43 (N-1 ), 71.30 (N-3 ), 39.37 (N-5 ), 37.94 (N-4 ) [4]. L-Bornesitol (4). White crystals, C7H14O6, mp 210–212°C, [ ]D 20 –19.0° (c 0.1, DMSO). 1H NMR spectrum (600 MHz, DMSO-d6, , ppm, J/Hz): 4.58 (1I, d, J = 4.2, 5-II), 4.55 (1I, d, J = 4.5, 6-II), 4.51 (1I, d, J = 4.3, 4-II), 4.46 (1I, d, J = 3.6, 2-II), 4.40 (1I, d, J = 5.6, 3-II), 3.92 (1I, dd, J = 3.6, 2.6, I-2), 3.43 (1I, td, J = 9.4, 4.5, I-6), 3.34 (1I, td, J = 9.4, 4.3, I-4), 3.29 (3I, s, OCH3), 3.10 (1I, ddd, J = 9.7, 5.6, 2.6, I-3), 2.91 (1I, td, J = 9.3, 4.2, I-5), 2.82 (1I, dd, J = 9.7, 2.6, I-1). 13C NMR spectrum (150 MHz, DMSO-d6, , ppm): 81.71 (N-1), 68.31 (N-2), 71.73 (N-3), 72.49 (N-4), 75.32 (N-5), 71.81 (N-6), 56.65 (OCH3) [5]. 2D NOESY: H-1/H-3; 3-OH/6-OH, 5-OH, 4-OH; 4-OH/6-OH, 5-OH, 3-OH; 5-OH/6-OH, 4-OH, 3-OH; 6-OH/5-OH, 4-OH, 3-OH. Trifolin (kaempferol-3-O-D-galactoside) (5). Yellow powder, C21H20O11, mp 256–257°C. Acid hydrolysis of 5 produced kaempferol and -D-galactose. 1H NMR spectrum (600 MHz, DMSO-d6, , ppm, J/Hz): 8.07 (1H, d, J = 8.9, H-2 , 6 ), 6.86 (2H, d, J = 8.9, H-3 , 5 ), 6.42 (1H, d, J = 2.0, H-8), 6.19 (1H, d, J = 2.0, H-6), 5.40 (1H, d, J = 7.7, H-1 ), 3.66 (1H, br.s, H-4 ), 3.54 (1H, t, J = 8.6, H-2 ), 3.46 (1H, dd, J = 10.4, 6.0, H-6 ), 3.37 (1H, dd, J = 9.5, 3.0, H-3 ), 3.34 (1H, t, J = 6.0, H-5 ), 3.30 (1H, dd, J = 10.4, 6.0, H-6 ). 13C NMR spectrum (150 MHz, DMSO-d6, , ppm): 177.44 (C-4), 164.60 (C-7), 161.17 (C-5), 159.94 (C-4 ), 156.40 (C-9), 156.24 (C-2), 133.19 (C-3), 130.94 (C-2 ), 120.86 (C-1 ), 115.03 (C-3 ), 103.76 (C-10), 101.69 (C-1 ), 98.79 (C-6), 93.70 (C-8), 75.76 (C-5 ), 73.08 (C-3 ), 71.19 (C-2 ), 67.86 (C-4 ), 60.17 (C-6 ) [6].