Flavonoids from Vaccinium axillare leaves

Abstract

Plants of the genus Vaccinium L. are well known as sources of valuable food and medicinal raw material. For example, compounds isolated from various parts of ordinary bilberry (V. myrtillus L.) possess antioxidant [1], vasoprotective, and antiinflammatory properties [2] and induce apoptosis in tumor cells [3]. Earlier pharmacological investigations of V. axillare Nakai showed promise for the use of its extracts in treating sugar diabetes [4]. Flavonoids are known to have a significant positive pharmacotherapeutic effect for this disease [5]. We isolated the flavonoid fractoin and identified its major components because the chemical composition of V. axillare has not previsouly been studied.Leaves of V. axillare were collected in Khabarovsk Krai and Sakhalin District in summer 2006. Ground air-dried leaves were successively extracted with 95 and 70% EtOH at 60-70°C. The combined extract was evaporated to an aqueous residue and filtered. The aqueous residue was successively treated with hexane and CHCl 3 . Then the total phenolic compounds were extracted with EtOAc from the aqueous layer. The EtOAc extract was chromatographed over polyamide (Woelm, Germany) in CHCl 3 with added MeOH (from 0 to 10%). The isolated compounds were recrystallized from MeOH and studied using UV, NMR ( 1 H and 13 C, DEPT, COSY, HSQC, HMBC), mass spectrometry, and chemical methods (acid hydrolysis). This identified quercetin [6], quercetin-3-O-β-D-galactopyranoside (hyperoside) [6], quercetin-3-O-α-L-arabinopyranoside [7], and quercetin-3-O-α-L-arabinofuranoside (avicularin) [8].The widely distributed flavonoids quercetin and hyperoside were previously observed in plants of the genus Vaccinium L. [9, 10]. However, quercetin-3-O-α-L-arabinopyranoside and quercetin-3-O-α-L-arabinofuranoside (avicularin) were found for the first time in plants of this genus. Quercetin-3-O-α-L-arabinopyranoside, mp 172-174°C, [α] D 28 −65.3° (c 0.075, MeOH), lit. [7] [α] D 20 −53.96°( c 1, MeOH). MALDI-TOF mass spectrum (+) (m/z): 457 [M + Na] + , 303 [algycon + H] + . UV spectrum (MeOH, λ max , nm): 257, 267sh, 305sh, 359; (AlCl 3 ) 275, 303sh, 430; (AlCl 3 + HCl) 270, 302sh, 346sh, 405; (CH 3 ONa) 273, 330sh, 408; (CH 3 COONa) 274, 323sh, 375; (H 3 BO 3 + CH 3 COONa) 262, 300sh, 378. IR spectrum (cm −1 ): 3400-3300 (OH), 1655 (γ-pyrone C=O), 1607, 1560, 1508 (arom. C=C). PMR spectrum (CD 3 OD, δ, ppm, J/Hz): 7.73 (d, J = 2.2, H-2′), 6.86 (d, J = 8.5, H-5′), 7.56 (dd, J = 8.5, 2.2, H-6′), 6.20 (d, J = 2.0, H-6), 6.39 (d, J = 2.0, H-8), 5.15 (d, J = 6.5, H-1Ara), 3.89 (dd, J = 6.6, 8.4, H-2Ara), 3.64 (dd, J = 8.4, 3.2, H-3Ara), 3.83 (m, H-4Ara), 3.80 (m, H-5Ara), 3.43 (dd, J = 13.4, 3.1, H-5′Ara) [5]. 13 C NMR spectrum (DMSO-d 6 , δ, ppm, δ DMSO-d 6 = 39.5 ppm): 122.