Labdane-type Diterpenoids from the Fruits of Vitex rotundifolia

Experimental Section

General Procedures. Melting points were determined on Kofler melting point apparatus and uncorrected. Optical rotations were measured on a Perkin-Elmer 341 polarimeter. IR spectra were obtained from Nicolet NEXUS 670 FT-IR spectrometer. 1H-, 13C-NMR (DEPT) and 2D NMR were recorded on Bruker AVANCE 500 spectrometer. HR-ESI-MS spectrum was obtained on Bruker APEX spectrometer. Silica gel used for column chromatography (CC) and silica GF254 for thin layer chromatography (TLC) were purchased from Qingdao Marine Chemical Factory in China. Silica gel C-18 used for low pressure CC was purchased from Merck. Spots were detected on TLC under UV light at 254 nm or by heating after spraying with 5% H2SO4 in EtOH.

Plant Material. The fruits of V. rotundifolia were collect-ed from Wendeng, Weihai, Shandong Province, P. R. China, in September 2010, and identified by Associate Prof. Hong Zhao (Shandong University at Weihai). A voucher specimen (No. KY201001) is deposited at the herbarium in the Labo-ratory of Botany, Marine College, Shandong University at Weihai.

Extraction and Isolation. The powered fruits (35 kg) of V. rotundifolia were extracted with MeOH at room temper-ature (7 days × 3). The extract was partitioned with petro-leum ether (60-90 °C), CHCl3 and H2O. The CHCl3 soluble fraction (1204g) was separated by silica gel CC eluting with hexane-acetone gradient (20:1 to 2:1) to give four fractions (Fr1-Fr4). Fr2 (hexane-acetone, 10:1, 155 g) was isolated by silica gel CC with hexane-EtOAc gradient (20:1 to 2:1) to afford subfractions f1-f4. Compound 3 (72 mg) was purified from f1 (hexane-EtOAc, 20:1). Fr3 (hexane-acetone, 5:1, 232 g) was isolated by silica gel CC with hexane-EtOAc gradient (20:1 to 2:1) to afford subfractions f5-f8. Subfraction f5 (hexane-EtOAc, 15:1) was subject to a silica gel CC puri-fication with hexane-acetone(10:1) elution, and further purified by C-18 CC (H 2O-MeOH 1:1) to give 2 (68 mg). Compounds 1 (45 mg) was obtained by repeated silica gel CC (hexane-acetone, 10:1) and C-18 CC (H2O-MeOH, 1:1) from f6 (hexane-EtOAc, 5:1). The Rf values of compounds 1 and 2 were 0.16 and 0.27 respectively when they were checked by TLC in silica gel developed with hexane-acetone (10:1).

Vitrifolin B (1). Colorless crystal; mp 171-173 °C; = +32 (c 0.625, CH3OH); IR (KBr): vmax 3414, 2964, 2928, 1739, 1686, 1463, 1384, 1261, 1098, 1051, 1020, 801, 637, 615 cm−1; HR-ESI-MS m/z : 403.2451 ([M + Na]+, Calcd for C22H36O5 Na+: 403.2455). 1H-NMR (500 MHz, CDCl3) and 13C-NMR (DEPT) (125 MHz, CDCl3): see Table 1.

Vitexlactam A (2). Colorless needle crystal; mp 205-207 °C; 1H-NMR (500 MHz, CDCl3) δ 6.70 (1H, brs, H-14), 5.32 (1H, brs, H-6), 3.90 (2H, brs, H2 -15), 1.97 (3H, s, H3 - 2'), 1.14 (3H, s, H3 -20), 0.92 (3H, s, H3-19), 0.89 (3H, s, H3 - 18), 0.85 (3H, d, J = 6.7 Hz, H 3 -17); 13C-NMR (125 MHz, CDCl3) δ 32.7 (C-1), 17.8 (C-2), 42.7 (C-3), 32.9 (C-4), 46.5 (C-5), 69.6 (C-6), 35.2 (C-7), 32.6 (C-8), 76.2 (C-9), 42.9 (C-10), 31.3 (C-11), 20.8 (C-12), 139.6 (C-13), 136.2 (C-14), 45.5 (C-15), 173.8 (C-16), 15.5 (C-17), 31.2 (C-18), 22.7 (C-19), 17.9 (C-20), 169.5 (C-1'), 20.9 (C-2').

Vitexilactone (3). Colorless needle crystal; mp 143 - 145 ° C; 1H-NMR (500 MHz, CDCl3) δ 5.77 (1H, m, H-14), 5.32 (1H, m, H-6), 4.68 (2H, brs, H2-16), 1.98 (3H, s, H3-2'), 1.18 (3H, s, H3-20), 0.94 (3H, s, H3-19), 0.89 (3H, s, H3-18), 0.83 (3H, d, J = 6.8 Hz, H3-17); 13C-NMR (125 MHz, CDCl 3) δ 31.0 (C-1), 17.5 (C-2), 42.5 (C-3), 32.9 (C-4), 46.6 (C-5), 68.7 (C-6), 34.9 (C-7), 32.5 (C-8), 75.4 (C-9), 42.7 (C-10), 30.5 (C-11), 24.3 (C-12), 170.1 (C-13), 113.9 (C-14), 173.0 (C-15), 72.1 (C-16), 15.0 (C-17), 31.0 (C-18), 22.6 (C-19), 17.9 (C-20), 169.4 (C-1'), 20.8 (C-2').