New adduct of abietane-type diterpene from Salvia leriifolia Benth.

Abstract A new adduct of abietane-type diterpene, salvialeriicone (1), was isolated from Salvia leriifolia Benth., along with a new chemical entity nor-abietane diterpene, 2-isopropyl-8,8-dimethyl-7,8-dihydrophenanthrene-1,4,5(6H)-trione (2). Their structures were determined using mass spectrometry, and 1D- and 2D-NMR spectroscopy. Graphical abstract Salvialeriicone: A new compound from Salvia leriifolia Benth.

Stereochemistry of compound 1 was deduced on the basis of biogenesis and the NOESY correlations, biogenetically in Salvia diterpenes, H-5 is α-oriented and CH 3 -20 is β-oriented. The NOESY correlation between axially oriented CH 3 -19 with CH 3 -20 indicated the β-orientation of CH 3 -20. The NOESY correlation of the α-oriented H-5 (assigned on biogenetic ground) with H-6 revealed the β-orientation of ether linkage between C-6 and C-7′. The NOESY correlations of H-14 with H-15′ and H-17′ and α-oriented H 3 -20′ with H-18′ were also observed.
Compound 2 (Figure 1) was obtained as a yellowish gum from the chloroform soluble fraction. The absorption band at 343 nm in the uV spectrum indicated the presence of extended conjugation in the compound. The IR spectrum showed the absorptions for conjugated carbonyl groups at 1671 and 1617 cm −1 . The chemical formula, C 19 H 20 O 3 , was deduced from the HREI-MS spectrum, which showed the molecular ion [M + ] at m/z 296.1381 (Calcd for C 19 H 20 O 3 = 296.1407).

General experimental conditions
JASCO DIP-360 digital polarimeter was used for the measurement of optical rotations. The infrared (IR) spectra were recorded on JASCO A-302 infrared spectrophotometer. For ultraviolet (uV) spectra, Thermo Evolution-300 spectrophotometer was used. 1D-and 2D -NMR spectra were recorded on a 500 MHz on Bruker Avance-500 nuclear magnetic resonance spectrometer. Electrospray ionisation mass spectra were recorded on LC-MS/MS Q STAR XL mass spectrometer (Applied Biosystems). Low-resolution EI was performed on Finnigan MAT 311 mass spectrometer. HREI-MS was recorded on the Finnigan MAT 95 XP mass spectrometer. Column chromatography was performed on silica gel (230-400 mesh, E. Merck), while TLC was carried out on pre-coated preparative silica gel plates, GF-254 (20 × 20 cm, 0.5 mm thick, E-Merck).

Plant material
The whole plant of S. leriifolia Benth. was collected from Sabzewar, Khorasan province at the north-west of Iran, and was identified by Professor Jamzadeh in the Botanical Garden of Tehran, Tehran, Iran. The voucher specimen (A.R. No. 112) was deposited to the Herbarium of the Department of Botany, Shahid Beheshti university of Medical Sciences, Tehran, Iran.

Extraction and isolation
The completely air-dried material of the plant S. leriifolia Benth., weighing 8.8 kg, was ground into a fine powder and extracted with a mixture of 95% EtOH/H 2 O at room temperature (3 × 4 days × 20 L). The reduced pressure was applied to the soluble part of the extract for complete evaporation of the solvent. This process resulted in a brownish material, weighing 469 g. The major water insoluble part of this gummy extract separated from the soluble part. The water soluble part of the extract (229 g) was fractionated with water and organic solvents, including hexanes, chloroform, ethyl acetate and n-butanol, to get corresponding 80 g of hexanes, 23.6 g of CHCl 3 , 4.2 g of ethyl acetate, 12.3 g of n-butanol and 102.1 g of water fractions.

Conclusion
The phytochemical investigation of S. leriifolia resulted in the isolation and structural elucidation of one new class of compound and one new natural product.

Supplementary material
All the mass and NMR spectra (with table) of compounds 1 and 2 are available online