Silica gel flash chromatography was accomplished using 230–400 mesh silica gel. Compounds were visualized with short-wavelength UV (254 nm) and by spraying with anisaldehyde-sulfuric acid reagent and heating until the spots appeared. ![]() Analytical thin-layer chromatography (TLC) was carried out on silica gel 60 F 254 aluminum-backed TLC plates (Merck), and preparative TLC was performed on Analtech silica gel 500 μm glass plates. Low-resolution MS spectra were recorded on a Thermo LQX mass spectrometer and high-resolution MS spectra on an Agilent G6224A TOF mass spectrometer. The chemical shift values (δ) are given in parts per million (ppm), and the coupling constants ( J values) are in Hz. One-dimensional (1D) and two-dimensional (2D) NMR spectra were recorded in CDCl 3 using the residual solvent as the internal standard on a Bruker AVANCE III 400 spectrometer at 400 MHz for 1H NMR and 100 MHz for 13C NMR, respectively. Electronic circular dichroism (ECD) spectra were measured with a JASCO J-810 spectropolarimeter. UV spectra were recorded with a Shimadzu UV 2601 spectrophotometer. Optical rotations were measured with a JASCO Dip-370 polarimeter using MeOH as the solvent. (8) In addition to argentatins and guayulins, several fatty acid triglycerides have been isolated and characterized from the resins of some cultivars of P. argentatum × Parthenium tomentosum, has afforded two pyridine alkaloids, guayulamines A and B, (9) in addition to argentatins E–H, of which argentatins G and H were characterized as their diacetates. (7) Investigation of the resin of the hybrid plant, P. argentatum resin have resulted in the isolation of some major constituents including the cycloartane-type triterpenoids, argentatins A–C, (5) and the sesquiterpenoids, guayulins A–D, (6) whereas lanostane-type triterpenoids isoargentatins A and B, together with argentatins A–D, have been encountered in the roots of P. It has been suggested that finding and/or developing high-value resin-based products could significantly ameliorate the manufacturing cost of guayule rubber. Commercial processing of guayule for rubber involves extraction of the dried and chopped plant biomass with an acetone–hexane azeotrope, which results in an equal or larger amount of guayule resin, (3) a byproduct with no current cost-effective commercial applications. ![]() (2) The outcome of this evaluation will determine the suitability of this plant as a commercially viable crop for arid land agriculture. ![]() Gray, Asteraceae), a plant native to the southwestern United States and the Chihuahuan desert of northern Mexico, (1) is currently undergoing economic assessment as a reliable and sustainable source of natural rubber. Of these, 13, 14, and 18 exhibited weak cytotoxic activity for several cancer cell lines. The structures of new triterpenoids 1– 12 and argentatin H ( 13), which has previously been characterized as its diacetate ( 23), were elucidated by extensive analysis of their spectroscopic data and chemical conversions, and the known compounds 14– 22 were identified by comparison of their spectroscopic data with those reported. A total of 12 new cycloartane- and lanostane-type triterpenoids including 16-deoxyargentatin A ( 1), 16-deoxyisoargentatin A ( 2), 7-oxoisoargentatin A ( 3), 24- epi-argentatin H ( 4), 24- O- p-anisoylargentatin C ( 5), 24- O- trans-cinnamoylargentatin C ( 6), 16-dehydroargentatin C ( 7), 16,17(20)-didehydroargentatin C ( 8), isoargentatin C ( 9), isoargentatin H ( 10), 3- epi-quisquagenin ( 11), and isoquisquagenin ( 12) together with 10 known triterpenoids ( 13– 22) were isolated from the resin of Parthenium argentatum AZ-2 obtained as a byproduct of Bridgestone guayule rubber production.
0 Comments
Leave a Reply. |