Four new compounds from Imperata cylindrica
Four new compounds, impecylone (1), deacetylimpecyloside (2), seguinoside K 4-methylether (3) and impecylenolide (4), were isolated from Imperata cylindrica along with two known compounds, impecyloside (5) and seguinoside K (6). Their structures were elucidated mainly by spectroscopic analyses including 1D- and 2D-NMR techniques, and the absolute configuration of 1 was confirmed by X-ray diffraction analysis. In calcium assay, the result indicated that compounds 1, 2, 4 and 5 cannot obviously inhibit the calcium peak value compared with the negative control, and suggested that the four compounds could not have anti-inflammatory activity.
Stereochemistry of Phellinsin A: A Concise Synthesis of α‐Arylidene‐γ‐Lactones
Abstract Phellinsin A (1a) was prepared in a concise way, thereby elucidating the relative stereochemistry of the aryl and carboxylic acid groups in 1a. The synthesis employed selective monohydrolysis of the dilactones derived from oxidative dimerization of cinnamic acid derivatives. This approach provided a practical synthetic route to α‐arylidene‐γ‐lactones.
Synthesis of the 5-hydroxymethyl-6-aryl-8-oxabicyclo[3.2.1]oct-3-en-2-one natural products descurainin and cartorimine
Abstract Reaction of pyranulose 6 with styrenes 12c or 13 and Et3N in CH2Cl2 at 25 °C afforded the [5+2] cycloadducts 14c and 15, which were hydrolyzed to give the natural products 1 and descurainin (2) in 24 and 27% overall yield, respectively. Heating pyranulose 6 with cinnamate ester 21 in the presence of 2,6-di-t-butylpyridine in CH3CN at 175 °C afforded the [5+2] cycloadduct, which was hydrolyzed to give cartorimine (3) in 13% yield.