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.
Acretoside, a new sucrose ester from Aristolochia cretica
A new sucrose ester, acretoside, has been isolated from the roots of the Greek endemic species Aristolochia cretica and identified as 6-O-p-coumaroyl-β-d-fructofuranosyl-(2 → 1)-α-d-glucopyranoside (1). In addition, a known sucrose ester, identified as arillatose B, two phenylpropanoid glucose esters, and five derivatives of aristolochic acids have been isolated. Their structures have been elucidated on the basis of MS and NMR data.
Studies on the Reaction of Dipeptides with Glyoxal
The reaction of various dipeptides with glyoxal at 100°C, pH 5.0 was studied. Carbon dioxide, ammonia, amino acids and aldehydes were detected from the reaction solutions. Besides, a series of new pyrazinones—2-(3′-alkyl-2′-oxo-pyrazin-1′-yl)alkyl acid—were isolated, and their chemical structures were confirmed by UV, IR, MS and NMR spectra. These pyrazinones seem to play a role in the browning of the reaction.In the reaction with glyoxal, acetaldehyde and glucose, reactivity of peptides was proved to be much higher than that of amino acids.The reaction mechanism of dipeptides with glyoxal was also proposed.