Three new diarylbutane lignans, named 9-acetyl-9'-pentadecanoil-dihydroclusin (1), 2,3-demethoxy-secoisolintetralin monoacetate (4) and dihydroclusin monoacetate (5), have been isolated from the resin of Bursera fagaroides, together with two known ones, 2,3-demethoxy-secoisolintetralin diacetate (2) and dihydroclusin diacetate (3). The complete structure assignments were obtained by means of (1)H and (13)C NMR spectra.
A new approach on the use of mass spectrometry direct-insertion and a quadrupole detector for analysis of organic compounds supported in solid phase has been developed. This is a simple and efficient method based on cleavage due to the thermal-instability of the benzylic group of most commercial resins. The cleavage of supported compounds takes place in the spectrometer as a consequence of the high temperature in the instrument's chamber. These compounds are detected using a similar fragmentation pattern and a molecular ion corresponding to the same compound obtained by traditional synthesis. Polymer degradation fragments do not interfere with the spectrum interpretation, because only a few peaks and low intensities are detected. We report here the identification of different types of compounds supported in Merrifield resin, such as bis-o-aminobenzamides and simple aromatic and aliphatic compounds, using this new approach.
A convenient method for the α-alkylation of (S)-asparagine with “self-regeneration of the stereogenic
center” is described. The synthetic protocol involves stereoselective conversion of (S)-asparagine
into enantiopure imino ether (2S,6S)-9, which is then alkylated with complete diastereoselectivity
to give trans products 10−13 in good yields. Hydrolysis of these alkylated heterocycles is
accomplished under mild acidic conditions to give the desired, enantiopure α-alkyl aspartic acids
in excellent yields.
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