PubMed · 13065919
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1953. [Cyclopropane].. https://pubmed.ncbi.nlm.nih.gov/13065919/
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The intrinsic conformational preferences of (2S,3S)-1-amino-2,3-diphenylcyclopropanecarboxylic acid, a phenylalanine cyclopropane analogue bearing two phenyl substituents, have been examined theoretically. For this purpose, its N-acetyl-N'-methylamide derivative, Ac-(2S,3S)c(3)diPhe-NHMe, has been investigated by using ab initio HF and DFT methods. Results have been compared with those previously reported for other cyclopropane analogues of phenylalanine, and with experimental data available for c(3)diPhe-containing peptides.
The mechanisms of formation of 4,4-dialkyl- and 4-alkoxycarbonyl-4-alkyl-2-azetidinones by silver-induced ring expansion of the corresponding 2,2-disubstituted N-chloro-1-hydroxycyclopropylamines were theoretically investigated by means of the B3LYP method and the PCM solvation model. The obtained results indicate that these reactions are facile two-step regioselective processes proceeding through a short-life nitrenium intermediate. The theoretical results thus predict that this synthetic strategy, which has already been used to obtain 4,4-dialkyl-2-azetidinones, could also be a new route to efficiently obtain in a regio- and stereoselective way 4-alkoxycarbonyl-4-alkyl-2-azetidinones, which are precursors of conformationally constrained amino acids.
d'Anjou cv. pear fruit (Pyrus communis L.) exposed at harvest to 0, 0.42, 4.2, or 42 micromol m(-)(3) 1-methylcyclopropene (1-MCP) for 12 h at 20 degrees C were stored at 1 degrees C for up to 8 months. After storage, half of the fruit was continuously exposed to ethylene (0.45 or 4-18 mmol m(-)(3)) for 7 days at 20 degrees C. All fruit treated with 1-MCP had lower respiration and ethylene production compared to untreated controls. Fruit quality changes were delayed following 1-MCP treatment, as was development of superficial scald and peel yellowing. The duration of 1-MCP-induced responses was dependent on 1-MCP treatment concentration. When 1-MCP-treated fruit began to ripen, softening and production of volatile compounds proceeded similar to that of untreated fruit. Post-storage ethylene exposure did not consistently stimulate ripening of fruit previously treated with 1-MCP. Efficacy of ethylene treatment depended on 1-MCP concentration and storage duration.