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21.
A user-friendly, one-pot procedure was developed to access racemic as well as enantiomerically enriched cyclopropanes. Thus, the cyclopropanation of olefin (3) was performed using Meldrum's acid (4) or dimethyl malonate (5) and diacetoxyiodobenzene PhI(OAc)2 (6) or iodosyl benzene PhI=O (7) for in situ generation and decomposition of the phenyliodonium ylide 1 and 2, respectively. The reaction proceeds well with 5 mol% of achiral rhodium (II)-catalyst [Rh2(OAc)4] and a 10-fold excess of olefin affording the cyclopropane derivates 10 and 11, respectively, with high yield. The system is compatible with chiral Rh(II)-catalysts 8 and 9 and an enantiomeric excess up to 66% was achieved. An effective baseline separation of the enantiomers of the resulting cyclopropane derivatives was achieved using gas chromatography on the chiral stationary phase Chirasil-beta-dex. 相似文献
22.
Zhe Cao Xiaowei Wang Xuhui Huang Ho Yi Mak 《BioEssays : news and reviews in molecular, cellular and developmental biology》2021,43(1)
Physical contact between organelles are widespread, in part to facilitate the shuttling of protein and lipid cargoes for cellular homeostasis. How do protein‐protein and protein‐lipid interactions shape organelle subdomains that constitute contact sites? The endoplasmic reticulum (ER) forms extensive contacts with multiple organelles, including lipid droplets (LDs) that are central to cellular fat storage and mobilization. Here, we focus on ER‐LD contacts that are highlighted by the conserved protein seipin, which promotes LD biogenesis and expansion. Seipin is enriched in ER tubules that form cage‐like structures around a subset of LDs. Such enrichment is strongly dependent on polyunsaturated and cyclopropane fatty acids. Based on these findings, we speculate on molecular events that lead to the formation of seipin‐positive peri‐LD cages in which protein movement is restricted. We hypothesize that asymmetric distribution of specific phospholipids distinguishes cage membrane tubules from the bulk ER. 相似文献
23.
Anne Gauvin Jacqueline Smadja Maurice Aknin Emile Marcel Gaydou 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》1998,121(4)
The sterols of the sponge Petrosia spheroïda collected in the Indian Ocean, were isolated by liquid chromatography and reverse-phase HPLC. Sterols were characterized by GC, GC–MS and in some cases by 1H- and 13C-NMR. P. spheroïda contained seven Δ5-unsaturated steroids with various C8–C10 side chains including petrosterol and 23,24-dihydrocalysterol, two cyclopropane-containing sterols. Chemotaxonomic considerations about the genus Petrosia are discussed. 相似文献