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991.
992.
A novel N‐containing compound, neoengleromycin ( 1 ) was isolated from the fruiting bodies of the ascomycete Engleromyces goetzii together with two known cytochalasins: cytochalasin D ( 2 ) and 19,20‐epoxycytochalasin D ( 3 ). Structures were established by spectroscopic (including 2D‐NMR) and chemical means. Neoengleromycin ( 1 ) possesses the rare structure of an N‐substituted hydroxamic acid and represents a new type of natural products.  相似文献   
993.
Fast pyrolysis of biomass materials impregnated with ZnCl2 offered a promising way to obtain a liquid product rich in furfural (FF) and acetic acid (AA), and the pyrolytic solids could be used as the precursors to prepare activated carbons (ACs). In this study, a lab-scale fast pyrolysis set was designed and used for the quantitative production of the three chemicals. The maximum FF was produced from the corncob impregnated with at least 15 wt% ZnCl2 and at the pyrolysis temperature around 340 °C, with the yield of more than 8 wt% compared with only 0.49 wt% from the raw corncob. Meanwhile, AA of around 4 wt% could be obtained. The content of the FF and AA was over 50 wt% and 25 wt% on the water-free basis of the pyrolytic liquids. In addition, ACs were prepared from the pyrolytic solids, and they exhibited similar properties as those prepared from direct activation of ZnCl2-impregnated biomass materials.  相似文献   
994.
Asymmetric functionalization of aromatic C? H bonds of N,N‐disubstituted anilines with diazo compounds and imines is reported for the efficient construction of α,α‐diaryl benzylic quaternary stereocenters in good yields with high diastereoselectivities and excellent enantioselectivities. This RhII/chiral phosphoric acid cocatalyzed transformation is proposed to proceed through a metal‐carbene‐induced zwitterionic intermediate which undergoes electrophilic trapping. To the best of our knowledge, this is the first asymmetric example of metal carbene‐induced intermolecular functionalization of aryl C? H bonds.  相似文献   
995.
A gold(I)‐catalyzed cross‐coupling of diazo compounds to afford tetrasubstituted alkenes has been developed by taking advantage of a trivial electronic difference between two diazo substrates. A N‐heterocyclic‐carbene‐derived gold complex is the most effective catalyst for this transformation. Based on this new strategy, a gold(I)‐initiated benzannulation has been achieved through a tandem reaction involving a diazo cross‐coupling, 6π electrocyclization, and oxidative aromatization.  相似文献   
996.
The N-loss predissociation mechanisms of the A 2Σ+ (2 2 A′) state of N2O+ to the first and second dissociation limits were studied in the C s symmetry. The potential energy curves (PECs) and minimum energy crossing points (MECPs) for the C s states of N2O+ were calculated at the CAS levels. On the basis of our CAS calculation results (CASPT2 energetic results and CASSCF spin orbit couplings), we suggest two processes for N-loss predissociation mechanisms of A 2Σ+ (2 2 A′) to the first and second limits. The first two steps in the two processes are the same: A 2Σ+ passes through the 2 2 A′/1 4 A″ MECP and then reaches the 1 4 A″ (1 4Σ) PEC. The 2 2 A′/1 4 A″ MECP has a bent geometry and is slightly higher in energy than the transition state along the 1 4 A″ PEC. Our mechanisms are different from the previously suggested mechanisms (via 1 4Π).  相似文献   
997.
998.
999.
Catalytic C-C double bond cleavage of α,β-enones with a 1-alkene and H2O was carried out in the presence of a (Ph3P)3RhCl catalyst, 2-amino-3-picoline, cyclohexylamine, benzoic acid, and alkyl group-immobilized silica spheres. Upon completion of the reaction, the corresponding ketones were obtained without needing a further hydrolysis step. In this reaction, alkyl group-immobilized silica spheres act as a water reservoir for hydrolysis of an intermediate ketimine and as a phase divider between the organic solution and H2O.  相似文献   
1000.
Based on the serum pharmacochemistry technique and high‐performance liquid chromatography/diode‐array detection (HPLC/DAD) coupled with electrospray tandem mass spectrometry (HPLC/ESI‐MS/MS), a method for screening and analysis of the multiple absorbed bioactive components and metabolites of Jitai tablets (JTT) in orally dosed rat plasma was developed. Plasma was treated by methanol precipitation prior to liquid chromatography, and the separation was carried out on a Symmetry C18 column, with a linear gradient (0.1% formic acid/water/acetonitrile). Mass spectra were acquired in negative and positive ion modes, respectively. As a result, 26 bioactive components originated from JTT and 5 metabolites were tentatively identified in orally dosed rat plasma by comparing their retention times and MS spectra with those of authentic standards and literature data. It is concluded that an effective and reliable analytical method was set up for screening the bioactive components of Chinese herbal medicine, which provided a meaningful basis for further pharmacology and active mechanism research of JTT. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   
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